U.S. patent application number 12/098898 was filed with the patent office on 2009-10-08 for method and apparatus for sampling and/or testing downhole formations.
This patent application is currently assigned to Baker Hughes Incorporated. Invention is credited to Michael P. May.
Application Number | 20090250207 12/098898 |
Document ID | / |
Family ID | 41132187 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090250207 |
Kind Code |
A1 |
May; Michael P. |
October 8, 2009 |
METHOD AND APPARATUS FOR SAMPLING AND/OR TESTING DOWNHOLE
FORMATIONS
Abstract
Performing a hydraulic fracture test includes conveying a
downhole sub in a borehole to a formation, the downhole sub
including a first sealing member, a second sealing member, and an
extendable member disposed between the first sealing member and the
second sealing member. The first sealing member and the second
sealing member are actuated to define a first isolated zone within
the borehole. A fluid is introduced to the borehole wall via the
extendable member to fracture the formation whether extended or
not, and a property of the formation is estimated at least in part
using an output signal from a downhole transducer.
Inventors: |
May; Michael P.; (Cypress,
TX) |
Correspondence
Address: |
CANTOR COLBURN LLP- BAKER ATLAS
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
Baker Hughes Incorporated
|
Family ID: |
41132187 |
Appl. No.: |
12/098898 |
Filed: |
April 7, 2008 |
Current U.S.
Class: |
166/250.1 ;
166/66 |
Current CPC
Class: |
E21B 49/008
20130101 |
Class at
Publication: |
166/250.1 ;
166/66 |
International
Class: |
E21B 49/00 20060101
E21B049/00 |
Claims
1. A method for performing a hydraulic fracture test comprising:
conveying a downhole sub in a borehole to a formation, the downhole
sub including a first sealing member, a second sealing member, and
an extendable member disposed between the first sealing member and
the second sealing member; actuating the first sealing member and
the second sealing member to establish a first isolated zone within
the borehole; introducing a fluid to the borehole wall via the
extendable member to fracture the formation; and estimating a
property of the formation at least in part using an output signal
from a downhole transducer.
2. A method according to claim 1, wherein conveying the downhole
sub comprises conveying using one or more of a drill string, a
wireline and a slickline.
3. A method according to claim 1, wherein estimating a property of
the formation includes estimating a hydraulic pressure of the
introduced fluid when the formation is initially fractured.
4. A method according to claim 1 further comprising continuing to
introduce the fluid to the formation to extend the fracture.
5. A method according to claim 4, wherein estimating a property of
the formation includes estimating a hydraulic pressure of the
introduced fluid during a time interval while fracture is
extending.
6. A method according to claim 4 further comprising halting the
introduction of fluid to the formation after the fracture is
extended to allow the fracture to close.
7. A method according to claim 6, wherein estimating a property of
the formation includes estimating a hydraulic pressure of the
introduced fluid during a time interval while fracture is
closing.
8. A method according to claim 1 further comprising estimating a
fracture treatment characteristic at least in part using the
estimated property of the formation.
9. A method according to claim 8, wherein the fracture treatment
comprises a subsequent hydraulic fracture treatment.
10. A method according to claim 8, wherein the fracture treatment
comprises a hydraulic fracture treatment and the estimated fracture
treatment characteristic includes a treatment fluid
characteristic.
11. A method according to claim 1, wherein the extendable member
includes one or more of an extendable probe and a pair of packers,
the method further comprising establishing a second isolated zone
within the borehole by extending the extendable member.
12. A method according to claim 11 further comprising controlling a
borehole pressure within the first isolated zone and in the second
isolated zone to create a first pressure differential between the
first isolated zone and a borehole annulus above the first isolated
zone and a second pressure differential between the first isolated
zone and the second isolated zone.
13. A method according to claim 12, wherein the second pressure
differential is less than the first pressure differential.
14. An apparatus for performing a hydraulic fracture test
comprising: a downhole sub that is conveyed in a borehole to a
formation; a first sealing member coupled to the downhole sub; a
second sealing member coupled to the downhole sub axially displaced
from the first sealing member, the first sealing member and the
second sealing member defining a first isolated zone; an extendable
member disposed between the first sealing member and the second
sealing member, the extendable member configured to introduce a
fluid to the formation for fracturing the formation; and a downhole
transducer coupled to the downhole sub that provides an output
signal, the output signal being used at least in part to estimate a
property of the formation.
