U.S. patent application number 11/084222 was filed with the patent office on 2006-02-02 for long-stroke deep-well pumping unit.
This patent application is currently assigned to Weatherford/Lamb, Inc.. Invention is credited to Robert T. Brooks, Clark E. Robison.
Application Number | 20060024177 11/084222 |
Document ID | / |
Family ID | 35732397 |
Filed Date | 2006-02-02 |
United States Patent
Application |
20060024177 |
Kind Code |
A1 |
Robison; Clark E. ; et
al. |
February 2, 2006 |
Long-stroke deep-well pumping unit
Abstract
Methods and apparatus for driving a positive displacement pump
disposed within a wellbore are disclosed herein. Embodiments of the
present invention provide a drive mechanism for driving the
downhole positive displacement pump. In embodiments of the present
invention, the positive displacement pump is hydraulically driven
and mechanically counterbalanced. The drive mechanism may be
mechanically or electrically controlled, or may be controlled by a
combination of mechanical and electrical controls.
Inventors: |
Robison; Clark E.; (Tomball,
TX) ; Brooks; Robert T.; (Houston, TX) |
Correspondence
Address: |
William B. Patterson;MOSER, PATTERSON & SHERIDAN, L.L.P.
Suite 1500
3040 Post Oak Blvd.
Houston
TX
77056
US
|
Assignee: |
Weatherford/Lamb, Inc.
|
Family ID: |
35732397 |
Appl. No.: |
11/084222 |
Filed: |
October 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10903574 |
Jul 30, 2004 |
|
|
|
11084222 |
Oct 22, 2004 |
|
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Current U.S.
Class: |
417/390 ;
417/424.1; 417/555.1 |
Current CPC
Class: |
Y10S 417/904 20130101;
F04B 47/04 20130101 |
Class at
Publication: |
417/390 ;
417/424.1; 417/555.1 |
International
Class: |
F04B 9/08 20060101
F04B009/08; F04B 53/00 20060101 F04B053/00 |
Claims
1. A drive mechanism for a downhole, reciprocating positive
displacement pump, comprising: a hydraulic drive comprising a
plurality of variable flow hydraulic pumps operatively connected to
a reversible rotary drive motor with a closed-loop, hydraulic
circuit; and a reciprocating counterbalance, wherein the hydraulic
drive is capable of dictating the pumping rate of the downhole
positive displacement pump and the reciprocating counterbalance is
capable of balancing a load on a rod string of the downhole
positive displacement pump and the drive mechanism.
2. The drive mechanism of claim 1, further comprising a plurality
of powering mechanisms which are capable of cooperating with the
hydraulic pumps and the drive motor to provide power for rotation
of the drive motor.
3. A drive mechanism for a downhole, reciprocating positive
displacement pump, comprising: a hydraulic drive comprising a
piston pump operatively connected to a reversible, variable-speed
electric motor; and a reciprocating counterbalance, wherein the
hydraulic drive is capable of dictating the pumping rate of the
downhole positive displacement pump and the reciprocating
counterbalance is capable of balancing a load on a rod string of
the downhole positive displacement pump and the drive
mechanism.
4. A drive mechanism for a downhole, reciprocating positive
displacement pump, comprising: a hydraulic drive comprising a pump
having a vane motor operatively connected to a reversible,
variable-speed electric motor; and a reciprocating counterbalance,
wherein the hydraulic drive is capable of dictating the pumping
rate of the downhole positive displacement pump and the
reciprocating counterbalance is capable of balancing a load on a
rod string of the downhole positive displacement pump and the drive
mechanism.
5. A drive mechanism for a downhole, reciprocating positive
displacement pump, comprising: a hydraulic drive comprising a
variable flow hydraulic pump operatively connected to a reversible,
variable-speed electric motor; and a hydraulic counterbalance,
wherein the hydraulic drive is capable of dictating the pumping
rate of the downhole positive displacement pump and the hydraulic
counterbalance is capable of balancing a load on a rod string of
the downhole positive displacement pump and the drive
mechanism.
6. The drive mechanism of claim 5, wherein the hydraulic
counterbalance is an accumulator.
7. The drive mechanism of claim 6, wherein the accumulator is
capable of reducing an amount of power expended by the hydraulic
drive during reciprocation.
8. A drive mechanism for a downhole, reciprocating positive
displacement pump, comprising: a hydraulic drive comprising a
variable flow hydraulic pump operatively connected to a reversible
rotary drive motor with a closed-loop, hydraulic circuit; and a
counterbalance reciprocatable downhole; wherein the hydraulic drive
is capable of dictating the pumping rate of the downhole positive
displacement pump and the reciprocating counterbalance is capable
of balancing a load on a rod string of the downhole positive
displacement pump and the drive mechanism.
9. A method of driving a downhole positive displacement pump,
comprising: providing a drive mechanism comprising a hydraulic
drive having a closed-loop hydraulic circuit; providing the
downhole positive displacement pump comprising a piston
reciprocatable within a cylinder, wherein the hydraulic drive is
operatively connected to the piston; operating the hydraulic drive
to pump downhole fluid using the positive displacement pump;
counterbalancing a load of the downhole fluid and the piston using
a hydraulic counterbalance; and controlling the speed and direction
of reciprocation of the piston within the cylinder using the drive
mechanism.
10. The method of claim 9, wherein the hydraulic counterbalance is
an accumulator capable of storing and releasing energy expended by
the hydraulic drive during reciprocation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S. patent
application Ser. No. 10/903,574, filed Jul. 30, 2004, which is
herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention generally relate to a
reciprocating positive displacement pump utilized downhole within a
wellbore to pump production fluid to a surface of the wellbore.
More specifically, embodiments of the present invention relate to a
drive mechanism for the downhole positive displacement pump.
[0004] 2. Description of the Related Art
[0005] To obtain hydrocarbon fluids from an earth formation, a
wellbore is drilled into the earth to intersect an area of interest
within a formation. Upon reaching the area of interest within the
formation, artificial lift means is often necessary to carry
production fluid (e.g., hydrocarbon fluid) from the area of
interest within the wellbore to the surface of the wellbore. Some
artificially-lifted wells are equipped with sucker rod lifting
systems.
[0006] Sucker rod lifting systems generally include a surface drive
mechanism, a sucker rod string, and a downhole positive
displacement pump. Fluid is brought to the surface of the wellbore
by reciprocating pumping action of the drive mechanism attached to
the rod string. Reciprocating pumping action moves a traveling
valve on the positive displacement pump, loading it on the
down-stroke of the rod string and lifting fluid to the surface on
the up-stroke of the rod string. A standing valve is typically
located at the bottom of a barrel of the pump which prevents fluid
from flowing back into the well formation after the pump barrel is
filled and during the down-stroke of the rod string.
[0007] The rod string of the sucker rod lifting system either
includes several rods connected together or one continuous rod.
Regardless of its make-up, the rod string provides the mechanical
link of the drive mechanism at the surface to the positive
displacement pump downhole. The typical rod string is constructed
from steel or some other elastic material.
[0008] To access hydrocarbon fluid within a well, it is often
necessary to drill a wellbore to a high depth within the formation,
often termed a "deep well." Pumping fluid from deep wells using a
sucker rod lifting system is problematic for several reasons.
First, the downhole positive displacement pump is submerged in the
downhole fluid so that the positive displacement pump may fill with
the surrounding production fluid upon reciprocation of the rod
string, and because the fluid level of a deep well is typically
located at a high depth within the wellbore, the rod string which
connects the positive displacement pump to the drive mechanism must
be long to access the fluids. A rod string of more than 10,000 feet
is not uncommon. Therefore, the high length of the rod string as
well as the material which makes up the rod string causes the rod
string to weigh a large amount.
