U.S. patent application number 14/023229 was filed with the patent office on 2014-03-20 for hydraulic oil well pumping system, and method for pumping hydrocarbon fluids from a wellbore.
The applicant listed for this patent is Tim Hankerd, Chris Hodges, Lance Mehegan, Walter Phillips, Nathan Terry. Invention is credited to Tim Hankerd, Chris Hodges, Lance Mehegan, Walter Phillips, Nathan Terry.
Application Number | 20140079560 14/023229 |
Document ID | / |
Family ID | 50274666 |
Filed Date | 2014-03-20 |
United States Patent
Application |
20140079560 |
Kind Code |
A1 |
Hodges; Chris ; et
al. |
March 20, 2014 |
HYDRAULIC OIL WELL PUMPING SYSTEM, AND METHOD FOR PUMPING
HYDROCARBON FLUIDS FROM A WELLBORE
Abstract
A hydraulic oil well pumping system is provided. The system uses
a pump to exert hydraulic pressure against a reciprocating piston
over a wellbore. The piston is connected to a rod string and
downhole pump for pumping oil from a wellbore. The system includes
an electronic control system that controls movement of the piston
as it moves between the upper and lower rod positions by cycling
the hydraulic system between (i) an "upstroke" condition wherein
the pump is pumping oil through the oil line into the hydraulic
cylinder to move the piston to its upper rod position, and (ii) a
"neutral" condition wherein the pump is no longer pumping oil into
the hydraulic cylinder, but is allowing oil to flow back through
the oil line in response to gravitational fall of the piston. The
control system is programmed to cycle based upon a volumetric
calculation of hydraulic oil in the cylinder without reference to
position sensors along the wellhead. Wellhead conditions or
placement of the hydraulic cylinder inside the wellbore may
prohibit attaching physical sensors at the wellhead. A method for
pumping oil from a wellbore using such a system is also provided
herein.
Inventors: |
Hodges; Chris; (Irvine,
CA) ; Hankerd; Tim; (Corona, CA) ; Mehegan;
Lance; (Valencia, CA) ; Terry; Nathan;
(Mission Viejo, CA) ; Phillips; Walter;
(Huntington Beach, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hodges; Chris
Hankerd; Tim
Mehegan; Lance
Terry; Nathan
Phillips; Walter |
Irvine
Corona
Valencia
Mission Viejo
Huntington Beach |
CA
CA
CA
CA
CA |
US
US
US
US
US |
|
|
Family ID: |
50274666 |
Appl. No.: |
14/023229 |
Filed: |
September 10, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61701064 |
Sep 14, 2012 |
|
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Current U.S.
Class: |
417/15 |
Current CPC
Class: |
E21B 43/126 20130101;
E21B 43/121 20130101; F04B 49/106 20130101; F04B 9/107 20130101;
F04B 23/023 20130101; F04B 49/20 20130101; E21B 43/129 20130101;
F04B 49/08 20130101; F04B 49/002 20130101; F04B 17/05 20130101;
F04B 49/22 20130101; F04B 23/02 20130101; F04B 47/026 20130101;
F04B 9/1073 20130101; F04B 47/04 20130101; F04B 19/22 20130101;
F04B 49/065 20130101 |
Class at
Publication: |
417/15 |
International
Class: |
F04B 17/05 20060101
F04B017/05 |
Claims
1. A hydraulic oil well pumping system, comprising: an elongated
hydraulic cylinder; a piston that is movable between upper and
lower rod positions within the cylinder; a rod string that is
mechanically connected to and that extends downwardly from the
piston, the rod string being configured to extend into a wellbore
for pumping oil from the wellbore; a prime mover; a hydraulic pump
that is powered by the prime mover; a control valve that moves
between upstroke and downstroke flow positions; an oil line
connecting the pump and the hydraulic cylinder, the directional
control valve being positioned in the oil line so that it can
direct flow between the pump and the cylinder; a fluid reservoir
for containing hydraulic fluid to be supplied to the pump; a
reservoir line that transmits hydraulic fluid from the cylinder to
the reservoir; an electronic control system that controls movement
of the piston as it moves between the upper and lower rod positions
by cycling the valve between (i) an "upstroke" condition wherein
the pump is pumping fluid through the oil line and into the
hydraulic cylinder to move the piston to its upper rod position,
and (ii) a "neutral" condition wherein the pump is no longer
pumping fluid into the hydraulic cylinder, but is allowing
hydraulic fluid to flow back through the oil line in response to
gravitational fall of the piston; and wherein the electronic
control system is programmed to cycle based upon a volumetric
calculation of hydraulic fluid in the cylinder without reference to
position sensors along the wellhead.
2. The hydraulic oil well pumping system of claim 1, wherein the
pump is a hydraulic pump.
3. The hydraulic oil well pumping system of claim 1, wherein the
hydraulic fluid is a refined oil or an aqueous fluid.
4. The hydraulic oil well pumping system of claim 3, wherein: the
system further comprises a filter placed along the reservoir line
to filter the hydraulic fluid in the reservoir.
5. The hydraulic oil well pumping system of claim 1, wherein: the
prime mover is an electric motor or an internal combustion engine;
and the rod string is mechanically connected to the piston through
a polished rod.
6. The hydraulic oil well pumping system of claim 1, further
comprising: a dual-chambered tank comprising an upper chamber, and
a lower chamber immediately below the upper chamber, wherein the
directional control valve and the downstroke control valve reside
in the upper chamber and the fluid reservoir resides in the lower
chamber.
7. The hydraulic oil well pumping system of claim 1, wherein the
electronic control system controls movement of the piston based on
(i) at least one of volume and rate of hydraulic fluid sent to the
cylinder during the "upstroke" valve condition, (ii) at least one
of volume and rate of fluid returned from the cylinder during the
"neutral" valve condition, or (iii) both.
8. The hydraulic oil well pumping system of claim 7, wherein the
electronic control system sends a signal to cause the pump to vary
its output, to cause a valve to adjust its proportional flow, or to
change an operating speed of the prime mover based upon either (i)
one or more of a relative volume and rate of fluid that has moved
into the hydraulic cylinder, or (ii) an absolute volume of fluid
that has moved into the hydraulic cylinder, during the "upstroke"
valve condition.
9. The hydraulic oil well pumping system of claim 1, wherein the
electronic control system sends a signal to cause the directional
control valve to change flow paths of the hydraulic fluid and to
initiate a down stroke of the piston rod based upon (i) one or more
of a relative measurement of a volume and rate of fluid that has
moved into the hydraulic cylinder, or (ii) an absolute volume of
fluid that has moved into the hydraulic cylinder, during the
"upstroke" valve condition.
10. The hydraulic oil well pumping system of claim 1, further
comprising: a downstroke control valve that chokes the flow of
hydraulic fluid from the cylinder back to the reservoir to limit
the rate of flow of hydraulic fluid.
11. A method of pumping oil from a wellbore, the wellbore having a
bore extending into an earth surface, and the method comprising:
providing an elongated hydraulic cylinder; providing a piston that
is movable between upper and lower rod positions within the
cylinder; mechanically connecting the piston to a rod string such
that the rod string extends downwardly from the piston and into an
oil well; providing a hydraulic pump that is powered by a prime
mover; connecting the pump and the hydraulic cylinder with an oil
line that transmits hydraulic fluid from the pump to the cylinder;
providing a control valve that moves between upstroke and
downstroke flow positions; providing a fluid reservoir for
containing hydraulic fluid to be supplied to the pump; providing a
reservoir line that transmits hydraulic fluid from the cylinder to
the reservoir; using an electronic control system, controlling
movement of the piston as it moves between the upper and lower rod
positions by cycling the pump between (i) an "upstroke" condition
wherein the pump is pumping hydraulic fluid through the directional
control valve, through the oil line and into the hydraulic cylinder
to move the piston to its upper rod position, and (ii) a "neutral"
condition wherein the pump is no longer pumping hydraulic fluid
into the hydraulic cylinder, but is allowing fluid to flow back
through the oil line and through the down stroke control valve in
response to gravitational fall of the rod string; reciprocating the
piston and mechanically connected rod string in order to pump fluid
from the wellbore; and wherein the electronic control system is
programmed to cycle based upon a volumetric calculation of
hydraulic oil in the cylinder without reference to position sensors
along the wellhead.
12. The method of claim 11, wherein the pump is a hydraulic
pump.
13. The method of claim 11, the hydraulic fluid is a refined oil or
an aqueous fluid.
14. The method of claim 11, further comprising: providing a filter
along the reservoir line to filter the hydraulic fluid in the
reservoir.
15. The method of claim 11, wherein: the prime mover is an electric
motor or an internal combustion engine; and the rod string is
mechanically connected to the piston through a polished rod.
16. The method of claim 11, the electronic control system controls
movement of the piston (i) based on at least one of volume and rate
of hydraulic fluid sent to the hydraulic cylinder during the
"upstroke" valve condition, (ii) based on at least one of volume
and rate of fluid returned from the hydraulic cylinder during the
"neutral" valve condition, or (iii) both.
17. The method of claim 16, wherein the measurement of at least one
of fluid volume and rate is based upon (i) pressure differential
upstream versus downstream of a fixed orifice placed along the oil
line, (ii) a flow meter, (iii) a fluid level in the reservoir, or
(iv) a combination thereof.
18. The method of claim 11, wherein controlling the movement of the
piston comprises sending a signal from the electronic control
system to cause the pump to vary its output, to cause a valve to
adjust its proportional flow, or to change an operating speed of
the prime mover based upon either (i) one or more of a relative
volume and rate of fluid that has moved into the hydraulic
cylinder, or (ii) an absolute volume of volume of fluid that has
moved into the hydraulic cylinder, during the "upstroke" valve
condition.
19. The method of claim 11, wherein controlling the movement of the
piston comprises sending a signal from the electronic control
system to cause the valve to redirect flow and to initiate a down
stroke of the piston rod based upon (i) one or more of a relative
measurement of a volume and rate of fluid that has moved into the
hydraulic cylinder, or (ii) an absolute measured volume of fluid
that has moved into the hydraulic cylinder, during the "upstroke"
valve condition.
