ASTM D4645-87(1997)
(Test Method)Standard Test Method for Determination of the In-Situ Stress in Rock Using the Hydraulic Fracturing Method
Standard Test Method for Determination of the In-Situ Stress in Rock Using the Hydraulic Fracturing Method
SCOPE
1.1 This test method covers the determination of the in-situ state of stress in rock by hydraulic fracturing. Note 1-Hydraulic fracturing for stress determination is also referred to as hydrofracturing, and sometimes as minifracing. Hydraulic fracturing and hydrofracturing may also refer to fracturing of the rock by fluid pressure for the purpose of altering rock properties, such as permeability and porosity.
1.2 Hydraulic fracturing is the only widely accepted field method available for in situ stress measurements at depths greater than 50 m. It can be used in drill holes of any diameter.
1.3 Hydraulic fracturing can also be used in short holes for which other stress measuring methods, such as overcoring, are also available. The advantage of hydraulic fracturing is that it yields stresses averaged over a few square metres (the size of the induced hydraulic fracture) rather than over grain size areas, as in the case of overcoring techniques.
1.4 The values stated in SI units are to be regarded as the standard.
1.5 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 4645 – 87 (Reapproved 1997)
Standard Test Method for
Determination of the In-Situ Stress in Rock Using the
Hydraulic Fracturing Method
This standard is issued under the fixed designation D 4645; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope induced hydrofracture after the test interval pressure has been
allowed to return to its initial condition.
1.1 This test method covers the determination of the in-situ
2.1.4 shut-in pressure (or ISIP (instantaneous shut-in
state of stress in rock by hydraulic fracturing.
pressure))—the pressure reached when the induced hydrofrac-
NOTE 1—Hydraulic fracturing for stress determination is also referred
ture closes back after pumping is stopped.
to as hydrofracturing, and sometimes as minifracing. Hydraulic fracturing
2.1.5 vertical and horizontal principal stresses—the three
and hydrofracturing may also refer to fracturing of the rock by fluid
principal stresses in situ are assumed to act one in the vertical
pressure for the purpose of altering rock properties, such as permeability
direction and the other two in the horizontal plane.
and porosity.
1.2 Hydraulic fracturing is the only widely accepted field
3. Summary of Test Method
method available for in situ stress measurements at depths
3.1 A section of the borehole is isolated by pressurizing two
greater than 50 m. It can be used in drill holes of any diameter.
inflatable rubber packers. The fluid pressure in the sealed-off
1.3 Hydraulic fracturing can also be used in short holes for
interval between the two packers is raised by pumping fluid
which other stress measuring methods, such as overcoring, are
into it at a controlled rate until a fracture occurs in the borehole
also available. The advantage of hydraulic fracturing is that it
wall. Pumping is stopped and the pressure in the interval is
yields stresses averaged over a few square metres (the size of
allowed to stabilize. The pressure is then reduced to the pore
the induced hydraulic fracture) rather than over grain size
pressure level of the rock formation, and the pressurization
areas, as in the case of overcoring techniques.
process is repeated several times maintaining the same flow
1.4 The values stated in SI units are to be regarded as the
rate. Additional pressure cycles can be conducted at different
standard.
flow rates. The magnitudes of the principal stresses are
1.5 This standard does not purport to address all of the
calculated from the various pressure readings. The orientation
safety problems, if any, associated with its use. It is the
of the fracture is detected in order to determine the orientation
responsibility of the user of this standard to establish appro-
of the transverse principal stresses. A typical pressure versus
priate safety and health practices and determine the applica-
time, flow rate versus time record for a test interval is shown in
bility of regulatory limitations prior to use.
Fig. 1.
2. Terminology
4. Significance and Use
2.1 Definitions of Terms Specific to This Standard:
4.1 Limitations:
2.1.1 breakdown (or critical) pressure—the pressure re-
4.1.1 The depth of measurement is limited only by the
quired to induce a hydraulic fracture in a previously intact test
length of the test hole.
interval.
4.1.2 Presently, the results of the hydraulic fracturing
2.1.2 in-situ stress—rock stress measured in situ (as op-
method can be interpreted in terms of in-situ stresses only if the
posed to by remote sensing).
boreholes are approximately parallel to one of the three
2.1.3 secondary breakdown (or fracture reopening, or re-
principal in-situ stresses. Unless evidence to the contrary
frac) pressure—the pressure required to reopen a previously
exists, vertical boreholes are assumed to be parallel to one of
the in-situ principal stresses.