[0009] Additionally, the stroking motion of the rod string must be
long to reduce the number of strokes required to displace the
production fluid. The length of the motion of the rod string and
the weight of the rod string cause the rod string to possess a high
momentum at the end of the up-stroke and down-stroke, often causing
the rod string to deform or break when motion is stopped between
the up-stroke and down-stroke (at the "turnaround"). Specifically,
the elastic nature of the material of which the rod string is
constructed makes the rod string vulnerable to rod stretch,
especially at the turnaround between the down-stroke and the
up-stroke where the momentum of the rod string is most difficult to
stop. Moreover, the stresses imposed on the rod string by a
mismatch between the dynamic characteristics of the surface drive
unit and the rod string may cause the rod string to break. This is
particularly true when the rod string bounces up and down when
attempting to switch the direction of the rod string at turnarounds
between the up-stroke and down-stroke. Generally, rod string motion
problems include premature rod string separation due to material
fatigue, damage to the well tubing in which the rod string
reciprocates and instantaneous rod string loads beyond the design
limit due to suddenly applied loads from dynamic mismatch.
[0010] The downhole pump efficiency is affected by unfavorable rod
string motion in other ways. A downhole pump needs time at the
bottom of each stroke to fill with fluid and time at the top of
each stroke to unload the fluid. Otherwise, the pump may cycle only
partially filled. Rod string motion problems, including rod string
damage, tubing damage, and only partial filling of the pump,
increase as the load on and speed of the rod string are
increased.
[0011] Sucker rod lifting systems include the additional problem
when the well is pumped down to the point where fluid only
partially fills the downhole pump barrel during the up-stroke of
the rod string. On the next down stroke, the rod string, including
the weight of the rod string and the fluid column, crashes into the
partially-filled pump barrel and upon the standing valve. This
crashing of the rod string is often termed "fluid pounding." The
condition at which fluid pounding occurs must be detectable by some
kind of monitoring system to relay the condition to pump
controls.
[0012] Another problem with deep-well sucker rod lifting systems is
that the difference between the loading on the rod string during
the up-stroke and the loading on the rod string during the
down-stroke is severe. The load on the rod string during the
up-stroke is much larger than the load on the rod string during the
down-stroke because the drive mechanism must lift the hydrocarbon
fluid from the wellbore on the up-stroke and must also contend with
gravitational forces acting downward on the rod string while
lifting the rod string for the up-stroke. In contrast, gravity aids
the rod string motion during the down-stroke by acting in the same
direction in which the rod string is moving, and fluid is not
lifted, eliminating the additional weight of the fluid. This uneven
loading requires a massive amount of horsepower for the drive
mechanism to lift the rod string on the up-stroke, while limited
horsepower is necessary for the rod string to fall into the
wellbore on the down-stroke. Uneven loading in deep well pumps
constitutes an inefficient use of horsepower because of the high
amount of work expended in moving the rod string upward which is
then not recovered upon the rod falling downward. Ideally, the rod
load is evenly divided between the up-stroke and down-stroke of the
pumping cycle to increase the efficiency of power use in the
pumping unit.
[0013] FIG. 5A illustrates the rod string motion in graphical form
for one drive mechanism currently used to cycle a rod string
through and between the up-stroke and down-stroke, the crank and
beam unit. Specifically, FIG. 5A shows a typical rod string motion
graph for a crank and beam pump mechanical drive mechanism. The
crank and beam pump mechanical drive mechanism articulates the rod
string upward and downward within the downhole cylinder with a
crank. The crank produces the sinusoidal rod string motion profile
shown in FIG. 5A.
[0014] As shown in FIG. 5A, the turnaround point between the
up-stroke and the down-stroke is at point T. The inter-cycle speed
of the rod string during the up-stroke and down-stroke is
sinusoidal and not constant, as indicated by the slope of the line
representing the up-stroke and the down-stroke. Namely, the rod
string moves at an uneven speed on the up-stroke and repeats the
up-stroke motion on the down-stroke.
[0015] Dyno-card loading graphs illustrate loading on the rod
string during a cycle, which includes the up-stroke, down-stroke,
and turnarounds of the rod string between the up-stroke and
down-stroke. The dyno-card graph represents load on the rod string
versus position of a defined point on the rod string with respect
to a defined point within or above the wellbore. Referring
specifically to FIG. 6A, which is the dyno-card profile of the beam
pump drive mechanism, the upper line between points J and K
represents the loading on the rod string during the up-stroke,
while the lower line between points J and K represents the loading
on the rod string during the down-stroke. Points J and K represent
the turnaround points of the rod string from the down-stroke to the
up-stroke and from the up-stroke to the down-stroke,
respectively.
[0016] The loading on the rod string is very erratic, as evidenced
by the loading profile on the dyno-card graph. From point J to
point K during the up-stroke, the rod string loading drastically
increases to point P, then drastically decreases to point Q, only
to increase and decrease again between points Q and K. The loading
on the rod string at point P, which is the highest load on the rod
string in this dyno-card profile, is higher than is healthy for the
rod string. Similarly erratic, on the down-stroke, the loading
drastically decreases to point R from point K, then increases to
point S, then decreases again before increasing back to point J.
This erratic loading on the rod string often stretches, breaks, or
otherwise damages the rod string. Additionally, this erratic
loading does not make efficient use of the horsepower which drives
the drive mechanism.
[0017] Another drive mechanism explored for cycling the rod string
through and between the up-stroke and the down-stroke is a
gear-driven mechanical drive system having a mechanical
counterbalance. As is shown in FIG. 5B, the mechanical drive system
induces constant rod string motion except at the turnaround point
T, so that inter-cycle speed is the same over the entire up-stroke
as well as the entire down-stroke. Because the slopes of the lines
on each side of the turnaround point T are not as severe as the
slopes of the lines on either side of the turnaround point T of
FIG. 5A, the inter-cycle speed of the rod string is lower for the
system of FIG. 5B than for the system of FIG. 5A.
[0018] Despite the decrease in inter-cycle speed, the mechanical
drive system with the mechanical counterbalance is generally an
improvement over the crank and beam pump drive mechanism because of
the more favorable loading profile evidenced in the dyno-card graph
of FIG. 6B. The loading on the rod string does not erratically vary
with position of the rod string; in fact, the loading on the rod
string is nearly constant on the upstroke, which is generally from
point L to point M and nearly constant on the down-stroke, which is
generally from point N to point O. The turnaround point between the
up-stroke and down-stroke is between points M and N, while the
turnaround point between the down-stroke and the up-stroke is
generally between points O and L.
[0019] While the inter-cyclic speed is good for this drive
mechanism, as is evidenced by the favorable rod string motion
profile shown in FIG. 5B, the loading on the rod string at the
turnarounds of the rod string is not desirable. The undulations on
the lines of FIG. 6B to the immediate right of the point L and to
the immediate left of the point N represent the jarring which the
rod string experiences at the abrupt stopping of motion and abrupt
beginning of motion in the opposite direction of the rod string at
the turnarounds. The jarring of the rod string also causes damage
to the rod string, which may include breaking or stretching of the
rod string. The amount of time the rod string spends at the top and
the bottom of the stroke is not long enough to produce a good,
smooth turnaround.
[0020] In gear-driven mechanical drive mechanisms, an electric
motor rotates a gear reducer, and the gear reducer restricts the
load and speed capacity of the mechanical drive mechanism. A
problem with the mechanically-driven pumping units is that
gear-driven pumping units are not very responsive to speed changes
of the polished rod. Gear-driven pumping units possess inertia from
previous motion so that it is difficult to stop the units or change
the direction of rotation of the units quickly. Therefore, jarring
(and resultant breaking/stretching) of the rod string results upon
the turnaround unless the speed (strokes/minute) of the rod string
during the up-stroke and down-stroke is greatly decreased at the
end of the up-stroke and down-stroke, respectively. Gear-driven
pumping units also are not sufficiently responsive to speed changes
because of the tendency of the belts to burn up at abrupt speed
changes and at high speeds and the torque limitations of gear
reducers present in these systems. Decreasing of the speed of the
rod string for such a great distance of the up-stroke and
down-stroke decreases the speed of fluid pumping, thus increasing
the cost of the well.
[0021] There is a need for a drive mechanism for a sucker rod
positive displacement pump which efficiently uses horsepower
provided to the drive mechanism. There is a further need for a
drive mechanism which controls loading on the rod string to reduce
rod string damage and to increase the amount of fluid volume pumped
by the downhole pump. There is a yet further need for a drive
mechanism which controls loading on the rod string during
turnarounds between the up-stroke and the down-stroke, and vice
versa. Finally, there is a need for a drive mechanism which is
sufficiently responsive to alter the speed of motion of the rod
string quickly.
