U.S. patent application number 15/475858 was filed with the patent office on 2017-07-20 for in-situ property determination.
The applicant listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Brice Lecampion, Romain Charles Andre Prioul, Eduard Siebrits.
Application Number | 20170204726 15/475858 |
Document ID | / |
Family ID | 44673875 |
Filed Date | 2017-07-20 |
United States Patent
Application |
20170204726 |
Kind Code |
A1 |
Lecampion; Brice ; et
al. |
July 20, 2017 |
IN-SITU PROPERTY DETERMINATION
Abstract
In one possible implementation an in-situ property determination
system includes a displacement tool configured for use in a
wellbore. The displacement tool includes four or more pads
symmetrically located about an axis of the displacement tool, with
each pad having a contact surface configured to contact a wall of
the wellbore. The four or more pads can extend from a first
position proximate an outer surface of the displacement tool to a
second position in contact with the wall of the wellbore such that
the four or more pads deform the wellbore into an at least
approximately circular cross section. The system also includes a
recordation device to record force displacement information
associated with extending the four or more pads from the first
position to the second position.
Inventors: |
Lecampion; Brice; (Paris,
FR) ; Siebrits; Eduard; (Salt Lake City, UT) ;
Prioul; Romain Charles Andre; (Cambridge, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Family ID: |
44673875 |
Appl. No.: |
15/475858 |
Filed: |
March 31, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61317084 |
Mar 24, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 27/2601 20130101;
H04B 10/677 20130101; H04L 27/2075 20130101; H04L 27/2096 20130101;
H04B 10/5561 20130101; E21B 49/006 20130101; E21B 47/002 20200501;
Y02D 70/46 20180101; H04L 27/223 20130101; H04B 7/18508 20130101;
E21B 47/007 20200501; Y02D 70/446 20180101; Y02D 30/70 20200801;
E21B 49/00 20130101; E21B 49/06 20130101; G01V 1/40 20130101; H04B
7/18521 20130101 |
International
Class: |
E21B 49/00 20060101
E21B049/00; E21B 47/00 20060101 E21B047/00 |
Claims
1. An in-situ property determination system comprising: a
displacement tool configured for use in a wellbore in a formation,
the displacement tool comprising: four or more pads symmetrically
located about an axis of the displacement tool, with each pad
having a contact surface configured to contact a wall of the
wellbore; wherein the four or more pads are further configured to
extend from a first position proximate an outer surface of the
displacement tool to a second position in contact with the wall of
the wellbore such that the four or more pads deform the wellbore
into an at least approximately circular cross section; and a
recordation device configured to record force displacement
information associated with extending the four or more pads from
the first position to the second position.
2. The in-situ property determination system of claim 1, wherein
the recordation device is located at least partially within the
displacement tool.
3. The in-situ property determination system of claim 1, further
comprising: a property determination module configured to utilize
at least a portion of the force displacement information associated
with extending the four or more pads from the first position to the
second position to estimate a far-field stress ratio associated
with the formation.
4. The in-situ property determination system of claim 1, wherein
the recordation device is further configured to record maintenance
force information associated with maintaining the four or more pads
at the second position.
5. The in-situ property determination system of claim 4, further
comprising: a property determination module configured to utilize
at least a portion of the maintenance force information associated
with maintaining the four or more pads at the second position to
estimate one or more of: one or more poroelastic properties of the
formation; a hydraulic diffusivity of the formation; and one or
more rock creep properties of the formation.
6. The in-situ property determination system of claim 1, wherein
the four or more pads are further configured to retract from the
second position to the first position, and further wherein the
recordation device is further configured to record force
displacement information associated with allowing the four or more
pads to retract from the second position to the first position.
7. The in-situ property determination system of claim 6, further
comprising: a property determination module configured to utilize
at least a portion of the force displacement information associated
with allowing the four or more pads to retract from the second
position to the first position to estimate Young's Modulus
associated with the formation.
8. A method of in-situ property determination comprising:
activating a displacement tool at a desired depth in a wellbore in
a formation to deform the wellbore from an at least approximately
elliptical cross section to an at least approximately circular
cross section; and recording force displacement information
associated with deforming the wellbore from the at least
approximately elliptical cross section to the at least
approximately circular cross section.
9. The method of in-situ property determination of claim 8, further
comprising: utilizing at least a portion of the force displacement
information associated with deforming the wellbore from the at
least approximately elliptical cross section to the at least
approximately circular cross section to estimate a far-field stress
ratio associated with the formation.
10. The method of in-situ property determination of claim 8,
further comprising: choosing the desired depth based at least in
part on one or more ultrasonic images associated with the
wellbore.
11. The method of in-situ property determination of claim 8,
further comprising: identifying a location of an axis of the at
least approximately elliptical cross section at least partially
through use of a wellbore image.
12. The method of in-situ property determination of claim 8,
further comprising: recording maintenance force information
associated with maintaining the at least approximately circular
cross section; and utilizing at least a portion of the maintenance
force information to estimate one or more of: one or more
poroelastic properties of the formation; a hydraulic diffusivity of
the formation; and one or more rock creep properties of the
formation.
13. The method of in-situ property determination of claim 8,
further comprising: recording force displacement information
associated with allowing the wellbore to return from the at least
approximately circular cross section to an at least approximately
elliptical cross section; and utilizing at least a portion of the
force displacement information associated with allowing the
wellbore to return from the circular cross section to the at least
approximately elliptical cross section to estimate Young's Modulus
associated with the formation at the desired depth.
14. The method of in-situ property determination of claim 8 wherein
activating the displacement tool includes: extending four or more
pads from a first position proximate an outer surface of the
displacement tool to a second position in which the four or more
pads have pushed a wall of the wellbore into the at least
approximately circular cross section.
15. The method of in-situ property determination of claim 14,
further comprising: orienting the four or more pads in a direction
of a maximum principal stress and a minimum principal stress in the
formation.
16. The method of in-situ property determination of claim 8,
further comprising: allowing the wellbore to return from the at
least approximately circular cross section to an at least
approximately elliptical cross section; turning the displacement
tool by a desired angle and activating the displacement tool to
deform the wellbore from an at least approximately elliptical cross
section to an at least approximately circular cross section; and
recording force displacement information associated with deforming
the wellbore from the at least approximately elliptical cross
section to the at least approximately circular cross section.
17. The method of in-situ property determination of claim 8,
further comprising: moving the displacement tool to a second
desired depth in the wellbore; activating the displacement tool at
the second desired depth to deform the wellbore from an at least
approximately elliptical cross section to an at least approximately
circular cross section; and recording force displacement
information associated with deforming the wellbore from the at
least approximately elliptical cross section to the at least
approximately circular cross section.
18. A computer-readable tangible medium with instructions stored
thereon that, when executed, direct a processor to perform acts
comprising: accessing force displacement information associated
with deforming a wellbore in a formation from an at least
approximately elliptical cross section to an at least approximately
circular cross section; and utilizing at least a portion of the
force displacement information associated with deforming the
wellbore from the at least approximately elliptical cross section
to the at least approximately circular cross section to estimate a
far-field stress ratio associated with the formation. The
computer-readable tangible medium of claim 18, wherein the
computer-readable tangible medium further includes instructions to
direct a processor to perform acts comprising: accessing
maintenance force information associated with maintaining the at
least approximately circular cross section of the wellbore; and
utilizing at least a portion of the maintenance force information
to estimate one or more of: one or more poroelastic properties of
the formation; a hydraulic diffusivity of the formation; and one or
more rock creep properties of the formation.
