ASTM D4631-95(2000)
(Test Method)Standard Test Method for Determining Transmissivity and Storativity of Low Permeability Rocks by In Situ Measurements Using Pressure Pulse Technique
Standard Test Method for Determining Transmissivity and Storativity of Low Permeability Rocks by In Situ Measurements Using Pressure Pulse Technique
SCOPE
1.1 This test method covers a field procedure for determining the transmissivity and storativity of geological formations having permeabilities lower than 10 -3 µm2 (1 millidarcy) using the pressure pulse technique.
1.2 The transmissivity and storativity values determined by this test method provide a good approximation of the capacity of the zone of interest to transmit water, if the test intervals are representative of the entire zone and the surrounding rock is fully water saturated.
1.3 The values stated in SI units are to be regarded as the standard.
1.4 This standard does not purport to address all of the safety concerns, 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. /p>
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Designation:D4631–95 (Reapproved 2000)
Standard Test Method for
Determining Transmissivity and Storativity of Low
Permeability Rocks by In Situ Measurements Using
Pressure Pulse Technique
This standard is issued under the fixed designation D4631; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
µ = fluid viscosity, and
g = acceleration due to gravity.
1.1 This test method covers a field procedure for determin-
2.1.2 storativity,S—thestorativity(orstoragecoefficient)of
ing the transmissivity and storativity of geological formations
−3 2
a formation of thickness, b, is defined as follows:
havingpermeabilitieslowerthan10 µm (1millidarcy)using
the pressure pulse technique.
S 5 S ·b (3)
s
1.2 The transmissivity and storativity values determined by
this test method provide a good approximation of the capacity
where:
of the zone of interest to transmit water, if the test intervals are
S = equivalent bulk rock specific storage (ebrss).
s
representative of the entire zone and the surrounding rock is
The ebrss is defined as the specific storage of a material if it
fully water saturated.
were homogeneous and porous over the entire interval. The
1.3 The values stated in SI units are to be regarded as the
specific storage is given as follows:
standard.
S 5rg C 1 nC (4)
~ !
1.4 This standard does not purport to address all of the s b w
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
where:
priate safety and health practices and determine the applica-
C = bulk rock compressibility,
b
bility of regulatory limitations prior to use.
C = fluid compressibility, and
w
n = formation porosity.
2. Terminology
2.2 Symbols:
2.1 Definitions of Terms Specific to This Standard: −1 2
2.2.1 C —bulk rock compressibility [M LT ].
b
−1 2
2.1.1 transmissivity, T—the transmissivity of a formation of
2.2.2 C —compressibility of water [M LT ].
w
thickness, b, is defined as follows: −1
2.2.3 K—hydraulic conductivity [ LT ].
T 5 K·b (1) 2.2.3.1 Discussion—The use of the symbol K for the term
hydraulic conductivity is the predominant usage in ground-
water literature by hydrogeolists, whereas the symbol k is
where:
commonly used for this term in rock mechanics and soil
K = equivalent formation hydraulic conductivity (efhc).
science.
Theefhcisthehydraulicconductivityofamaterialifitwere
2.2.4 L—length of packed-off zone [ L].
homogeneous and porous over the entire interval. The hydrau-
−1 −2
2.2.5 P—excess test hole pressure [ ML T ].
lic conductivity, K, is related to the equivalent formation, k,as
−1 −2
2.2.6 P —initial pressure pulse [ML T ].
o
follows:
2.2.7 S—storativity (or storage coefficient) (dimensionless).
−1
K 5 krg/µ (2)
2.2.8 S —specific storage [ L ].
s
2 −1
2.2.9 T—transmissivity [L T ].
2.2.10 V —volume of water pulsed [L ].
where: w
2.2.11 b—formation thickness [ L].
r = fluid density,
2.2.12 e—fracture aperture [ L].
−2
2.2.13 g—acceleration due to gravity [ LT ].
2.2.14 k—permeability [L ].
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
RockandisthedirectresponsibilityofSubcommitteeD18.21onGroundWaterand
2.2.15 n—porosity (dimensionless).
Vadose Zone Investigations.
2.2.16 r —radius of test hole [L].
w
Current edition approved Oct. 10, 1995. Published March 1996. Originally
published as D4631–86. Discontinued April 1995 and reinstated as D4631–95.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4631
2.2.17 t—time elapsed from pulse initiation [T]. 4.2 Analysis—The transient pressure data obtained using
2.2.18 a—dimensionless parameter. the suggested method are evaluated by the curve-matching
2.2.19 b—dimensionless parameter. technique described by Bredehoeft and Papadopulos (1),orby
−1 −1
2.2.20 µ—viscosity of water [ML T ]. an analytical technique proposed by Wang et al (2). The latter
−3
2.2.21 r—density of water [ ML ]. is particularly useful for interpreting pulse tests when only the
early-time transient pressure decay data are available.