SUMMARY OF THE INVENTION
[0022] In one aspect, embodiments of the present invention include
a drive mechanism for a downhole positive displacement pump,
comprising a hydraulic drive comprising a variable flow hydraulic
pump operatively connected to a reversible drive motor with a
closed-loop, hydraulic circuit; and a reciprocating counterbalance,
wherein the hydraulic drive is capable of dictating the pumping
rate of the downhole positive displacement pump and the
reciprocating counterbalance is capable of balancing a load on a
rod string of the positive displacement pump and the drive
mechanism.
[0023] In another aspect, embodiments of the present invention
provide a method of driving a downhole positive displacement pump,
comprising providing a drive mechanism comprising a hydraulic drive
having a closed-loop hydraulic circuit; providing the downhole
positive displacement pump comprising a piston reciprocatable
within a cylinder, wherein the hydraulic drive is operatively
connected to the piston; operating the hydraulic drive to pump
downhole fluid using the positive displacement pump;
counterbalancing a load of the downhole fluid and the piston using
a reciprocating counterbalance; and controlling the speed and
direction of reciprocation of the piston within the cylinder using
the drive mechanism.
[0024] In yet another aspect, embodiments of the present invention
include a drive mechanism for a downhole, reciprocating positive
displacement pump, comprising a hydraulic drive comprising a pump
operatively connected to a reversible, variable-speed electric
motor; and a reciprocating counterbalance, wherein the hydraulic
drive is capable of dictating the pumping rate of the downhole
positive displacement pump and the reciprocating counterbalance is
capable of balancing a load on a rod string of the downhole
positive displacement pump and the drive mechanism. Embodiments of
the present invention also include a drive mechanism for a
downhole, reciprocating positive displacement pump, comprising a
hydraulic drive comprising a variable flow hydraulic pump
operatively connected to a reversible, variable-speed electric
motor; and an accumulator, wherein the hydraulic drive is capable
of dictating the pumping rate of the downhole positive displacement
pump and the accumulator is capable of balancing a load on a rod
string of the downhole positive displacement pump and the drive
mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0026] FIG. 1 is a side view of a drive mechanism for a positive
displacement pump.
[0027] FIG. 2 is a front view of the drive mechanism of FIG. 1.
[0028] FIG. 3 is a perspective view of a portion of a mechanical
control system for the drive mechanism of FIGS. 1-2.
[0029] FIG. 3A is a cross-sectional view of a portion of the
mechanical control system of FIG. 3.
[0030] FIG. 3B is a section view of a portion of the mechanical
control system of FIG. 3.
[0031] FIG. 4 is a perspective view of an electrical control system
for the drive mechanism of FIGS. 1-2.
[0032] FIG. 5A is a graph of rod string motion during a rod string
cycle of a prior art beam pump drive mechanism.
[0033] FIG. 5B is a graph of rod string motion during a rod string
cycle of a prior art mechanical drive mechanism.
[0034] FIG. 5C is a graph of rod string motion during a rod string
cycle using embodiments of the present invention.
[0035] FIG. 6A is a dyno-card loading graph showing the loading on
the rod string during a rod string cycle using the prior art beam
pump drive mechanism.
[0036] FIG. 6B is a dyno-card loading graph showing the loading on
the rod string during a rod string cycle using the prior art
mechanical drive mechanism.
[0037] FIG. 6C is a dyno-card loading graph showing the loading on
the rod string during a rod string cycle using embodiments of the
present invention.
[0038] FIG. 7 is a side view of an alternate embodiment of a drive
mechanism for a positive displacement pump.
DETAILED DESCRIPTION
[0039] Embodiments of the present invention include a drive
mechanism including a highly responsive hydraulic drive motor
driven with a closed loop hydraulic circuit. The responsiveness of
the hydraulic drive motor results because the closed loop hydraulic
circuit works on both sides of the hydraulic drive motor to power
one side of the motor and brake one side of the motor when there is
a need to stop rotation of the hydraulic drive motor suddenly.
Additionally, the hydraulic drive motor is highly responsive to
speed changes because of the lack of revolving parts in the drive
mechanism, as revolving parts in a mechanical drive mechanism are
difficult to quickly reduce in speed or stop because of
inertia.
[0040] FIGS. 1 and 2 show side and front views, respectively, of a
drive mechanism 5 used to drive a positive displacement pump (not
shown) from a surface of a wellbore (not shown). The drive
mechanism 5 is preferably disposed at least partially within a
tower 19 having a base frame 4 connected by one or more beams 3 to
a platform 8. The positive displacement pump is preferably a
plunger pump or sucker rod pump and is located downhole within the
wellbore. The wellbore, which is a bore drilled within an earth
formation for conveying hydrocarbons, is located below and within a
wellhead 10 disposed at the surface of the wellbore.
[0041] The positive displacement pump is used to pump reservoir
fluid such as hydrocarbons, or combinations of water and
hydrocarbons, from within the wellbore to the surface of the
wellbore. To this end, the positive displacement pump is placed
within fluid within the wellbore. A rod string including a polished
rod 11 is disposed within a cylinder (not shown) of the positive
displacement pump to act as a piston upon upward and downward
movement within the cylinder. The positive displacement pump is a
one-way positive displacement pump which lifts fluid on the rod
string up-stroke and refills with fluid on the rod string
down-stroke. The drive mechanism 5 is used to cycle the positive
displacement pump to lift production fluid (preferably hydrocarbons
or combinations of water and hydrocarbons) from within the
wellbore.
[0042] The polished rod 11, part of the rod string portion of the
positive displacement pump, extends through the wellhead 10 as well
as above and below the wellhead 10. The polished rod 11 is
connected to the drive mechanism 5 by a hanging mechanism 9.
Specifically, the hanging mechanism 9 rigidly connects an upper end
of the polished rod 11 to a first end of at least one first
strapping member, preferably one or more lift belts 12, of the
drive mechanism 5. The first strapping member may in the
alternative include one or more chains.
[0043] The lift belt 12 is wound over the top of a lift pulley 13
and is operatively connected to an upper end of a counterbalancing
member, such as a counterweight 14, at a second end. The lift
pulley 13 is operatively connected to the platform 8 by one or more
bearings mechanisms 17A, as shown in FIG. 2. The one or more
bearings mechanisms 17A allow the lift pulley 13 to rotate relative
to the platform 8. The lift belt 12 is moveable around the lift
pulley 13 to lower the polished rod 11 by raising the counterweight
14 or to raise the polished rod 11 by lowering the counterweight
14.
[0044] The counterweight 14 includes one or more reciprocating
weights which counterbalance the load of the rod string. Weight may
be added or removed from the counterweight 14 as needed to
counterbalance the load of the rod string weight (on the rod string
up-stroke and down-stroke) and/or the downhole fluid weight (when
the rod string lifts fluid on the up-stroke). Preferably, the load
of the rod string is considered counterbalanced when the
counterweights are approximately equal to the rod string weight
plus approximately one half of the fluid column weight. The
counterbalance 14 advantageously reduces the volume and pressure of
hydraulic fluid utilized in the operation of the drive mechanism 5,
as described below.
[0045] Also operatively connected to the counterweight 14 is at
least one second strapping member, preferably one or more chains
22. A first end of the chain 22 is operatively connected to an
upper end of the counterbalance 14, so that the second end of the
lift belt 12 is connected to the counterbalance 14 closer in
proximity to the polished rod 11 than the first end of the chain
22. Additionally, a second end of the chain 22 is operatively
connected to a lower end of the counterbalance 14. The first and
second ends of the chain 22 are connected to the counterbalance 14
substantially in line with one another. In an alternate embodiment
of the present invention, one or more gear belts may be utilized in
lieu of the one or more chains 22.
[0046] The chain 22 is moveable around an idle sprocket 16 and a
drive sprocket 18, which are substantially coaxial with one
another. The idle sprocket 16 is operatively connected to the
platform 8 by one or more bearings mechanisms 17B which allow the
idle sprocket 16 to rotate relative to the platform 8. In an
alternate embodiment of the present invention, the idle sprocket 16
may be operatively connected to an additional platform (not shown)
above, adjacent to, or below the platform 8 on which the lift
pulley 13 is located by one or more bearings mechanisms.
