U.S. patent application number 14/888436 was filed with the patent office on 2016-03-31 for resuming interrupted communication through a wellbore.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. The applicant listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Benjamin P. Jeffryes.
Application Number | 20160090800 14/888436 |
Document ID | / |
Family ID | 51843948 |
Filed Date | 2016-03-31 |
United States Patent
Application |
20160090800 |
Kind Code |
A1 |
Jeffryes; Benjamin P. |
March 31, 2016 |
RESUMING INTERRUPTED COMMUNICATION THROUGH A WELLBORE
Abstract
Resuming communication along a wellbore after a drilling stand
or other occurrence that reduces the flow rate of the drilling
fluid into a borehole being drilled in a drilling procedure or
causes perturbations in the pressure of the drilling fluid in the
borehole by measuring a first flow rate of drilling fluid being
pumped into the drillstring during the drilling procedure before
adding a section of drill pipe to the drillstring or before the
pressure perturbation and increasing the flow rate of the drilling
fluid being pumped into the drillstring above the first flow rate
after the section of drill pipe has been added to the drillstring
or the pressure perturbation has occurred.
Inventors: |
Jeffryes; Benjamin P.;
(Cambridge, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
Sugar Land
TX
|
Family ID: |
51843948 |
Appl. No.: |
14/888436 |
Filed: |
May 1, 2014 |
PCT Filed: |
May 1, 2014 |
PCT NO: |
PCT/US14/36354 |
371 Date: |
November 1, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61818175 |
May 1, 2013 |
|
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|
Current U.S.
Class: |
175/25 ; 175/48;
175/57 |
Current CPC
Class: |
E21B 47/06 20130101;
E21B 47/18 20130101; E21B 21/08 20130101 |
International
Class: |
E21B 21/08 20060101
E21B021/08; E21B 47/06 20060101 E21B047/06 |
Claims
1. A method for controlling drilling fluids in a drilling procedure
to drill a borehole from a surface location through an earth
formation to reduce interrupted communication through the borehole,
comprising: receiving a range of desired optimal flow rates for
pumping the drilling fluids into a drillstring, wherein the
drillstring extends from the surface location down the borehole and
the optimal flow rates are determined so as to keep a bottomhole
pressure of the drilling fluid in the borehole within an optimal
operating pressure window having upper and lower pressure bounds;
pumping the drilling fluids into the drillstring at a first optimal
flow rate configured to maintain the pressure within the optimal
operating pressure window; reducing the flow rate of the drilling
fluid below the first optimal flow rate; increasing the flow rate
of the drilling fluid to a value above said first optimal flow
rate; and reducing the flow rate of the drilling fluid from the
increased flow rate to a second optimal flow rate, wherein the
second flow rate is within the desired optimal flow rates and may
be the same or different to the first optimal flow rate, and
wherein reduction of the flow rate of the drilling fluid from the
increased flow rate to the second optimal flow rate occurs over a
period of time.
2. The method of claim 1, wherein the reduction in flow rate to a
rate below said first optimal flow rate is performed to provide for
connecting a drill pipe stand to the drillstring.
3. The method of claim 1, wherein the increased flow rate and/or
the period of time are processed to provide that pressure in the
borehole is kept within the optimal operating pressure window.
4. The method of claim 1, wherein the increased flow rate is up to
30% greater than the first optimal flow rate, up to 20% greater
than the first optimal flow rate and/or up to 10% greater than the
first optimal flow rate.
5. The method of claim 1 wherein the period of time is less than 5
minutes or less than 2 minutes or less than 1 minute.
6. The method of claim 1, further comprising performing mud pulse
telemetry after the second optimal flow rate is achieved.
7. The method according to claim 1, wherein the steps of the method
of claim 1 are repeated at a later point in time and data from the
earlier steps are used to improve the effectiveness of the method
carried out at the later point in time.
8. A system for controlling flow rates of drilling fluids being
pumped into a drillstring during a drilling procedure to drill a
borehole from a surface location through an earth formation to
resume communication through the drilling fluids after an
interruption, the system comprising: a stored range of desired
optimal flow rates for pumping the drilling fluids into the
drillstring, wherein the optimal flow rates are determined so as to
keep a bottomhole pressure in the borehole within an optimal
operating pressure window having upper and lower pressure levels,
wherein the upper pressure level comprises a pressure below a
fracture pressure of the formation being drilled and the lower
pressure level comprises a pressure above a pore pressure of the
formation one or more pumps configured to pump drilling fluid into
the drillstring; and a processor configured to control the one or
more pumps, wherein the processor controls the pumps: to pump the
drilling fluid at a first optimum flow rate, wherein the optimum
flow rate is within the range of desired optimal flow rates; after
a reduction in the rate at which the drilling fluid is pumped falls
below the optimum flow rate, to pump the drilling fluid into the
drillstring at an increased flow rate that is greater than the
optimal flow rate; and to reduce the flow rate from the increased
flow rate to a second optimal flow rate, wherein the second optimal
flow rate is within the range of desired optimal flow rates and may
be the same or different to the first optimal flow rate.
9. The system of claim 8, further comprising: a pressure sensor in
communication with the processor configured to measure a pressure
in the drillstring.
10. The system of claim 8, further comprising: a choke configured
to control the pressure in the drillstring.
11. The system of claim 8, further comprising: a mud pulse
telemetry system.
12. The system of claim 8, further comprising: a sensor for
determining when a connection has been made in the drillstring.