4.1.3 When the principal stress parallel to the borehole axis
This test method is under the jurisdiction of ASTM Committee D-18 on Soil
is not the least principal stress, only the two other principal
and Rock and is the direct responsibility of Subcommittee D18.12 on Rock
stresses can be determined directly from the test. If the
Mechanics.
Current edition approved March 9, 1987. Published May 1987. minimum stress acts along the borehole axis, fractures both
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D 4645
NOTE 1—In this test the flow rate was maintained constant during the first three cycles. In the fourth cycle a very slow flow rate was maintained such
that the top level of the pressure–time curve could be considered as the upper limit for the shut-in pressure.
FIG. 1 Typical Pressure − Time, Flow Rate − Time Records During Hydrofracturing
parallel and perpendicular to the axis of the borehole are strapped to the outside of the tubing facilitates packer infla-
sometimes induced by the test, allowing for the determination tion). The hose or the tubing, or both, are connected hydrau-
of all three principal stresses.
lically at one end to pumps or pressure generators (0.70 MPa,
4.1.4 In the unlikely event that the induced fracture changes 0 to 25 L/min are recommended ratings), and at the other to the
orientation away from the borehole, its expression in the
straddle packer and the test interval between the packers (Fig.
borehole wall cannot be used in stress determinations.
2). It has been found that pump capacities similar to those
4.2 Assumptions:
given here can overcome almost any common rock permeabil-
4.2.1 The rock tested is assumed to be linearly elastic,
ity and facilitate pressurization.
homogeneous, and isotropic. Any excessive departure from
5.4 Pressure Transducers and Flow Meter—Pressure trans-
these assumptions could affect the results.
ducers (10 to 70 MPa) are used to monitor the test interval
4.2.2 Vertical boreholes are assumed to be substantially
pressure either on the surface or at the test depth (or both). In
parallel to one of the in-situ principal stresses, since it has been
some setups, the packer pressure is also monitored in the same
established from many geological observations and stress
way as the test interval. A flow meter is used to monitor the
measurements by other methods that in most cases one of the
flow rate of fluid into the test interval. The sensing devices feed
principal stresses is vertical to subvertical.
into multichannel analog time-base recorders for real-time
4.3 Hydraulic fracturing determination of in-situ stresses
continuous permanent recording. Additional options available
can be complicated by rock matrix porosity, naturally occur-
are analog-data tape recording and digital computer recording
ring fractures, the presence of nearby underground openings,
for the storage of test pressure and flow rate information which
and local variations in the stress field.
can later be used to provide a thorough analysis of the test data.
5.5 Hydrofracture Delineation Equipment:
5. Apparatus
5.5.1 Impression Packer—The presence and orientation of
5.1 Tripod or Drilling Rig—Equipment for lowering the
the induced hydrofracture is commonly recorded by the use of
hydraulic fracturing tool into and lifting it from the test hole is
an impression packer, which is an inflatable packer with an
necessary. To facilitate the lowering and lifting of the down-
outer layer of very soft semicured rubber. An orienting device,
hole hydrofracturing tool, a tripod or a drilling rig is set up on
in the form of a magnetic borehole surveying tool or a
top of the test hole. When high-pressure tubing or drilling pipes
gyroscopic borehole surveying tool, is used to determine the
(rods) are used for lowering the tool, it is necessary to use a
direction and inclination of the hydrofracture traced on the
drilling rig with a derrick and hoist capable of lifting the
impression packer (Fig. 3).
combined weight of the pipe and instruments. When a
5.5.2 Borehole Televiewer—An alternative to the oriented
wireline-flexible hose system is used for hydrofracturing, a
impression packer is the borehole televiewer, which is a sonic
well-designed tripod capable of carrying the weight of the
logging tool that takes an oriented acoustic picture of the
testing tool, wireline, and hoses is employed.
borehole wall. This tool is considerably faster than the impres-
5.2 Straddle Packer—Borehole sealing is accomplished by
sion packer because it can take readings from an entire test hole
two inflatable rubber packers, spaced apart a distance equal to
at least six hole diameters, and interconnected mechanically in one trip. The impression packer requires retrieval after each
test so that the outer cover can be properly marked or replaced
and hydraulically to form one unit called the straddle packer.
5.3 High-Pressure Tubing or Hose—Packer and test- before lowering the tool to the next zone. However, the
borehole televiewer is considerably more expensive to own or
interval pressurization is accomplished either by a high-
pressure tubing (drilling rod is often a good substitute) or by rent, does not always discern hydrofractures that have closed
tightly after the pressurization stage of the test, and requires a
high-pressure hose, or by a combination of the two (where
tubing is used to pressurize the interval, and the hose, which is fluid filled borehole.