20. The method of claim 11, wherein the control system generates an
electrical signal that alters the flow path of the hydraulic fluid
during the "upstroke" condition and again alters the hydraulic flow
path of the hydraulic fluid during the "neutral" condition.
21. The method of claim 11, further comprising: providing a down
stroke control valve that chokes the flow of fluid from the
cylinder back to the reservoir to limit the rate of flow of
hydraulic fluid.
22. A method of determining location of a hydraulically actuated
piston within a cylinder disposed over a wellbore, comprising:
determining a volume of hydraulic fluid needed to fill a hydraulic
cylinder during a piston upstroke; measuring a dynamic rate for
filling the cylinder during the upstroke using a pump and an oil
line providing fluid communication between the pump and the
cylinder; based upon the determined volume and rate, determining a
first time for filling the cylinder during the upstroke;
determining a second time for draining the fluid from the cylinder
through a down-stroke control valve, the down stroke control valve
having a sized orifice for reducing a rate at which the piston
falls during draining; using an electronic control system,
controlling movement of the piston as it reciprocates between upper
and lower rod positions by cycling the valve between (i) an
"upstroke" condition wherein the pump is pumping oil through the
directional control valve, through the oil line and into the
hydraulic cylinder to move the piston to its upper rod position
over the first time, and (ii) a "neutral" condition wherein the
pump is no longer pumping oil into the hydraulic cylinder, but is
allowing oil to flow back through the oil line and through the down
stroke speed control valve in response to gravitational fall of the
piston during the second time, wherein the cycling is performed
without reference to position sensors along the wellhead;
monitoring hydraulic fluid pressure in the oil line during the
first time and the second time; and reciprocating the piston and
mechanically connected rod string in order to pump oil from the
wellbore.
23. The method of claim 22, further comprising: determining a
position of the piston during the upstroke based upon (i) one or
more of a relative volume and rate of hydraulic fluid injected by
the pump during the "upstroke" condition, (ii) the absolute volume
of fluid injected by the pump during the "upstroke" condition, or
(iii) the ratio of a pressure reading in the oil line to a baseline
pressure representing a pressure value just before the piston has
reached a mechanical top of its upstroke.
24. The method of claim 22, further comprising: sending a signal
from the electronic control system to cause the pump vary its
output, to cause a valve to adjust its proportional flow, or to
change an operating speed of the prime mover based upon the
location of the piston during its upstroke.
25. The method of claim 22, further comprising: calculating a
position of the piston during the down stroke based upon (i) one or
more of a relative volume and rate of hydraulic fluid drained from
the hydraulic cylinder during the "neutral" condition, (ii) the
absolute volume of hydraulic fluid drained from the hydraulic
cylinder during the "neutral" condition, or (iii) when the pressure
reading in the oil line has reached a value of substantially 0,
indicating a mechanical bottom of the piston's down stroke.
26. The method of claim 25, further comprising: sending a signal
from the electronic control system to cause the pump to vary its
output, to cause a valve to adjust its proportional flow, or to
change an operating speed of the prime mover based upon the
location of the piston during its down stroke.
27. A dynamometer card for a hydraulically actuated rod pumping
system having a piston, a rod string that moves with the piston, a
hydraulic pump, and a cylinder dimensioned to contain hydraulic
fluid, the dynamometer card comprising: an "x"-axis representing a
piston position within the cylinder; and a "y"-axis representing
fluid load applied on a downhole pump during a pumping cycle; and
wherein the piston position is calculated based on (i) one or more
of a relative measurement of a volume and rate of fluid that has
moved to and from the cylinder, or (ii) an absolute measured volume
of fluid that has moved to and from the cylinder, and without
reference to a position sensor located at least one of at and near
a wellhead.
28. The dynamometer card of claim 27, wherein the hydraulically
actuated rod pumping system further comprises: a directional
control valve that moves between upstroke and downstroke flow
positions; an oil line connecting the pump and the hydraulic
cylinder, the directional control valve being positioned in the oil
line so that it can direct flow between the pump and the cylinder;
a fluid reservoir for containing hydraulic fluid to be supplied to
the pump; a reservoir line that transmits hydraulic fluid from the
cylinder to the reservoir; a down stroke control valve that chokes
the flow of hydraulic fluid from the cylinder back to the reservoir
to limit the rate of flow of hydraulic fluid; and an electronic
control system that controls movement of the piston as it moves
between upper and lower rod positions by cycling the valve between
(i) an "upstroke" condition wherein the pump is pumping fluid
through the oil line and into the hydraulic cylinder to move the
piston to its upper rod position, and (ii) a "neutral" condition
wherein the pump is no longer pumping fluid into the hydraulic
cylinder, but is allowing hydraulic fluid to flow back through the
oil line in response to gravitational fall of the piston.
29. The dynamometer card of claim 27, wherein the fluid load is
calculated using hydraulic pressure and effective cylinder area.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Application No.
61/701,064, dated Sep. 14, 2012.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT
[0003] Not applicable.
[0004] This section is intended to introduce various aspects of the
art, which may be associated with exemplary embodiments of the
present disclosure. This discussion is believed to assist in
providing a framework to facilitate a better understanding of
particular aspects of the present disclosure. Accordingly, it
should be understood that this section should be read in this
light, and not necessarily as admissions of prior art.
BACKGROUND OF THE INVENTION
[0005] 1. Field of the Invention
[0006] The present disclosure relates to the field of hydrocarbon
recovery operations. More specifically, the present invention
relates to hydraulically actuated pumping units for the production
of hydrocarbon fluids and for dewatering gas wells.
[0007] 2. Technology in the Field of the Invention
[0008] In the drilling of oil and gas wells, a wellbore is formed
using a drill bit that is urged downwardly at a lower end of a
drill string. After drilling to a predetermined depth, the drill
string and bit are removed and the wellbore is lined with a string
of casing. An annular area is thus formed between the string of
casing and the surrounding formations.
[0009] To prepare the wellbore for the production of hydrocarbon
fluids, a string of tubing is run into the casing. A packer is set
at a lower end of the tubing to seal an annular area formed between
the tubing and the surrounding strings of casing. The tubing then
becomes a string of production pipe through which hydrocarbon
fluids may be lifted.
[0010] In order to carry the hydrocarbon fluids to the surface, a
pump may be placed at a lower end of the production tubing. This is
known as "artificial lift." In some cases, the pump may be an
electrical submersible pump, or ESP. ESP's utilize a hermetically
sealed motor that drives a multi-stage pump. More conventionally,
oil wells undergoing artificial lift use a downhole reciprocating
plunger-type of pump. The reciprocating downhole pump is relatively
long and thin to avoid restricting oil flow up the well. The pump
has one or more valves that capture fluid on a down stroke, and
then lift the fluid on the upstroke. This is known as "positive
displacement." In some designs such as that disclosed in U.S. Pat.
No. 7,445,435, the pump may be able to both capture fluid and lift
fluid on each of the down stroke and the upstroke.
[0011] Conventional positive displacement pumps have a barrel that
is reciprocated at the end of a "rod string." The rod string
comprises a series of long, thin joints of pipe that are threadedly
connected through couplings. The rod string is pivotally attached
to a pumping unit at the surface. The rod string moves up and down
within the production tubing to incrementally lift production
fluids from subsurface intervals to the surface.
[0012] Most pumping units on land are so-called rocking beam drive
units. Rocking beam units typically employ electric motors or
internal combustion engines having a rotating drive shaft. The
shaft turns a crank arm, or possibly a pair of crank arms. The
crank arms, in turn, have heavy, counter-weighted flywheels. The
flywheels rotate along with the crank arms. Rocking beam units also
have a walking beam. The walking beam pivots over a fulcrum. One
end of the walking beam is mechanically connected to the crank
arms. As the crank arms and flywheels rotate, they cause the
walking beam to reciprocate up and down over the fulcrum.
[0013] The opposite end of the walking beam is a so-called horse
head. The horse head is positioned over the well head at the
surface. As the walking beam is reciprocated, the horse head cycles
up and down over the wellbore. This, in turn, translates the rod
and attached pump up and down within the wellbore. A drawing and
further description of a walking beam unit are provided in U.S.
Pat. No. 7,500,390, which is incorporated herein in its entirety by
reference.
[0014] Another type of pumping unit is a hydraulic actuator system.
These systems employ a cylinder residing over a wellbore. The
cylinder is axially aligned with the wellbore and holds a
reciprocating piston. The cylinder cyclically receives fluid
pressure through an oil line. As fluid is injected through the oil
line and into the cylinder, the piston is caused to move linearly
within the cylinder. This, in turn raises the connected rod string,
causing the pump to undergo an upstroke. When fluid pressure is
released from the cylinder, the rod string is lowered due to
gravitational forces, causing the downhole pump to undergo a
downstroke.
[0015] Surface hydraulic actuator systems have been used
successfully for many years. Such systems offer a beneficially long
stroke length for the downhole plunger pump. Such systems are also
ideal for urban environments where a small footprint is demanded.
Further, such systems offer the ability to operate more than one
well from a single surface installation.
[0016] During operation of any rod pump system for a producing
well, it is desirable to be able to monitor the position of the rod
string and specifically, the piston within the cylinder. In this
respect, it is helpful to know when the piston is about to reach a
top or bottom of a stroke. Knowing this position allows the
operator to slow or stop the motion of the piston and rod-string
pro-actively, eliminating the "slamming" of the piston against a
plate within the cylinder.
[0017] Further, it is desirable to be able to measure the load on
the sucker rods making up the rod string. The load can be recorded
and printed out on a so-called surface dynamometer card. The "dyno
card" offers a plot of the measured rod loads at various positions
throughout a complete stroke. The load is usually displayed in
pounds of force, while the position is usually displayed in inches.