[0047] The drive sprocket 18 is operatively connected to the base
frame 4 by one or more bearings mechanisms 17C. The one or more
bearings mechanisms 17C allow the drive sprocket 18 to rotate
relative to the base frame 4 by a drive shaft 27 extending through
the bearings mechanisms 17C and through the drive sprocket 18.
[0048] The drive shaft 27, in addition to extending through the
drive sprocket 18, extends through a drive motor 21. The drive
motor 21 provides the rotational force to rotate the drive shaft 27
as well as other members of the drive mechanism 5 through which the
drive shaft 27 extends. Referring primarily to FIG. 2, in addition
to the drive motor 21, the drive shaft 27 extends through and
rotates a rotating drum 15, a gear reducer 28, and a brake 24, all
of which are thus substantially co-axial with one another as well
as substantially co-axial with the drive sprocket 18 and drive
motor 21. The one or more bearings mechanisms 17C permit the drive
shaft 27 to rotate relative to the base frame 4, thereby allowing
the rotating drum 15, gear reducer 28, drive motor 21, and brake 24
to rotate relative to the base frame 4.
[0049] In the preferred embodiment shown, on one side of the drive
sprocket 18, the drive motor 21 and brake 24 are located in line
with the drive sprocket 18, with the drive motor 21 closest to the
drive sprocket 18 and the brake 24 farthest from the drive sprocket
18. On the other side of the drive sprocket 18, the gear reducer 28
and rotating drum 15 are located in line with the drive sprocket
18, with the gear reducer 28 disposed closest to the drive sprocket
18 and the rotating drum 15 located farthest from the drive
sprocket 18. Other configurations and location orders of the
components of the drive mechanism 5 rotatable by the drive shaft 27
are contemplated in embodiments of the present invention.
[0050] As mentioned above, the drive motor 21 rotates the drive
shaft 27, thereby rotating the drive sprocket 18, brake 24, and
control drum 15. The brake 24 stops rotation of the drive shaft 27
and functioning of the drive mechanism 5, for example if an
emergency occurs or if unsafe conditions are encountered which
necessitate the need to halt operation of the system.
[0051] The drive motor 21 may be a rotary piston, vane, or gear
drive motor, and is preferably a high torque, slow speed, reversing
motor which responds to hydraulic pump 23 (see below) fluid flow
rate and directional changes. The gear reducer 28 reduces the
amount of revolutions the rotating drum 15 must make relative to
the amount of revolutions traveled by the brake 24, drive motor 21,
and drive sprocket 18 during a controlled cycling of the polished
rod 11. As shown, the gear reducer 28 may be housed within the
rotating drum 15. Preferably, the gear reducer 28 causes the
rotating drum 15 to rotate approximately 270 degrees in a direction
on the up-stroke of the polished rod 11 and, conversely,
approximately 270 degrees in the opposite direction on the
down-stroke of the polished rod 11.
[0052] Referring now to FIG. 1, a variable-speed hydraulic pump 23
is disposed on the base frame 4 across from and substantially in
line with the rotating drum 15. As shown in FIG. 3, the hydraulic
pump 23 ultimately drives the drive motor 21 using a hydrostatic,
closed-loop hydraulic circuit 33 which includes at least two
hydraulic lines 33A and 33B. Fluid to power the drive motor 21,
which is supplied by the hydraulic pump 23, travels in two
directions around the closed loop circuit 33. The hydraulic drive
motor 21, therefore, is reversible to reverse the direction of the
chain 22, thereby reversing the direction of the polished rod
11.
[0053] A hydraulic pump usable as the hydraulic pump 23 and having
a closed-loop hydraulic circuit is shown and described in the Sauer
Danfoss Series 90 Axial Piston Pumps Technical Information
catalogue, which is herein incorporated by reference in its
entirety. Specifically, on page 6 of the Sauer Danfoss Series 90
catalogue, FIG. 1 shows a system circuit description of a
hydrostatic transmission using a series 90 axial piston variable
displacement Sauer Danfoss pump with a swash plate piston or a
Rineer 125 series high torque reversible vane motor, with the
working loop having high pressure and the working loop having lower
pressure. On page 7 of the catalogue, a sectional view of the
variable displacement pump is shown in FIG. 2. When incorporating
the figures in the catalogue into embodiments of the drive
mechanism 5 of this application, the reversible variable
displacement pump represents the hydraulic pump 23, the input shaft
represents a pump control shaft 44 (described in more detail
below), the fixed displacement rotary motor represents the drive
motor 21, the output shaft represents the drive shaft 27, and the
high pressure and lower pressure loops, along with the other fluid
lines illustrated, represent the closed loop circuit 33 and the
hydraulic fluid lines 33A and 33B therein.
[0054] Referring specifically to FIG. 3, the hydraulic pump 23 is
powered by a powering mechanism 29 operatively connected thereto,
which may be any form of power, including one or more windmills or
a type of electric power such as an electric motor. The powering
mechanism 29 and hydraulic pump 23 are preferably capable of
rotating in only one direction (the same direction for both the
powering mechanism 29 and the hydraulic pump 23) at constant
speeds, while the drive motor 21 is capable of rotating in both
directions to reciprocate the polished rod 11 alternately up and
down within the wellbore and at variable speeds, as determined by
the flow rate and direction of hydraulic fluid flowing from the
hydraulic pump 23 to the drive motor 21 through the hydraulic lines
33A and 33B. Preferably, the hydraulic drive is rotary rather than
linear, thus avoiding the problems which may result from debris
contaminating a linear piston/cylinder drive unit.
[0055] Fluid is supplied to the closed loop circuit 33 by one or
more fluid supply lines 51. A fluid supply pump 40 pumps fluid from
a fluid tank 42 into the fluid supply lines 51. Fluid is purged
from the closed loop circuit 33 using one or more purge fluid lines
41. In one embodiment, the fluid purged from the closed loop
circuit 33 is recycled into the fluid tank 42 by treating the fluid
with one or more fluid filters 34 and cooling the fluid using one
or more fluid coolers 35 prior to the fluid entering the fluid tank
42.
[0056] The hydraulic pump 23 has a pump control shaft 44
operatively connected thereto for controlling the speed of the
fluid entering the drive motor 21 from the hydraulic pump 23,
ultimately controlling the inter-cyclic speed of the polished rod
11. The pump control shaft 44 is manipulated by a mechanical or
electrical control system, or by a combination of mechanical and
electrical controls. The control system controls the inter-cycle
speed of the polished rod 11 (the speed of the polished rod 11
during the up-stroke or the down-stroke), thus controlling the
nature and severity of the turnaround of the polished rod 11 (the
transition point of the polished rod 11 between the up-stroke and
down-stroke).
[0057] When using a mechanical control system, as shown in FIGS.
1-3, FIG. 3A, and FIG. 3B, a cam roller groove 26 is formed in the
rotating drum 15 and extends around a portion of the rotating drum
15. The rotating drum 15 is shown in a flattened condition in FIG.
3 to illustrate the cam roller groove 26, while only an upper
portion of the rotating drum 15 is shown in a flattened condition
in FIG. 3B. The cam roller groove 26 is shaped in a predetermined
pattern and curved at predetermined angles to create a motion
profile for the polished rod 11 to cause the polished rod 11 to
travel upward and downward during the up-stroke and down-stroke at
predetermined inter-cyclic speeds. A cam roller 25 travels through
the cam roller groove 26 in the predetermined pattern of the cam
roller groove 26 as the rotating control drum 15 rotates.
[0058] Referring now to FIGS. 1, 3, 3A, and 3B, the cam roller 25
is operatively connected to the pump control shaft 44 by a pump
control lever 20. The pump control lever 20 is pivotably mounted to
an upper surface of the pump control shaft 44 to allow the pump
control lever 20 to move left and right within the cam roller
groove 26 in the rotating drum 15 during the operation (most easily
seen in FIGS. 3 and 3B). The movement of the pump control lever 20
through the cam roller groove 26 controls the fluid flow rate
outputted by the hydraulic pump 23, thereby controlling the speed
of rotation of the drive motor 21. The speed of rotation of the
drive motor 21 is thus directly correlated to the angle of the cam
roller groove 26 within the rotating drum 15. Additionally, the
movement of the pump control lever 20 through the cam roller groove
26 controls the direction of rotation of the drive motor 21,
thereby controlling the direction of rotation of the drive sprocket
18 and ultimately of the polished rod 11 (the direction being up or
down). The direction of rotation of the drive motor 21 is
controlled by whether the rotating drum 15 moves upward or
downward, which is dictated by the direction at which the pump
control lever 20 must move through the cam roller groove 26 to exit
one of the turnaround points 53A, 53B in the cam roller groove 26
(see FIG. 3).