15. An apparatus according to claim 14, wherein a fracture
treatment characteristic is estimated using at least in part the
estimated property of the formation.
16. An apparatus according to claim 15, wherein a treatment fluid
characteristic is estimated using at least in part the estimated
property of the formation.
17. An apparatus according to claim 14, wherein the extendable
member is extended to establish a second isolated zone within the
borehole, a first pressure differential being established between
the first isolated zone and a borehole annulus above and below the
first isolated zone and a second pressure differential being
established between the first isolated zone and the second isolated
zone.
18. An apparatus according to claim 14, wherein the downhole sub is
conveyed in the borehole using one or more of a drill string, a
wireline and a slickline.
19. A method for performing a hydraulic fracture test comprising:
conveying a downhole sub in a borehole to a formation, the downhole
sub including a first sealing member, a second sealing member, and
an extendable member disposed between the first sealing member and
the second sealing member; actuating the first sealing member and
the second sealing member to define a first isolated zone within
the borehole; introducing a fluid to the borehole wall via the
extendable member to fracture the formation; estimating a hydraulic
pressure of the introduced fluid when the formation is initially
fractured; extending the extendable member to a position in sealing
engagement with the borehole wall; continuing to introduce the
fluid to the formation via the extendable member to extend the
fracture; estimating a hydraulic pressure of the introduced fluid
during a time interval while fracture is extending; halting the
introduction of fluid to the formation after the fracture is
extended to allow the fracture to close; estimating a hydraulic
pressure of the introduced fluid during a time interval while
fracture is closing; and estimating a treatment fluid
characteristic at least in part using the estimated hydraulic
pressures of the formation.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present disclosure generally relates to hydrocarbon
recovery from a well and in particular to methods and apparatus for
drilling, sampling, and/or testing formations.
[0003] 2. Background Information
[0004] Oil and gas wells have been drilled at depths ranging from a
few hundred feet to as deep as six miles or more. A large portion
of the current drilling activity involves directional drilling that
includes drilling boreholes deviated from vertical by a few degrees
to horizontal boreholes to increase the hydrocarbon production from
earth formations.
[0005] Production of fluids from formations may be enhanced using
techniques known as fracturing. One type of fracturing is known as
hydraulic fracture stimulation or hydraulic fracture treatment, and
the purpose of hydraulic fracture stimulation is to maximize the
productivity of the well. Hydraulic fracture stimulation methods
typically include increasing hydraulic pressure in the borehole at
a selected formation area to the point that the hydraulic pressure
initially fractures or "cracks" the formation. The pressure at the
point of the initial fracture is known as the formation breakdown
pressure. The hydraulic pressure used for the hydraulic fracture
stimulation may be applied to extend the fracture far into the
formation and in one or more directions from the well borehole. The
length of the fractures for these stimulation techniques may be up
to 1000 ft or more from the borehole and typically extend from
about 100 ft to 1000 ft.
[0006] Information about the subterranean formations traversed by
the borehole may be obtained by any number of techniques. The more
that is known about the properties of the formation prior to
performing hydraulic fracture stimulation, the better opportunity
there is to design an effective and optimum fracture treatment.
SUMMARY
[0007] The following presents a general summary of several aspects
of the disclosure in order to provide a basic understanding of at
least some aspects of the disclosure. This summary is not an
extensive overview of the disclosure. It is not intended to
identify key or critical elements of the disclosure or to delineate
the scope of the claims. The following summary merely presents some
concepts of the disclosure in a general form as a prelude to the
more detailed description that follows.
[0008] An exemplary method for determining formation properties
using a hydraulic fracture test includes conveying a downhole sub
in a borehole to a formation, the downhole sub including a first
sealing member, a second sealing member, and an extendable member
disposed between the first sealing member and the second sealing
member. The first sealing member and the second sealing member are
actuated to define a first isolated zone within the borehole. A
fluid is introduced to the borehole wall via the extendable member
to fracture the formation, and a property of the formation is
estimated at least in part using an output signal from a downhole
transducer.