19. The computer-readable tangible medium of claim 18, wherein the
computer-readable tangible medium further includes instructions to
direct a processor to perform acts comprising: accessing force
displacement information associated with allowing the wellbore to
return from an at least approximately circular cross section to an
at least approximately elliptical cross section; and utilizing at
least a portion of the force displacement information associated
with allowing the wellbore to return from the at least
approximately circular cross section to the at least approximately
elliptical cross section to estimate Young's Modulus associated
with the formation.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of US Provisional
Application having Ser. No. 62/317,084 entitled "In-Situ Property
Determination" filed Apr. 1, 2016, which is incorporated in its
entirety by reference herein.
BACKGROUND
[0002] Logging tools have long been used in wellbores to help
operators infer properties associated with a formation, such as,
for example, the permeability of a section of the formation, the
types and amounts of fluids in the formation, etc. Common logging
tools include resistivity (electromagnetic) tools, nuclear tools,
acoustic tools, and nuclear magnetic resonance (NMR) tools, though
various other types of tools for evaluating formation properties
are also available. Common logging tools also include measurements
tools that are in contact with the formation and stationary at a
given depth for a short period of time while performing a
measurement, such as dual-packer stress testing and/or fluid
analyzer tools.
[0003] Early logging tools were run into a wellbore on a wireline
cable after the wellbore had been drilled. Modern versions of such
wireline tools are still used extensively.
[0004] The above descriptions and examples are not admitted to be
prior art by virtue of their inclusion in this section.
SUMMARY
[0005] In-situ property determination is provided. In one possible
implementation an in-situ property determination system includes a
displacement tool configured for use in a wellbore. The
displacement tool includes four or more pads symmetrically located
about an axis of the displacement tool, with each pad having a
contact surface configured to contact a wall of the wellbore. The
four or more pads can extend from a first position proximate an
outer surface of the displacement tool to a second position in
contact with the wall of the wellbore such that the four or more
pads deform the wellbore into an at least approximately circular
cross section. The system also includes a recordation device to
record force displacement information associated with extending the
four or more pads from the first position to the second
position.
[0006] In another possible implementation, a method of in-situ
property determination includes activating a displacement tool at a
desired depth in a wellbore to deform the wellbore from an at least
approximately elliptical cross section to an at least approximately
circular cross section. The method also includes recording force
displacement information associated with deforming the wellbore
from the at least approximately elliptical cross section to the at
least approximately circular cross section.
[0007] In yet another possible implementation, a computer-readable
tangible medium has instructions stored thereon that, when
executed, direct a processor to access force displacement
information associated with deforming a wellbore from an at least
approximately elliptical cross section to an at least approximately
circular cross section. The computer-readable tangible medium also
has instructions stored thereon that, when executed, direct a
processor to utilize at least a portion of the force displacement
information associated with deforming the wellbore from the at
least approximately elliptical cross section to the at least
approximately circular cross section to estimate a far-field stress
ratio associated with the formation.
[0008] This summary is not intended to identify key or essential
features of the claimed subject matter, nor is it intended to be
used as an aid in limiting the scope of the claimed subject
matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Features and advantages of the described implementations can
be more readily understood by reference to the following
description taken in conjunction with the accompanying
drawings.
[0010] FIG. 1 illustrates an example wellsite in which embodiments
of in-situ property determination can be employed;
[0011] FIG. 2 illustrates an example computing device that can be
used in accordance with various implementations of in-situ property
determination;
[0012] FIG. 3 illustrates an example concept of stress compensation
for a wellbore configuration in accordance with implementations of
in-situ property determination;
[0013] FIG. 4 illustrates an example displacement tool in
accordance with implementations of in-situ property
determination;
[0014] FIG. 5 illustrates example schematic force versus
displacement curves for two pads at different angles with respect
to the in-situ horizontal stress direction in accordance with
implementations of in-situ property determination;
[0015] FIG. 6 illustrates an example ratio of forces acting on a
first pad over a second pad for different positions of the first
pad with respect to the maximum stress direction in accordance with
implementations of in-situ property determination;
[0016] FIG. 7 illustrates an example ratio of the radial
displacement u.sub.r over radius "a" induced by the release of the
far-field stress for different azimuthal positions with respect to
the direction of maximum stress (.sigma..sub.1) in accordance with
implementations of in-situ property determination; and
[0017] FIG. 8 illustrates example method(s) in accordance with
implementations of in-situ property determination.
DETAILED DESCRIPTION
[0018] In the following description, numerous details are set forth
to provide an understanding of some embodiments of the present
disclosure. However, it will be understood by those of ordinary
skill in the art that systems and/or methodologies may be practiced
without these details and that numerous variations or modifications
from the described embodiments may be possible.
[0019] Additionally, some examples discussed herein involve
technologies associated with the oilfield services industry. It
will be understood however that the techniques of in-situ property
determination may also be useful in a wide range of other
industries outside of the oilfield services sector, including for
example, mining, geological surveying, etc.
[0020] Moreover, it will also be understood that the term
"optimize" as used herein can include any improvements up to and
including optimization. Similarly, the term "improve" can include
optimization. Other terms like "minimize" and "maximize" can also
include actions reducing and increasing, respectively, various
quantities and qualities.
[0021] As described herein, various techniques and technologies
associated with in-situ property determination can be used, for
example, to estimate various properties of a formation by recording
the forces used to alter the shape of a cross section of a
wellbore. In one possible implementation, this can include
recording forces to restore a wellbore from an at least
approximately elliptical cross section to an at least approximately
circular cross section. In another possible implementation, forces
applied to hold the wellbore in the at least approximately circular
cross section can be recorded. In still another possible
implementation, forces applied to allow the wellbore to deform back
to an at least approximately elliptical cross section from the at
least approximately circular cross section can be recorded. It will
be understood that the term "at least approximately elliptical
cross section" as used herein, can denote an elliptical cross
section as well as cross sections that fall short of being
elliptical due to shape affecting wellbore issues including, for
example, irregularities, small washouts, etc.
Example Wellsite
[0022] FIG. 1 illustrates a wellsite 100 in which embodiments of
in-situ property determination can be employed. Wellsite 100 can be
onshore or offshore. In this example system, a wellbore 102 is
formed in a subsurface formation 104 by drilling in any manner
known in the art, including for example, rotary drilling,
directional drilling, etc.
[0023] In one possible implementation, a wellbore logging tool 106,
such as, for example, a wireline tool (including a wireline
measurement tool configured to take station measurements), can be
used to acquire data that is associated with formation 104.
Wellbore logging tool 106 can be disposed within wellbore 102 in
any way known in the art and can be moved anywhere desired along
wellbore 102 by, for example, an operator. In one possible
implementation, wellbore logging tool 106 can include a variety of
tools, including, for example, an NMR tool 108 to perform NMR
measurements of formation 104, other nuclear tools, such as neutron
porosity tools, to gather porosity data associated with formation
104, etc.
[0024] In one possible embodiment, wellbore logging tool 106 can
also include a displacement tool 110 to perform various actions in
accordance with the principles of in-situ property measurement
described herein. In one possible aspect, displacement tool 110 can
be alone on wellbore logging tool 106. In another possible aspect,
displacement tool 110 can be accompanied by other tools on wellbore
logging tool 106. It will also be understood that in other possible
implementations, displacement tool 110 can be deployed in wellbore
102 on its own, using any deployment technologies and/or equipment
known in the art.
