1、Designation: D4645 08Standard Test Method forDetermination of In-Situ Stress in Rock Using HydraulicFracturing Method1This standard is issued under the fixed designation D4645; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the in-situstate of stress in rock by hydraulic fracturing.NOTE 1H
3、ydraulic fracturing for stress determination is also referredto as hydrofracturing, and sometimes as minifracing. Hydraulic fracturingand hydrofracturing may also refer to fracturing of the rock by fluidpressure for the purpose of altering rock properties, such as permeabilityand porosity.1.2 Hydrau
4、lic fracturing is the widely accepted field methodavailable for in situ stress measurements at depths greater than50 m. It can be used in drill holes of any diameter.1.3 Hydraulic fracturing can also be used in short holes forwhich other stress measuring methods, such as overcoring, arealso availabl
5、e. The advantage of hydraulic fracturing is that ityields stresses averaged over a few square metres (the size ofthe induced hydraulic fracture) rather than over grain sizeareas, as in the case of overcoring techniques.1.4 All observed and calculated values shall conform to theguidelines for signifi
6、cant digits and rounding established inPractice D6026.1.4.1 The method used to specifiy how data are collected,calculated, or recorded in this standard is not directly related tothe accuracy to which the data can be applied in design or otheruses, or both. How one applies the results obtained using
7、thisstandard is beyond its scope.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user o
8、f this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2113 Practice for Rock Core Drilling and Sampling ofRo
9、ck for Site ExplorationD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD5079 Practices for Preserving and Transporting Rock CoreSamplesD6026 Practice for Using Significant Digits in GeotechnicalDat
10、a3. Terminology3.1 For terminology used in this test method, refer toTerminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 breakdown pressurethe pressure required to inducea hydraulic fracture in a previously intact test interval.3.2.2 in-situ stressrock stress measured in situ (
11、as op-posed to by remote sensing).3.2.3 secondary breakdown (or fracture reopening, or re-frac) pressure the pressure required to reopen a closed,previously induced hydrofracture after the test interval pressurehas been allowed to return to its initial condition.3.2.4 shut-in pressure (or ISIP (inst
12、antaneous shut-inpressure)the pressure reached when the induced hydrofrac-ture closes back after pumping is stopped.3.2.5 vertical and horizontal principal stresses the threeprincipal stresses in situ are generally assumed to act one in thevertical direction and the other two in the horizontal plane
13、.4. Summary of Test Method4.1 Asection of the borehole is isolated by pressurizing twoinflatable rubber packers. The fluid pressure in the sealed-off1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.12 on Rock Mechan
14、ics.Current edition approved July 1, 2008. Published July 2008. Originally approvedin 1987. Last previous edition approved in 2004 as D4645 041. DOI: 10.1520/D4645-08.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual
15、Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesNOTICE: This sta
16、ndard has either been superseded and replaced by a new version or withdrawn.Contact ASTM International (www.astm.org) for the latest information1interval between the two packers is raised by pumping fluidinto it at a controlled rate until a fracture occurs in the boreholewall. Pumping is stopped and
17、 the pressure in the interval isallowed to stabilize. The pressure is then reduced to the porepressure level of the rock formation, and the pressurizationprocess is repeated several times maintaining the same flowrate. Additional pressure cycles can be conducted at differentflow rates. The magnitude
18、s of the principal stresses arecalculated from the various pressure readings. The orientationof the fracture is detected in order to determine the orientationof the transverse principal stresses. A typical pressure versustime, flow rate versus time record for a test interval is shown inFig. 1.5. Sig
19、nificance and Use5.1 Limitations:5.1.1 The depth of measurement is limited only by thelength of the test hole.5.1.2 Presently, the results of the hydraulic fracturingmethod can be interpreted in terms of in-situ stresses only if theboreholes are approximately parallel to one of the threeprincipal in