[0009] In several embodiments, a method for performing a hydraulic
fracture test includes conveying a downhole sub in a borehole to a
formation, the downhole sub including a first sealing member, a
second sealing member, and an extendable member disposed between
the first sealing member and the second sealing member, actuating
the first sealing member and the second sealing member to define a
first isolated zone within the borehole, and introducing a fluid to
the borehole wall via the extendable member to fracture the
formation. One particular embodiment further includes estimating a
hydraulic pressure of the introduced fluid when the formation is
initially fractured, continuing to introduce the fluid to the
formation to extend the fracture, estimating a hydraulic pressure
of the introduced fluid during a time interval while one or more
fractures are extending, halting the introduction of fluid to the
formation after the fracture is extended to allow the fracture to
close, estimating a hydraulic pressure of the introduced fluid
during a time interval while one or more fractures are closing, and
estimating a treatment fluid characteristic at least in part using
the estimated hydraulic pressures of the formation.
[0010] Disclosed is an apparatus for performing a hydraulic
fracture test includes a downhole sub that is conveyed in a
borehole to a formation. A first sealing member is coupled to the
downhole sub and a second sealing member is coupled to the downhole
sub axially displaced from the first sealing member, the first
sealing member and the second sealing member defining a first
isolated zone. An extendable member is disposed between the first
sealing member and the second sealing member, the extendable member
introducing a fluid to the first isolated zone for fracturing the
formation. A downhole transducer is coupled to the downhole sub
that provides an output signal, the output signal being used at
least in part to estimate a property of the formation. In one
particular apparatus embodiment, a fracture treatment
characteristic is estimated using at least in part the estimated
property of the formation. A treatment fluid characteristic may be
estimated using at least in part the estimated property of the
formation in another particular embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a detailed understanding of the present disclosure,
reference should be made to the following detailed description of
the several non-limiting embodiments, taken in conjunction with the
accompanying drawings, in which like elements have been given like
numerals and wherein:
[0012] FIG. 1 depicts an elevation view of a non-limiting
simultaneous drilling and logging system according to one or more
embodiments of the disclosure;
[0013] FIG. 2 depicts a schematic of a non-limiting exemplary
downhole sub according to one or more embodiments;
[0014] FIG. 3 depicts an illustrative example of a pressure profile
plot of the pressure in an isolated zone as a function of time
during an illustrative hydraulic fracture test according to one or
more embodiments; and
[0015] FIG. 4 depicts a schematic of a non-limiting downhole sub
having an extendable member disposed between two extended packers
defining an isolated zone according to one or more embodiments.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0016] The present disclosure uses terms, the meaning of which
terms will aid in providing an understanding of the discussion
herein. For the purposes of the present disclosure, fracture
treatment means the fracturing of a given formation within a
borehole. Hydraulic fracture stimulation is used synonymously
herein with hydraulic fracture treatment to mean hydraulic
fracturing methods for increasing the productivity of wells. The
length of the fractures for these stimulation techniques may be up
to 1000 ft or more from the borehole and typically extend from 100
ft to 1000 ft. A hydraulic fracture test is distinguished from a
hydraulic fracture treatment in that the hydraulic fracture test
induces small fractures on the order of about 0-10 feet but much
less that the fractures propagated during hydraulic fracture
stimulation. Breakdown pressure is the pressure required to
fracture a surrounding formation. A propagation pressure profile is
a pressure profile used to increase the length of a fracture to an
estimated desired length. The closure stress of a formation is the
stress in the formation at the time when the fracture closes.
Closure may not occur at all points in a fracture at the same time.
When relative rock movement ceases, then there may still be gaps in
the fracture, but nonetheless the fracture is closed.
[0017] FIG. 1 depicts an elevation view of a non-limiting
simultaneous drilling and logging system according to one or more
embodiments of the disclosure. The drilling and logging system 100
may be used to drill a well borehole 102 into the earth under
control of surface equipment including a drilling rig 104. In
accordance with a conventional arrangement, the drilling rig 104
may include a drill string 108. The drill string 108 may be a
coiled tube, jointed pipes or wired pipes as understood by those
skilled in the art. The drill string 108 may include a downhole sub
106 for making measurements of properties of the earth formations
110. The term formation as used herein is inclusive of any
subterranean location where hydraulic fracture testing may be
performed or desired. The term includes productive formations,
formations thought to be unproductive and unproductive strata.
[0018] While-drilling tools may use a drilling fluid 114 circulated
from a mud pit 116 through a mud pump 118, past a desurger 120, and
through a mud supply line 122. The drilling fluid 114 in the
example shown flows down through a longitudinal central bore in the
drill string and through jets (not shown) in the lower face of a
drill bit 124. Return fluid that includes drilling mud, cuttings
and formation fluid flows up through the annular space between the
outer surface of the drill string and the inner surface of the
borehole to be circulated to the surface where it may be returned
to the mud pit or mud tanks.