The pump dynamometer card represents the load the pump applies to
the bottom of the rod string. Dynamometer cards are displayed by
predictive and diagnostic software for the purposes of design and
diagnosing sucker rod pumping systems.
[0018] Historically, hydraulic pressure has been used to measure
rod loads for dynamometer cards. Then, separate physical
measurements have been made on the piston and polished rod for
determining position. This requires the use of sensors at the
wellhead to directly measure piston position. Such sensors may be
either discrete position switches or more advanced linear position
sensors. SPE Paper No. 113186 entitled "Optimizing Downhole Fluid
Production of Sucker-Rod Pumps With Variable Speed Motor" (2009)
describes some of the mathematics behind the dynagraph
calculations, and is incorporated herein by reference in its
entirety.
[0019] A need exists to be able to use the hydraulic fluid data to
determine not only the load on the rod string, but also the
position of the piston using only the hydraulic fluid as the
measurement for both position and load without the need for data
gathered from devices or sensors at or near the wellhead. Removal
of electronic or other methods of directly attached instrumentation
from areas around the wellhead reduces risk of sparking and also
eliminates the cost of placing and maintaining such
instrumentation. Further, it is desirable to be able to determine
the position of the piston within the cylinder on both the upstroke
and the down stroke at a safe distance without using position
sensors at the wellhead.
BRIEF SUMMARY OF THE INVENTION
[0020] An oil well pumping system is first provided herein. The
pumping system uses a set of valves and an electrical control
system to cyclically direct hydraulic fluid into and release
hydraulic fluid from a cylinder. The pressure created by the
hydraulic fluid causes a piston and connected rod string and
downhole pump to reciprocate. This, in turn, causes reservoir
fluids to be produced from a wellbore to the surface through
positive displacement.
[0021] In one aspect, the oil well pumping system first includes an
elongated hydraulic cylinder. The cylinder is positioned over the
wellbore. The cylinder may either be over an associated wellhead,
or inside the wellbore and below the wellhead.
[0022] The hydraulic cylinder may be placed above the wellhead,
where sensors are easily attached, but the cylinder may also be
placed inside the wellbore. This aspect places the entirety of the
hydraulic cylinder length within the wellbore, below the wellhead.
Because the length of the cylinder is inaccessible, it is
impossible to place sensors along the cylinder in this
configuration. The need exists for an alternate method of
determining position without the use of direct instrumentation of
the hydraulic cylinder when positioned entirely in the wellbore and
submerged in crude oil.
[0023] The oil well pumping system also includes a piston and a
polished rod. The polished rod defines an elongated rod that is
movable with the piston between upper and lower rod positions
within the cylinder. The piston, in turn, provides an annular seal
between the polished rod and the surrounding cylinder. Hydraulic
pressure cyclically acts against the piston to create an upstroke
and a down stroke of the polished rod.
[0024] The oil well pumping system further has a rod string. The
rod string is mechanically connected to the lower end of the
polished rod. This means that when the piston reciprocates, the rod
string reciprocates with it. The rod string extends downwardly from
the polished rod and into the wellbore. The rod string has a
downhole pump connected to it for lifting fluids to the surface in
response to reciprocation of the rod string.
[0025] The oil well pumping system also includes a hydraulic pump.
The pump is powered by a prime mover. The prime mover may be an
electric motor, an internal combustion engine, or other driver.
[0026] The oil well pumping system further includes a directional
control valve. The directional control valve shifts between
upstroke and downstroke flow positions. When the valve is in its
upstroke position, it directs hydraulic fluid such as oil from the
pump and into the annular area formed below the piston between the
polished rod and the surrounding cylinder. When the directional
control valve is in its downstroke (or neutral) position, it
receives reverse flow from the annular area and allows the
gravity-induced fall of the piston and connected rod string.
[0027] The oil well pumping system also has an oil line. The oil
line connects the pump and the hydraulic cylinder. The control
valve is positioned in the oil line so that it can control flow
between the pump and the cylinder in response to electrical
signals. The signals are sent by an electrical control system that
shifts the directional control valve between its upstroke and
downstroke flow positions.
[0028] A fluid reservoir is also provided. The fluid reservoir
contains hydraulic fluid to be supplied to the pump.
[0029] The oil well pumping system next comprises a reservoir line.
The reservoir line transmits hydraulic fluid from the cylinder back
to the reservoir. Optionally, a filter is provided along the
reservoir line to filter the return oil. Optionally, a pressure
bypass line is also provided to bypass the filter as part of the
reservoir or return line.
[0030] The oil well pumping system also includes a downstroke
control valve. The downstroke control valve has a restricted
orifice that chokes the flow of fluid from the cylinder back to the
reservoir. The downstroke control valve limits the speed with which
the piston and operatively connected rod string fall within the
cylinder during the down stroke. This serves to control the rate of
flow of hydraulic fluid returning from the cylinder.
[0031] As noted, an electronic control system is also provided for
the oil well pumping system. The control system controls movement
of the piston as it moves between the upper and lower rod
positions. This is done by cycling the directional control valve
between (i) an "upstroke" condition wherein the pump is pumping oil
through the oil line into the hydraulic cylinder to move the piston
to its upper rod position, and (ii) a "neutral" condition wherein
the pump is no longer pumping oil into the hydraulic cylinder, but
is allowing oil to flow back through the oil line in response to
gravitational fall of the piston and connected rod string. The
electronic control system is programmed to cycle based upon a
volumetric capacity of the hydraulic cylinder and the volume of oil
delivered to the cylinder, and without reference to position
sensors along the wellhead.
[0032] In one aspect, the electronic control system controls
movement of the piston and polished rod based on time. This may be
based on (i) time for the "upstroke" pump condition, (ii) time for
the "neutral" pump condition, or (iii) both. In this embodiment,
the control system is simply a clock for turning the pump on and
off at calculated or estimated time intervals.
[0033] In another aspect, the electronic control system controls
movement of the piston based on volume. The volume may be (i) the
volume of hydraulic fluid sent to the cylinder during the
"upstroke" valve condition, (ii) the volume of fluid returned from
the cylinder during the "neutral" valve condition, or (iii) both.
Note that flow rate and volume are intimately associated. Flow rate
is the volume of fluid which passes through a given point in a
system per unit time. Flow rate can be calculated as the product of
a given cross sectional area for flow and an average flow velocity.
A series of flow rate measurements over a cross sectional area
taken over a period of time may be used to determine fluid volume
passing through the cross section over the time period.
Accordingly, direct measurements of total volume and a series of
instantaneous measurements of flow rate over time provide
equivalent volume information.
[0034] A method of pumping oil from a wellbore is also provided
herein. The wellbore has a bore extending into an earth surface.
The method employs a unique pumping system that uses a set of
valves and an electrical control system. The valves cyclically
direct hydraulic fluid into a cylinder. The pressure created by the
hydraulic fluid causes the piston and a connected rod string and
downhole pump to reciprocate. This, in turn, causes reservoir
fluids to be produced from a wellbore to the surface through
positive displacement.
[0035] In one aspect, the method first comprises providing an
elongated hydraulic cylinder. The cylinder is positioned over the
wellbore. The cylinder may either be over an associated wellhead,
or inside the wellbore and below the wellhead.
[0036] The method also includes providing a piston and a polished
rod. The piston and connected polished rod are movable between
upper and lower rod positions within the cylinder. The piston
creates an annular seal above the polished rod and the surrounding
cylinder. Hydraulic pressure cyclically acts against the piston to
create an upstroke and a downstroke.
[0037] The method further includes mechanically connecting the
piston and polished rod to a rod string. This means that when the
piston reciprocates, the rod string reciprocates with it. The rod
string extends downwardly from the piston and into the wellbore.
The rod string has a downhole pump connected to it for lifting
fluids to the surface in response to reciprocation of the rod
string.
[0038] The method also includes providing a hydraulic pump. In one
aspect, the pump is a positive displacement pump. The pump is
powered by a prime mover. The prime mover may be an electric motor,
an internal combustion engine, or other driver.
[0039] The method also has the step of connecting the pump and the
hydraulic cylinder with an oil line. The oil line transmits
hydraulic fluid from the pump to the cylinder.
[0040] Still further, the method includes providing a directional
control valve that moves between open upstroke and downstroke flow
positions. When the valve is in its upstroke flow position, it
directs hydraulic fluid such as oil from the pump, through the oil
line and into the annular area formed between the polished rod and
the surrounding hydraulic cylinder below the piston. When the valve
is in its downstroke flow position, it allows hydraulic fluid to
bleed from the cylinder.
[0041] The method also has the step of providing a fluid reservoir.
The reservoir contains hydraulic fluid to be supplied to the
pump.
[0042] The method next includes providing a reservoir line. The
reservoir line transmits hydraulic fluid from the cylinder back to
the reservoir. Optionally, a filter is provided along the reservoir
line. It is understood that the term "reservoir line" may mean more
than one line, such as a pressure bypass line.
[0043] The method also has the step of providing a down stroke
control valve. The down stroke control valve chokes the flow of
fluid from the cylinder back to the reservoir. This, in turn,
limits the rate of flow of hydraulic fluid during the down stroke
of the piston.
[0044] The method also offers the step of controlling movement of
the piston as it moves between upper and lower rod positions. This
is done by using an electronic control system. The control system
controls the valves and the pump to cycle the pump between (i) an
"upstroke" condition wherein the pump is pumping oil through the
directional control valve, through the oil line and into the
hydraulic cylinder to move the piston to its upper rod position,
and (ii) a "neutral" condition wherein the pump is no longer
pumping oil into the hydraulic cylinder, but is allowing oil to
flow back through the oil line and the down stroke control valve in
response to gravitational fall of the piston and connected polished
rod. The electronic control system is programmed to cycle based
upon a volumetric calculation of the capacity of the hydraulic
cylinder and the oil delivered to, or received back from, the
cylinder without reference to position sensors located in the
wellhead environment.