3. Summary of Test Method
4.3 Units:
3.1 Aboreholeisfirstdrilledintotherockmass,intersecting
4.3.1 Conversions—The permeability of a formation is
the geological formations for which the transmissivity and often expressed in terms of the unit darcy. A porous medium
storativity are desired. The borehole is cored through potential
has a permeability of 1 darcy when a fluid of viscosity 1 cP(1
3 −6 3 2
zonesofinterest,andislatersubjectedtogeophysicalborehole mPa·s) flows through it at a rate of 1 cm /s (10 m /s)/1 cm
−4 2
logging over these intervals. During the test, each interval of
(10 m )cross-sectionalareaatapressuredifferentialof1atm
interest is packed off at top and bottom with inflatable rubber (101.4kPa)/1cm(10mm)oflength.Onedarcycorrespondsto
packers attached to high-pressure steel tubing. After inflating
0.987 µm . For water as the flowing fluid at 20°C, a hydraulic
the packers, the tubing string is completely filled with water. conductivity of 9.66 µm/s corresponds to a permeability of 1
3.2 The test itself involves applying a pressure pulse to the darcy.
water in the packed-off interval and tubing string, and record- 4.3.2 Viscosity of Water—Table 1 shows the viscosity of
ing the resulting pressure transient. A pressure transducer, water as a function of temperature.
located either in the packed-off zone or in the tubing at the
5. Apparatus
surface,measuresthetransientasafunctionoftime.Thedecay
characteristics of the pressure pulse are dependent on the
NOTE 1—A schematic of the test equipment is shown in Fig. 2.
transmissivity and storativity of the rock surrounding the
5.1 Source of Pressure Pulse—Apump or pressure intensi-
intervalbeingpulsedandonthevolumeofwaterbeingpulsed.
fier shall be capable of injecting an additional amount of water
Alternatively,undernon-artesianconditions,thepulsetestmay
to the water-filled tubing string and packed-off test interval to
be performed by releasing the pressure on a shut-in well,
produce a sharp pressure pulse of up to 1 MPa (145 psi) in
thereby subjecting the well to a negative pressure pulse.
magnitude, preferably with a rise time of less than 1% of one
Interpretationofthistestmethodissimilartothatdescribedfor
half of the pressure decay (P/P =0.5).
o
the positive pressure pulse.
5.2 Packers—Hydraulically actuated packers are recom-
mended because they produce a positive seal on the borehole
4. Significance and Use
wall and because of the low compressibility of water they are
4.1 Test Method—The pulse test method is used to deter-
alsocomparativelyrigid.Eachpackershallsealaportionofthe
mine the transmissivity and storativity of low-permeability
borehole wall at least 0.5 m in length, with an applied pressure
formations surrounding the packed-off intervals. This test
at least equal to the excess maximum pulse pressure to be
method is considerably shorter in duration than the pump and
applied to the packed-off interval and less than the formation
slug tests used in more permeable rocks. To obtain results to
fracture pressure at that depth.
the desired accuracy, pump and slug tests in low-permeability
5.3 Pressure Transducers—The test pressure may be mea-
formationsaretootimeconsuming,asindicatedinFig.1(from
sured directly in the packed-off test interval or between the
Bredehoeft and Papadopulos (1)).
fast-acting valve and the test interval with an electronic
pressure transducer. In either case the pressure shall be
recorded at the surface as a function of time. The pressure
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
transducer shall have an accuracy of at least 63 kPa (60.4
the text.
FIG. 1 Comparative Times for Pressure Pulse and Slug Tests
D4631
TABLE 1 Viscosity of Water as a Function of Temperature
from a full water column to a falling water-level column
Temperature, °C Absolute Viscosity, mPa·s because of formation of a free surface at or near zero absolute
pressure (Neuzil (3)).
0 1.79
2 1.67
4 1.57 6. Procedure
6 1.47
6.1 Drilling Test Holes:
8 1.39
6.1.1 Number and Orientation—The number of test holes
10 1.31
12 1.24
shall be sufficient to supply the detail required by the scope of
14 1.17
the project. The test holes shall be directed to intersect major
16 1.11
18 1.06 fracture sets, preferable at right angles.
20 1.00
6.1.2 Test Hole Quality—The drilling procedure shall pro-
22 0.96
vide a borehole sufficiently smooth for packer seating, shall
24 0.91
26 0.87 contain no rapid changes in direction, and shall minimize
28 0.84
formation damage.
30 0.80
6.1.3 Test Holes Cored—Core the test holes through zones
32 0.77
34 0.74
of potential interest to provide information for locating test
36 0.71
intervals.
38 0.68
6.1.4 Core Description—Describe the rock core from the
40 0.66
test holes with particular emphasis on the lithology and natural
discontinuities.
6.1.5 Geophysical Borehole Logging—Log geophysically
the zones of potential interest. In particular, run electrical-
induction and gamma-gamma density logs. Run other logs as
required.