20、-situ stresses. Unless evidence to the contraryexists, vertical boreholes are assumed to be parallel to one ofthe in-situ principal stresses.5.1.3 When the principal stress parallel to the borehole axisis not the least principal stress, only the two other principalstresses can be determined directly
21、 from the test. If theminimum stress acts along the borehole axis, fractures bothparallel and perpendicular to the axis of the borehole aresometimes induced by the test, allowing for the determinationof all three principal stresses.5.1.4 In the unlikely event that the induced fracture changesorienta
22、tion away from the borehole, its trace on the boreholewall cannot be used in stress determinations.5.2 Assumptions:5.2.1 The rock tested is assumed to be linearly elastic,homogeneous, and isotropic. Any excessive departure fromthese assumptions could affect the results.5.2.2 Vertical boreholes are a
23、ssumed to be substantiallyparallel to one of the in-situ principal stresses, since it has beenestablished from many geological observations and stressmeasurements by other methods that in most cases one of theprincipal stresses is vertical to subvertical.5.3 Hydraulic fracturing determination of in-
24、situ stressescan be complicated by rock matrix porosity, naturally occur-ring fractures, the presence of nearby underground openings,and local variations in the stress field.NOTE 2The quality of the result produced by this standard isdependent on the competence of the personnel performing it, and th
25、esuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D3740 are generally considered capable of competentand objective testing/sampling/inspection, etc. Users of this standard arecautioned that compliance with Practice D3740 does not in itself assurereliable r
26、esults. Reliable results depend on many factors; Practice D3740provides a means of evaluating some of those factors.6. Apparatus6.1 Tripod or Drilling RigEquipment for lowering thehydraulic fracturing tool into and lifting it from the test hole isnecessary. To facilitate the lowering and lifting of
27、the down-hole hydrofracturing tool, a tripod or a drilling rig is set up ontop of the test hole.When high-pressure tubing or drilling pipes(rods) are used for lowering the tool, it is necessary to use adrilling rig with a derrick and hoist capable of lifting thecombined weight of the pipe and instru
28、ments. When awireline-flexible hose system is used for hydrofracturing, awell-designed tripod capable of carrying the weight of thetesting tool, wireline, and hoses is employed.6.2 Straddle PackerBorehole sealing is accomplished bytwo inflatable rubber packers, spaced apart a distance equal toat lea
29、st six hole diameters, and interconnected mechanicallyand hydraulically to form one unit called the straddle packer.6.3 High-Pressure Tubing or HosePacker and test-intervalpressurization is accomplished either by a high-pressure tubing(drilling rod is often a good substitute) or by high-pressurehose
30、, or by a combination of the two (where tubing is used topressurize the interval, and the hose, which is strapped to theoutside of the tubing facilitates packer inflation). The hose orthe tubing, or both, are connected hydraulically at one end topumps or pressure generators (0 to 70 MPa, 0 to 25 L/m
31、in arerecommended ratings), and at the other to the straddle packerand the test interval between the packers (Fig. 2). It has beenNOTE 1In this test the flow rate was maintained constant during the first three cycles. In the fourth cycle a very slow flow rate was maintained suchthat the top level of
32、 the pressuretime curve could be considered as the upper limit for the shut-in pressure.FIG. 1 Typical Pressure Time, Flow Rate Time Records During HydrofracturingD4645 082found that pump capacities similar to those given here canovercome almost any common rock permeability and facilitatepressurizat
33、ion.6.4 Pressure Transducers and Flow MeterPressure trans-ducers (10 to 70 MPa) are used to monitor the test intervalpressure either on the surface or at the test depth (or both). Insome setups, the packer pressure is also monitored in the sameway as the test interval. A flow meter is used to monito
34、r theflow rate of fluid into the test interval. The sensing devices feedinto multichannel analog time-base recorders for real-timecontinuous permanent recording. Digital computer recording iscarried out for the storage of test pressure and flow rateinformation which can later be used to provide a th
35、oroughanalysis of the test data.6.5 Hydrofracture Delineation Equipment :6.5.1 Impression PackerThe presence and orientation ofthe induced hydrofracture is commonly recorded by the use ofan impression packer, which is an inflatable packer with anouter layer of very soft semicured rubber. An orientin
