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タイトル Japanese Geotechnical Society Standard (JGS3761-2017) Method for initial stress measurement by hydraulic fracturing technique
著者 The Japanese Geotechnical Society
出版 Japanese Geotechnical Society Standard (JGS3761-2017) Method for initial stress measurement by hydraulic fracturing technique
ページ 発行 2020/04/01 文書ID os202004010002
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  • Japanese Geotechnical Society Standard (JGS3761-2017) Method for initial stress measurement by hydraulic fracturing technique
  • 著者
  • The Japanese Geotechnical Society
  • 出版
  • Japanese Geotechnical Society Standard (JGS3761-2017) Method for initial stress measurement by hydraulic fracturing technique
  • ページ
  • 発行
  • 2020/04/01
  • 文書ID
  • os202004010002
  • 内容
  • Japanese Geotechnical Society Standard (JGS3761-2017)Method for initial stress measurement by hydraulic fracturing technique1ScopeThis test method covers the measurement of the initial stress in rock by hydraulic fracturing in a borehole. Themethod assumes the test is applied to rocks with no apparent pre-existing fractures.2Normative referencesThe following standards shall constitute a part of this standard by virtue of being referenced herein. The latestversions of this standard shall apply (including supplements).JGS A 0207:2018 Technical terms for geotechnical engineering3DefinitionThe definition of terms used in this document is as follows.3.1 Initial stressThe state of stress of the rock prior to being affected by artificial disturbances such as tunneling3.2 Hydraulic fracturingInducing new fractures at the borehole wall by injecting water into a test interval to apply pressure.3.3 BreakdownAbrupt pressure decline in a test interval due to fracture initiation at the borehole wall while continuing to injectwater into the test interval.3.4 Shut-inStop water injection by closing a valve installed in the water injection pipe.3.5 ComplianceThe amount of water for injection required to raise the pressure by a unit magnitude in a part between a testinterval in a borehole and a flow meter for measuring the rate of water injection to the test interval.3.6 Injection rateThe term indicating the amount of water injected into a test interval in a unit time, where it is represented by aunit of ml/min. JGS 3761-20183.7 Breakdown pressure PbThe pressure at which fractures are initiated at the borehole wall.3.8 Shut-in pressure PsThe pressure at which the tip of the induced fracture starts to close while the pressure decreases after shut-in.3.9 Reopening pressure PrThe pressure at which the induced fractures, which have closed completely, start to reopen at the borehole wallby applying pressure at the test interval.4ApparatusThe test apparatus shall be as given in the following.4.1 Equipment for hydraulic fracturing testThe equipment consists of surface units, a hydraulic fracturing sonde, and pipes connecting the sonde and thesurface units. The surface units consist of hydraulic pumps for hydraulic fracturing and packer inflation and adata logger. The sonde is lowered and lifted on a wireline or drill rods as illustrated in Figs. 1 and 2, respectively.The compliance of the sonde and pipe system shall be so small that the reopening pressure can be detectedcorrectly.BoreholeWinchHigh pressurehose forpacker inflationData loggerWire lineHousing for pressuretransducer and flow meterPackerWater discharge portTestintervalPump forpacker inflationBoreholePackerFig. 1 Typical hydraulic fracturing test using wireline.Pump forhydraulicfracturingSurface unitsPump forhydraulicfracturingData loggerDrill rodHousing for pressuretransducer and flow meterPackerWater discharge portTestintervalHydraulic fracturing sondePump forpacker inflationHigh pressurehose forpacker inflationWater injection pipeWater injection pipeSurface unitsSheaveHydraulic fracturing sondeArmored cablePackerFig. 2 Typical hydraulic fracturing test using drill rod.