13. The system of claim 8, further comprising a display configured
to display at least one of a flow rate of the drilling fluid into
the drillstring, a pressure in the drillstring at the surface, a
pressure in the drillstring at a lower end of the borehole and the
pressure window.
14. A method for controlling drilling fluids in a drilling
procedure to drill a borehole from a surface location through an
earth formation to reduce interrupted communication through the
borehole, comprising: measuring a first flow rate of drilling fluid
pumped into a drillstring during the drilling procedure before
adding a section of drill pipe to the drillstring; and increasing
flow rate of the drilling fluid pumped into the drillstring above
the first flow rate immediately after the section of drill pipe has
been added to the drillstring.
15. The method of claim 14, further comprising: sending a mud pulse
telemetry signal through the drilling fluid in the wellbore.
16. The method of claim 14, further comprising: reducing the flow
rate of the drilling fluid from the increased flow rate to a
reduced flow rate.
17. The method of claim 14, wherein the reduced flow rate comprises
a flow rate configured to provide that a downhole pressure of the
drilling fluid in the borehole is within an optimal operating
pressure window
18. The method of claim 17, wherein the flow rate of the drilling
fluid exceeds the reduced flow rate for a period of time.
19. The method of claim 18, wherein the increased flow rate and/or
the period of time are determined to provide that the downhole
pressure does not exceed the optimal operating pressure window.
20. The method of claim 18, wherein the first flow rate is provided
to be a flow rate within a desired range of flow rates, and wherein
the desired range of flow rates comprise flow rates that maintain a
bottomhole pressure within an operating pressure window having an
upper pressure below a fracturing pressure of the earth formation
and a lower pressure above a pore pressure of the earth
formation.
21. The method of claim 20, wherein the increase flow rate is
outside of the desired range of flow rates.
22. A system for controlling drilling fluids in a drilling
procedure to drill a borehole from a surface location through an
earth formation to reduce interrupted communication through the
borehole, comprising: a sensor for measuring a flow rate of
drilling fluid pumped into a drillstring during the drillstring
procedure; and a processor in communication with the sensor and
configured to control the pump to increase a flow rate of the
drilling fluid pumped into the drillstring above a first flow rate
immediately after a section of drill pipe has been added to the
drillstring, wherein the first flow rate is a flow rate of the
drilling fluid pumped into the drillstring before the section of
drill pipe has been added to the drillstring.
23. The system of claim 24, wherein the processor controls the pump
to reduce the flow rate of the drilling fluid from the increased
flow rate to a reduced flow rate.
24. The method of claim 25, wherein the reduced flow rate comprises
a flow rate configured to provide that a downhole pressure of the
drilling fluid in the borehole is within an optimal operating
pressure window
25. The method of claim 26, wherein the flow rate of the drilling
fluid exceeds the reduced flow rate for a period of time.
26. The method of claim 27, wherein the increased flow rate and/or
the period of time are processed by the processor to provide that
the downhole pressure does not exceed the optimal operating
pressure window.
Description
BACKGROUND
[0001] Wells/boreholes are generally drilled into the ground to
recover natural deposits of hydrocarbons and other desirable
materials trapped in geological formations in the Earth's crust. A
well/borehole is typically drilled using a drill bit attached to
the lower end of a drillstring. The well is drilled so that it
penetrates the subsurface formations containing the trapped
materials and the materials can be recovered.
[0002] At the bottom end of the drillstring is a "bottom hole
assembly" ("BHA"). The BHA includes the drill bit along with
sensors, control mechanisms, and the required circuitry. A typical
BHA includes sensors that measure various properties of the
formation and of the fluid that is contained in the formation. A
BHA may also include sensors that measure the BHA's orientation and
position.
[0003] The drilling operations may be controlled by an operator at
the surface or operators at a remote operations support center. The
drill string is rotated at a desired rate by a rotary table, or top
drive, at the surface, and the operator controls the weight-on-bit
and other operating parameters of the drilling process.
[0004] Another aspect of drilling and well control relates to the
drilling fluid, called "mud." The mud is a fluid that is pumped
from the surface to the drill bit by way of the drill string. The
mud serves to cool and lubricate the drill bit, and it carries the
drill cuttings back to the surface. The density of the mud is
carefully controlled to maintain the hydrostatic pressure in the
borehole at desired levels.
[0005] In order for the operator to be aware of the measurements
made by the sensors in the BHA/along the drillstring etc. and/or
for the operator to be able to control the direction of the drill
bit, communication between the operator at the surface and the BHA
are necessary. A "downlink" is a communication from the surface to
the BHA. Based on the data collected by the sensors in the BHA, an
operator may desire to send a command to the BHA. A common command
is an instruction for the BHA to change the direction of
drilling.
[0006] Likewise, an "uplink" is a communication from the
BHA/downhole sensors/processor to the surface. An uplink is
typically a transmission of the data collected by the downhole
sensors. For example, it is often important for an operator to know
the BHA orientation. Thus, the orientation data collected by
sensors in the BHA is often transmitted to the surface. Uplink
communications are also used to confirm that a downlink command was
correctly understood.
[0007] One common method of communication is called "mud pulse
telemetry." Mud pulse telemetry is a method of sending signals,
either downlinks or uplinks, by creating pressure and/or flow rate
pulses in the mud. These pulses may be detected by sensors at the
receiving location. For example, in a downlink operation, a change
in the pressure or the flow rate of the mud being pumped down the
drill string may be detected by a sensor in the BHA. The pattern of
the pulses, such as the frequency, the phase, and the amplitude,
may be detected by the sensors and interpreted so that the command
may be understood by the BHA.