[0019] The system 100 in FIG. 1 may use any conventional telemetry
methods and devices for communication between the surface and
downhole components. The surface controller 112 may be used for
processing commands and other information used in the drilling
operations. In one or more embodiments, mud pulse telemetry
techniques may be used to communicate information from downhole to
the surface during drilling operations. For example, techniques to
transmit information with a hydraulic transmission: positive
mud-pulse, negative mud-pulse, and continuous mud-pulse.
[0020] Simultaneous recording to a downhole memory device, not
shown, may be performed in a while drilling environment as shown,
while the drilling is stopped or when using a slickline or wireline
to convey the downhole sub to store collected downhole information
for analysis and comparison after the downhole sub 106 is removed
from the borehole 102. In a wire-line environment, the recorded
data may be transmitted to the surface, for example, using a
wire-line tool with an inductive coupling. The downhole sub 106 may
be configured to convey information to a surface controller 112
using acoustic telemetry, electrical telemetry, optical fiber
telemetry with or any other suitable telemetry technique.
[0021] The drill string 108 may carry a downhole drill motor 126
for rotating the drill bit 124. In one or more embodiments, the
downhole sub 106 may incorporate an extendable member shown here as
an extendable probe 130, which may be used to perform formation
sampling, pressure testing and hydraulic fracture tests to be
described later in this disclosure. Those skilled in the art with
the benefit of the above examples and description will appreciate
that the tools described herein may be configured and used in a
wire-line or slick-line environment. The several embodiments
described herein may be configured for open hole or cased hole
environments, and the downhole sub 106 may be configured to
perforate a casing pipe using any number of perforating devices
without the need for further description or illustration here.
[0022] FIG. 2 depicts a schematic of a non-limiting downhole sub
according to one or more embodiments. The downhole sub 200 shown
may be used with any suitable carrier that may convey the downhole
sub 200 in a borehole to a formation. In several examples, the
downhole sub 200 may be conveyed using a drilling system
substantially as described above and shown in FIG. 1, on a
wireline, and/or on a slickline. The exemplary downhole sub 200 is
shown disposed in a borehole 102 at a location within the formation
110. The exemplary downhole sub 200 as shown here includes a fluid
supply line 202. A pump 204 and a pressure measurement transducer
or gauge 206 are coupled in fluid communication with the fluid
supply line 202. An upper sealing member, for example an upper
packer 208 and a lower sealing member, for example a lower packer
210 are coupled to the downhole sub to straddle an extendable probe
130 shown disposed between the upper packer 208 and the lower
packer 210. The fluid supply line 202, the pump 204, the gauge 206,
and the extendable probe 130 in several non-limiting embodiments
may be in fluid communication with each other. The pump 204 may be
disposed anywhere along a drill string, may be disposed on the
surface above the borehole 102, or may be disposed anywhere where
the pump 206 may be placed in fluid communication with the fluid
supply line 202. The fluid supply line 202 may be in fluid
communication with a fluid source, for example a fracture fluid
source, a drilling fluid source, a borehole fluid source, another
fluid source, or combinations thereof. The fluid supply line 202
may deliver a fluid to the extendable probe 130 for introduction
into the formation 110 as shown or into non-productive strata not
shown here. For example, the fluid supply line 202 may operate in
concert with the pump 204 to deliver fluid to or draw fluid from an
opening or port, not shown, in the extendable probe 130, for
introduction of fluid into or for removal of fluid from the
formation 110. In some embodiments, fluid may be introduced to an
isolated section of the borehole 102 with sufficient pressure to
force the fluid into the formation 110.
[0023] In one or more non-limiting embodiments, the packers or
sealing members 208, 210 may be selectively expanded or actuated.
When actuated, each packer 208, 210 may expand and sealingly engage
an adjacent borehole wall area to form at least a partial fluid
barrier across an annulus portion of the borehole 102. When the
packers 208, 210 are sealingly engaged with the adjacent borehole
wall area, an annular section or "isolated zone" may be established
between the packers 208, 210. The packers 208, 210 may be of the
fixed head type, the sliding-head type, or of any type known in the
art. The packers 208, 210 may be actuated by any number of
actuating mechanisms. For example, the packers 208, 210 may be
mechanically compressed or actuated using hydraulically actuated
pistons or the like. In one or more examples, the packers 208, 210
may include flexible bladders that may deform sufficiently to
maintain a sealing engagement with the borehole wall even though
the downhole sub 200 may not be centrally positioned in the
borehole 102. One or more of several formation tests and sampling
techniques disclosed herein may be conducted within the isolated
zone.