[0025] In one possible implementation, wellbore logging tool 106
(and/or displacement tool 110) can be coupled to a processing
system 112 using any technology known in the art, including, for
example, wireless technologies, wireline technologies, etc.
Processing system 112 can receive and process a variety of
information associated with the various tools on wellbore logging
tool 106, including displacement tool 110. Processing system 112
can also control a variety of equipment, including wellbore logging
tool 106, displacement tool 110, etc.
[0026] Processing system 112 can be used with a wide variety of
oilfield applications, including logging while drilling, artificial
lift, measuring while drilling, wireline, etc. Processing system
112 can be located at a surface 114 of wellsite 100, below surface
114, proximate to wellbore 102, on displacement tool 110, remote
from wellbore 102, and/or any combination thereof.
[0027] For example, in one possible implementation, information
associated with displacement tool 110 can be processed by
processing system 112 at one or more locations, including any
configuration known in the art, such as in one or more handheld
devices proximate and/or remote from wellsite 100, at a computer
located at a remote command center, etc. In one possible
implementation, processing system 112 can also perform various
aspects of in-situ property determination, as described herein, to
process various measurements and/or information.
[0028] The term "processing system" is not limited to any
particular device type or system. For example, processing system
112 may include a single processor, multiple processors, or a
computer system. Such a computer system may include a computer
processor (e.g., a microprocessor, microcontroller, digital signal
processor, or general purpose computer) for executing any of the
methods and processes described herein. The computer system may
further include a memory such as a semiconductor memory device
(e.g., a RAM, ROM, PROM, EEPROM, or Flash-Programmable RAM), a
magnetic memory device (e.g., a diskette or fixed disk), an optical
memory device (e.g., a CD-ROM), a PC card (e.g., PCMCIA card), or
other memory device.
[0029] Some of the methods and processes described herein, can be
implemented as computer program logic for use with the computer
processor. The computer program logic may be embodied in various
forms, including a source code form and/or a computer executable
form. Source code may include a series of computer program
instructions in a variety of programming languages (e.g., an object
code, an assembly language, and/or a high-level language such as C,
C++, Matlab, JAVA or other language or environment known in the
art.). Such computer instructions can be stored in a non-transitory
computer readable medium (e.g., memory) and executed by the
computer processor. The computer instructions may be distributed in
any form as a removable storage medium with accompanying printed or
electronic documentation (e.g., shrink wrapped software), preloaded
with a computer system (e.g., on system ROM or fixed disk), and/or
distributed from a server and/or electronic bulletin board over a
communication system (e.g., the Internet or World Wide Web).
[0030] Alternately or additionally, processing system 112 may
include discrete electronic components coupled to a printed circuit
board, integrated circuitry (e.g., Application Specific Integrated
Circuits (ASIC)), and/or programmable logic devices (e.g., a Field
Programmable Gate Arrays (FPGA)). In one possible aspect, any of
the methods and processes described herein can be implemented using
such logic devices.
[0031] In one possible implementation, wellbore logging tool 106
can take "continuous" measurements (such as, for example, as
wellbore logging tool 106 is continuously pulled along wellbore 102
without contacting the wall of wellbore 102 or any completions
elements in wellbore 102 such as pads, packers, etc.). Alternately,
or additionally, measurements such as, for example, "station"
wireline measurements may be taken where wellbore logging tool 106
and/or displacement tool 110 stops and anchors itself to the wall
of wellbore 102 to collect sampling measurements, stress
measurements (such as, for example, MDT stress tests), force
measurements, etc.
Example Computing Device
[0032] FIG. 2 illustrates an example device 200, with a processor
202 and memory 204 for hosting a property determination module 206
configured to implement various embodiments of in-situ property
determination as discussed in this disclosure. Memory 204 can also
host one or more databases and can include one or more forms of
volatile data storage media such as random access memory (RAM),
and/or one or more forms of nonvolatile storage media (such as
read-only memory (ROM), flash memory, and so forth).
[0033] Device 200 is one example of a computing device or
programmable device, and is not intended to suggest any limitation
as to scope of use or functionality of device 200 and/or its
possible architectures. For example, device 200 can comprise one or
more computing devices, programmable logic controllers (PLCs),
laptop computers, handheld devices, mainframe computers,
high-performance computing (HPC) clusters, clouds, etc., including
any combination thereof.
[0034] Further, device 200 should not be interpreted as having any
dependency relating to one or a combination of components
illustrated in device 200. For example, device 200 may include one
or more of a computer, such as a laptop computer, a desktop
computer, a mainframe computer, an HPC cluster, cloud, etc., or any
combination and/or accumulation thereof.
[0035] Device 200 can also include a bus 208 configured to allow
various components and devices, such as processors 202, memory 204,
and local data storage 210, among other components, to communicate
with each other.
[0036] Bus 208 can include one or more of any of several types of
bus structures, including a memory bus or memory controller, a
peripheral bus, an accelerated graphics port, and a processor or
local bus using any of a variety of bus architectures. Bus 208 can
also include wired and/or wireless buses.
[0037] Local data storage 210 can include fixed media (e.g., RAM,
ROM, a fixed hard drive, etc.) as well as removable media (e.g., a
flash memory drive, a removable hard drive, optical disks, magnetic
disks, and so forth), cloud storage, etc.
[0038] One or more input/output (I/O) device(s) 212 may also
communicate via a user interface (UI) controller 214, which may
connect with I/O device(s) 212 either directly or through bus
208.
[0039] In one possible implementation, a network interface 216 may
communicate outside of device 200 via a connected network, and in
some implementations may communicate with hardware, such as
displacement tool 110, wellbore logging tool 106, etc.
[0040] In one possible embodiment, hardware, such as displacement
tool 110, wellbore logging tool 106, etc., may communicate with
device 200 as input/output device(s) 212 via bus 208, such as via a
USB port, for example.
[0041] A media drive/interface 218 can accept removable tangible
media 220, such as flash drives, optical disks, removable hard
drives, software products, etc. In one possible implementation,
logic, computing instructions, and/or software programs comprising
elements of in-situ property determination module 206 may reside on
removable media 220 readable by media drive/interface 218.
[0042] In one possible embodiment, input/output device(s) 212 can
allow a user to enter commands and information to device 200, and
also allow information to be presented to the user and/or other
components or devices. Examples of input device(s) 212 include, for
example, sensors, a keyboard, a cursor control device (e.g., a
mouse), a microphone, a scanner, and any other input devices known
in the art. Examples of output devices include a display device
(e.g., a monitor or projector), speakers, a printer, a network
card, and so on.
[0043] Various processes of property determination module 206 may
be described herein in the general context of software or program
modules, or the techniques and modules may be implemented in pure
computing hardware. Software generally includes routines, programs,
objects, components, data structures, and so forth that perform
particular tasks or implement particular abstract data types. An
implementation of these modules and techniques may be stored on or
transmitted across some form of tangible computer-readable media.
Computer-readable media can be any available data storage medium or
media that is tangible and can be accessed by a computing device.
Computer readable media may thus comprise computer storage media.
"Computer storage media" designates tangible media, and includes
volatile and non-volatile, removable and non-removable tangible
media implemented for storage of information such as computer
readable instructions, data structures, program modules, or other
data. Computer storage media include, but are not limited to, RAM,
ROM, EEPROM, flash memory or other memory technology, CD-ROM,
digital versatile disks (DVD) or other optical storage, magnetic
cassettes, magnetic tape, magnetic disk storage or other magnetic
storage devices, or any other tangible medium which can be used to
store the desired information, and which can be accessed by a
computer.