[0045] Preferably, the electronic control system controls movement
of the piston based on volume. The volume may be (i) the volume of
hydraulic fluid sent to the cylinder during the "upstroke" pump
condition, (ii) the volume of fluid returned from the cylinder
during the "neutral" pump condition, or (iii) both. In another
aspect, the electronic control system controls movement of the rod
based on (i) time for the "upstroke" valve condition, (ii) time for
the "neutral" valve condition, or (iii) both. Time on the
downstroke or "neutral" pump condition may be limited, as the next
upstroke may take place at a fixed interval.
[0046] Optionally, the control system may send a signal to cause
the pump to vary its output, to cause a valve to adjust its
proportional flow, or to change an operating speed of the prime
mover based upon either (i) a relative volume of fluid that has
moved into the hydraulic cylinder, or (ii) an absolute volume of
fluid that has moved into the hydraulic cylinder, during the "on"
pump condition.
[0047] Also, the method includes reciprocating the piston and
mechanically connected rod string in order to pump oil from the
wellbore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] So that the manner in which the present inventions can be
better understood, certain illustrations, charts and/or flow charts
are appended hereto. It is to be noted, however, that the drawings
illustrate only selected embodiments of the inventions and are
therefore not to be considered limiting of scope, for the
inventions may admit to other equally effective embodiments and
applications.
[0049] FIG. 1A is a side view of a hydraulic oil well pumping
system of the present invention, in one embodiment. The hydraulic
oil well pumping system is used for producing reservoir fluids from
a subsurface formation to the surface. Portions of the system are
shown schematically.
[0050] FIG. 1B is a perspective engineering view of a portion of
the hydraulic oil well pumping system of FIG. 1A. Here, the
cylinder is seen over the wellhead. The reservoir and the valving
are also shown in an integral tank.
[0051] FIG. 2A is a cross-sectional view of the hydraulic cylinder
of FIG. 1A in an enlarged view. The cylinder is again positioned
above a wellhead and has a hydraulically actuated piston
therein.
[0052] FIG. 2B is a photographic view of the hydraulic cylinder of
FIG. 1A, in one embodiment.
[0053] FIG. 3 is an engineering model showing a side, cut-away view
of a cylinder having a hydraulically actuated piston therein. Here,
the cylinder is disposed below the wellhead, inside the
wellbore.
[0054] FIG. 4A is a perspective view of a skid having certain
components of the hydraulic oil well pumping system of FIG. 1. An
internal combustion engine is shown as the prime mover for powering
a hydraulic pump.
[0055] FIG. 4B is a perspective view of a skid having components of
the hydraulic oil well pumping system of FIG. 1, in an alternate
embodiment. Here, an electric motor is shown as the prime mover for
powering a hydraulic pump.
[0056] In each of FIGS. 4A and 4B, a novel two-chambered tank is
provided. Valves and hoses are housed in an upper chamber, while
working oil is housed in a lower chamber.
[0057] FIG. 5 is an exploded perspective view of the valve stack
from FIGS. 4A and 4B. This valve stack includes a directional
control valve and a downstroke control valve.
[0058] FIG. 6 is an engineering diagram showing illustrative
hydraulic circuitry of the hydraulic oil well pumping system of
FIG. 1, in one embodiment. Fluid lines and certain components for
the system are shown schematically.
[0059] FIG. 7 is a flow chart showing steps that may be performed
for a method of pumping oil from an oil well, in one
embodiment.
[0060] FIG. 8A and FIG. 8B are another flow chart. Here, steps are
shown for a method of determining the position of a hydraulically
actuated piston within a cylinder.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
Definitions
[0061] For purposes of the present application, it will be
understood that the term "hydrocarbon" refers to an organic
compound that includes primarily, if not exclusively, the elements
hydrogen and carbon. Hydrocarbons may also include other elements,
such as, but not limited to, halogens, metallic elements, nitrogen,
oxygen, and/or sulfur. Hydrocarbons generally fall into two
classes: aliphatic, or straight chain hydrocarbons, and cyclic, or
closed ring hydrocarbons, including cyclic terpenes. Examples of
hydrocarbon-containing materials include any form of natural gas,
oil, coal, and bitumen that can be used as a fuel or upgraded into
a fuel.
[0062] As used herein, the term "hydrocarbon fluids" refers to a
hydrocarbon or mixtures of hydrocarbons that are gases or liquids.
For example, hydrocarbon fluids may include a hydrocarbon or
mixtures of hydrocarbons that are gases or liquids at formation
conditions, at processing conditions or at ambient conditions
(15.degree. C. and 1 atm pressure). Hydrocarbon fluids may include,
for example, oil, natural gas, coalbed methane, shale oil,
pyrolysis oil, pyrolysis gas, a pyrolysis product of coal, and
other hydrocarbons that are in a gaseous or liquid state.
[0063] As used herein, the terms "produced fluids," "reservoir
fluids" and "production fluids" refer to liquids and/or gases
removed from a subsurface formation, including, for example, an
organic-rich rock formation. Produced fluids may include both
hydrocarbon fluids and non-hydrocarbon fluids. Production fluids
may include, but are not limited to, oil, natural gas, pyrolyzed
shale oil, synthesis gas, a pyrolysis product of coal, carbon
dioxide, hydrogen sulfide and water (including steam).
[0064] As used herein, the term "fluid" refers to gases, liquids,
and combinations of gases and liquids, as well as to combinations
of gases and solids, combinations of liquids and solids, and
combinations of gases, liquids, and solids.
[0065] As used herein, the term "wellbore fluids" means water, mud,
hydrocarbon fluids, formation fluids, or any other fluids that may
be within a string of drill pipe during a drilling operation.
[0066] As used herein, the term "gas" refers to a fluid that is in
its vapor phase at 1 atm and 15.degree. C.
[0067] As used herein, the term "subsurface" refers to geologic
strata occurring below the earth's surface.
[0068] As used herein, the term "formation" refers to any definable
subsurface region regardless of size. The formation may contain one
or more hydrocarbon-containing layers, one or more non-hydrocarbon
containing layers, an overburden, and/or an underburden of any
geologic formation. A formation can refer to a single set of
related geologic strata of a specific rock type, or to a set of
geologic strata of different rock types that contribute to or are
encountered in, for example, without limitation, (i) the creation,
generation and/or entrapment of hydrocarbons or minerals, and (ii)
the execution of processes used to extract hydrocarbons or minerals
from the subsurface.
[0069] As used herein, the term "wellbore" refers to a hole in the
subsurface made by drilling or insertion of a conduit into the
subsurface. A wellbore may have a substantially circular cross
section, or other cross-sectional shapes. The term "well," when
referring to an opening in the formation, may be used
interchangeably with the term "wellbore." The term "bore" refers to
the diametric opening formed in the subsurface by the drilling
process. (Note that this is in contrast to the term "cylinder bore"
which may be used herein, and which refers to a hydraulic cylinder
over a wellbore.)
Description of Selected Specific Embodiments
[0070] FIG. 1A is a side view of a hydraulic oil well pumping
system 100 of the present invention, in one embodiment. The
hydraulic oil well pumping system 100 is used for producing
reservoir fluids from a subsurface formation (not shown) to the
surface 101. Portions of the system 100 are shown
schematically.
[0071] In FIG. 1A, it is first seen that the system 100 includes an
elongated cylinder 150. In this arrangement, the cylinder 150
resides over a wellhead 105. The wellhead 105 serves to support a
string of production tubing 110 that extends from the surface 101
and down into a wellbore 115.
[0072] Above the wellhead 105 is a set of control valves. The
valves are part of a "Christmas tree," shown at 108. The Christmas
tree 108 generally supports the cylinder 150. The valves of the
Christmas tree 108 direct the flow of production fluids and also
permit an operator to inject treatment chemicals or otherwise
access the production tubing 110.
[0073] Residing within the wellbore 115 is a rod string 120. The
rod string 120 is comprised of a plurality of long, slender joints
of steel, known as sucker rods. Each sucker rod is typically 25 or
30 feet in length. The rod string 120 supports a pump (not shown)
downhole. The pump, in turn, moves production fluids from the
subsurface formation, up the production tubing 110, and to the
wellhead 105 through positive displacement. The pump is generally
positioned next to a perforated zone of the wellbore 115. The
production fluids then flow out of a valve in the Christmas tree
108 where they may undergo some initial fluid separation and are
then directed into a flow line or a gathering tank (not shown).
[0074] Each sucker rod includes a coupling. In FIG. 1A, a coupling
122 is shown above the rod string 120. In this view, the coupling
122 connects the rod string 120 to a polished rod 160. The polished
rod 160, in turn, extends up through the wellhead 105, through the
Christmas tree 108, and into the cylinder 150. The polished rod 160
defines an elongated cylindrical body.
[0075] At an upper end of the polished rod 160 is a piston 165. The
piston 165 seals an annular area 155 formed between the polished
rod 160 and the surrounding cylinder 150. The piston 165 prevents
the hydraulic oil from migrating into a chamber above the piston
165. The annular area 155 is filled with a working fluid, typically
a clean hydraulic oil.
[0076] The piston 165 and connected polished rod 160 reciprocate
within the cylinder 150 between two heads. A first or upper head
142 is at a distal end of the cylinder 150, while a second or lower
head 144 is at a proximal end of the cylinder 150. The second head
144 has an internal bore to slidably receive the polished rod
160.
[0077] The hydraulic oil well pumping system 100 also includes a
pair of fluid lines 170, 175. A first fluid line 170 is an oil
line. The oil line 170 is in fluid communication with the annular
area 155 of the cylinder 150 just above the second (or lower) head
144. The oil line 170 injects and receives oil from the annular
area 155 in order to move the piston 160 up and down within the
cylinder 150. In this way, an up stroke and a downstroke are
created for the piston 165 and mechanically connected rod string
120 and downhole pump.
[0078] The second fluid line 175 is essentially a vent line. The
vent line 175 receives air and any leaked oil from the piston 165
during the upstroke. The vent line 175 is supported by one or more
brackets 156 disposed along the outer wall of the cylinder 150.