D 4645
FIG. 2 Suggested Schematic Downhole and Surface Equipment Set Up for Hydraulic Fracturing
6. Personnel Prequalification and Equipment Verification because it yields a continuous core and leaves a smooth and
uniformly circular borehole wall.
6.1 Test Personnel—The performance of a hydraulic frac-
7.2 Select for testing zones of solid unfractured rock within
turing test may vary from location to location, and from one
the drilled hole, making use of the core, if available, or one of
rock type to the next. Quick decisions, which are often required
ore geophysical logs (such as caliper, density, borehole tele-
in the field, may change the outcome of the tests. Hence, the
viewer) if they have been run.
test supervisor should be a person who thoroughly understands
7.3 To seal off the test interval, lower the straddle packer to
the theoretical aspects of the test method, and who has had
the predetermined depth of testing and pressurize hydraulically
substantial experience in conducting such tests in a variety of
so as to inflate packers onto the wall of the borehole. The
rock types, depths, and locations.
pressurization, typically using water, is generated on the
6.2 Drilling Personnel—Quality drilling is important to
surface by a high-pressure pump and is conveyed to the packer
maintaining a reasonably straight vertical hole and in keeping
by means of tubing or flexible hose.
a nearly circular cross-section.
7.4 With the packers well anchored to the sidewalls (a
6.3 Equipment Verification—The compliance of all equip-
packer pressure of 3 MPa is usually sufficient at this stage of
ment and apparatus with performance specifications shall be
the test), pressurize hydraulically (typically using water) the
verified. Performance specification is generally done by cali-
test interval between the packers at a constant flow rate. This
brating the equipment and measurement systems.
rate may change from one test hole to the next, often depending
7. Procedure
on the permeability of the rock (the higher the permeability the
7.1 Drill a borehole (in most cases in the vertical direction) higher the rate). The general principle is to affect hydrofrac-
to the depth of interest. Diamond bit coring is recommended turing within a minute or so from the beginning of interval
D 4645
FIG. 3 Suggested Schematic Downhole and Surface Equipment Set Up for Taking a Packer Impression of the
Hydraulic Fracture
pressure rise. Throughout the interval pressurization, maintain straddle packer assembly can then either be moved to the next
packer pressure at a level of about 2 MPa higher than the test zone or pulled out of the borehole.
interval to ensure that no leak-offs occur. As the rock hydrof-
7.7 The most common tool for determining hydraulic frac-
ractures, a critical (or breakdown) pressure is reached. If
turing orientation is the oriented impression packer. Lower the
pumping is then stopped without venting the hydraulic line, the
packer on the drill-rod or wireline to the test interval after
pressure will suddenly drop and settle at a lower level called
hydrofracturing, and inflate to a pressure higher than the
the shut-in pressure. Repeated cycling of the pressurization
secondary breakdown pressure or the shut-in pressure (which-
procedure using the same flow rate will yield the secondary
ever is larger). This ensures that the packer will slightly open
breakdown pressure (the pressure required to reopen a preex-
the hydrofracture and enable the soft rubber covering to take a
isting hydrofracture), and additional values of the shut-in
good imprint of the fracture. A magnetic compass or a
pressure.
gyroscopic borehole surveying tool is used to determine the
7.5 Continuously record the entire pressurization process
azimuth of a fixed point on the packer. After some 30 to 60 min
both as pressure versus time and as flow rate versus time.
of pressurization, deflate the impression packer and retrieve.
7.6 At the conclusion of the test, vent the packer pressure to
Trace the fracture impression and determine its orientation
allow the packers to return to their original diameter. The entire
D 4645
with respect to the fixed point on the packer so that it can also pointing the shut-in pressure on the pressure–time curves are
be oriented with respect to north. described by Zoback and Haimson.
8.2.3 The tensile strength (T) is not a constant parameter and
varies with loading rate, specimen size, grain size, and mode of
8. Calculation
testing. There is no direct way of determining T in the test hole.
8.1 General—The calculation of in-situ principal stresses
However, when it can be assumed that the hydrofractured rock
given here is for the commonly used vertical test holes. The
closes back completely once the fluid pressure is brought back
pressure−time record, such as the one shown in Fig. 1, is used
to the original pore pressure level, the pressure required to
to obtain the test results required for the calculation; knowl-
reopen the fracture in the second pressurization cycle (fracture
edge of the attitude
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