[0059] The cam roller 25 preferably moves through the cam roller
groove 26 in the same direction continuously, as dictated by a
solenoid mechanism 52. Referring to FIG. 3, the solenoid mechanism
52 acts as an assist to force the pump control lever 20 to move
from a steady state position within the cam roller groove 26 over
center at the turnaround points 53A, 53B or into an inter-cyclic
portion 55A, 55B of the cam roller groove 26 from a turnaround
point 53A, 53B, thereby beginning the movement of the rotating drum
15 (and thus the polished rod 11) in a direction upward or
downward. Although a solenoid mechanism 52 is described herein as
the assist for moving the pump control lever 20 within the cam
roller groove 26, other assist mechanisms may be utilized in the
control system instead of or in addition to the solenoid mechanism.
Also, the solenoid mechanism shown and described herein is a double
solenoid mechanism, but a single solenoid mechanism is also
contemplated for use with the embodiments shown in FIGS. 1-3B. Any
solenoid mechanism known to those skilled in the art may be
utilized in embodiments of the present invention.
[0060] As shown in FIGS. 3A and 3B, the solenoid mechanism 52 is
preferably a double electrical solenoid mechanism. The solenoid
mechanism 52 preferably includes two push-type solenoids 31A and
31B. As shown in FIG. 3B, a stop 56B located on a side of the
rotating drum 15 at or near the turnaround point 53A is utilized to
actuate the reversing switch 32B so that the solenoid 31B pulls the
cam roller 25 and the pump control lever 20 towards the solenoid
31B to travel downward within the cam roller groove 26, beginning
the up-stroke or down-stroke. A corresponding stop (not shown) is
located on the opposite side of the rotating drum 15 at or near the
turnaround point 53B (see FIG. 3). In the same manner as described
above in relation to the stop 56B and switch 32B, at or near the
turnaround point 53B, the switch 32A comes into contact with the
stop (corresponding stop not shown), thereby activating the
solenoid 31A which pulls the cam roller 25 and the pump control
lever 20 towards the solenoid 31A to travel downward within the cam
roller groove 26 to begin the up-stroke or down-stroke. While the
cam roller 25 and pump control lever 20 are traveling through the
inter-cyclic portions 55A, 55B of the cam roller groove 26, neither
reversing switch 32B, 32A is activated until one of the stops 56B,
(not shown) comes into contact with its corresponding reversing
switch 32B, 32A.
[0061] Referring specifically to FIGS. 3A and 3B, each solenoid
31A, 31B typically includes a solenoid coil 45A, 45B surrounding a
moveable actuator such as a plunger 46A, 46B. A connecting member
such as a push pin 47 usually connects the plungers 46A and 46B to
one another. In the embodiment shown in FIGS. 3A and 3B, the push
pin 47 is also connected to the cam roller 25 so that the movement
of the plunger 46A, 46B in a direction causes the push pin 47 to
move in that direction, thereby forcing the cam roller 25 and pump
control lever 20 to move in that direction.
[0062] The operation of solenoids is known by those skilled in the
art. Generally, one of the solenoid coils 45B, 45A may be energized
by an electric current (when the stop 56B, (not shown) contacts the
designated reversing switch 32B, 32A), creating a magnetic force
which causes the plunger 46B, 46A to travel in a direction within
the coil 45B, 45A. The solenoid 31B, 31A loses its magnetic force
when input electric power is removed (when the stop 56B, (not
shown) is not in contact with the corresponding reversing switch
32B, 32A).
[0063] FIG. 4 shows the electrical control system for use in
embodiments of the present invention to control the speed,
acceleration, and direction of movement of the polished rod 11 of
the drive mechanism 5. The electrical control system may be
utilized in conjunction with or in lieu of the mechanical control
system shown and described in relation to FIGS. 1-3B.
[0064] Because of its similarity to portions of the drive mechanism
having the mechanical control system shown and described in
relation to FIGS. 1-3B, like parts of the drive mechanism having
the electrical control system shown in FIG. 4 are labeled with the
same numbers as like parts of portions of the drive mechanism
having the mechanical control system of FIGS. 1-3B. Therefore, the
above description of the parts and their method of use relating to
embodiments of the drive mechanism of FIGS. 1-3B applies equally to
the parts of the drive mechanism embodiment of FIG. 4 which are
labeled with the same numbers.
[0065] Referring to FIG. 4, instead of the cam roller groove 26 in
the rotating drum 15 and the pump control lever 20 with the cam
roller 25 thereon controlling the drive mechanism 5 as in FIGS.
1-3B, an electrical pump control 36 controls the fluid introduced
through the closed loop circuit 33 by the hydraulic pump 23 to the
drive motor 21. The electrical pump control 36, which is
operatively connected to the hydraulic pump 23, determines the
fluid flow rate and direction of fluid pumped to the drive motor 21
by the hydraulic pump 23.
[0066] The electrical pump control 36 is in electrical
communication with a computer processor 30 by a pump control
circuit 39. The computer processor 30 is, in turn, in electrical
communication with one or more sensors 38, preferably one or more
magnetic sensors. One or more magnets 37 are located in the
rotating drum 15 at intervals from one another. Preferably,
approximately twenty-five magnets are located in the rotating drum
at intervals equal to approximately one magnet for each foot of
stroke length over the preferred approximately 270-degree distance
of rotating drum 15 rotation. The magnets 37 are preferably, but
not necessarily, permanent in nature. The magnets 37 preferably
rotate along with the rotating drum 15.
[0067] The magnets 37 are capable of transmitting one or more
signals to the sensor 38. The sensor 38 transfers the one or more
signals to the computer processor 30, which then sends
pre-programmed control signals to the electrical pump control 36
through the pump control circuit 39. The electrical pump control 36
then determines the fluid flow rate and direction of the fluid
being pumped through the closed loop circuit 33 by the hydraulic
pump 23 to the drive motor 21. In embodiments of the electrical
control system, the magnets 37 and magnetic sensor 38 may be
substituted with any type of sensing mechanism capable of
transmitting a signal to a computer processor.
[0068] In the above description, the drive mechanism 5 includes
bearings mechanisms 17A, 17B, and 17C. Any or all of the bearings
mechanisms 17A, 17B, 17C may be substituted with one or more
bushings or any other mechanism known to those skilled in the art
which facilitates rotation of an object relative to an attached
surface.
[0069] In the operation of the mechanically controlled drive
mechanism embodiment shown in FIGS. 1-3B, the power 29 is initially
activated. The power 29 preferably rotates in one direction to
power the drive mechanism 5. Activating the power 29 causes the
hydraulic drive (which includes the hydraulic pump 23 and the drive
motor 21) to commence operation. The hydraulic drive provides the
driving force for the drive mechanism 5, and the amount of force
the hydraulic drive puts forth to move the rod string 11 is
determined by the mechanical control system.
[0070] The hydraulic pump 23 preferably rotates in the same
direction as the power 29 and only in one direction. In contrast,
the drive motor 21 rotates in both directions, as the drive motor
21 is disposed on the same drive shaft 27 as the drive sprocket 18
which manipulates the upward and downward movement of the rod
string 11 within the wellbore. The direction of movement (up or
down) of the drive motor 21 (and therefore the rod string 11) is
determined by the predetermined pattern of the cam roller groove 26
in the rotating drum 15. Additionally, the predetermined pattern of
the cam roller groove 26 determines the flow rate of fluid pumped
into the drive motor 21 through the closed loop circuit 33 by the
hydraulic pump 23, which dictates the inter-cyclic speed of the rod
string 11 and the turnaround points 53A, 53B of the rod string
11.