[0044] In one possible implementation, device 200, or a plurality
thereof, can be employed at wellsite 100. This can include, for
example, in displacement tool 110, in wellbore logging tool 106, in
processing system 112, etc.
Example System(s) and/or Technique(s)
[0045] In one possible implementation, various techniques and
technologies associated with in-situ property determination can be
used to measure in situ stresses and/or in situ mechanical rock
properties in a formation 104 using displacement tool 110. In one
possible implementation, displacement tool 110 can include anything
deployable downhole in wellbore 102 that can be used to change a
cross section of wellbore 102. In one possible aspect, displacement
tool 110 can include, for example, a displacement controlled
downhole mechanical tester. Further, in another possible aspect,
displacement tool 110 can employ, for example, a stress
compensation method to measure stresses and/or mechanical rock
properties of formation 104.
[0046] As will be discussed in more detail below, in some possible
implementations, displacement tool 110 can be used to estimate, for
example: (i) a ratio of the far-field stresses (aka in-situ
stresses) acting perpendicular to an axis of wellbore 102; (ii) an
orientation of the far-field stress directions acting perpendicular
to the axis of wellbore 102; and (iii) rock elastic moduli in a
direction perpendicular to the axis of wellbore 102.
[0047] In one possible implementation, knowledge of the in-situ
state of stress and/or knowledge of the pore-pressure field in
formation 104 can be useful information for a wide variety of
geomechanical applications from wellbore stability to hydraulic
fracturing design and fluid production induced deformation
(compaction/up-heave), etc. In one possible aspect, the state of
in-situ stress at a point in the earth can be defined by six
quantities: three principal stresses (the principal values of the
stress tensor) and three corresponding principal directions. At
depth, away from discontinuities and complex surface topographies,
the vertical direction can be one of the principal directions of
the stress state and the vertical stress magnitude (.sigma..sub.v)
can be estimated from the overburden weight:
.sigma..sub.V(z)=.intg..sub.0.sup.zg.rho.(z)dz
where g is the gravitational constant and .rho. is the rock bulk
density. Density logs can therefore be used to estimate the
vertical stress. At depth, three additional quantities related to
horizontal stresses can be used to characterize the initial in-situ
state of stress: (1) the minimum horizontal in-situ stress
magnitude (.sigma..sub.h); (2) the maximum horizontal in-situ
stress magnitude (.sigma..sub.H); and (3) the direction of the
maximum horizontal stress, or the direction of the minimum
horizontal stress (which is perpendicular to the direction of the
maximum horizontal stress). Often, measuring the horizontal in-situ
stresses can be quite difficult.
[0048] FIG. 3 illustrates an example concept 300 of stress
compensation for a configuration of wellbore 102 in accordance with
implementations of in-situ property determination. In order to
simplify calculations, it can be assumed, for example, that
wellbore 102 has been drilled in the direction of one of the
principal in-situ stress directions (i.e., wellbore 102 is either a
vertical or a horizontal well). This does not mean, however, that
the principles of in-situ property determination cannot be applied
in other instances in which wellbore 102 is neither horizontal nor
vertical (i.e., such as a deviated well), because the principles
can. However, in such non vertical and/or non horizontal cases,
estimation of stress magnitudes can be more lengthy and
complicated.
[0049] As shown, a trace 302 of wellbore 102 prior to deformation
due to stresses in formation 104 is approximately circular in cross
section and has a diameter approximately equal to that of a drill
bit used to create wellbore 102 in formation 104.
[0050] When the drill bit used to create wellbore 102 is removed, a
cross section of wellbore 102 converges due to far field stresses
(aka, in situ stresses) .sigma..sub.1 and .sigma..sub.2 in
formation 104 such that trace 302 of the converged wellbore 102
becomes an elliptical converged trace 304.
[0051] In one possible implementation, four or more normal forces
306 exerted on a wall of wellbore 102 can be used to restore a
shape of wellbore 102 from elliptical converged trace 304 to an at
least approximately circular cross section 308. In one possible
aspect, at least approximately circular cross section 308 can match
trace 302, thus restoring the cross sectional shape of wellbore 102
to what it was before convergence due to the far field stresses
(aka, in situ stresses) .sigma..sub.1 and .sigma..sub.2 in
formation 104.
[0052] Normal forces 306 can differ at different points on the wall
of wellbore 102, due to, for example, differences in the magnitudes
of .sigma..sub.1 and .sigma..sub.2. Moreover, the magnitudes of
normal forces 306 to deform the cross section of wellbore 102 from
elliptical converged trace 304 to at least approximately circular
cross section 308 can be directly related to stresses .sigma..sub.1
and .sigma..sub.2 in formation 104 and the pressure on wellbore
102.
[0053] For example, if it is assumed that wellbore 102 is drilled
with a diameter d=2a in the direction of a principal stress,
wellbore 102 can deform from its initial diameter d under the
action of the far-field stresses .sigma..sub.1 and .sigma..sub.2
(aka the in situ stresses) and the pressure on wellbore 102. In
such a scenario, the far-field stresses .sigma..sub.1 and
.sigma..sub.2 can be denoted as the far-field stresses acting on a
plane perpendicular to an axis of wellbore 102 (i.e.,
.sigma..sub.1=.sigma..sub.H and .sigma..sub.2=.sigma..sub.h in the
case of a vertical well).
[0054] In one possible implementation, wellbore convergence
deformation due to the drilling can be compensated for and the
cross section of wellbore 102 can be restored to its initial shape.
When such restoration is accomplished, the normal stresses to
restore wellbore 102 to its initial shape (i.e., trace 302) can be
directly related to the initial stress field from formation 104
acting on wellbore 102. Such a method can therefore involve the
imposition of a shape (i.e., a radial displacement) and the
recordation of associated forces used to produce such a
displacement.
[0055] In some implementations the deformation of wellbore 102 can
be relatively small (including, for example, displacement in
10.sup.-3 mm) but the stresses can be large (O(10.sup.6 Pa)).
[0056] FIG. 4 illustrates an example of displacement tool 110 with
an axis 400 in accordance with various implementations of in-situ
property determination. Displacement tool 110 is illustrated as
having a cylindrical shape, however it will be understood that
displacement tool can have any shape known in the art.
[0057] As shown, displacement tool is deployed within wellbore 102.
An initial cross section of wellbore 102 is illustrated as trace
302 and a cross section of wellbore 102 deformed due to the
far-field stresses in formation 104 is illustrated as elliptically
converged trace 304.
[0058] In one possible implementation, a plurality of pads 402 can
extend from displacement tool 110 and contact a wall 404 of
wellbore 102. Pads 402 can comprise any shape known in the art,
including, for example, a substantially half cylinder shape, such
as is shown in a three dimensional view in FIG. 4.
[0059] Pads 402 can be symmetrically placed relative to an outer
surface 406 of displacement tool 110 with each pad 402 having an
equal angular arc .phi.. Even though four pads 402 are illustrated
in FIG. 4, it will be understood that more than four pads 402 can
also be employed. Similarly, even though the side view in FIG. 4
illustrates three rows (aka rings) of pads 402, it will be
understood that more or fewer rings of pads 402 can also be
deployed on displacement tool 110.
[0060] In addition to being extendible from outer surface 406, pads
402 can also be retractable back to outer surface 406. In one
possible aspect, when fully retracted, pads 402 can be inside outer
surface 406, flush with outer surface 406, protrude from outer
surface 406, and/or any combination thereof.