[0024] It will be appreciated from the present disclosure that
isolating a zone along the wellbore axis increases the likelihood
that formation fluid may be efficiently extracted from a formation.
An isolated axial zone when used with or without an additional
extendable sampling probe 130 having a sealing pad provides a
greater likelihood that a region or area having favorable flow
characteristics will be captured. Utilizing an isolated zone may
increase the flow rate of fluid into the borehole isolated zone and
therefore reduce the time needed to obtain a fluid sample. The
extendable probe 130 may include a pump that may cause the isolated
zone between the packers 208, 210 to have an environmental
condition different than the environment of the regions above and
below the isolated zone. In several examples, the different
environmental condition may include a differential pressure. Using
an isolated zone also helps in hydraulic fracture testing by
directing hydraulic pressure to a selected portion of the borehole
wall.
[0025] Referring again to FIG. 2, the exemplary downhole sub 200 in
one or more embodiments may be used to perform a hydraulic fracture
test on a formation 110 to determine one or more formation
properties. In one or more embodiments, the downhole sub 200 may be
conveyed in the borehole 102 to one or more productive or
non-productive zones of formation 110. The packers 208, 210 may be
actuated to sealingly engage the borehole wall and to define, that
is, establish an isolated zone 212 within the borehole 102. The
fluid in the isolated zone 212 may enter the probe 130 and the
pressure in the isolated zone may be determined using the gauge
206. The fluid pressure in the isolated zone may be continuously
and/or intermittently monitored using the gauge 206 or any other
suitable mechanism or technique.
[0026] At the beginning of one or more hydraulic fracture or other
tests, the pump 204 may be engaged to introduce a fluid, for
example a borehole fluid from the borehole 102 outside the isolated
zone 212 to increase hydraulic pressure in the isolated zone via
the extendable probe 130. As the fluid is introduced into the
isolated zone, the pressure in the isolated zone may be monitored
using the gauge 206. One or more properties of the formation 110
may be determined or estimated from a pressure profile created by
plotting the pressure in the isolated zone over time. In one or
more embodiments, the slope and curvature of time-based pressure
curves may be used to estimate various formation properties.
[0027] Referring to FIGS. 2 and 3 an illustrative example of a
pressure profile plot of the pressure in an isolated zone as a
function of time during an illustrative hydraulic fracture test
according to one or more embodiments is provided. As the pump 204
introduces fluid into the isolated zone, the pressure in the
isolated zone increases non-linearly as shown between
t.sub.1-t.sub.2. When the pressure in the isolated zone reaches the
formation breakdown pressure, the formation is fractured, and the
formation breakdown pressure may be estimated from the pressure at
t.sub.2. At formation breakdown, a short, unstable fracture may
form having a radial extent that is less than the borehole
diameter. When the fracture forms, the deformation modulus of the
rock decreases and the rock anisotropy increases. Associated with
the decreased formation stiffness are an increase in the volume of
the isolated zone and a simultaneous decrease in the pressure in
the isolated zone from t.sub.2 to t.sub.3. The pressure from
t.sub.3 to t.sub.4 may be substantially constant, and a propagation
pressure profile may be estimated from the estimated pressures
between times t.sub.3 and t.sub.4.
[0028] The pump 204 may continue to pump fluid into the isolated
zone to extend or propagate the fracture at a roughly constant
pressure from t.sub.3 to t.sub.4. In one or more embodiments, the
fluid is pumped into the isolated zone to propagate the fracture to
a desired, estimated length. The length of the propagated fracture
may be in a range of about zero to 10 feet. Between times t.sub.2
and t.sub.3, the gauge 206 and pump flow rate information may be
used to estimate the pressure decay in the isolated zone as the
fracture continues to propagate and the fluid in the fracture leaks
off into the formation 110. At time t.sub.4, when the fracture has
been propagated to the maximum and/or desired length, the pump 204
may be shut off and the non-linear pressure profile for at least a
portion of the time interval t.sub.4 to t.sub.5 may be used to
estimate a closure stress. The fracture closing stops at time
t.sub.5 and the non-linear pressure decline will eventually reach
the reservoir pressure at time t.sub.6, and thereafter the pressure
is substantially constant. The procedure and sequence of time
interval t.sub.1-t.sub.6 may be repeated as desired for any number
of cycles. For example, multiple fracture pressurization flow back
cycles may be performed where the injected volume will be such that
the fracture diameter is limited to the design diameter and fluid
returned is not greater than the volume injected into the
fracture.