[0008] One method of mud pulse telemetry is disclosed in U.S. Pat.
No. 3,309,656, comprises a rotary valve or "mud siren" pressure
pulse generator which repeatedly interrupts the flow of the
drilling fluid, and thus causes varying pressure waves to be
generated in the drilling fluid at a carrier frequency that is
proportional to the rate of interruption. Downhole sensor response
data is transmitted to the surface of the earth by modulating the
acoustic carrier frequency. A related design is that of the
oscillating valve, as disclosed in U.S. Pat. No. 6,626,253, wherein
the rotor oscillates relative to the stator, changing directions
every 180 degrees, repeatedly interrupting the flow of the drilling
fluid and causing varying pressure waves to be generated.
[0009] Referring now to FIG. 1A, a wellbore telemetry system 100 is
depicted including a downhole measurement while drilling (MWD) tool
34 is incorporated in the drill string 14 near the drill bit 16 for
the acquisition and transmission of downhole data or information.
The MWD tool 34 includes an electronic sensor package 36 and a
mudflow wellbore telemetry device 38. The mudflow telemetry device
38 can selectively block the passage of the mud 20 through the
drill string 14 to cause pressure changes in the mud line 26. In
other words, the wellbore telemetry device 38 can be used to
modulate the pressure in the mud 20 to transmit data from the
sensor package 36 to the surface 29. Modulated changes in pressure
are detected by a pressure transducer 40 and a pump piston sensor
42, both of which are coupled to a surface system processor (not
shown). The surface system processor interprets the modulated
changes in pressure to reconstruct the data collected and sent by
the sensor package 36. The modulation and demodulation of a
pressure wave are described in detail in commonly assigned U.S.
Pat. No. 5,375,098, which is incorporated by reference herein in
its entirety.
[0010] The surface system processor may be implemented using any
desired combination of hardware and/or software. For example, a
personal computer platform, workstation platform, etc. may store on
a computer readable medium (e.g., a magnetic or optical hard disk,
random access memory, etc.) and execute one or more software
routines, programs, machine readable code or instructions, etc. to
perform the operations described herein. Additionally or
alternatively, the surface system processor may use dedicated
hardware or logic such as, for example, application specific
integrated circuits, configured programmable logic controllers,
discrete logic, analog circuitry, passive electrical components,
etc. to perform the functions or operations described herein.
[0011] Still further, while the surface system processor can be
positioned relatively proximate to the drilling rig (i.e.,
substantially co-located with the drilling rig), some part of or
the entire surface system processor may alternatively be located
relatively remotely from the rig. For example, the surface system
processor may be operationally and/or communicatively coupled to
the wellbore telemetry component 18 via any combination of one or
more wireless or hardwired communication links (not shown). Such
communication links may include communications via a packet
switched network (e.g., the Internet), hardwired telephone lines,
cellular communication links and/or other radio frequency based
communication links, etc. using any desired communication
protocol.
[0012] Additionally one or more of the components of the BHA may
include one or more processors or processing units (e.g., a
microprocessor, an application specific integrated circuit, etc.)
to manipulate and/or analyze data collected by the components at a
downhole location rather than at the surface.
[0013] Mud pulse systems may use a single modulator, typically
consisting of a stator and a rotor. The relative position between
the stator and rotor, together with the drilling mud/fluid
conditions, determine the amplitude of the telemetry signal
generated. In addition, for a single modulator, the amplitude of
the differential pressure signal generated is proportional to the
square of the inverse of the flow area. The speed at which the
rotor can be moved relative to the stator limits the bandwidth of
the signal generated.
SUMMARY
[0014] A summary of certain embodiments disclosed herein is set
forth below. It should be understood that these aspects are
presented merely to provide the reader with a brief summary of
these certain embodiments and that these aspects are not intended
to limit the scope of this disclosure. Indeed, this disclosure may
encompass a variety of aspects that may not be set forth.
[0015] In one embodiment of the present invention, a method is
provided for resuming communication through a drilling fluid being
used in a borehole for a drilling procedure after an interruption.
Merely by way of example, an interruption may comprise adding a
section of pipe to a drillstring that is being used in the drilling
procedure, where the flow rate of drilling fluid being pumped into
the borehole is reduced when the drill pipe section is added to the
drillstring causing perturbations in the drilling fluid in the
borehole. The method to restore communication after an interruption
may according to one embodiment comprise measuring a first flow
rate of the drilling fluid being pumped into a drillstring during
the drilling procedure before adding a section of drill pipe to the
drillstring and increasing the flow rate of the drilling fluid
pumped into the drillstring above the first flow rate immediately
after the section of drill pipe has been added to the
drillstring.
[0016] In another embodiment, a system for resuming communication
through a drilling fluid being used in a borehole for a drilling
procedure after an interruption. Merely by way of example, an
interruption may comprise adding a section of pipe to a drillstring
that is being used in the drilling procedure, where the flow rate
of drilling fluid is reduced when the drill pipe section is added
to the drillstring causing perturbations in the drilling fluid in
the borehole. The system for resuming communication after an
interruption in accordance with an embodiment of the present
invention comprising a sensor configured to measuring a flow rate
of drilling fluid being pumped into a drillstring during the
drilling procedure, and a processor in communication with the
sensor and configured to control the pump to increase a flow rate
of the drilling fluid pumped into the drillstring above a first
flow rate immediately after a section of drill pipe has been added
to the drillstring, wherein the first flow rate is a flow rate of
the drilling fluid pumped into the drillstring before the section
of drill pipe has been added to the drillstring.