[0061] In one possible embodiment, pads 402 can be equidistantly
extended from outer surface 406 of displacement tool 100. This can
include instances when displacement tool 110 is positioned at a
center of wellbore 102. In such scenarios, contact surfaces 408 on
pads 402 configured to contact wall 404 of wellbore 102 can form an
at least approximately circular cross section 410. In some
instances, such as when wellbore 102 is deformed into an ellipsoid
cross section (such as elliptically converged trace 304), some pads
402 can come into contact with wall 404 of wellbore 102 earlier
than other pads 402.
[0062] In one possible implementation, pads 402 can be extended to
such an extent as to restore wellbore 102 to its original cross
section (i.e. trace 302). In one possible aspect, tool 110 can
extend pads 402 from a first position relative to outer surface 406
to a second position in which trace 302 is restored in a
displacement control mode.
[0063] In one possible aspect, once a pad 402 touches wall 404 of
wellbore 102, the rock of formation 104 can resist any imposed
displacement represented by the further extension of pad 402. In
such a case, the forces used to extend and/or hold each pad 402
(such as normal forces relative to each pad 402) in order to impose
displacement of wall 404 can be recorded. In one possible aspect, a
ratio of the normal forces acting on the various pads 402 for a
given displacement of wall 404 of wellbore 102 can be related to
the ratio of the far-field stresses in formation 104. Similarly, a
force-displacement curve for each pad 402 can be used to estimate
the in-situ elastic modulus of the rock in formation 104 in
different directions perpendicular to an axis of wellbore 102. In
the case of time-dependent deformation, force measurements under
constant displacement (aka in a holding phase) during a sufficient
amount of time can allow for an estimation of one or more
time-dependent properties of formation 104 (such as, for example,
drained/undrained moduli and hydraulic diffusivity in the case of a
poroelastic formation, see Wang, H. F., 2000, Theory of linear
poroelasticity, Princeton, ISBN: 9781400885688; creep properties
for a viscoplastic formation, see Cornet, F. H., 2015, Elements of
crustal geomechanics, Cambridge University Press, ISBN:
9780521875783 and Cristescu, N., 1989, Rock rheology, Volume 7,
Series: Mechanics of Elastic and Inelastic Solids, Springer
Netherlands, ISBN: 978-94-010-7654-8 (Print) 978-94-009-2554-0
(Online), DOI: 10.1007/978-94-009-2554-0).
[0064] Recordation of forces acting on pads 402 can be accomplished
in any manner known in the art, and can be conducted using
equipment, such as a recordation device, in one or more locations
including subsurface equipment (such as within displacement tool
110, within other tool(s) on wellbore logging tool 106, etc.),
surface equipment (such as within processing system 112, etc.),
and/or any combination thereof.
[0065] In one possible implementation, one or more imaging modules,
such as an ultrasonic wellbore imager module, can be used to select
measurement depths with desirable wellbore quality at which
displacement tool 110 can be placed in order to estimate a
horizontal stress direction in formation 104 acting on wellbore
102. In one possible aspect, one or more such imaging modules can
be located, entirely or in part, for example, in property
determination module 206.
[0066] FIG. 5 illustrates example schematic force versus
displacement curves 500 for two pads 402 at different angles with
respect to the in-situ horizontal stress directions in accordance
with implementations of in-situ property determination. Force
versus displacement curve 500 (aka force-displacement curve 500) is
associated with a pad #1 (aka, pad 402(1)) and force-displacement
curve 500(2) is associated with a pad #2 (aka, pad 402(2)).
[0067] Loading curve 502 of force-displacement curve 500 denotes a
loading phase in which pads 402 extend from a first position to a
second, extended, position in order to push wall 404 of wellbore
102 in an effort to restore wellbore 102 from an elliptically
converged trace 304 to an at least approximately circular cross
section 308 (such as, for example, trace 302). The slope of loading
curve 502 can be associated with the elastic modulus of rock in
formation 402 being contacted by pads 402).
[0068] Portion 504 of force-displacement curve 500 illustrates a
holding phase of force-displacement curve 500 in which a constant
displacement of wall 404 or wellbore 102 can be maintained (such
as, for example, when wellbore has an at least approximate circular
cross section 308). Portion 504 can be used to measure a
time-dependent response of the rock in formation 104. This can be
accomplished, for example, by recording the forces applied to pads
402 to maintain a constant displacement of wall 404 of wellbore 102
(i.e., stresses can relax in the rock in formation 104 due to creep
and/or poroelasticity (aka pore-pressure consolidation)).
[0069] Unloading curve 506 of force-displacement curve 500
illustrates the forces applied to pads 402 during an un-loading
phase in which pads 402 retract from their extended position back
towards their first position proximate outer surface 406 of
displacement tool 110 (i.e., allowing the cross section of wellbore
102 to be deformed from at least approximate circular cross section
308 to elliptically converged trace 304 under, for example, the
stresses in formation 104. The slope of unloading curve 506 can be
associated with an elastic modulus of the rock of formation 104 in
contact with pads 402.
[0070] In one possible aspect, for a given extension of a pad 402
from outer surface 406 of displacement tool 110, the value of
forces F.sub.1 and F.sub.2 acting on pad 402(1) and pad 402(2)
respectively, can differ due to the original deformation of the
wellbore 102 due to the in situ stresses in formation 104 acting on
wellbore 102. In one possible implementation, a ratio of forces
F.sub.1/F.sub.2 on force-displacement curves 500, 500(2) can be a
function of the far-field stresses in formation 104.
[0071] In one possible embodiment, a force-displacement curve 500
can be constructed for each set of pads 402 diametrically opposite
to one another on displacement tool 110.
[0072] As noted above in conjunction with FIG. 4, as many rings of
pads 402 as desired can be employed on displacement tool 110. In
one possible implementation, an increase in the number of rings of
pads 402 at different depths on displacement tool 110 can result in
improved measurements from displacement tool 110 (i.e., an improved
response of displacement tool 110).
[0073] Alternately, or additionally, any other designs involving
arms to help stiffen the response of displacement tool 110 during
deployment of tool 110 may be used. For example, in one possible
implementation, arms lying approximately parallel to axis 400 of
displacement tool 110 could be configured to extend out from axis
400 at an ever increasing angle to contact and displace the wall of
wellbore 102. Such angularly extending arms could be reinforced by
other arms or various constructions, including, for instance,
supports extending approximately orthogonally from axis 400,
between axis 400 and the angularly extending arms. In one possible
aspect, displacement tool 110 can be approximately five times
stiffer than formation 104.
[0074] In one possible implementation, displacement tool 110 can
include an ultrasonic wellbore imager module (e.g., UBI) to allow
for one or more additional measurements to: (i) get a 360 degree
shape of wellbore 102 and the ellipse axes for the in situ stress
direction, and (2) estimate the conditions of wellbore 102 and
decide where to put displacement tool 110. In such a manner, pads
402 can be oriented in the directions of the in situ stresses
.sigma..sub.1 and .sigma..sub.2, while avoiding various issues
(i.e., frac, key seat, reaming, etc., can be avoided).
[0075] In one possible implementation, a far-field stress ratio
and/or principal stress direction can be determined using aspects
of in-situ property measurement. For example, in the case of a well
drilled in the direction of one of the principal stresses, the
forces acting on pads 402 can be associated with the remaining two
far-field stresses acting perpendicular to the axis of wellbore
102. These stresses can be different for each set of pads 402 if
the two far-field stresses are not equal. Imposing the same radial
displacement U from the tool center on each pad 402 while recording
the forces (F) being applied to pads 402 can result in different F
versus U curves for the different pads 402.