[0071] The pattern of motion of the rod string 11 is automatic upon
turning on the power 29. As mentioned above, the hydraulic pump 23
begins to introduce fluid into the drive motor 21, beginning the
automatic cycling of the drive mechanism 5. At this point, the
speed of rotation and direction of rotation of the drive motor 21
and its drive shaft 27 dictate the speed of the rod string 11
during the up-stroke or down-stroke and the direction of the rod
string 11 (upward or downward). The speed of rotation of the drive
motor 21 and drive shaft 27 is dictated by the rate of fluid flow
from the hydraulic pump 23 into the drive motor 21. The rate of
fluid flow from the hydraulic pump 23 into the drive motor 21 is
dictated by the slope of the predetermined pattern on the cam
roller groove 26. The direction of rotation of the drive motor 21
and drive shaft 27 is determined by the predetermined pattern on
the cam roller groove 26 and the direction the solenoid mechanism
52 manipulates the cam roller 25 within the cam roller groove 26,
and ultimately whether the cam roller 25 is traveling upward or
downward within the cam roller groove 26.
[0072] A preferred embodiment of a pattern of the cam roller groove
26 on the rotating drum 15 is shown in FIG. 3. The preferred
embodiment includes merely one example of inter-cycle speed control
of the rod string 11 possible with the drive mechanism 5 of the
present invention. In one embodiment, the cam roller 25 is at rest
at the turnaround point 53B initially with the rod string 11 at its
lowermost point within the wellbore.
[0073] When the cam roller 25 is at this turnaround point 53B,
there is no fluid flow from the hydraulic pump 23 into the drive
motor 21, and the drive motor 21 and drive shaft 27 are at rest. In
the preferable embodiment, when the pump control lever 20 is
substantially centered on the rotating drum 15 and therefore
substantially perpendicular to an axis of the hydraulic pump 23,
which occurs when the cam roller 25 is at one of the turnaround
points 53A or 53B, there is no fluid flow from the hydraulic pump
23 to the drive motor 21; therefore, the rod string 11 is at rest
when the pump control lever 20 is centered on the rotating drum 15.
Fluid flow from the hydraulic pump 23 gradually increases as the
pump control lever 20 pivots to the left or to the right from the
center of the rotating drum 15 by the cam roller 25 moving through
the cam roller groove 26.
[0074] At the turnaround point 53B, the stop (not shown) on the
side of the rotating drum 15 contacts the reversing switch 32A, so
that the solenoid 31A pulls the cam roller 25 towards the solenoid
31A. This initial pull of the solenoid 31A provides the force to
initiate the movement of the cam roller 25 through the inter-cyclic
portion 55A of the cam roller groove 26. The cam roller 25 first
travels through portion A of the cam roller groove 26. Portion A is
sloped so that the speed of the rod string 11 constantly increases
during the upstroke. Portion A, with respect to a line through the
turnaround point 53B coaxial with the rotating drum 15, gradually
slopes upward at an angle until it reaches portion B. The slope of
portion A takes into account the gradual increase in speed desired
to prevent breaking, stretching, or otherwise damaging the rod
string 11 when initializing the up-stroke of the rod string 11
(necessary due to the high load on the rod string 11 during the
initial up-stroke caused by the previous inactivity of the rod
string 11 in combination with the weight of the rod string 11 and
the weight of the fluid which is being lifted during the
up-stroke). Because the rate (also volume of fluid introduced over
time) of fluid introduced into the drive motor 21 directly
corresponds with the slope of portion A (because the pump control
lever 20 connects the cam roller 25 to the hydraulic pump 23), the
flow rate of fluid pumped to the drive motor 21 gradually and
constantly increases from zero flow rate at the turnaround point
53B to full speed at the juncture between portion A and portion
B.
[0075] The maximum preset flow rate of fluid from the hydraulic
pump 23 to the drive motor 21 is reached at the juncture between
portion A and portion B during the up-stroke, as at this juncture
the pump control lever 20 is pivoted to its farthest point from the
center of the rotating drum 15. The maximum preset flow rate of
fluid from the hydraulic pump 23 is maintained during portion B of
the up-stroke because portion B is at a ninety-degree angle with
respect to a line through the turnaround point 53B drawn from one
side of the rotating drum 15 to the other side. This maximum preset
flow rate is maintained as the cam roller 25 travels through the
maximum-sloped portion B for a predetermined period of time, as
determined by the predetermined length of portion B. Thus, the
maximum speed of the rod string 11 is maintained by the flow rate
of hydraulic fluid through portion B during the up-stroke.
[0076] Before reaching the turnaround point 53A between the
up-stroke and the down-stroke, the rod string 11 is gradually
decelerated from its maximum speed to its stopping point between
the up-stroke and down-stroke to prevent damage to the rod string
11 such as stretching or breaking caused by abrupt stopping of
inertia of the rod string 11 at the end of the up-stroke. To
provide the gradual deceleration of the fluid flow from the
hydraulic pump 23 and thus the gradual deceleration of the rod
string 11 at the end of the up-stroke, portion C is sloped towards
the center of the rotating drum 15 from the juncture between
portions B and C to the turnaround point 53A. As the cam roller 25
travels through portion C, the flow rate of fluid from the
hydraulic pump 23 to the drive motor 21 is constantly decreased
proportional to the slope of portion C, thus reducing the speed of
movement of the rod string 11 during the up-stroke. Preferably, the
slope of portion C is different than the slope of portion A, but
any slope of portions of the cam roller groove 26 may be utilized
in embodiments of the present invention which produces the desired
motion pattern for the rod string 11.
[0077] When the cam roller 25 reaches the turnaround point 53A, the
rod string 11 is temporarily at rest at its uppermost point,
between the up-stroke and the down-stroke of the rod string 11. As
the stop 56B contacts the reversing switch 32B, the solenoid 31B
pulls the cam roller 25 past the steady state, turnaround point 53A
to induce motion of the rod string 11, initiating the
down-stroke.
[0078] For the down-stroke, hydraulic fluid flow is constantly
increased from the hydraulic pump 23 to the drive motor 21
according to slope of portion D as the cam roller 25 travels
through portion D. The rate of movement of the rod string 11
constantly increases in direct proportion to the flow rate of the
hydraulic fluid. The flow rate thus changes from zero flow rate at
the turnaround point 53A to the maximum preset reverse flow rate at
the juncture between portion D and portion E, and the rod string 11
correspondingly increases in speed from stopped to maximum speed
through portion D.
[0079] The maximum flow rate of fluid from the hydraulic pump 23
continues as the cam roller 25 moves through portion E; therefore,
the rod string 11 continues at the maximum predetermined speed at
this point in the cycle for a predetermined time, as dictated by
the length of portion E. When the cam roller 25 reaches portion F,
the flow of hydraulic fluid from the hydraulic pump 23 gradually
decreases in rate proportional to the slope of portion F, causing
the rod string 11 speed to gradually decrease at the end portion of
the down-stroke movement. The rod string 11 speed decreases from
its maximum speed at the junction between portions E and F to no
speed as its movement halts at the turnaround point 53B. Another
cycle of the rod string 11 may be initiated by activation of
movement of the cam roller 25 into portion A by the solenoid 31A,
as described above, so that the rod string 11 automatically repeats
the motion pattern dictated by the cam roller groove 26. The cam
roller 25 repeats movement through the motion profile until power
29 is halted or the brake 24 is activated.
[0080] Therefore, the preferred rod string motion profile produced
by embodiments of the present invention includes slowly increasing
speed of the rod string on the up-stroke to full speed, having a
turnaround which lasts for a sufficient amount of time, and
increasing to full speed on the down-stroke. Embodiments of the rod
string motion profiles of the present invention may include a slow
up-stroke and fast down-stroke. Alternatively, embodiments may
include a fast up-stroke and slow down-stroke. The rod string
motion profile may be altered depending upon the viscosity of the
fluid which is being lifted from the wellbore. If the fluid has a
high viscosity, it is often desirable to induce a motion profile
having a slower down-stroke than up-stroke because only gravity is
pushing the rod string down into the heavy fluid in the wellbore.
The rod string profile of embodiments of the present invention may
be easily altered to fit the desired cyclic motion of the rod
string. The inter-cyclic rod string speed may be changed to produce
desirable motion profiles that produce desirable loading
profiles.