[0017] In one embodiment of the present disclosure, a method is
provided for controlling flow rates of drilling mud being pumped
into a drillstring during a drilling procedure to drill a borehole
from a surface location through an earth formation in order to
resume communication through the drilling fluid after an
interruption, the method comprising:
[0018] establishing a range of desired optimal flow rates for
pumping the drilling mud into the drillstring, wherein the optimal
flow rates are determined so as to keep a bottomhole pressure in
the borehole within an optimal operating pressure window having
upper and lower pressure bounds;
[0019] drilling for a first period of time at a first optimal flow
rate;
[0020] reducing the flow rate, wherein the reduced flow rate causes
the interruption;
[0021] increasing the flow rate to a value above said first optimal
flow rate;
[0022] reducing the flow rate to a second optimal flow rate, which
may be the same or different to the first optimal flow rate, and
wherein the second optimal flow rate, wherein the second optimal
flow rate is configured to keep the bottomhole pressure in the
borehole within the optimal operating pressure window.
[0023] In one embodiment of the present disclosure, a system is
provided for controlling flow rates of drilling fluids being pumped
into a drillstring during a drilling procedure to drill a borehole
from a surface location through an earth formation, the system
comprising:
[0024] a stored range of desired optimal flow rates for pumping the
drilling fluids into the drillstring, wherein the optimal flow
rates are determined so as to keep a bottomhole pressure in the
borehole within an optimal operating pressure window having upper
and lower pressure levels, wherein the upper pressure level
comprises a pressure below a fracture pressure of the formation
being drilled and the lower pressure level comprises a pressure
above a pore pressure of the formation
[0025] one or more pumps configured to pump drilling fluid into the
drillstring; and
[0026] a processor configured to control the one or more pumps,
wherein the processor controls the pumps [0027] to pump the
drilling fluid at a first optimum flow rate, wherein the optimum
flow rate is within the range of desired optimal flow rates; [0028]
after a reduction in the rate at which the drilling fluid is pumped
below the optimum flow rate, to pump the drilling fluid into the
drillstring at an increased flow rate that is greater than the
optimal flow rate; and [0029] to reduce the flow rate to a second
optimal flow rate, wherein the second optimal flow rate is within
the range of desired optimal flow rates and may be the same or
different to the first optimal flow rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The present disclosure is described in conjunction with the
appended figures. It is emphasized that, in accordance with the
standard practice in the industry, various features are not drawn
to scale. In fact, the dimensions of the various features may be
arbitrarily increased or reduced for clarity of discussion.
[0031] FIG. 1A illustrates a wellbore telemetry system that may be
used with some embodiments of the present invention;
[0032] FIG. 1B illustrates an apparatus for resuming interrupted
communication down a wellbore, according to one embodiment of the
present invention;
[0033] FIG. 2 illustrates a flow rate transition according to
current practice (solid line), and according to a method in
accordance of the present invention;
[0034] FIG. 3 shows flow rates through a drill bit versus time for
a conventional wellbore procedure and a according to one embodiment
of the present invention; and
[0035] FIG. 4 shows stand-pipe pressures for a conventional
wellbore procedure and a according to one embodiment of the present
invention.
[0036] In the appended figures, similar components and/or features
may have the same reference label. Further, various components of
the same type may be distinguished by following the reference label
by a dash and a second label that distinguishes among the similar
components. If only the first reference label is used in the
specification, the description is applicable to any one of the
similar components having the same first reference label
irrespective of the second reference label.
DESCRIPTION
[0037] Reference will now be made in detail to embodiments,
examples of which are illustrated in the accompanying drawings and
figures. In the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding
of the subject matter herein. However, it will be apparent to one
of ordinary skill in the art that the subject matter may be
practiced without these specific details. In other instances,
well-known methods, procedures, components, and systems have not
been described in detail so as not to unnecessarily obscure aspects
of the embodiments.
[0038] It will also be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. For example, a first
object or step could be termed a second object or step, and,
similarly, a second object or step could be termed a first object
or step. The first object or step, and the second object or step,
are both objects or steps, respectively, but they are not to be
considered the same object or step.
[0039] The terminology used in the description of the disclosure
herein is for the purpose of describing particular embodiments only
and is not intended to be limiting of the subject matter. As used
in this description and the appended claims, the singular forms
"a", "an" and "the" are intended to include the plural forms as
well, unless the context clearly indicates otherwise. It will also
be understood that the term "and/or" as used herein refers to and
encompasses any and all possible combinations of one or more of the
associated listed items. It will be further understood that the
terms "includes," "including," "comprises," and/or "comprising,"
when used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0040] As used herein, the term "if" may be construed to mean
"when" or "upon" or "in response to determining" or "in response to
detecting," depending on the context. Similarly, the phrase "if it
is determined" or "if [a stated condition or event] is detected"
may be construed to mean "upon determining" or "in response to
determining" or "upon detecting [the stated condition or event]" or
"in response to detecting [the stated condition or event],"
depending on the context.