[0076] In one possible aspect, pads 402 facing the direction of the
maximum principal stress can come in contact with formation 104
(i.e., wall 404 of borehole 102) earlier than pads 402 facing the
minimum stress given the ellipsoid cross section of elliptically
converged trace 304.
[0077] In one possible implementation, for a given value of the
imposed displacement U, the ratio of the corresponding forces
between the two pads 402 in a vertical well can be associated with
the ratio of the horizontal far-field stress magnitudes of
.sigma..sub.1 and .sigma.2.
[0078] FIG. 6 illustrates an example graph 600 of a ratio of forces
.sigma..sub.1/.sigma..sub.2 acting on pad 402(1) (aka pad #1) over
pad 402(2) (aka pad #2) for different positions of pad 402(1) with
respect to the maximum stress direction in accordance with
implementations of in-situ property determination. As illustrated,
x-axis 602 represents an azimuthal position of a center of pad
402(1) from a direction of .sigma..sub.1, and y-axis 604 represents
a ratio of force applied to pad 402(1))/force applied to
402(2).
[0079] In one possible implementation, a span .phi. of each pad 402
can have an angle of approximately 20 degrees (though other spans
can also be used), and the pads 402 can be assumed to be
perpendicular to one another. The stresses in this implementation
are taken as .sigma..sub.1=20 MPa, .sigma..sub.2=7 MPa: i.e.
.sigma..sub.1/.sigma..sub.2.about.2.8,
.sigma..sub.2/.sigma..sub.1=0.35, though other stresses can also be
experienced.
[0080] In one possible embodiment, as a preliminary estimate, the
effect of contact associated with a finite arc size of contact 408
of a pad 402 can be neglected. In one possible aspect, a numerical
model (e.g., Finite Element, Boundary Element, etc.) can be
performed to take into account such effects. Moreover, in one
possible aspect, it can be assumed that the initial deformation due
to the drilling of the well can be restored: i.e., the final radial
extension of pads 402 on displacement tool 110 can be equal to the
bit size used to drill wellbore 102. In one possible
implementation, the final value of the forces applied to pads 402
once the original wellbore convergence has been restored (i.e., to
trace 302) can be found.
[0081] In one possible implementation, for the sake of
completeness, it is possible that the radial displacement u.sub.r
induced by the release of the far-field stress due to the drilling
can be obtained from the poroelastic solution for isotropic elastic
rocks (see, for example, Detournay, E. & Cheng, A.-D.,
Poroelastic response of a borehole in a non-hydrostatic stress
field, International Journal of Rock Mechanics and Mining Sciences
& Geomechanics Abstracts, 1988, 25, 171-182):
u r ( .theta. ) = a 2 G ( 1 2 ( .sigma. 1 + .sigma. 2 ) P b + 1 2 (
.sigma. 1 .sigma. 2 ) ( 4 ( 1 v ) 1 ) cos ( 2 .theta. ) )
##EQU00001##
where v is the Poisson's ratio, Pb is the wellbore pressure,
.sigma..sub.1 and .sigma..sub.2 are the far-field stresses acting
in the plane and .theta. is the angle from the direction of the
maximum far field stress .sigma..sub.1. G can denote the shear
modulus of the rock in formation 104 and "a" in the equation above
can be the radius of wellbore 102. In one possible aspect, this
method can be done without knowledge of the elastic parameters of
the rock in formation 104.
[0082] For anisotropic elastic rocks, if the elastic stiffness
constants are known from other sources, the radial displacement can
be analytically computed using, for example, the expression from
Karpfinger et al. See Karpfinger et al., "Theoretical estimate of
the tube-wave modulus in arbitrarily anisotropic media: Comparisons
between semianalytical, FEM, and approximate solutions",
Geophysics, Vol. 77, No. 5 (September-October 2012).
[0083] In one possible implementation, the extension of pads 402 to
restore such a displacement of wellbore 102 can be equal to the
original bit-size used to drill wellbore 102. In one possible
aspect, the forces to be exerted on pads 402 in order to restore
the elastic displacement u.sub.r(.theta.) can be found. The normal
force acting on a pad 402 of angle (aka span) .phi. and height
(located at an angle 9 from the maximum principal stress as
illustrated in FIG. 4) at restoration of wellbore 102 to trace 302
can be given by the normal far-field in-situ stresses
.sigma..sub.n(.theta.)=(.sigma..sub.1 P.sub.b) (cos
.theta.).sup.2+(.sigma..sub.2 P.sub.b) (sin .theta.).sup.2 to the
"restored" wellbore 102:
F ( .theta. ) = .intg. .theta. - .PHI. / 2 .theta. + .PHI. / 2
.sigma. n ( .theta. ) a d .theta. = a 2 ( ( ( .sigma. 1 + .sigma. 2
) 2 Pb ) .PHI. + ( .sigma. 1 .sigma. 2 ) sin ( .PHI. ) cos ( 2
.theta. ) ) ##EQU00002##
[0084] In one possible implementation, if it is known that the
initial displacement of wellbore 102 has been restored (i.e. to
trace 302), one can quantitatively estimate the two principal
stress magnitudes from the forces applied to pads 402.
[0085] In one possible aspect, it may be difficult to know in
practice when a restoration of the original wellbore deformation to
trace 302 is obtained. In one possible implementation, the ratio of
the forces acting on different pads 402 for the same radial
extension of pads 402 can be taken, and the ratio of the far-field
stress can be estimated with such a method, along with the absolute
value of each far-field stress magnitude.
[0086] In one possible implementation, this can be accomplished by
taking the ratio of the forces between different pads 402. When the
wellbore deformation is restored to trace 302, for example, the
ratio of the forces between two pads 402 separated by an angle can
be a function of the wellbore pressure, and the ratio of the
far-field stress.
[0087] FIG. 6 illustrates the ratio of the forces acting on pad
402(1) (aka pad #1) over pad 402(2) (aka pad #2) for different
positions of pad 402(1) with respect to the direction of maximum
stress (GO in accordance with implementations of in-situ property
determination.
[0088] FIG. 7 illustrates an example graph 700 showing the ratio of
the radial displacement u.sub.r over radius "a" induced by the
release of the far-field stress for different azimuthal positions
with respect to the direction of maximum stress (GO in accordance
with implementations of in-situ property determination. X-axis 702
represents an azimuthal position with respect to a position of
.sigma..sub.1, and y-axis 704 represents a ratio of the radial
displacement u.sub.r over radius "a".
[0089] In the implementation shown in FIG. 6, a span .phi. of each
pad 402 has an angle of approximately 20 degrees (though other
spans can also be used), and the pads 402(1), 402(2) are
perpendicular to one another. The stresses are taken as
.sigma..sub.1=20 MPa, .sigma..sub.2=7 MPa: i.e.
.sigma..sub.1/.sigma..sub.2.about.2.8 and
.sigma..sub.2/.sigma..sub.1=0.35 (though other stresses can also be
experienced).
[0090] In one possible embodiment, the orientation of the principal
stress may not be known and/or displacement tool 110 may not be
oriented such that a pad 402, such as 402(1), is oriented in a
direction of the principal stress. FIG. 6 illustrates that an
orientation of pad 402(1) with respect to a direction of the
principal stress can have a first order effect on a value of the
ratio of the forces acting on the two perpendicular pads 402(2),
402(2). In the case of four pads 402, due to the automatic
centering of displacement tool 110 in wellbore 102 when pads 402
are symmetrically deployed from a center (aka about axis 400) of
displacement tool 110, the forces on the opposite pads 402 can be
equal. In one possible aspect, two independent measurements and one
force ratio can exist. In such a case, a direction of the principal
stress in formation 104 may not be measured.