36、g device,in the form of a magnetic borehole surveying tool or agyroscopic borehole surveying tool, is used to determine thedirection and inclination of the hydrofracture traced on theimpression packer (Fig. 3).6.5.2 Borehole TeleviewerAn alternative to the orientedimpression packer is the borehole t
37、eleviewer, which is a soniclogging tool that takes an oriented acoustic picture of theborehole wall. This tool is considerably faster than the impres-sion packer because it can take readings from an entire test holein one trip. The impression packer requires retrieval after eachtest so that the oute
38、r cover can be properly marked or replacedbefore lowering the tool to the next zone. However, theborehole televiewer is considerably more expensive to own orrent, does not always discern hydrofractures that have closedtightly after the pressurization stage of the test, and requires afluid filled bor
39、ehole.7. Personnel Prequalification and Equipment Verification7.1 Test PersonnelThe performance of a hydraulic frac-turing test may vary from location to location, and from onerock type to the next. Quick decisions, which are often requiredin the field, may change the outcome of the tests. Hence, th
40、etest supervisor should be a person who thoroughly understandsthe theoretical aspects of the test method, and who has hadsubstantial experience in conducting such tests in a variety ofrock types, depths, and locations.7.2 Drilling PersonnelQuality drilling is important tomaintaining a reasonably str
41、aight vertical hole and in keepinga nearly circular cross-section.7.3 Equipment VerificationThe compliance of all equip-ment and apparatus with performance specifications shall beverified. Performance specification is generally done by cali-brating the equipment and measurement systems.8. Procedure8
42、.1 Drill a borehole (in most cases in the vertical direction)to the depth of interest. Diamond bit coring is recommendedbecause it yields a continuous core and leaves a smooth anduniformly circular borehole wall.FIG. 2 Suggested Schematic Downhole and Surface Equipment Set Up for Hydraulic Fracturin
43、gD4645 0838.2 Select testing zones of solid unfractured rock within thedrilled hole, making use of the core, if available, or one ormore geophysical logs (such as caliper, density, boreholeteleviewer) if they have been run.8.3 To seal off the test interval, lower the straddle packer tothe predetermi
44、ned depth of testing and pressurize hydraulicallyso as to inflate packers onto the wall of the borehole. Thepressurization, typically using water, is generated on thesurface by a high-pressure pump and is conveyed to the packerby means of tubing or flexible hose.8.4 With the packers well anchored to
45、 the sidewalls (apacker pressure of 3 MPa is usually sufficient at this stage ofthe test), pressurize hydraulically (typically using water) thetest interval between the packers at a constant flow rate. Thisrate may change from one test hole to the next, often dependingon the permeability of the rock
46、 (the higher the permeability thehigher the rate). The general principle is to affect hydrofrac-turing within a minute or so from the beginning of intervalpressure rise. Throughout the interval pressurization, maintainpacker pressure at a level of about 2 MPa higher than theinterval pressure to ensu
47、re that no leak-offs occur. As the rockhydrofractures, the breakdown pressure is reached. If pumpingis then stopped without venting the hydraulic line, the pressurewill suddenly drop and settle at a lower level called the shut-inpressure. Repeated cycling of the pressurization procedureusing the sam
48、e flow rate will yield the secondary breakdownpressure (the pressure required to reopen a preexistinghydrofracture), and additional values of the shut-in pressure.8.5 Continuously record the entire pressurization processboth as pressure versus time and as flow rate versus time.8.6 At the conclusion
49、of the test, vent the packer pressure toallow the packers to return to their original diameter. The entireFIG. 3 Suggested Schematic Downhole and Surface Equipment Set Up for Taking a Packer Impression of theHydraulic FractureD4645 084straddle packer assembly can then either be moved to the nexttest zone or pulled out of the borehole.8.7 The most common tool for determining hydraulic frac-turing orientation is the oriented impression packer. Lower thepacker on the drill-rod or wireline to the test interval afterhydrofracturing, and inf