[0041] Hydrocarbon drilling operations require a large quantity of
downhole data to be collected and transmitted to the surface. Such
data may include characteristics of the earth formations
surrounding the borehole being drilled, drilling parameters, data
relating to the size and configuration of the borehole and/or the
like. The collection of information relating to conditions downhole
is commonly referred to as "logging," can be performed by several
methods. One of these methods requires sensing devices to be
lowered into the borehole on a wireline cable. However, collecting
data using sensors suspended on a wireline requires cessation of
the drilling process and/or removal of the drilling apparatus from
the borehole. This is extremely costly and slows down the drilling
process. Moreover, conditions may be changed by the cessation of
the drilling procedure and/or removal of the drilling
apparatus.
[0042] As a result, it is often desirable to collect data during
the drilling process. By collecting and processing data during the
drilling process, without the necessity of ceasing the drilling
procedure or tripping the drilling assembly out of the borehole to
insert a wireline logging tool, the driller can make accurate
modifications or corrections, as necessary, to optimize performance
while minimizing down time. Measuring conditions in the borehole
and/or downhole operating parameters of the drilling system
downhole during the drilling process is often referred to as
"measurement-while-drilling" or "MWD." Measuring properties of the
formation being drilled and/or surrounding the borehole being
drilled is often referred to as "logging while drilling" or "LWD."
While distinctions between MWD and LWD may exist, the terms MWD and
LWD are often used interchangeably.
[0043] Drilling oil and gas wells may be carried out using a string
of drill pipes connected together so as to form a drillstring. The
drillstring extends from a drive mechanism at the surface, such as
a top drive, down to the face of the formation being drilled.
Connected to the lower end of the drillstring is a drill bit that
is used to drill through the formation. In the drilling process,
the drill bit is rotated in the borehole against the formation.
Power is provided to the drill bit either from the top drive via
the drillstring or from a downhole motor.
[0044] Drilling fluid, often referred to as drilling mud/mud, is
pumped down through the drillstring during the drilling process at
high pressures and volumes (for example, such pressures may be
around 3000 p.s.i. at flow rates of up to 1400 gallons per minute)
to emerge through nozzles and/or jets in the drill bit. The mud is
used, among other things, to remove cuttings produced by the
drilling of the formation from the bottom of the borehole. The mud
pumped into the borehole travels down the drillstring, through the
drill bit then back up to the surface via an annulus formed between
the exterior of the drillstring and the wall of the borehole being
drilled. On the surface, the drilling mud may be cleaned and then
recirculated. The drilling mud not only carries the cuttings from
the base of the borehole to the surface, it may also be used to
cool the drill bit and, importantly, to balance the hydrostatic
pressure in the rock formations.
[0045] If the pressure in the borehole produced by the drilling mud
is less than the surrounding formation, fluids from the rock
formations may enter the borehole during the drilling process and
produce a kick, which is an undesirable drilling event. However, if
the pressure in the borehole produced by the drilling mud exceeds
the fracture pressure of the formation a fracture will be created
in the wall of the borehole, which may result in loss of fluids
from the borehole into the formation, this is also an undesirable
drilling event. As such, it is very important that the pressure in
the borehole is tightly controlled to avoid kicks and fluid loss.
Considering that boreholes may be of the order of kilometers in
length, management of the pressure in the borehole as it is being
drilled is an extremely complicated task.
[0046] This optimal pressure which avoids kicks and fluid loss is
termed herein the "optimal operating pressure window". Because the
pressure in the borehole is strongly influenced by the flow rate of
drilling mud, the flow rate that provides this optimal pressure at
steady state is termed herein as the "optimal operating flow rate
window". In general, a bottomhole pressure, the pressure at the
bottom of the borehole is the pressure that is used to determine an
optimal pressure in the borehole since the bottomhole pressure is
in general the most extreme of the pressures in the borehole. As
such, the optimal operating flow rate window may in general be
calculated using the bottomhole pressure. Often there are no
sensors to measure the bottomhole pressure and the pressure must be
interpolated for other parameters, such as drilling mud properties,
choke pressure, stand pipe pressure and/or the like.
[0047] In LWD and MWD sensors or transducers are often located at
the lower end of the drillstring, which sensors/transducers, while
drilling is in progress, continuously or intermittently sense
downhole parameters. Telemetry systems are used to communicate the
data acquired by the sensors to the surface. There are a number of
telemetry systems, but mud pulse telemetry is one of the most
widely used telemetry systems.
[0048] In mud pulse telemetry, acoustic signals are transmitted
through the drilling mud in the borehole, where the drilling mud is
circulated under pressure through the drill string during drilling
operations. Information contained in the acoustic signals may be
transmitted from the surface to the bottom of the borehole or from
the bottom of the borehole to the surface. Data acquired by the
downhole sensors is transmitted by suitably timing the generation
of pressure pulses in the flowing drilling mud. The acoustic
signals are received and decoded by a pressure transducer and
computer.
[0049] In a mud pulse telemetry system, the drilling mud pressure
in the drillstring may be modulated by means of a valve and control
mechanism, generally termed a pulser or mud pulser. The pulser is
usually mounted in a specially adapted drill collar positioned
above the drill bit. The generated pressure pulse travels up the
mud column inside the drillstring at the velocity of sound in the
mud. Depending on the type of drilling fluid used, the velocity may
vary between approximately 3000 and 5000 feet per second. The rate
of transmission of data, however, is relatively slow due to pulse
spreading, distortion, attenuation, modulation rate limitations,
and other disruptive forces, such as the ambient noise in the drill
string.