[0091] In one possible embodiment, measurements of forces applied
to pads 402 can be combined with an ultrasonic wellbore imager
(UBI) to independently resolve a direction of the principal stress
in formation 104 and thus relate the ratio of: (force applied to
pad 402(2))/(force applied to pad 402(2)) to the ratio of the
in-situ stresses .sigma..sub.1/.sigma..sub.2 (as shown in FIG. 6).
In one possible aspect, an accuracy of such an estimation can be
improved by using more pads 402 (for example, six or more pads 402)
on displacement tool 110.
[0092] In another possible embodiment, once pads 402 have been
extended and retracted as described herein, and corresponding
measurements of forces applied to pads 402 to deform wellbore 102
from an elliptically converged trace 304 to an at least
approximately circular cross section 308, and back again, etc.,
have been recorded, the number of force-ratio measurements of pads
402 relative to the principal stress in formation 104 can be
increased by maintaining displacement tool 110 at the same depth
while rotating displacement tool 100 a given angle (such as, for
example, 45 degrees, etc.), and repeating the extension and
retraction routine of pads 402 described herein while measuring the
forces applied to pads 402. Rotation of displacement tool 110 in
order to collect additional measurements of forces applied to pads
402 in this manner can be performed as many times as desired.
[0093] In one possible embodiment, the addition of an image from an
ultrasonic wellbore imager may allow for the assessment of the
quality of the deformation of wellbore 102 prior to stress
compensation in order to ensure that no artifact linked to wellbore
failures, reaming etc., affects the stress ratio estimation. Such
an image would also allow for an estimation of the principal stress
direction in formation 104 from measurement of the ovalization of
the wellbore due to drilling.
[0094] In one possible implementation, a rock modulus of the rock
in formation 104 can be estimated using a stress compensation test
approach akin to an indentation test for each pad 402. For
instance, in one possible aspect the loading curve 502 and the
unloading curve 506 of the force-displacement curve 500 for a pad
402 can be used to estimate an elastic rock modulus for each pad
402. Estimation of elastic modulus from such indentation responses
can be performed using any techniques known in the art including
those, for example, described in Oliver W C, Pharr G M (1992) An
improved technique for determining hardness and elastic modulus
using load and displacement sensing indentation experiments; J
Mater Res 7(6):1564-1583).
[0095] In one possible aspect, responses illustrated in curve 500
may vary based on the shape of a pad 402, so a model corresponding
to the shape of a given pad 402 can be used in order to estimate
the rock modulus from the force-displacement curve 500 for the
given pad 402.
[0096] In one possible implementation, the above techniques can be
used to provide a measurement of the quasi-static elastic modulus
of rocks in formation 104 in-situ. Such a measurement can be made
in a direction perpendicular to an axis of wellbore 102. In the
case of an anisotropic rock (e.g., transverse isotropy) in
formation 104, such a measurement can complement sonic
measurements.
[0097] In another possible implementation, one or more time
dependent properties can be estimated. This can be done, for
instance, using information associated with forces applied to one
or more pads 402 during a holding phase (i.e., portion 504 of
force-displacement curve 500) at the end of a loading phase
(loading curve 502) and prior to an unloading phase (unloading
curve 506). During the holding phase an at least approximately
circular cross section 308 is maintained in wellbore 102 by pads
402 on displacement tool 110 for a predetermined amount of time.
This predetermined amount of time can vary based on the type of
rock in formation 104. In one possible aspect, the predetermined
amount of time can include a few minutes or more.
[0098] During the holding phase, rock in formation 104 contacting a
pad 402 may exhibit a time-dependent response due to, for example,
pore-pressure dissipation associated with a transition between an
undrained to a drained response for a poroelastic material, etc.
The intensity of such pore pressure consolidation may be associated
with the rock permeability and/or the characteristic length of
drainage which can be related to a size of pad 402 pressing against
the rock. Such an effect may therefore be seen, for example, for
very tight rock.
[0099] Some types of rock which may be in formation 104 (such as,
for example salt) may also exhibit a viscoplastic behavior (see,
for example, Cristescu, N., 1989, Rock rheology, Volume 7, Series:
Mechanics of Elastic and Inelastic Solids, Springer Netherlands,
ISBN: 978-94-010-7654-8 (Print) 978-94-009-2554-0 (Online), DOI:
10.1007/978-94-009-2554-0). For example, under a constant imposed
displacement for a period of time, such as during the holding
phase, the stresses inside a viscoplastic rock can relax: i.e., the
forces acting on pad 402 in contact with the viscoplastic rock can
decrease with time. Such a decay in the forces acting on pad 402 to
maintain a constant displacement of wellbore 102 during the holding
phase can be analyzed to estimate intrinsic creep time scales of
the rock.
[0100] In one possible implementation, in order for a measurement
to be sensitive to rock deformation, it may be desirable for
displacement tool 110 and pads 402 to be substantially stiffer than
the rock in formation 104.
[0101] In one possible embodiment, it may be desirable for a
complete measurement analysis to account for the geometry of the
contact between a pad 404 and displacement tool 110. In one
possible aspect, it may be desirable for the finite arc size and
the arc shape of the pads 402 to be included in calculations used
to estimate the stress ratio and elastic modulus of the rock in
formation 104. Such calculations (using, for example, the Finite
Element Method) can be performed in order to take into account the
geometry of displacement tool 110 in field applications.
[0102] In one possible aspect, the impact of a lower quality of
wellbore 102 (i.e. due to tripping, etc.) on the stress estimations
described herein can be assessed. In such an instance the addition
of an image of wellbore 102 could be desirable.
Example Methods
[0103] FIG. 8 illustrates example method(s) for implementing
aspects of in-situ property determination. The methods are
illustrated as a collection of blocks and other elements in a
logical flow graph representing a sequence of operations that can
be implemented in hardware, software, firmware, various logic,
manually, or by any combination thereof. The order in which the
methods are described is not intended to be construed as a
limitation, and any number of the described method blocks can be
combined in any order to implement the methods, or alternate
methods. Additionally, individual blocks and/or elements may be
deleted from the methods without departing from the spirit and
scope of the subject matter described therein. In the context of
software, the blocks and other elements can represent computer
instructions that, when executed by one or more processors, perform
the recited operations. Moreover, for discussion purposes, and not
purposes of limitation, selected aspects of the methods may be
described with reference to elements shown in FIGS. 1-7. Moreover,
in some possible implementation, all or portions of the methods
may, at least partially, be conducted using, for example, computing
device 200.
[0104] FIG. 8 illustrates an example method 800 associated with
embodiments of in-situ property determination. At block 802, a
displacement tool (such as, for example, displacement tool 110) can
be activated at a desired depth in a wellbore (such as wellbore
102) in a formation (such as formation 104) to deform the wellbore
from an at least approximately elliptical cross section (such as
elliptically converged trace 304) to an at least approximately
circular cross section (such as at least approximately circular
cross section 308). The displacement tool can be lowered into the
wellbore using any methods and/or equipment known in the art, and
the desired depth can be chosen using any methods known in the art,
including a study of one or more images (including, for example
ultrasonic images) of the wellbore at different depths.