[0079] FIG. 1B is a perspective view of a portion of the hydraulic
oil well pumping system 100 of FIG. 1A. Here, the cylinder 150 is
seen over the wellhead 105. The two fluid lines 170, 175 are seen
along with the supporting brackets 156.
[0080] Returning to FIG. 1A, additional components of the hydraulic
oil well pumping system 100 are shown schematically. These include
a prime mover 182, a hydraulic pump 184, a valve stack 190, and a
fluid reservoir 195. These components are optionally supported
together on a skid 180.
[0081] The prime mover 182 provides power to the pump 184. The
prime mover 182 may be a gasoline engine, a diesel engine, or other
internal combustion engine. Such a prime mover is shown at 482A in
FIG. 4A and is discussed more fully below. Alternatively, the prime
mover 182 may be an electric motor as shown at 482B in FIG. 4B and
discussed below. When the prime mover 182 is started, it activates
the hydraulic pump 184. Beneficially, changing the operating speed
of the prime mover 182 will vary the output of the pump 184.
Alternatively, different types of controlled valving can be used to
vary the hydraulic output with a fixed RPM in the pump.
[0082] The pump 184 serves to pump fluid into the oil line 170. The
pump 184 is preferably a vane style pump. However, other types of
pumps such as a piston-type pump may be employed. The pump 184 may
be a fixed displacement pump or a variable displacement pump.
[0083] Oil is directed from the pump 184 and into the oil line 170
by means of a set of valves 190. The valves 190 preferably include
a discrete four-way valve. Such a valve is shown in detail at 500
in FIG. 5 as part of a valve stack. Alternatively, the valves 190
may include a proportional valve or even a variable speed prime
mover as the valve.
[0084] In one preferred embodiment, the valves 190 are discrete
valves housed together with the reservoir 195 in a dual-chambered
tank. Such a tank is shown generally at 190' in FIG. 1B. The tank
is shown in greater detail in FIGS. 4A and 4B.
[0085] Moving now to FIGS. 2A and 2B, FIG. 2A is a cross-sectional
view of the hydraulic cylinder 150 of FIG. 1A, shown in an enlarged
view. FIG. 2B is a perspective (photographic) view of the hydraulic
cylinder 150 of FIG. 2A, in one embodiment.
[0086] Referring primarily to FIG. 2A, the hydraulic cylinder 150
is again seen residing over a wellhead 205 and a Christmas tree
208. The wellhead 205 and the Christmas tree 208 are shown somewhat
schematically. The cylinder 150 is secured to the Christmas tree
208 and connected wellhead 205 by means of a coupling 290. The
wellhead 205, in turn, is secured over a wellbore 215.
[0087] The wellbore 215 is formed by a string of casing 210. Within
the casing 210 is the string of production tubing 110. The
production tubing 110, in turn, holds the rod string 120 and
receives production fluids.
[0088] At a top of the cylinder 150 is a threaded connector 280.
The threaded connector 280 is optionally used to pick up the
cylinder 150 during installation over the wellhead 205. The
connector 280 is part of the upper head 142.
[0089] In some embodiments, a frame or a tripod (not shown) are
used to stabilize the cylinder 150 over the wellhead 205. This
optional feature is most commonly used in windy locations.
[0090] In FIG. 2A, the oil line 170 is seen entering the annular
area 155 above the lower head 144. Further, the vent line 175 is
seen in fluid communication with the annular area 155 below the
upper head 142. In addition, the piston 160 is seen residing within
the cylinder 150, forming the annular area 155.
[0091] The polished rod 160 has a distal end 162 and a proximal end
164. The distal end 162 connects to the piston 165. In FIG. 2A, one
or more steel or composite rings 266 can be seen along the piston
165, providing the needed seal to keep hydraulic oil within the
annular area 155. In addition, a seal 244 comprised of "Vee"
packing or other material is preferably provided along the lower
head 144 to provide fluid sealing along the polished rod 160.
[0092] The cylinder 150 shown in FIGS. 1A and 1B and FIGS. 2A and
2B reside above the wellhead 105, 205. However, it is possible to
place the cylinder (and housed piston) inside the wellbore and
below the wellhead. This may be of benefit on offshore production
platforms where vertical height is a concern.
[0093] FIG. 3 is an engineering model showing a side, cut-away view
of a cylinder 350 having a hydraulically actuated piston 360
therein. Here, the cylinder 350 is disposed below a Christmas tree
308 and a wellhead 305. Of interest, a vent line (not shown) comes
directly out of the upper head (as in the above ground cylinder).
The oil line also goes into the upper head, but is directed down
through a double walled cylinder to the lower head.
[0094] Moving now to FIGS. 4A and 4B, each of FIGS. 4A and 4B
presents certain components of the hydraulic oil well pumping
system 100 of FIG. 1A. These components are supported on the skid
180. First, each figure shows a unique dual-chamber tank 490.
Working oil is housed in a lower chamber 495, while valves and
hoses are housed in an upper chamber 492. A lid 494 is provided
over the upper chamber 492.
[0095] The valves are not clearly seen in FIGS. 4A and 4B; however,
FIG. 5 shows an exploded view of the valves, or valve stack 500.
The valve stack 500 generally includes a valve body 510, a
downstroke control valve 520, and a sub-plate manifold 530. These
components work together to form a four-way valve that allows
hydraulic oil to be pumped from the pump 184 to the annular area
155 through oil line 170. The four-way arrangement also allows the
operation and control of two wells stroking alternately.
[0096] As another feature, the valve stack 500 permits oil to
return to the fluid reservoir chamber 495 via a restricted orifice.
In this arrangement, the restricted orifice is referred to as a
downstroke control valve, shown at 520. Oil returns to the fluid
reservoir chamber 495 through the downstroke control valve 520 in
response to gravitational forces applied to the piston 160 by means
of the rod string 120 and connected downhole pump.
[0097] In FIG. 5, various components of the valve stack 500 are
shown in perspective view. First, the valve body 510 is seen. The
valve body 510 serves as the directional control valve, which
controls fluid flow during the upstroke. A pair of four-way valve
end caps 512 are placed at either end of the valve body 510. The
end caps 512 are secured in place via a plurality of head cap
screws 513. O-rings 517 are seen placed between the end caps 512
and the valve body 510 to prevent oil leakage. These end caps 512
also allow for the insertion of a four-way spool 590, discussed
below.
[0098] The valve body 510 includes additional components. These
include a four way valve spring 514, studs 515, and insert nuts
516. The studs 515 and insert nuts 516 are used to connect the
valve body 510 to the downstroke control valve 520 and the
sub-plate 530. The valve spring 514 serves the purpose of returning
the four-way spool 590 to a neutral position in the absence of an
explicit control signal.
[0099] The downstroke control valve 520 represents an essentially
rectangular block that is located between the sub-plate manifold
530 and the valve body 510. The downstroke control valve 520 has
various passages allowing unrestricted flow in one direction (the
upstroke direction), and restricted flow in the other direction
(the downstroke direction). The downstroke control valve 520
includes a pair of valve cartridges 522. The cartridges 522 are
mechanically adjustable to restrict the return flow during a
downstroke. In this way, the cartridges 522 serve as restricted
orifices to limit the return flow of hydraulic fluid, e.g., a
refined oil or a clean aqueous fluid, from the cylinder during a
downstroke. One cartridge 522 may control one well ("Well A"),
while another cartridge 522 limits the rate of flow of oil from the
cylinder of another well ("Well B").
[0100] As noted, the valve stack 500 also includes a sub-plate 530.
The sub-plate 530 represents a rectangular block having various
openings. These openings receive hydraulic pressure from the
high-pressure discharge of the hydraulic pump The openings also
interface the hydraulic lines 170, 175 that are in fluid
communication with the cylinder. The openings further interface
with various ports on the rest of the valve stack 500, starting
with the downstroke control valve 520.
[0101] In the arrangement of FIG. 5, the sub-plate 530 receives a
high pressure bypass cartridge 532 at one end. The cartridge 532
serves the purpose of limiting pressure delivered to the valve
stack 500 and to the cylinder via line 170. Under normal operating
conditions, the high pressure bypass cartridge 532 should not
activate--it is merely a safety precaution if, for example, the
valve stack 500 is compromised by a foreign object.
[0102] It is also seen that the sub-plate 530 has four ports 534.
The oil line 170 comes in at two of the ports 534--one for one well
("Well A") and one for another well ("Well B"). In addition, the
vent line 175 exits at two of the ports 534--one for one well
("Well A") and one for another well ("Well B"). The sub-plate 530
also includes head cap screws 535. The head cap screws 535
mechanically secure components of the valve stack 500 together as a
unitary tool.
[0103] Other parts of the valve stack 500 are also seen in FIG. 5.
These include an optional soft shift body 540 with an opposing pair
of soft shift cartridges 542. When used, the soft shift cartridges
542 serve the purpose of reducing shock while shifting the four-way
valve 510.
[0104] A pilot valve 550 is also provided. The pilot valve 550
receives an opposing pair of pilot solenoid coils 552. Further, the
pilot valve 550 has a body seal plate 554. The pilot valve 550
utilizes a small and manageable amount of hydraulic fluid,
controlled by the solenoid coils 552, to shift the much larger
four-way valve 510. Pilot pressure is directed from the pilot valve
550 to the valve body 510 to shift the spool 590. This pilot
pressure acts on either end of the spool 590 and against the end
caps 512 to force the spool 590 and to shift the valve position.
Once the spool 590 is shifted, the main hydraulic flow path through
the valve body 510 is redirected.
[0105] An alignment plate 545 is seen between the soft shift body
540 and the pilot valve 550. The alignment plate 545 receives a
plurality of screws 555, and insures alignment of the soft shift
body 540 and the pilot valve 550.
[0106] Returning to FIGS. 4A and 4B, the dual-chamber tank 490
presents a unique arrangement for the valve stack 500 and a fluid
reservoir. Because the valve stack 500 resides in the upper chamber
492 over the fluid reservoir, any nuisance leaks from the valve
stack 500 will drip into the lower chamber 495. At the same time,
because the valve stack 500 is isolated from the hydraulic oil in
the lower chamber 495, the electronics need not be
explosion-proof.