[0050] By way of example, a typical pulse rate is on the order of a
pulse per second (1 Hz). The mud pulse signal is comprised of a
pressure pulse at one of two amplitudes, indicating whether the mud
pulser is open or closed. If the pulser is closed, a high pressure
pulse is generated, to indicate, for example, a digital "1." If the
pulser is opened, a digital "0" is indicated. The primary method of
increasing the data rate of the transmitted signal is to increase
the frequency (f) of the pulses. As the frequency f of the pulses
increases, however, it becomes more and more difficult to
distinguish between adjacent pulses because the resolution period
is too short.
[0051] Mud pressure pulses can be generated in various different
ways and the mud pulses may comprise modulation of pulse amplitude,
pulse frequency and/or pulse phase. Whatever type of pulse system
is employed, detection of the pulses at the surface is sometimes
difficult due to attenuation and distortion of the signal and the
presence of noise generated by the mud pumps, the downhole mud
motor and elsewhere in the drilling system. Typically, a pressure
transducer is mounted directly on the line or pipe that is used to
supply the drilling fluid to the drillstring.
[0052] In MWD/LWD, the measured data may be communicated to the
surface through mud pulse telemetry techniques, in which drilling
fluid or "mud" is used as a propagation medium for a signal wave,
such as a pressure wave. More specifically, data may be
communicated by modulating one or more features of the wave to
represent the data. For instance, the amplitude, the frequency,
and/or the phase of the wave may be varied such that each variation
represents either a single data bit (i.e., binary modulation) or
multiple data bits (i.e., non-binary modulation) of digital data.
As the wave propagates to the surface, these modulations may be
detected and the data bits may be determined from the modulations.
Mud pulse telemetry is discussed in more detail in U.S. Pat. No.
8,302,685, which is hereby incorporated by reference for all
purposes.
[0053] As described above, during the drilling process mud is
circulated through the drillstring. However, in order to drill a
borehole, lengths of drill pipe must be added to the drillstring
during the drilling procedure as the length of the borehole is
increased. The adding of a section of drill pipe, which may be
referred to as a stand, requires that a connection be made to
connect the addition section of the drill pipe to the drillstring
in the borehole. During the connection, the flow rate/pressure of
the drilling mud in the drillstring drops. This typically results
in the pressure of the mud dropping below the optimal operating
pressure window.
[0054] When resuming drilling after a connection has been made, or
after any other form of drilling break, the flow rate of the mud,
and hence in turn the operating pressure, in the drillstring must
be brought up to the level required for drilling.
[0055] As described above, the pressure of the drilling mud is
critical to an effective drilling process and the pressure is
repeatedly monitored and, in general, controlled to be in the
optimal operating pressure window, where the pressure of the
drilling mud is greater than the pore pressure of the formation to
prevent fluid ingress into the borehole, and below a fracture
pressure of the formation, to prevent fracturing the formation.
[0056] Because the drilling fluid pressure is so important for an
effective drilling process, after a connection has been made, the
drilling system is controlled so that the drilling fluid pressure
in the top of the drillstring is increased back up to the desired
drilling pressure. Most commonly, drilling pressure in the top of
the drillstring is increased by pumping drilling fluid into the
drillstring at the surface.
[0057] Commonly, because of the importance of maintaining the
pressure in the drilling process within the pressure window,
drilling fluid is pumped into the drillstring at a rate that
increases the pressure in the drillstring to a level below the
optimal operating pressure window, and then the pump rate is slowly
increased to enter the optimal operating flow rate window, which
slow increase in flow results in a slow increase in the pressure of
the drilling fluid in the drillstring so that it slowly returns to
a pressure within the optimal operating pressure window.
Alternatively, the pumps may be brought straight up to the optimal
operating flow rate required for drilling.
[0058] As will be appreciated, there will be a time delay between
changes in flow rate at the top of the well and changes in pressure
in the mud. Moreover these delays will become greater the deeper
the well. In deep wells, even though the surface flow rate of
drilling fluid is at the required level and the pressure at the top
of the drillstring is at the desired level, it takes significant
time for the flow rate of the drilling fluid throughout the pipe to
stabilize, during which transition period mud pulse telemetry
communication is unreliable.
[0059] Additionally, during the period when the new section of
drill pipe is being added to the drillstring, it is standard
practice for surveying instruments close to the bit to make
measurements of the earth's magnetic and/or gravitational field,
and these measurements are sent to the surface using pressure waves
in the drilling fluid once flow is resumed. In order for these
measurements to be received clearly at surface, it is advantageous
if the flow rate in the drillstring is constant or near-constant.
However, in long/deep wells and especially in wells drilled with
oil-based drilling fluid (which drilling fluids are more
compressible than water-based drilling fluid), there can be a
considerable time before the flow rate along the drillstring, and
through the drill bit, has stabilized after the flow rate from the
pumps has reached its final level. This is due to the compressible
nature of the drilling fluid, combined with the pressure created in
the drilling fluid from the fluid flow along the pipe and through
the bit.
[0060] Applicant has found that this transition period,
particularly for deep wells, can be significantly and surprisingly
reduced by increasing the flow rate of the drilling fluid at the
top of the drillstring to a rate above an optimal operating flow
rate for a limited time before dropping back to a lower, optimal
flow rate. Moreover, Applicant has found that if the increase is
only provided for a short period of time, the volume of additional
fluid pumped into the drillstring is small, and as a result the
pressure in the drillstring and the operation of the system does
not have an opportunity to rise to an undesirable level outside the
optimum pressure window.