[0081] The operation of the electrical control system embodiment
shown in FIG. 4 with the drive mechanism 5 is similar to the
operation of the mechanical control system embodiment. In the
electrical control system embodiment, the cam roller groove 26, cam
roller 25, and pump control lever 20 are replaced by the electrical
control system. The pattern of movement, including the speed of
movement as well as the direction of movement, of the rod string 11
is predetermined by a program within the computer processor 30 in
the embodiment shown in FIG. 4.
[0082] As the control drum 15 rotates by fluid flow from the
hydraulic pump 23 into the drive motor 21, the sensor 38 receives
signals from the magnets 37. The sensor 38 transmits the signals to
the computer processor 30, which then sends one or more
pre-programmed control signals to the electrical pump control 36.
The pump control 36 determines the fluid flow rate and direction of
fluid pumped to the drive motor 21 by the hydraulic pump 23
according to the pre-programmed control signals sent by the
computer processor 30. The electrical control system allows for the
program to be changed within the computer processor 30 at the well
site or at any location remote from the well site. Alternatively,
the pattern or movement of the rod string 11 may be controlled by a
timer controlling the application of fluid from the hydraulic pump
23 to the drive motor 21.
[0083] In the predetermined pattern of movement of the rod string
11 as dictated by the mechanical control system and/or the
electrical control system, a pause may be placed in the down-stroke
right before the turnaround of the rod string 11 to the up-stroke
to lessen the stress of the transition to movement of the rod
string 11. A pause may also be placed before the turnaround of the
rod string 11 from the up-stroke to the down-stroke if desired.
[0084] During the cycle of the rod string 11, both inter-cycle and
between cycles of the rod string 11, the quick responsiveness of
the hydraulic drive as dictated by the cam roller groove 26 or the
computer processor 30 decreases stress on the rod string 11 and
allows precise control of the motion of the rod string 11 to
increase overall speed of hydrocarbon fluid recovery. The
mechanical counterbalance 14 decreases the amount of power
necessary to drive the rod string 11 within and between cycles by
counteracting the load of the rod string 11 and/or the load of the
fluid being lifted by the rod string 11.
[0085] FIG. 5C shows the rod string motion profile when using the
drive mechanism 5 of embodiments of the present invention shown in
FIGS. 1-4. The up-stroke of the rod string 11 is represented by the
portion of the line to the left of turnaround point T, while the
down-stroke of the rod string 11 is represented by the portion of
the line to the right of the turnaround point T. The portion of the
line representing the up-stroke of the rod string 11 shows the
gradual increase in speed of the rod string 11 from the point of
zero loading at the turnaround point between the down-stroke and
up-stroke caused by the mechanical and/or electrical control system
of the drive mechanism 5. The increase in the slope of the portion
of the line representing the down-stroke of the rod string 11
delineates the faster speed of the rod string 11 during the
down-stroke using the drive mechanism 5. Also evidenced in the rod
string profile of FIG. 5C is the increased amount of time spent at
the turnarounds of the rod string 11, as shown at the hills and
valleys of the rod string motion profile curve.
[0086] FIG. 6C illustrates the improvements in the loading to which
the rod string 11 is exposed during the rod string 11 cycle using
the drive mechanism 5 of FIGS. 1-4. The up-stroke of the rod string
11 is shown between the points U and V, while the down-stroke is
shown between points Y and X. The turnarounds are shown between
points U and Y (between the down-stroke and the up-stroke) and
between points V and X (between the up-stroke and the down-stroke).
The erratic loading of the beam pump system shown in FIG. 6A is
substantially eliminated, as shown by the constant amount of
loading on the up-stroke between points U and V and by the constant
amount of loading on the down-stroke between points Y and X. Also,
when using the drive mechanism 5 of embodiments of the present
invention, the rod string 11 does not experience the unhealthy high
loading thereon at, for example, point P of FIG. 6A, as is seen in
FIG. 6C. Additionally, the undesirable jarring of the rod string 11
at the turnarounds between the up-stroke and down-stroke and vice
versa experienced by the rod string of FIG. 6B does not occur when
using embodiments of the drive mechanism 5 shown in FIGS. 1-4, as
evidenced by the lack of undulations to the right of point U and to
the left of point X.
[0087] Several advantages are gained by using embodiments of the
drive mechanism 5 shown and described above in relation to FIGS.
1-4 to reciprocate a downhole positive displacement pump.
Specifically, combining the hydraulic drive with mechanical
counterbalancing reduces the hydraulic fluid needed to cycle the
rod string 11 significantly. The necessary hydraulic fluid for
cycling the rod string 11 may in some embodiments be reduced by as
much as 2/3 by the mechanical counterbalancing of the mechanical
counterbalance 14 along with the hydraulic drive of the hydraulic
pump 23. The counterbalancing uses during the up-stroke the energy
from the falling mass of the rod string 11 which is accumulated
during the down-stroke. The counterbalance 14 alleviates the burden
on the hydraulic pump 23 of lifting the load of the polished rod
11, so that only the work of lifting the well fluid is exerted by
the hydraulic pump 23.
[0088] An additional advantage of the drive mechanism 5 is its
dependability. First, the drive mechanism 5 is a dependable unit
because the internal workings of the hydraulic drive are not
exposed to the elements in the environment with each stroke of the
rod string 11. Second, the drive mechanism 5 is a dependable unit
because of the use of motion profiles of the mechanical and/or
electrical control systems to control the rate and direction of
fluid flow from the hydraulic pump 23 driving the drive motor
21.
[0089] Inter-cyclic speed control of the rod string 11 is provided
by the electrical and/or mechanical control system. The quick
responsiveness of the hydraulic pump 23 to the control system
reduces stress on the rod string 11, thereby minimizing stretching
and/or failure of the rod string 11, especially at the turnarounds
of the rod string 11 cycle. Because of the inter-cycle speed
control of the rod string motion during the cycles and at the
turnarounds and because of the reduced time necessary to repair or
replace broken or damaged rod strings, the overall speed of the
pumping unit is ultimately increased by using the drive mechanism
5. Increasing the overall speed of the positive displacement pump
allows increased production of hydrocarbon fluid from within the
wellbore over a period of time, thereby decreasing the hydrocarbon
fluid pumping costs of the well. In addition to the decreased
pumping costs of the well caused by increased efficiency of the
positive displacement pump brought about by the drive mechanism 5,
the cost of the well is also decreased because the amount of
replacement rod strings as well as the time required to repair rod
strings is decreased due to the decreased number of occurrences and
amounts of stress imparted on the rod string 11 by the drive
mechanism 5 as compared to other drive mechanisms.
[0090] The drive mechanism 5 of embodiments of the present
invention is highly responsive to speed changes due to less inertia
of moving parts when changing speeds, as the hydraulic pump 23 runs
at a constant speed. The change of speed and direction of the rod
string 11 is not caused by the direction or speed of rotation of
the hydraulic pump 23, but is instead determined by the hydraulic
fluid flow rate from the hydraulic pump 23. The rotary drive motor
21 operating within the closed loop hydraulic circuit 33 is
responsive to sudden speed changes of the rod string 11 because it
has pressurized fluid on the inlet and outlet sides of the drive
motor 21 that can act as a brake. With the drive mechanism 5 shown
in FIGS. 1-4, it is possible to tailor inter-cycle speeds or the
smoothness of the turnarounds of the polished rod 11 by modifying
the rod string profile determined by the cam roller groove 26 or by
the computer program within the computer processor 30.
[0091] Although the drive mechanism 5 shown and described herein in
relation to FIGS. 1-4, 5C, and 6C is advantageous for use in a deep
wells, it is also useful in other well pumping applications, such
as in ordinary depth or shallow wells. Additionally, the drive
mechanism 5 does not necessary have to be used in a long-stroke
pumping unit, but may be used in a medium-stroke, short-stroke, or
ultra-long-stroke pumping unit. In other embodiments, the drive
mechanism 5 may be sized to operate under agricultural sprinkler
irrigation systems.
[0092] FIG. 7 depicts an alternate embodiment of the present
invention. To reduce the height profile of the drive mechanism
above the surface of the earth relative to the height profile of
the drive mechanism 5 shown in FIGS. 1-4, the drive mechanism is
modified as shown in FIG. 7. Decreasing the height of the drive
mechanism above the surface of the earth would allow other types of
equipment such as pivot irrigation systems to exist above the drive
mechanism.