[0107] As an additional feature, the dual-chamber tank 490 employs
a pair of inhale and exhale lines (not shown). The inhale and
exhale lines create something of a bellows approach to pump fresh
air into the tank 490 and to purge the air and potentially
explosive gas from the fluid reservoir chamber 490 by way of the
fluctuating fluid level. Because the hydraulic cylinder 150 mounts
directly in the production line, that is, over the wellhead 105,
there is a possibility of migrating gas from the wellbore 115 to
the hydraulic oil reservoir chamber 495 via seal 244.
[0108] In operation, the hydraulic fluid level will rise and fall
in the reservoir chamber 495 on each stroke of the piston 160. Two
check valves are placed in the bulkhead (not shown) separating the
upper 492 and lower 495 chambers. One check valve allows air (and
residual oil drips) to flow from the upper chamber 492 in to the
lower chamber; the other check valve allows air from the lower
(fluid reservoir) chamber 495 to be safely vented outside the
cabinet 490. Optionally, a vent line (not shown) may be run from
the upper chamber 492, where applicable, to the outside of a
building or other enclosure. In this way, the fluctuating hydraulic
fluid level is used to "pump" fresh air from the upper chamber 492,
through the lower reservoir chamber 495, and then safely directed
outside.
[0109] As noted above, each of FIGS. 4A and 4B show a prime mover.
The prime mover is designed to provide working power to a pump
(seen at 184 in FIG. 1). In FIG. 4A, the prime mover 482A is shown
as an internal combustion engine 482A. In FIG. 4B, the prime mover
482B is shown as an electric motor.
[0110] Also seen in each of FIGS. 4A and 4B is an electronics
cabinet 484A, 484B. The illustrative cabinets 484A, 484B present
two separate chambers--one for 480 volt AC motor controls, and one
for programmable logic controller (low voltage) wiring. In the case
of electronics cabinet 484A (for the gasoline engine), the cabinet
484A may optionally have only one box.
[0111] FIG. 6 is an engineering diagram showing illustrative
hydraulic circuitry 600 of the hydraulic oil well pumping system
100 of FIG. 1, in one embodiment. Fluid lines and certain
components for the system 100 are shown schematically.
[0112] First, a motor is shown at 682. The motor 682 is an electric
motor that serves as a prime mover for powering a pump. It is
understood that the prime mover may alternatively be an internal
combustion engine. Alternatively, the motor 682 may utilize
pneumatic cylinders, weight or gravity-driven cylinders, mechanical
spring-driven cylinders or other source of fluid power.
[0113] Next, a hydraulic pump is shown at 684. The illustrative
pump 684 is a vane pump. However, it is understood that the pump
684 may be any type of fixed or variable displacement hydraulic
pump. The hydraulic discharge of the vane pump 684 is directed
under the control of a programmable logic controller, either to the
cylinder 155 or back to the tank 490.
[0114] The pump 684 pumps a working fluid such as a clean or
refined oil from a reservoir 695. The reservoir may be, for
example, the lower chamber 495 of FIGS. 4A and 4B. A line 686 is
shown pulling oil from the reservoir 695 into the pump 684. The oil
is then delivered through line 672 and then to lines 670 to a pair
of wells 615A, 615B.
[0115] Each well 615A, 615B employs a hydraulic cylinder 650. Each
cylinder 650, in turn, has a piston 665 and polished rod 660 that
together reciprocate in response to fluid pressure applied by the
cyclic injection of oil through lines 670. An annular area 655 is
formed below the piston 660 and between the polished rod 660 and
surrounding cylinders 650. Each piston 665 has a piston ring (seen
in FIG. 2A at 266) that provides a seal for holding fluid pressure
within the cylinders 650. The cylinders 650 are illustrative of
cylinder 150 described above, while the oil lines 670 are
representative of oil lines 170 from FIGS. 1A and 2A.
[0116] En route to the cylinders 650, the oil will travel through a
directional control valve 692. The control valve 692 may be, for
example, the discrete four-way valve stack 500 of FIG. 5.
Alternatively, the control valve 692 may be a proportional valve or
may be part of a variable speed prime mover. In any embodiment, the
control valve 692 allows hydraulic oil to be pumped from the pump
684 to the annular area 655 through oil line 670. Pumping is
controlled by a programmable logic controller (not shown).
[0117] The hydraulic circuitry 600 also includes a downstroke
control valve 694. The down stroke control valve 694 may be part of
the discrete valve stack 500 of FIG. 5. To this end, the
directional control valve 692 and the downstroke control valve 694
are shown in FIG. 6 by a common bracket at 690. The down stroke
control valve 694 permits oil to return to the fluid reservoir 695
via a restricted orifice, and then through reservoir line 688. This
takes place when the directional control valve 692 is in its
"neutral" position. Since pressure no longer forces the piston 660
upwardly, it begins to drop in response to gravitational forces
applied to the pistons 660 by means of the rod string 120 and
connected downhole pump.
[0118] Several additional components are seen in FIG. 6 as part of
the hydraulic circuitry 600. These include a vent line 675, a heat
exchanger 676, and an oil filter 678. The vent line 675 is
comparable to line 175 of FIGS. 1A and 2A. The heat exchanger 676
is, preferably, an air-over-oil heat exchanger that utilizes a fan
for cooling oil. The oil filter 678 filters return oil before it is
deposited into the reservoir 695. A 25 psi bypass valve may
optionally be provided so that excess pressure is not applied to
the filter media in the filter 678. The four-way valve 692 or the
bypass valve 673 directs return oil through the heat exchanger 676
and filter 678.
[0119] It is again noted that the hydraulic circuitry 600 of FIG. 6
shows two different cylinders 650 in two different wells 615A,
615B. The valve stack 690 is capable of driving two different wells
concurrently, provided the requirements of the two wells are
similar. The system can only operate one upstroke at a time, but
can operate two wells alternating upstrokes. While one well 615A is
upstroking, the other well 615B is downstroking. However, the valve
stack 690 may be used to drive a piston 660 in only a single well
should the operator so choose. Operating two wells is a capability,
not a requirement.
[0120] In either design, it is desirable for the operator to know
where the piston 665 is within the cylinder 650 during any given
part of the cycle. One reason is so that speed control may be
applied to the pump 684. Specifically, the operator may wish to
decrease the speed of the pump 684, and thus decelerate the piston
665 and rod string at the ends of the upstrokes and
downstrokes.
[0121] As noted above, hydraulically actuated reciprocating sucker
rod pump systems have historically employed sensors along the
wellhead. The sensors may be mechanical, hydro-mechanical,
pneumatic, pneumatic-mechanical, acoustic, electronic or
electro-mechanical position indicating devices to detect the
position of the piston. For example, U.S. Pat. No. 7,762,321
teaches the use of a plurality of "proximity switches" along the
actuation cylinder to detect the location of an object along the
piston. When a proximity switch detects the object, a limit switch
is activated that de-energizes a valve. Sensors have also been used
to detect travel speed or direction and are used to control piston
position, speed or direction.
[0122] Position feedback on hydraulically actuated rod pumping
systems has been required to intelligently react to, control,
monitor, or record the effects of dynamic load changes to the
bottom-hole equipment. For example, it is known to mount the
cylinder above the wellhead with the cylinder's rod exposed to the
atmosphere for attachment of position indicating devices or linear
position transducers. However, it is desirable to employ a
simplified system that does not require the presence of sensors at
or above the wellhead. Placing exposed electrical components in
such an environment is undesirable. Furthermore, the wellhead is an
area that sees much activity during well work and the small sensor
components and cabling could be easily damaged. Thus, it is
proposed herein to employ a rod pumping system and method that
mathematically infer the piston position from a remote location.
This is done by measuring cumulative or volumetric flow of the
hydraulic working fluid into and out of the cylinder.
[0123] In connection with a hydraulic oil well pumping system, it
is possible to use the hydraulic pressure in the annular area 155
to measure load on the piston 160. Generally, hydraulic pressure
may be calculated as:
L=F.times.A [0124] where: [0125] L=load on the piston (pounds);
[0126] F=Force against the piston (psi); and [0127] A=Annular area
(in.sup.2).
[0128] However, it is believed by the inventors herein that
hydraulic fluid dynamics, in addition to the load calculation, may
also be used to determine the relative position of the piston 165
within the cylinder 150. This may be done by measuring the total
fluid volume or flow rate of fluid going into, and returning from,
the annular area 155 of the hydraulic cylinder 150 during the
upstroke and the down stroke. The position of the piston 165 within
the cylinder 150 is then inferred from the volumetric measurements,
all at a safe distance from the wellhead 105.
[0129] Various techniques may be employed for measuring fluid flow.
In one aspect, differential pressure measurements may be used to
measure the flow rate of hydraulic fluid. A cumulative series of
flow rate measurements over a known cross sectional area is
equivalent to a total fluid volume over that time period. The
pressure measurements are made at the valve stack 500 and not at
the wellhead 105 or cylinder 150. Preferably, pressure sensors and
transmitters are located along the sub-plate 530, but could be
placed anywhere along the main hydraulic (or oil) line 170 as
well.
[0130] In another aspect, a flow meter such as a paddle wheel may
be used. A paddle wheel has a shaft that is turned in response to
hydraulic forces on a paddle. A correlation can be made between the
number of rotations of the shaft at or near the valve stack 500
during a given period of time and a volume of fluid that passes
across the paddle wheel during that time period. Of course, the
present system and methods are not limited to the technique used
for measuring volumetric flow unless expressly stated in the
claims.
[0131] Next, the volume of the annular area is calculated:
V.sub.A=L.sub.s.times.A.sub.A [0132] where: [0133] V.sub.A=Volume
of the annular area (gallons); [0134] L.sub.S=Stroke length of the
piston (inches); and [0135] A.sub.A=Annular area [Cylinder
area-piston area] (in.sup.2)
[0136] From this, it is possible to calculate gallons of fluid
pumped per stroke inch:
F=V.sub.A/L.sub.s [0137] where: [0138] F=Fluid pumped (gallons per
stroke inch); [0139] V.sub.A=Volume of the annular area (gallons);
and [0140] L.sub.S=Stroke length of the piston (inches).