[0061] As such, one embodiment of the present invention provides a
method for controlling flow rates of drilling fluids being pumped
into a drillstring during a drilling procedure to drill a borehole
from a surface location through an earth formation, the method
comprising: establishing a range of desired optimal flow rates for
pumping the drilling fluids into the drillstring, wherein the
optimal flow rates are determined so as to keep drilling mud
pressure in the borehole within an optimal operating pressure
window having upper and lower pressure bounds; drilling for a first
period of time at a first optimal flow rate, maintaining the
pressure within the optimal operating pressure window; reducing the
flow rate to cause the pressure to fall below the lower bound of
the pressure window; increasing the flow rate to a value above said
first optimal flow rate; reducing the flow rate to a second optimal
flow rate, which may be the same or different to the first optimal
flow rate.
[0062] In such an embodiment, once the pressure drops below the
minimum level for optimal operation, e.g. as happens when adding a
section of drill pipe to the drillstring, the flow rate of drilling
mud is increased so as to overshoot the final desired optimal flow
rate for a period of time before falling back to the optimal flow
rate. In this way the time required to achieve stable flow in the
drillpipe may be reduced and the transition period, where mud pulse
telemetry, is unreliable may be reduced. A benefit of this
invention is that a stable flow rate at which reliable data
communication can occur is achieved substantially faster providing
for enhanced communication in the borehole.
[0063] In practicing the present invention it should be borne in
mind that there can be a substantial time delay between a change in
flow rate at the top of a wellbore causing an associated change in
pressure of the mud, particularly mud near the bottom of the
wellbore. Thus, in embodiments of the present invention increases
in flow rates above that which it is desirable to operate at may be
tolerable, provided they are for a limited period of time before
the flow rate is reduced to an optimal level. Moreover, in
embodiments of the present invention, an overshoot time and a flow
rate may be used to process a volume of excess mud being pumped
into the borehole and this volume may be processed to be a volume
that will not increase the downhole pressure above the desired
pressure window. Furthermore, as noted previously, the drilling
fluid is compliant and the effect of changes in the flow rate of
the drilling fluid being pumped into the borehole on the downhole
pressure may be affected by this compliance, especially in deep
boreholes.
[0064] In embodiments of the present invention, the pressure window
for the downhole pressure determined from the reservoir pressure
etc., the compliance properties of the drilling fluid and/or the
like may be used to process a maximum flow rate increase above the
flow rate of drilling fluid being pumped into the drillstring prior
to a drilling stand and/or a period of time that such a flow rate
increase can be performed. The amount of increase above the
operating flow rate and the period of time this increase is applied
during the drilling procedure will both increase the downhole
pressure so in embodiments of the present invention, the two
variables are processed to provide either a large increase in flow
rate above the optimum flow rate for a short period of time or a
lower increase for a longer period of time. By monitoring operation
of the mud pulse telemetry after a drilling stand a determination
may be made as to which of the alternatives is better for the
ongoing drilling procedure. In embodiments of the present
invention, a sensor or the like may be used to measure a flow rate
of drilling fluid into the drillstring before a drilling stand and
a processor may control pumps to increase the flow rate of the
drilling fluid into the drillstring above the measured flow rate
after the drilling stand is performed.
[0065] In embodiments of the present invention, the overshoot of
the flow rate and the direction of the overshoot are determined
such that the pressure in the drillstring does not exceed a desired
pressure window and/or so that the perturbation in the flow
rate/pressure of the drilling fluid is minimal and/or returns to
the desired flow rate as quickly as possible.
[0066] In embodiments of the present invention, it has been found
that even a small degree of overshoot in the flow rate for a
relatively short period of time can significantly reduce the time
taken for the pressure in the wellbore to stabilize, especially at
the bottom of the wellbore.
[0067] Thus, the increased flow rate may be up to 30%, up to 20%
and/or up to 10% greater than an optimal flow rate. Also the
increased flow rate may persist for a period of time of the order
of minutes and/or 10 s of seconds, e.g. less than 5 minutes. In
some aspects it may be less than 2 minutes or even 1 minute.
[0068] Deciding on the how much faster to flow, and for how long,
can be decided in a variety of different ways. There are a number
of criteria that may to be accounted for as well as reducing the
downhole time to stable flow, such as flow rate limitations imposed
for the pumps, and the need to keep the surface pressure below a
limit.
[0069] In accordance with an embodiment of the present invention, a
first method for determining overshoot parameters is provided by
modeling the flow/pressure of the drilling fluid in the
drillstring, such as by using the theory of flow rate adjustments,
as described in U.S. Pat. No. 8,196,678, which patent is
incorporated by reference herein for all purposes.
[0070] In accordance with an embodiment of the present invention, a
second method for controlling overshoot is to gradually increase
the overshoot parameters from one connection to the next, while
monitoring the pressure at surface (such as by monitoring
stand-pipe pressure) to check that the maximum pressure stays
within bounds that are acceptable, and preferably checking the
observations with theoretical calculations to approximately infer
the downhole flow rate from the observed pressures at surface. In
some aspects, the overshoot may be outside of a range of flow rates
that are determined as being necessary to maintain the downhole
pressure within an operating pressure window--i.e., a pressure
window bounded by the formation fracture pressure and the formation
pore pressure--but because of the short duration of time of the
overshoot may not introduce a sufficient volume of drilling fluid
to take the bottomhole pressure out of the bounds of operating
pressure window. Additionally, in some embodiments, choke pressure
may be adjusted at the same time as the overshoot is performed to
mitigate changes in bottomhole pressure produced by the
overshoot.