[0029] In one or more embodiments, the estimated breakdown
pressure, propagation profile, and closure stress may be used to
estimate the pore pressure and overburden pressure within the
formation 110. The pore pressure is the pressure of the fluid in
the pores of the formation 110. The overburden pressure is the
pressure or stress imposed on the formation 110 by the weight of
the overlying formations.
[0030] Referring again to FIG. 2, in one or more embodiments, the
one or more estimated formation properties may be used to determine
or estimate one or more hydraulic fracture treatment
characteristics. For example, the estimated breakdown pressure,
propagation pressure, and closure stress may be used to design a
hydraulic fracture stimulation. Fracturing fluids may include water
and/or various combinations of water and polymer-water solutions,
gels and oil emulsions, foams, acid based fluids, other fluids,
and/or combinations thereof. One characteristic of the fracturing
fluid may be the particular proppant used in the fracture fluid.
Proppants are sized particles that may be mixed with the fracturing
fluid to hold fractures open after a hydraulic fracturing
treatment. In addition to naturally occurring sand grains, man-made
or specially engineered proppants, such as resin-coated sand or
high-strength ceramic materials like sintered bauxite, may be used.
The particular proppant size and sphericity may also be selected,
based on the hydraulic fracture test results. Other fracturing
fluid characteristics that may be selected based on the hydraulic
fracture test results include the fluid shear thinning or
thickening, history dependence, normal stress differences,
viscosity change with respect to temperature change, and/or other
characteristics. The one or more selected formation properties may
be used to engineer the entire fracture treatment including
engineering a particular fracturing fluid for a particular
hydraulic fracture treatment of the tested formation. In one or
more embodiments, the engineered fracturing fluid may be used to
create or establish an efficient conduit for production of fluid
from a reservoir located in the formation 110, to the borehole
102.
[0031] FIG. 4 depicts a schematic of a non-limiting downhole sub
200 having an extendable probe 130 disposed between two extendable
packers 208, 210 according to one or more embodiments. The downhole
sub 200, which may be substantially similar to the downhole sub
described above and shown in FIG. 2, is shown disposed in the
borehole 102 and the extendable probe 130 may be disposed within an
extendable probe mechanism 402. The extendable probe mechanism 402
may be disposed between the extendable upper packer 208 and the
extendable lower packer 210. The extendable packers 208, 210 when
extended may define a first or outer isolated zone 212. The
extendable probe 130, when in a retracted position, may deliver or
remove fluid to or from the outer isolated zone 212 via an orifice
404 formed in one end of the probe 130. The extendable probe 130
may be extended to place the orifice 404 end of the probe in
sealing engagement with a portion of the borehole wall. The
extendable probe 130 may include a sealing member or pad 406 for
sealing engagement with the portion of the borehole wall. It should
be understood that the extendable probe mechanism 402 may be any
suitable mechanism or device that may be used to extend a probe 130
from a downhole sub 200 toward a borehole wall and no limitations
should be implied by the use of the word "mechanism." Non-limiting
examples of mechanisms for extending the extendable probe 130
include hydraulic mechanisms, electromechanical mechanisms, and
mechanical mechanisms. In some embodiments, the probe 130 may be in
a retracted position and moved to engage the borehole wall by
moving the downhole sub 200 to the borehole wall. This may be
accomplished using a decentralizer, such as a bowspring, a back-up
shoe or other extendable member disposed on the downhole sub
opposite the probe 130. The decentralizer may be axially displaced
or disposed diametrically to the extendable probe 130.
[0032] A second or inner isolated zone 408 may be established by
extending the extendable probe 130 to contact the borehole wall.
The inner isolated zone 408 in the example of FIG. 4 includes the
volume within the probe 130 and the borehole wall that is in
pressure communication with the probe adjacent the orifice 404. The
inner isolated zone may be defined within the outer isolated zone
212 as shown. In this configuration, a pressure in the outer
isolated zone 212 may be controlled in relation to a pressure in
the inner isolated zone 408 and in relation to the borehole outside
of the packers 208, 210. In this way, a first pressure differential
between the outer isolated zone 212 and the borehole annulus
outside of the packers 208, 210 may be controlled and a second
pressure differential between the outer isolated zone 212 and the
inner isolated zone 408 may be controlled. In one or more
embodiments, the second pressure differential may be controlled to
be less than the first pressure differential.