[0141] By way of example, assume the effective volume of the
cylinder (the annular area 155 under the piston 165) is 10 gallons,
and the stroke is 288 inches:
F = 10 gallons / 288 inches = 0.035 gallons / stroke inch .
##EQU00001##
[0142] In a pumping cycle, the volume of hydraulic oil pumped into
a cylinder and the corresponding rod piston position are linearly
related. Thus, F (gallons/stroke inch) is not dependent on the
velocity at which the piston is traveling or the pump pressure
applied. It is also noted that a fixed displacement pump offers a
unique advantage in that it is known how long it takes to fill the
annular area V.sub.a. Thus, if the pump is pumping at 10
gallons/minute, the annular area V.sub.a will be filled in 10
minutes when V.sub.a is 10 gallons. Of course, the use of the fixed
displacement pump is only of benefit on the upstroke. On the down
stroke, the velocity of the piston will be dependent on the
free-fall of the piston 160 and the size of the restricted orifice
in the downstroke control valve 520 or 694. Therefore, the
calculations concerning F are critical to knowing the position of
the piston 160 on the down stroke.
[0143] Another advantage to the present method is that no sensors
are needed at the wellhead to determine piston location. Downhole
well conditions may be monitored remotely by combining the
cylinder's piston load and position without attaching devices on or
near the wellhead. This enables remote monitoring and control of
the cylinder's position, load and acceleration, while remotely
monitoring the effects of the downhole dynamics on the fluid power
system.
[0144] It is noted that diagnosis of a rod-pumped well based upon
surface parameters was first presented by Gibbs in U.S. Pat. No.
3,343,409. Surface load and piston position are measured at
consistent time intervals during the complete stroke cycle at the
surface. The dynamics of the rod string and fluid are known, and
from these pieces of information, it is possible to calculate the
downhole load and position. This is a known procedure. However,
this procedure requires that the operator or system know both the
load and position of the polished rod at the surface. This further
requires directly attached pressure and load sensors in the
wellhead environment. It should be noted that directly attached
sensors may not be used in the configuration where the hydraulic
cylinder is placed inside the wellbore and submerged in crude
oil.
[0145] The operator may wish to monitor hydraulic fluid pressure
during the upstroke. For example, a pressure limit switch may be
employed to cut off the pump in the event pressure spikes above a
certain value. This is a safety feature that comes into play if,
for example, the pump becomes stuck downhole. If excess pressure is
detected along oil line 672, a relieve valve 673 may be used to
release oil from line 672.
[0146] In one aspect, the absolute volume value (V.sub.A) is not
required; rather, a relative volume, or flow rate, value may be
used. Using a measurement of fluid volume pumped, the operator can
correlate the amount of fluid volume injected into a cylinder
(annular area 155) to push the piston to the top of its stroke
length and the position of the piston ring. Thus, for example, if a
cylinder (annular area 155) has received 10 gallons for a full
stroke length, then the operator knows that the piston is half way
up the cylinder (144 inches) when 5 gallons have been pumped into
the annular area 155. This relation between position and volume
within the cylinder is linear. This also assumes little to no
piston ring leakage during the stroke. If there is piston ring
leakage, that oil is recovered through the vent line 175. This
limits the effect of any consistent piston ring leakage to
individual strokes; the effects are not cumulative.
[0147] FIG. 7 is a flow chart showing steps that may be performed
for a method 700 of pumping oil from a wellbore, in one embodiment.
The wellbore has a bore extending into an earth surface. The method
700 employs the unique pumping system described above, including
the set of valves shown in FIG. 5 that are controlled by an
electrical control system. The valves cyclically direct hydraulic
fluid into a cylinder. The pressure created by the hydraulic fluid
causes a piston and connected rod string and downhole pump to
reciprocate. This, in turn, causes reservoir fluids to be produced
from a wellbore to the surface through positive displacement.
[0148] Referring to FIG. 7, the method 700 first comprises
providing an elongated hydraulic cylinder. This is shown at Box
710. The cylinder is positioned over the wellbore. The cylinder may
either be over an associated wellhead as shown in FIG. 2A, or
inside the wellbore below the wellhead as shown in FIG. 3.
[0149] The method 700 also includes providing a piston. This step
is provided at Box 715. The piston may be in accordance with the
piston 165 of FIG. 1A. The piston is movable between upper and
lower rod positions within the cylinder. The piston creates an
annular seal below the piston between a connected polished rod and
the surrounding cylinder. Hydraulic pressure acts against the
piston.
[0150] The method 700 further includes mechanically connecting the
piston to a rod string, such as through a threaded coupling. This
may be done through a polished rod between the piston and the rod
string. When the piston reciprocates, the polished rod and
connected rod string reciprocate with it. This is shown at Box 720.
The rod string extends downwardly from the piston and into the
wellbore. The rod string has a downhole pump connected to it for
lifting fluids to the surface in response to reciprocation of the
rod string.
[0151] The method 700 also includes providing a hydraulic pump.
This is seen at Box 725. Preferably, the pump is a fixed
displacement pump. The pump is powered by a prime mover. The prime
mover may be an electric motor, an internal combustion engine, or
other driver.
[0152] The method 700 also has the step of connecting the pump and
the hydraulic cylinder with an oil line. This is indicated at Box
730. The oil line transmits hydraulic fluid from the pump to the
cylinder.
[0153] Still further, the method 700 includes providing a
directional control valve. This is given at Box 735. The
directional control valve moves between upstroke and downstroke
(neutral) flow positions in response to signals from an electrical
control system. The electrical control system may be, for example,
a programmable logic controller. When the valve is in its open
position, it directs hydraulic fluid such as oil from the pump,
through the oil line and into an annular area formed between the
piston and the surrounding cylinder. In the neutral position, the
control valve allows oil to flow back from the cylinder to the
reservoir through a downstroke control valve.
[0154] It is understood that the downstroke control valve need not
be a discrete valve. The downstroke control valve may be a nitrogen
accumulator or any other device that captures the energy from the
gravitational fall of the piston and connected polished rod, rod
string and downhole pump.
[0155] The method 700 also has the step of providing a fluid
reservoir. This is shown at Box 740. The reservoir contains
hydraulic fluid to be supplied to the pump.
[0156] The method 700 next includes providing a reservoir line.
This is seen at Box 745. The reservoir line transmits hydraulic
fluid from the cylinder to the reservoir. An example of a reservoir
line is seen at line 688 of FIG. 6. Optionally, a filter is
provided along the reservoir line. A filter is seen at 678 of FIG.
6.
[0157] The method 700 also has the step of providing a down stroke
control valve. This is shown at Box 750 of FIG. 7. The down stroke
control valve chokes the flow of fluid from the cylinder back to
the reservoir. This, in turn, limits the rate of flow of hydraulic
fluid. An example of a down stroke control valve is shown
schematically at 694 in FIG. 6.
[0158] The method 700 also offers the step of controlling movement
of the piston as it moves between upper and lower rod positions.
This step is provided at Box 755. The step of Box 755 is done by
using an electronic control system. The control system controls the
valves and the pump to cycle the pump between (i) an "upstroke"
condition wherein the pump is pumping oil through the control
valve, through the oil line and into the hydraulic cylinder to move
the piston to its upper rod position, and (ii) a "neutral"
condition wherein the pump is no longer pumping oil into the
hydraulic cylinder, but is allowing oil to flow back through the
oil line in response to gravitational fall of the piston. The
electronic control system is programmed to cycle based upon a
volumetric calculation of hydraulic fluid in the cylinder and
without reference to position sensors along the wellhead.
[0159] Preferably, and as noted above, the electronic control
system controls movement of the rod based on (i) the volume, or
rate, of hydraulic fluid sent to the cylinder during the "upstroke"
valve condition, (ii) the volume, or rate, of hydraulic fluid
returned from the cylinder during the "neutral" valve condition, or
(iii) both. Optionally, the control system may send a signal to
cause the pump to vary its output, to cause a valve to adjust its
proportional flow, or to change an operating speed of the prime
mover based upon either (i) a volume of fluid that has moved into
the hydraulic cylinder during the "upstroke" valve condition, or
(ii) a volume of fluid that has returned from the hydraulic
cylinder during the "neutral" valve condition.
[0160] In one aspect, the electronic control system sends a signal
to cause the valve to change flow paths and to initiate a down
stroke of the piston based upon (i) a relative measurement of a
volume, or rate, of fluid that has moved into the hydraulic
cylinder, or (ii) an absolute volume of fluid that has moved into
the hydraulic cylinder, during the "upstroke" valve condition. The
measurement of fluid volume may be based upon (i) pressure
differential across a fixed orifice, (ii) a flow meter such as a
paddle wheel, or (iii) fluid level in the reservoir. Alternatively,
some combination of these approaches, or other methods of measuring
a moving fluid volume may be used.
[0161] Also, the method 700 includes reciprocating the piston and
mechanically connected rod string in order to pump oil from the
wellbore. This is indicated at Box 760. The step of Box 760 is the
natural result of operation of the control system and pump over
time.
[0162] It is noted that by taking volumetric measurements over
time, the operator can plot the position of the piston during the
strokes. In addition, velocities, and accelerations can be
calculated. Using a programmable logic controller, the system may
be controlled to operate at a constant speed during the upstroke of
the piston. Further, the pump speed may be altered prior to and
during changes of direction to reduce load on the rod string and
connected pump. In this respect, the surface stroke velocity can be
proactively altered to minimize the stress on the sucker rod string
and pump. This can be done by controlling the pump speed, and by
controlling the bleed-down rate for the relief line 675 through the
down stroke control valve 694. This helps to reduce fatigue of the
sucker rod string 120 and to minimize fluid or gas pounding effects
upon the bottom hole pump.