[0071] In accordance with an embodiment of the present invention,
the pump flow rate time series may either be controlled using an
automated system, which follows the determined rate profile, or by
an operator, who manually attempts to follow the time operations of
the rate profile.
[0072] A processor in communication with a surface sensor may
control the overshoot and the system may learn from previous
overshoots to find optimum overshoot parameters for the drilling
system and to improve the effectiveness of subsequent overshoots.
Experience, knowledge of other drilling systems, modeling,
experimentation and/or the like may be used to determine the
overshoot parameters. Overshoot parameters and the surface pressure
may be recorded, displayed, stored and/or the like to provide for
an understanding/record/real-time analysis of the overshoot process
and its effects. Additionally, characteristics of the operation of
the mud pulse telemetry system may also be recorded, displayed,
stored and/or the like to provide an understanding of the effect of
the overshoot on the mud pulse telemetry operation.
[0073] In some embodiments, overshoot systems and methods may be
integrated with a managed pressure drilling system, including an
automated managed pressure drilling system. In some embodiments,
properties of the drilling mud may be used to process the overshoot
parameters.
[0074] FIG. 1B illustrates an apparatus for resuming interrupted
communication down a wellbore, according to one embodiment of the
present invention. As illustrated, a drillstring 101 is located in
a borehole 102 that is penetrating through an earth formation 104.
At the distal end of the drillstring 101 is a bottomhole assembly
("BHA") 103 and a drill bit 105. The BHA 103 may comprise a turbine
109, a pressure pulse based communication system 110 and/or means
of determining the orientation of the BHA with respect to the
earth's magnetic and/or gravitational field 108.
[0075] At surface the drillstring 101 is suspended by sheaves 107,
and there is a means for fluid to enter the drillstring 101 through
a swivel 106. The swivel 106 is connected to a pump 112, which is
controlled by an electrical control system 113. The control system
113 includes settings that may either come from an operator and/or
a computer (not shown).
[0076] Although the apparatus illustrated in the figure uses
jointed pipe, and sheaves, some embodiments of the invention may be
used with systems such as coiled tubing drilling when flow is
initiated through the tubing.
[0077] FIGS. 2-4 illustrate simulations of flows and pressures in a
normal/previous wellbore operation, and simulations of flows and
pressures in wellbore procedure operated in accordance with
embodiments of the present invention.
[0078] FIG. 2 illustrates a flow rate transition according to
current practice (solid line), and according to a method in
accordance of the present invention (dashed line). In current
practice the flow is brought up to a steady level (here 3000
litres/minute). According to one embodiment of the present
invention the flow is first brought up to 3300 litres/minute, and
then down to 3000 litres/minute after 30 seconds.
[0079] FIG. 3 shows flow rates through a drill bit versus time for
a conventional wellbore procedure and a according to one embodiment
of the present invention. With the normal practice, the flow rate
downhole takes nearly two minutes to stabilize. With the flow rates
following an embodiment of the present invention, this is achieved
in about 40 seconds.
[0080] FIG. 4 shows stand-pipe pressures for a conventional
wellbore procedure and a according to one embodiment of the present
invention. Although a higher flow rate is used following the
invention, the extra pressure seen at the surface is minimal,
because of the short duration of the extra flow.
[0081] In accordance with an embodiment of the present invention, a
processor controls the pumps. The processor controls the pumps to
increase the flow rate of the drilling fluid so that is overshoots
the flow rate that has been determined will produce the desired
pressure in the drillstring/borehole for effective drilling, i.e,
within the pressure window (as described in more detail above).
[0082] In aspects of the present invention, the processor may
control the overshoot to minimize perturbations in the drilling
fluid pressure. In some aspects, the processor may determine
overshoot parameters that both provide for the quickest move from
the transition period to the downhole flow rate necessary for
effective mud pulse telemetry and only an acceptable increase in
drilling fluid pressure in the borehole with respect to the
pressure window. Because the pressure in the drillstring is of such
importance, the processor may be in communication with a surface
pressure sensor, such as located in the stand pipe, and may provide
a display of the pressure changes produced by the overshoot.
Tolerances may be built into the processor, to provide that the
overshoot parameters provide for pressure perturbations that are a
defined amount below a maximum pressure of the pressure window.
[0083] Although only a few example embodiments have been described
in detail above, those skilled in the art will readily appreciate
that many modifications are possible in the example embodiments
without materially departing from this invention. Accordingly, all
such modifications are intended to be included within the scope of
this disclosure as defined in the following claims. In the claims,
means-plus-function clauses are intended to cover the structures
described herein as performing the recited function and not only
structural equivalents, but also equivalent structures. Thus,
although a nail and a screw may not be structural equivalents in
that a nail employs a cylindrical surface to secure wooden parts
together, whereas a screw employs a helical surface, in the
environment of fastening wooden parts, a nail and a screw may be
equivalent structures. It is the express intention of the applicant
not to invoke 35 U.S.C. .sctn.112, paragraph 6 for any limitations
of any of the claims herein, except for those in which the claim
expressly uses the words `means for` together with an associated
function.
* * * * *