[0033] Those skilled in the art with the benefit of the present
disclosure will recognize that the inner isolated zone 408 may be
established using another extendable member such as a second set of
packers not shown in the example embodiment of FIG. 4. A
four-packer arrangement is therefore considered within the scope of
the disclosure. It is sufficient that the orifice 404 may be in a
side of the sub 200 where the extendable probe 130 and seal pad 406
are replaced by a second pair of packers 208, 210 that are
positioned between the shown packers 208, 210. In this manner, the
inner packers may be used to establish the inner isolated zone 408.
Whether using the extendable probe embodiments or four-packer
arrangements, hydraulic fracture tests may be performed for
determining one or more formation properties.
[0034] In one or more embodiments, a hydraulic fracture test may be
performed to determine at least one characteristic of the formation
110. For example, drilling fluid or another fluid carried by the
tool may be introduced into the outer isolated zone 212 to increase
the pressure in the outer isolated zone 212. In one or more
embodiments, the pressure in the outer isolated zone 212 may be
increased above the pressure in the borehole annulus above the
upper packer 208.
[0035] The extendable probe 130 or a second pair of packers may be
extended and placed in sealing engagement with a portion of the
borehole wall to establish the inner isolated zone 408 with an
inner isolated zone pressure. In one or more embodiments, an
extendable sealing member 406 can be used to sealingly engage the
borehole wall to establish the inner isolated zone 408. The
hydraulic fracture test may be performed by selectively introducing
fluid into the inner isolated zone 408 to determine the breakdown
pressure, propagation pressure, closure stress, and/or other
properties of the formation 110 by using techniques as described
above with reference to FIGS. 2 and 3.
[0036] Returning to FIG. 4, by controlling the pressure
differential between the outer isolated zone 212 and the inner
isolated zone 408, the seal establishing the inner isolated zone
may be more easily maintained. An advantage of using a sealed probe
or a second pair of packers for introducing a fracturing fluid
include reducing the amount of fracturing fluid used for fracturing
a formation and extending the fracture into the formation. Another
advantage is that the formation fracturing for the hydraulic
fracture test is faster than with other formation fracturing
techniques, that is, the time segment t.sub.0 to t.sub.6 in FIG. 3
is reduced. Another advantage is that the location of the fracture
is more precisely controlled.
[0037] In one or more embodiments, a first hydraulic fracture test
may be performed as described above with reference to FIG. 2 and
FIG.3 to estimate one or more formation characteristics, for
example breakdown pressure, propagating pressure, pore pressure,
closure stress, etc. One or more subsequent hydraulic fracture
tests may then be performed as described above with reference to
FIG. 4. During the one or more subsequent hydraulic fracture tests,
the pressure in the outer isolated zone 212 may be set based on the
estimated results from a preceding hydraulic fracture test for
controlling the second pressure differential.
[0038] Having described above the several aspects of the
disclosure, one skilled in the art will appreciate several
particular embodiments useful in the determination of one or more
properties of a formation. In one particular embodiment a method
for performing a hydraulic fracture test includes conveying a
downhole sub in a borehole to a formation, the downhole sub
including a first sealing member, a second sealing member, and an
extendable member disposed between the first sealing member and the
second sealing member. The first sealing member and the second
sealing member are actuated to define a first isolated zone within
the borehole. A fluid is introduced to the borehole wall via the
extendable member to fracture the formation, and a property of the
formation is estimated at least in part using an output signal from
a downhole transducer.
[0039] In several particular embodiments, a method for performing a
hydraulic fracture test includes conveying a downhole sub in a
borehole via a drill string, a wireline and/or a slickline.
[0040] In another particular embodiment, a method for performing a
hydraulic fracture test includes estimating a hydraulic pressure of
a fluid introduced to a formation when the formation is initially
fractured by the procedure.