6.1.6 Washing Test Holes—The test holes must not contain
any material that could be washed into the permeable zones
during testing, thereby changing the transmissivity and storat-
ivity. Flush the test holes with clean water until the return is
free from cuttings and other dispersed solids.
6.2 Test Intervals:
6.2.1 Selection of Test Intervals—Test intervals are deter-
mined from the core descriptions, geophysical borehole logs,
and, if necessary, from visual inspection of the borehole with a
borescope or television camera.
6.2.2 Changes in Lithology—Test each major change in
lithology that can be isolated between packers.
6.2.3 Sampling Discontinuities—Discontinuities are often
the major permeable features in hard rock. Test jointed zones,
fault zones, bedding planes, and the like, both by isolating
individual features and by evaluating the combined effects of
several features.
6.2.4 Redundancy of Tests—Toevaluatevariabilityintrans-
missivity and storativity, conduct several tests in each rock
type,ifhomogeneous.Iftherockisnothomogeneous,eachset
of tests should encompass similar types of discontinuities.
FIG. 2 Schematic of Test Equipment
6.3 Test Water:
6.3.1 Quality—Water used for pressure pulse tests shall be
psi), including errors introduced by the recording system, and clean and compatible with the formation. Even small amounts
a resolution of at least 1 kPa (0.15 psi). of dispersed solids in the injection water could plug the rock
5.4 Hydraulic Systems—The inflatable rubber packers shall face of the test interval and result in a measured transmissivity
be attached to high-pressure steel tubing reaching to the value that is erroneously low.
surface. The packers themselves shall be inflated with water 6.3.2 Temperature—The lower limit of the test water tem-
using a separate hydraulic system. The pump or pressure perature shall be 5°C below that of the rock mass to be tested.
intensifier providing the pressure pulse shall be attached to the Cold water injected into a warm rock mass causes air to come
steeltubingatthesurface.Ifthepumpisused,afast-operating out of solution, and the resulting bubbles will radically modify
valve shall be located above, but as near as practical to the the pressure transient characteristics.
upper packer. That valve should be located less than 10 m 6.4 Testing:
above the anticipated equilibrium head in the interval being 6.4.1 Filling and Purging System—Allow sufficient time
testedtoavoidconditionsinthetubingchangingduringthetest afterwashingthetestholeforanyinducedformationpressures
D4631
to dissipate. Once the packers have been set, slowly fill the
where:
tubing string and packed-off interval with water to ensure that
V = volume of water being pulsed,
w
no air bubbles will be trapped in the test interval and tubing. r = well radius,
w
t = time elapsed from pulse initiation,
6.4.2 Pressure Pulse Test—This range of pressures is in
C = compressibility of water,
w
most cases sufficiently low to minimize distortion of fractures
T = transmissivity,
adjacent to the test hole, but in no case should the pressure
S = storage coefficient,
exceed the minimum principal ground stress. Record the
r = density of water, and
resulting pressure pulse and decay transient detected by the
g = gravitational acceleration.
pressure transducer as a function of time. A typical record is
Tables of the function F (ab) have been provided by
shown in Fig. 3.
Cooper, et al (4), Papadopulos (5), and Bredehoeft and Papa-
6.4.2.1 Before the pressure pulse test can be started it is
dopulos (1).
necessary to reliably estimate the natural pressure in the test
7.1.1 In Fig. 3 the pressure, p, shown before (to the left of)
interval. See 7.1.1 and Fig. 3 for a description of a method to
Time t representstheunknownnaturalpressureintheinterval
preparethesystemforthepulsetest.Afterthepressureisat,or
eventually to be tested. The drill hole encounters that interval
estimated to be approaching at a predictable rate, near-
at Time t and from then until Time t the pressure variation
1 2
equilibrium conditions, then rapidly pressurize the tubing,
reflects the effects of drilling and test hole development. If the
typically to between 300 and 600 kPa (50 to 100 psi), and then
interval consists of rocks or sediments of low hydraulic
shut in.
conductivity, there might be a long time period before the
water level in an open hole would stabilize to the equilibrium
7. Calculation and Interpretation of Test Data
level. For that reason before a pulse test can be conducted we
want to establish a condition that provides a reasonable
7.1 The type of matching technique developed by Brede-
estimate of the undisturbed pressure for the interval. The
hoeft and Papadopulos (1) involves plotting normalized pres-
following procedure is intended to provide that condition. At
sure (the ratio of the excess borehole pressure, P, at a given
Time t the packers are inflated, and then the system is filled
time to the initial pressure pulse, P ) against the logarithm of
o
withwaterandshutin.Bythisoperationthechangeinpressure
time,asindicatedinFig.1andFig.3.Thepulsedecayisgiven
inthepacked-offintervalwillreflectacompressivesystemand
as follows:
should approach the pressure in the interval being tested much
P
5 F~a,b! (5)
more rapidly than would the water level in an open test hole.
P
o
Monitorin
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