[0163] In one aspect, the operator sets the cycle for the down
stroke based on time. The operator estimates how long it takes the
piston 660 to fall to the bottom of the cylinder 650. The pumping
of hydraulic fluid is not resumed until a designated period of time
for the down stroke has lapsed. By monitoring volume, or rate, of
flow out of the cylinder 650, the system may make small adjustments
or change valve states in order to minimize stress on the
mechanical system.
[0164] FIGS. 8A and 8B are another flow chart. Here, steps are
shown for a method 800 of determining the position of a piston
within a hydraulic cylinder. The piston is a hydraulically actuated
piston that resides within a cylinder. The cylinder, in turn, is
positioned over a wellbore.
[0165] The method 800 first includes determining a volume of
hydraulic fluid needed to fill the cylinder. In one aspect, the
volume is an annular area below the piston and between a connected
polished rod and a surrounding hydraulic cylinder. This is shown at
Box 810.
[0166] The method 800 also includes determining a rate for filling
the cylinder during the upstroke of the piston. This is provided at
Box 820. The annular area is filled using a pump along with an oil
line that provides fluid communication between the pump and the
annular area. The rate at which the cylinder can be filled is a
function of the hydraulic pump output and the speed at which that
pump is driven.
[0167] The method 800 further has the step of determining a first
time. This first time is the time it takes to fill the annular area
(or cylinder) during the upstroke. This is seen at Box 830. The
step of box 830 is based upon the determined volume and rate from
the steps of Boxes 810 and 820. This provides a baseline to which
subsequent strokes can be calibrated against. In general, the
theoretical time to fill the cylinder is a minimum. Other factors
such as degraded pump efficiencies or piston ring leakage may
increase the time required to fill the cylinder.
[0168] The method 800 still further includes determining a second
time. This second time is the time it takes to drain the fluid from
the cylinder through a down stroke control valve. This is shown at
Box 840. The down stroke control valve has a restricted orifice for
reducing or restricting a rate at which the piston falls during
draining. The rate at which the downstroke occurs is not constant.
Downhole loads fluctuate significantly depending on changing
conditions, and as the loads shift during a downstroke, the rate at
which fluid is allowed to pass through the orifice also changes. It
is therefore critical to closely monitor both of these changing
loads and position measurements to apply Gibbs' method for
calculating the conditions during the full stroke cycle.
[0169] The method 800 also has the step of controlling movement of
the piston as it reciprocates between upper and lower rod
positions. This step is provided at Box 850. The step of Box 850 is
done by using an electronic control system. The control system
causes the pump to cycle between (i) an "upstroke" condition
wherein the pump is pumping oil through the control valve, through
the oil line and into the hydraulic cylinder to move the piston to
its upper rod position over the first time, and (ii) a "neutral"
condition wherein the pump is no longer pumping oil into the
hydraulic cylinder, but is allowing oil to flow back through the
oil line and through the down stroke control valve in response to
gravitational fall of the piston over the second time. Of interest,
the cycling is performed without reference to position sensors
along the wellhead.
[0170] The method 800 further includes monitoring hydraulic fluid
pressure in the oil line. This is shown at Box 860. The pressure is
monitored during the first time and the second times. In one
aspect, monitoring is conducted at regular intervals to correlate
to the position samples.
[0171] The method 800 then includes reciprocating the piston and
mechanically connected rod string in order to pump oil from the
wellbore. This is provided at Box 870. In practical effect, the
step of Box 870 is the result of the step of Box 850 over time.
[0172] In one aspect, the method 800 further includes calculating a
position of the piston during the upstroke. This calculation is
based upon (i) the relative volume, or rate, of hydraulic fluid
injected by the pump during the "upstroke" condition, (ii) the
absolute volume of fluid injected by the pump during the "upstroke"
condition, or (iii) a full scale calibration from the ratio of a
pressure reading in the oil line to a baseline pressure
representing a pressure value just before the piston has reached a
mechanical top of its upstroke. This is provided at Box 880. The
method 800 may then include the step of sending a signal from the
electronic control system to cause the pump to vary its output, to
cause a valve to adjust its proportional flow, or to change an
operating speed of the prime mover based upon the location of the
piston during its upstroke. This is shown at Box 885.
[0173] In another aspect, the method 800 further includes
calculating a position of the piston during the downstroke based
upon (i) the relative volume, or rate, of hydraulic fluid drained
from the hydraulic cylinder during the "neutral" condition, (ii)
the absolute volume of hydraulic fluid drained from the hydraulic
cylinder during the "neutral" condition, or (iii) when the pressure
reading in the oil line has reached a value of substantially 0,
indicating a mechanical bottom of the down stroke. This is provided
at Box 890. When the piston noticeably hits the bottom of the
stroke, the volumetric measurements can be reset, allowing each
stroke to be measured independently without influence from previous
strokes. The method 800 then includes the step of sending a signal
from the electronic control system to cause the pump to vary its
output, to cause a valve to adjust its proportional flow, or to
change an operating speed of the prime mover based upon the
location of the piston during its down stroke. This is shown at Box
895.
[0174] As can be seen, a method for measuring and controlling the
position of the hydraulic piston in a linear stroking fluid power
cylinder, used specifically for actuating a sucker rod string and
bottom hole plunger pump in oil or gas wells is offered herein. The
system and method provide the ability to remotely measure or
control a piston's position, speed and direction in the absence of
direct measurements of position and/or load at the wellhead.
[0175] Beneficially, the operator will be able to stop or slow the
piston and connected rod string at various positions during the
upstroke or downstroke. This allows the operator to run various
down-hole valve tests. This is in addition to the slowing of the
piston at the ends of the strokes to minimize mechanical stresses
on the complete system.
[0176] Under one embodiment of the systems and methods described
herein, differential pressure measurements taken at a given orifice
(which corresponds to square of the fluid velocity through a give
orifice) may be used to "calibrate" a system onto itself. Under
such embodiment, there would be no need to account for certain
parameters including location of pressure taps relative to fixed
orifice, hydraulic fluid viscosity, oil temperature, orifice
diameter, or even cylinder volume, etc, because all such factors
may be corrected for in a calibration operation. Under this
embodiment, it is known that the piston within a hydraulic system
always starts from position zero, and that full stroke length can
be periodically detected through a spike in hydraulic pressure.
Although the goal is to prevent hitting the mechanical top of a
piston upstroke on each stroke, such piston position may be
periodically probed to perform the calibration operations described
below. Data samples of differential pressure before and after a
given orifice (and therefore data samples of fluid velocity through
a give orifice) may be logged and scaled according to a percentage
of the full stroke length. The known piston stroke length can be
applied to this percentage to derive the unitized measurement of
actual piston position. The process yields a calibration factor,
which may be pro-actively used to determine real-time position of a
piston on subsequent strokes, or between calibration cycles. Note
that differential pressure measurements may be taken across a fixed
orifice, or by other such flow rate measurement techniques, located
at or near the valve stack or along an oil line to or from the
cylinder, but embodiments are not so limited.
[0177] The calibration approach described above may be implemented
using the following steps. assuming a data sampling rate of 10 ms:
[0178] Calculate the square root of sampled differential pressure
data (which corresponds to the fluid velocity through the orifice)
[0179] Multiply that instantaneous fluid velocity data by a 10 ms
sample interval and add result to a running total (a preferred
method would be to use the trapezoidal rule to calculate the
average velocity over this sample period) [0180] Assume "System
performs X units of velocity for 10 ms" [0181] Subsequent data
samples sweep out the area under a velocity curve which is
equivalent to position data of a piston (i.e. data samples capture
information of a piston's position, velocity, and acceleration, as
all three are related over time) [0182] At any given point, a
running total register holds what amounts to a cumulative position
reading of the piston; note that such values are scaled by a yet
unknown factor (unknown until the end of stroke, where we can
derive it from the stroke length) [0183] Samples from the running
total register (along with the piston load) may be read, and logged
for later processing, from the register at a more reasonable sample
rate than the high frequency data sampling rate; note that since
differential pressure/velocity is being processing at a very high
sample rate, the position value derived (or more accurately,
integrated) from the velocity data at any given point should be
nearly as precise as the inputs [0184] At the end of piston
upstroke, the position value of the piston is assumed to be 100% of
the stroke length which is to be mechanically calibrated/verified
periodically by deadheading the piston [0185] Gathered position
samples over the total stroke (logged from the high frequency,
velocity over time, register) may then be scaled according to a
calibration percentage/factor and known overall stroke length to
yield actual piston position in inches [0186] The same procedure as
described above starts over for the piston downstroke, which might
have some different fluid dynamics in the return path; such
difference should not matter since upstroke and downstroke are
treated independently [0187] Starting with an assumed top of piston
stroke, as previously determined, bottom of stroke may be detected
when the hydraulic pressure effectively drops to zero, meaning the
piston is resting on the mechanical bottom of stroke.
[0188] Under this embodiment, a relatively simple sensor and method
may be used to measure differential pressure across a given
orifice. One does not need to know anything about certain
parameters including location of pressure taps relative to fixed
orifice, hydraulic fluid viscosity, oil temperature, orifice
diameter, or even cylinder volume, etc, because they are more or
less constants embedded in the "position" data. Those details all
become irrelevant once end of the stroke is determined. These
variable factors are all contained in a single calibration factor
that, along with the stroke length, will scale the individually
calculated position samples into familiar units such as inches.
This process yields a calibration factor which may be pro-actively
used to determine real-time position of the piston (and that
scaling/calibration factor will most likely be different from
upstroke to downstroke).
[0189] It is understood that the hydraulic oil well pumping system
100 of FIG. 1 and the method 700 for pumping oil of FIG. 7 are
merely illustrative. Other arrangements may be employed in
accordance with the claims set forth below. Further, variations of
the method for determining position of the piston may fall within
the spirit of the claims, below. It will be appreciated that the
inventions are susceptible to modification, variation and change
without departing from the spirit thereof.
* * * * *