[0041] In several particular embodiments, a method for performing a
hydraulic fracture test includes continuing to introduce a fluid to
a formation to extend a fracture. A method for performing a
hydraulic fracture test may further include continuing to introduce
a fluid to a formation to extend a fracture and estimating a
hydraulic pressure of the introduced fluid during a time interval
while fracture is extending. A method for performing a hydraulic
fracture test may further include continuing to introduce a fluid
to a formation to extend a fracture and halting the introduction of
fluid to the formation after the fracture is extended to allow the
fracture to close. In some aspects, an estimated downhole sub
parameter includes estimating a hydraulic pressure of the
introduced fluid during a time interval while the fracture is
closing.
[0042] In one particular embodiment a method for performing a
hydraulic fracture test includes estimating a fracture treatment
characteristic at least in part using an estimated property of a
formation. The fracture treatment may comprise a subsequent
fracture treatment. In some particular embodiments, the fracture
treatment may comprise a hydraulic fracture treatment and the
estimated fracture treatment characteristic includes a treatment
fluid characteristic.
[0043] In several particular embodiments a method for performing a
hydraulic fracture test includes extending an extendable member to
define a second or inner isolated zone within a borehole. A method
may include controlling a borehole pressure within the first
isolated zone and in the second isolated zone to create a first
pressure differential between the first isolated zone and the
second isolated zone and a second pressure differential between the
first isolated zone and a borehole annulus above the first isolated
zone, and the first pressure differential may be less than the
second pressure differential.
[0044] In a particular apparatus embodiment, an apparatus for
performing a hydraulic fracture test includes a downhole sub that
is conveyed in a borehole to a formation. A first sealing member is
coupled to the downhole sub and a second sealing member is coupled
to the downhole sub axially displaced from the first sealing
member, the first sealing member and the second sealing member
defining a first isolated zone. An extendable member is disposed
between the first sealing member and the second sealing member, the
extendable member introducing a fluid to the first isolated zone
for fracturing the formation. A downhole transducer provides an
output signal, the output signal being used at least in part to
estimate a property of the formation. In several particular
embodiments, a hydraulic fracture stimulation characteristic may be
designed, engineered or estimated using at least in part the
estimated property of the formation. A hydraulic fracture treatment
fluid may be selected, designed or engineered. The additives and
the pump volumes of each of the fluids may be selected. The
sequence for pumping the fluids may be selected and the treating
pressures may be selected based on the information obtained during
the hydraulic fracture test. Selected hydraulic fracture treatment
parameters may include surface and downhole treating pressures,
pump volumes, pump rates, perforating program, charge selection,
order of fracture or stage fractures, the intervals of the
perforations, the maximum distance for extending the stimulation
fracture, or any combination thereof. The stimulation fracture
length and the proper management thereof may affect and improve the
economics of the project.
[0045] In a particular apparatus embodiment, an apparatus for
performing a hydraulic fracture test includes an extendable member
that is extended defining a second isolated zone within the
borehole, the pressure within a first isolated zone and the second
isolated zone establishing a first pressure differential between
the first isolated zone and the second isolated zone and
establishing a second pressure differential between the first
isolated zone and a borehole annulus above the first isolated
zone.
[0046] In other particular apparatus embodiments, an apparatus for
performing a hydraulic fracture test includes a drill string, a
wireline or a slickline conveying a downhole sub in the
borehole.
[0047] In one particular method embodiment, a method for performing
a hydraulic fracture test includes conveying a downhole sub in a
borehole to a formation, the downhole sub including a first sealing
member, a second sealing member, and an extendable member disposed
between the first sealing member and the second sealing member,
actuating the first sealing member and the second sealing member to
define a first isolated zone within the borehole, and introducing a
fluid to the borehole wall via the extendable member to fracture
the formation. The particular embodiment further includes
estimating a hydraulic pressure of the introduced fluid when the
formation is initially fractured, continuing to introduce the fluid
to the formation to extend the fracture, estimating a hydraulic
pressure of the introduced fluid during a time interval while
fracture is extending, halting the introduction of fluid to the
formation after the fracture is extended to allow the fracture to
close, estimating a hydraulic pressure of the introduced fluid
during a time interval while fracture is closing, and estimating a
treatment fluid characteristic at least in part using the estimated
hydraulic pressures of the formation.
[0048] The present disclosure is to be taken as illustrative rather
than as limiting the scope or nature of the claims below. Numerous
modifications and variations will become apparent to those skilled
in the art after studying the disclosure, including use of
equivalent functional and/or structural substitutes for elements
described herein, use of equivalent functional couplings for
couplings described herein, and/or use of equivalent functional
actions for actions described herein. Such insubstantial variations
are to be considered within the scope of the claims below.
* * * * *