[0105] In one possible implementation, an axis of the at least
approximately elliptical cross section of the displaced wellbore
can be located and/or measured using one or more images of the
wellbore. Such information can then be used to orient the
displacement tool in the directions of maximum and minimum stress
(such as .sigma..sub.1 and .sigma..sub.2) in the wellbore. In
embodiments in which the displacement tool has pads, such as pads
402, this can include orienting at least one set of pads in the
direction of maximum stress and another set of pads in a direction
of minimum stress.
[0106] Once activated, the displacement tool 110 can restore the
displaced wellbore back to an at least approximately circular cross
section using any means known in the art, including through the use
of four or more pads (such as pads 402), placed symmetrically
around a body of the displacement tool. In one possible
implementation, the displacement tool can displace the wellbore
back into an at least approximately circular cross section with a
diameter at least approximately equal to that of a drill bit used
to create the wellbore.
[0107] At block 804, during the displacement of the wellbore, force
displacement information associated with deforming the wellbore
from its at least approximately elliptical cross section to the at
least approximately circular cross section (such as forces being
applied to pads if pads are present of the displacement tool) can
be recorded. Recordation of such forces can be accomplished in any
manner known in the art, and can be conducted using any equipment
known in the art, including, for example, a recordation device, in
one or more locations including in subsurface equipment (such as
within displacement tool, within other tool(s) on a wellbore
logging tool, etc.), in surface equipment (such as within a
processing system, etc.), and/or any combination thereof.
[0108] At block 806, at least a portion of the force displacement
information associated with deforming the wellbore from the at
least approximately elliptical cross section to the at least
approximately circular cross section (such as during a loading
phase) can be utilized to estimate a far-field stress ratio
associated with the formation. This can be accomplished using any
of the methods disclosed herein, including use of a module, such as
property determination module 206.
[0109] In one possible implementation, for example, when pads are
employed on the displacement tool, loading curves (such as loading
curves 502) can be created from the force displacement information
for one or more of the pads on the displacement tool and be used to
estimate the far-field stress ratio associated with the
formation.
[0110] In one possible embodiment, the displacement tool can be
used to maintain the displaced wellbore at the at least
approximately circular cross section for a desired period of time
(aka a holding phase). During this desired period of time,
maintenance force information associated with maintaining the at
least approximately circular cross section during the holding phase
can be recorded. In one possible aspect, at least a portion of the
maintenance force information can be used to estimate one or more
time dependent properties, such as: poroelastic properties
associated with the formation (see, for example, Wang, H. F., 2000,
Theory of linear poroelasticity, Princeton, ISBN: 9781400885688); a
hydraulic diffusivity of the formation (see, for example, Wang, H.
F., 2000, Theory of linear poroelasticity, Princeton, ISBN:
9781400885688); and/or one or more rock creep properties of the
formation (see, for example, Cristescu, N., 1989, Rock rheology,
Volume 7, Series: Mechanics of Elastic and Inelastic Solids,
Springer Netherlands, ISBN: 978-94-010-7654-8 (Print)
978-94-009-2554-0 (Online), DOI: 10.1007/978-94-009-2554-0), using
any of the methods disclosed herein, including use of a module,
such as property determination module 206.
[0111] In instances when pads are utilized on displacement tool
110, maintenance curves (such as portions 504) can be created from
the maintenance force information associated with one or more of
the pads on the displacement tool and used to estimate one or more
of the time dependent properties associated with the formation.
[0112] In another possible implementation, force displacement
information associated with allowing the wellbore to return from
the circular cross section to an at least approximately elliptical
cross section in an unloading phase can be recorded (aka an
unloading phase). At least a portion of such force displacement
information can be used to estimate Young's Modulus associated with
the formation at the desired depth, using any of the methods
described herein, including use of a module, such as property
determination module 206.
[0113] In instances when pads are utilized on displacement tool
110, unloading curves (such as unloading curves 506) can be created
from the force displacement information associated with allowing
the wellbore to return from the circular cross section to an at
least approximately elliptical cross section associated with one or
more of the pads on the displacement tool and used to estimate
Young's Modulus associated with the formation at the desired
depth.
[0114] At block 808, once the wellbore has been allowed to be
displaced from the at least approximately circular cross section to
an at least approximately elliptical cross section, in one possible
implementation, the displacement tool can be turned a desired angle
at the desired depth in the wellbore. The displacement tool can
then be activated as described above and forces can be recorded
during one or more of a loading phase, a holding phase and an
unloading phases, and used to estimate various rock and stress
properties associated with the formation as described above.
Rotation of the displacement tool at a given depth in this manner
can occur as many times as desired.
[0115] Further, if desired, any and/or all of the blocks above can
be repeated at one or more other depths along the wellbore. For
example, after some or all of the above has been completed, the
displacement tool can be moved to a new depth in the wellbore and
any of the blocks/techniques above can be repeated. For instance,
at the new depth the displacement tool can be activated to initiate
a loading phase, a holding phase, and/or an unloading phase, and
force information associated with each phase can be collected and
used to estimate various rock and stress properties associated with
the formation. After the unloading phase has been completed, the
displacement tool can then be turned a desired angle, and the
loading phase, the holding phase, and/or the unloading phase can be
repeated with more force information associated with each phase
being collected and used to improve the various estimated rock and
stress properties associated with the formation. This can be done
as many times as desired.
[0116] In one possible implementation, the recorded information and
various estimated rock and stress properties associated with the
formation can be used to improve an operator's (or other interested
party's) understanding of the formation.
[0117] In one possible implementation, a robust one dimensional
(1D) Mechanical Earth Model can be constructed along all or
portions of wellbore 102 using aspects of in-situ property
determination as described herein. In one possible aspect this can
be done by, for example, forming an estimation of an overburden
stress from one or more density log(s) and well survey(s)
associated with wellbore 102. Further, in a vertical well, the
ratio .sigma..sub.1/.sigma..sub.2 of the horizontal stresses in
formation 104 can be estimated using any of the methods described
above. Still further, an estimation of a direction of the
horizontal stresses .sigma..sub.1 and .sigma..sub.2 in formation
104 can be produced from (1) the methods presented previously
and/or from (2) one or more image logs associated with wellbore
102. Also, an estimation of the minimum horizontal stress
.sigma..sub.2 can be gleaned through use of, for example, a Modular
Formation Dynamic Tester marketed by the Schlumberger Technology
Corporation of Houston Tex., and/or leak off test (LOT) closure
stress tests at a number of given depths in wellbore 102.
[0118] The maximum horizontal stress .sigma..sub.1 can then be
estimated from the ratio .sigma..sub.1/.sigma..sub.2 of the
horizontal stresses in formation 104 and the estimation of the
minimum horizontal stress .sigma..sub.2. Moreover, elastic
properties of rock in formation 104 can be derived from sonic
measurements and combined with estimates of the rock modulus
described above (e.g., estimates of the rock modulus from the
force-displacement curve 500) to build a static to dynamic
correction for a Mechanical Earth Model. Further a continuous depth
profile of the minimum and maximum horizontal stresses
(.sigma..sub.2 and .sigma..sub.1, respectively) can be built using,
for example, the estimation of the overburden stress, the
estimation of the minimum horizontal stress .sigma..sub.2, the
estimation of the maximum horizontal stress .sigma..sub.1, and the
static to dynamic correction for a Mechanical Earth Model.
[0119] Although 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 disclosure. Accordingly, such
modifications are intended to be included within the scope of this
disclosure as defined in the following claims. Moreover,
embodiments may be performed in the absence of any component not
explicitly described herein.
[0120] In the claims, means-plus-function clauses are intended to
cover the structures described herein as performing the recited
function and not just 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.
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