[0093] The drive mechanism 105 shown in FIG. 7 is substantially the
same in several respects to the drive mechanism 5 shown and
described above in relation to FIGS. 1-3B. The sprocket/chain
portion and the lift belt/lift pulley portion of the drive
mechanism 5 shown and described above in relation to FIGS. 1-3B
exist upright where the drive sprocket 18 and idle sprocket 16
exist generally coaxially with one another, and the idle sprocket
16 is located some height above the drive sprocket 18. In general,
the counterbalance 14 provides counterbalancing force for the
polished rod 11 due at least partially to gravity; therefore, the
drive mechanism 5 cannot simply be turned on its side to lower the
height profile of the drive mechanism 5.
[0094] In the embodiment shown in FIG. 7, the idle sprocket 16 is
moved to a location close to the surface of the earth, and the
rotational axis of the idle sprocket 16 is located at substantially
at the same height above the surface as the rotational axis of the
drive sprocket 18. The tower 19, as configured in FIG. 7, is
eliminated and possibly replaced with a support structure having a
lower height profile above the surface than the tower 19 to reduce
the height of the drive mechanism 105 above the surface.
[0095] In other modifications from the embodiments shown in FIGS.
1-3B evident in the embodiment shown in FIG. 7, the counterbalance
14 is moved from its location within the chain 22. In its place, a
first connector mechanism 149 exists. The first connector mechanism
149 is connected within the chain 22, and the lift belt 12 is also
connected to the first connector mechanism 149 at a second end. The
lift belt 12 travels over the pulley 13, but the location of the
pulley 13 is moved as shown in FIG. 7 so that the pulley 13 is
disposed underneath the top of the lift belt 12 (the top as shown
in FIG. 1). Instead of the polished rod 11, the counterweight 14 is
connected to the first end of the lift belt 12. In this
arrangement, gravity may act on the counterweight 14 to provide a
clockwise-direction rotational force to the chain 22.
[0096] A second connector mechanism 151 is connected within a
portion of the chain 22 across the idle and drive sprockets 16 and
18 from the first connector mechanism 149. A second end of a second
lift belt 112 is connected to the second connector mechanism 151.
The second lift belt 112 is disposed around a second lift pulley
113, and connected to a first end of the second lift belt 112 is
the polished rod 11. The polished rod 11 is acted upon by gravity
to provide a counterclockwise-direction rotational force to the
chain 22.
[0097] The same components are located substantially parallel and
coaxial to the drive sprocket 18 as shown in FIG. 7, but all
components are located on the surface of the earth or on a support
structure, and not on the tower 19. Additionally, in the mechanical
control embodiment, the cam roller groove 26 (not shown in FIG. 7)
is located at the upper end of the rotating drum 15 (essentially,
the drum 15 is rotated approximately 45 degrees from the embodiment
shown in FIG. 1). The pump control mechanism 44 is disposed beside
the drive sprocket 18 so that the pump control lever 20 is capable
of traveling through the cam roller groove 26.
[0098] The operation of the embodiment shown in FIG. 7 is
substantially similar to the embodiment shown in FIGS. 1-3B, except
that the counterbalancing force is provided by the counterbalance
14 in a different configuration and at a different location.
Gravitational forces may act on the polished rod 11 and the
counterbalance 14 during the operation of the drive mechanism
5.
[0099] In another embodiment, the same concept as shown and
described in relation to FIG. 7 may be utilized with the electronic
control embodiment shown in FIG. 4. The arrangement of similar
components of the drive mechanism in the electronic control
situation is the same as the arrangement of components of the drive
mechanism 105, except that the cam roller groove 26 and pump
control lever 20 are not present.
[0100] In either of the embodiments of the low height profile
system or in any other embodiment of the present invention (e.g.,
embodiments shown in FIGS. 1-4), the counterweight 14 may be
disposed underground and travel underground at any or all stages of
the operation. Furthermore, in the low height profile system
embodiments as well as in any of the embodiments shown and
described above in relation to FIGS. 1-4, instead of the mechanical
counterbalance 14, the counterbalance may be hydraulic. The
hydraulic counterbalance may be an accumulator, the structure and
operation of which is known by those skilled in the art. The
accumulator would reduce the power required from the drive motor 21
to cycle the polished rod 11 as desired.
[0101] In some previously-existing drive mechanisms, the
counterweight is attached by a carriage or mechanical reversing
mechanism to the chain. Because of the arrangement of the
above-shown and described embodiments of the present invention, the
counterweight 14 may be directly attached to the chain 22 by
bolting or some other means, as the carriage or mechanical
reversing mechanism is not necessary.
[0102] In the electrical control embodiments of the present
invention shown and described above, a hydraulic hose may be hooked
up to connect the hydraulic pump 23 to the drive motor 21 to allow
hydraulic communication between the two components. In this way,
the electric motor 29 and the hydraulic pump 23 may be located at
some location away from the wellbore to provide remote power to the
drive mechanism 5, 105. This configuration reduces or eliminates
the electrical components at the well site, providing a lower
explosion risk and possibly allowing closer compliance with
electrical regulations at the well site.
[0103] In any of the above embodiments, the brake 24 may be
hydraulic instead of mechanical. This hydraulic brake would include
one or more valves disposed in the hydraulic lines or hoses between
the hydraulic pump 23 and the drive motor 21 in lieu of the
mechanical brake 24. The valves may then act to stop rotation of
the drive motor 21 and other components by closing off flow from
the hydraulic pump 23 to the drive motor 21 if a system shut-down
is desired (e.g., an emergency occurs which requires shut-down of
the system). In addition to the valves or in the alternative, the
swash plate within the hydraulic pump 23 may be switched to a
position that would brake the system, eliminating the need for a
separate brake 24 or valve within the hydraulic line or hose.
[0104] In any of the embodiments shown and described above
espousing electrical controls, the sensors within the system may be
used to detect the speed and/or location of the rod string 11 and
alter the speed and/or location of the rod string 11 according to
load on the rod string 11. Moreover, instead of the sensors 37
being located on the rotating drum 15, the sensors 37 may be
located on the lift pulley 13, lift belt 12, a portion of the rod
string 11, the counterbalance 14, or any other portion of the drive
mechanism 5, 105 capable of detecting speed of movement and/or
position of the rod string 11. The sensors 37 may be used to detect
the speed and/or pressure of the drive motor 21 operation at any
desired location on the drive mechanism 5, 105.
[0105] In lieu of the hydraulic pump 23 and the electric motor 29
shown and described above in relation to FIGS. 1-4 and 7 above, the
drive mechanism 5, 105 may be powered by a piston pump or vein pump
with a reversible variable speed electric motor. Alternately, the
drive mechanism 5, 105 may be powered by multiple motors and pumps,
including a combination of any of the types of motors and pumps
described in the present application.
[0106] Embodiments of the present invention having an electrical
control mechanism allow control, regulation, and modification of
the stroke length and/or speed of the sucker rod 11 without having
to change the gear reducer or cam profile within the rotating drum
15. Using electrical control mechanism embodiments eliminates the
need to modify the rotating drum 15 due to wearing of the cam.
[0107] The size of the hydraulic pump 23 and/or electric motor 29
increases with increasing torque required to turn the drive
sprocket 18. Increasing the size of the hydraulic pump 23 or
electric motor 29 increases the expense of the components. To
reduce the size of the hydraulic pump 23 and electric motor 29, one
or more accumulators may be provided between the hydraulic pump 23
and the drive motor 21. Accumulators, used to store previously
built up hydraulic energy until needed and then release the
hydraulic energy to provide power, are known by those skilled in
the art. The accumulator essentially pressurizes fluid to a volume
to use the accumulated fluid pressure when needed for energy.
Accumulators reduce the amount of horsepower needed to provide
sufficient torque to the drive sprocket 18 because most of the
horsepower is needed during the acceleration of the rod string 11,
thereby reducing the size of the hydraulic pump 23 and electric
motor 29 necessary. Power is expended during deceleration of the
rod string 11. A solenoid valve may be utilized to open the
accumulator when necessary to use the work recovered during
deceleration in acceleration of the rod string 11.
[0108] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
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