© JGS 2018 – All rights reserved a)Hydraulic fracturing sonde The sonde consists of straddle packer, pressure transducer and flowmeters, in which a water discharge port is placed between two packers.Note1: The length of the test interval should be 3 ~ 6 times the borehole diameter.Note2: The pressure transducer should have a resolution of 0.01 MPa or higher and a measurement range of more than 30MPa.Note3: The flow meter should have a resolution of 0.1 ml/min or higher and a measurement range of more than 100 ml/min.b)Pump for hydraulic fracturing The pump shall be capable of raising pressure at a test interval morethan the breakdown pressure estimated in advance.Note4: The pump should supply water continuously at more than 30 MPa and 100 ml/min.c)Pump for packer inflation The pump shall be capable of raising the packer pressure more than thebreakdown pressure estimated in advance.Note5: The pump should supply pressure more than 30 MPa.d)Data loggere)Water injection pipe The pipe shall be capable of holding pressure more than the breakdown pressureestimated in advance.The logger shall be capable of collecting data for intervals less than 0.1 sec.4.2 Fracture delineation equipmentThe equipment consists of an impression packer and a pump. The impression packer consists of a packer, aplastic or rubber sheet fitted to the packer surface for getting fracture imprint, an orienting tool and pressuretransducers etc. The packer shall be longer than the test interval. The sonde is lowered and lifted in the sameway for the case of the hydraulic fracturing sonde.5Test procedureThe hydraulic fracturing sonde is lowered to a planned depth of measurement in a borehole, and the packersare pressurized contacting firmly with the borehole wall. By using the hydraulic fracturing pump, the tests offracture initiation and reopening are carried out to observe the breakdown pressure, the shut-in pressure andthe reopening pressure. After the retrieval of the hydraulic fracturing sonde, the impression packer is lowered tothe depth of measurement, and the packers are pressurized for getting the imprint of the fractures induced bythe hydraulic fracturing tests. The procedure is described specifically in the following.5.1 PreparationPreparations for measurement borehole as following:a)Understanding of geology The geology of the test site shall be understood for the purpose of stressmeasurement, collecting results investigated previously by the other researchers.b)Selection of test boreholesmooth inner surface.The borehole is chosen on condition that it has a circular cross section andNote1: The borehole should be 76 mm - 96 mm in diameter.Note2: The borehole should be vertical. JGS 3761-2018c)Selection of test intervalbedding, fault etc.The test intervals shall be devoid of apparent discontinuities such as joint,5.2 Test procedurea)Setting the sonde for hydraulic fracturing The sonde is lowered to a planned depth of measurementin a borehole, and the packers are pressurized contacting firmly with the borehole wall.Note3: The packers should be inflated by a pressure larger than the shut-in pressure estimated in advance.b)Fracture initiation test The test interval is pressurized by injecting water until the breakdown isobserved, and subsequently the shut-in is carried out. After the pressure decay in the test interval isrecorded, the test interval is vented.Note4: An actual record of hydraulic fracturing test is shown in Fig. A.1 of Annex A.Note5: The injection rate should be constant.c)Fracture reopening test The test interval is pressurized by injecting water until the pressure almostlevels off, and subsequently the shut-in is carried out. After the pressure decay in the test interval isrecorded, the test interval is vented.Note6: The injection rate should be constant.Note7: The fracture reopening test should be repeated more than 3 times.d)Retrieval of the hydraulic fracturing sondeborehole.e)Test for getting fracture imprint The impression packer is set at the measurement depth. The sheetfitted to the packer is pressed against the borehole wall to get the imprint of the fractures induced by thehydraulic fracturing test. Upon pulling the sonde out of the borehole, the fracture imprint recorded on thesheet is traced, and it is confirmed that the fractures have been induced in almost parallel to the boreholeaxis.After the packers are vented, the sonde is pulled out of theNote8: The packer should be pressurized to a pressure more than twice as large as the reopening pressure and thepressure should be maintained for a period of time more than 10 min.5.3 Obtaining the breakdown, reopening and shut-in pressures and fracture orientationa)Breakdown pressuretest.b)Shut-in pressure The pressure shall be taken as the higher pressure at points where the curvaturechanges on the pressure vs time curves after the shut-in.The pressure shall be taken as the peak pressure attained in the fracture initiationNote9: Examples of applying typical methods for detecting the shut-in pressure are shown in Figs. B.1 and B.2 of Annex B.c)Reopening pressure The pressure shall be taken as the higher pressure at points where the curvaturechanges on the ascending portion of the curve pf pressure vs accumulated volume of injected-water.Note10: An example of applying a method for detecting the reopening pressure is shown in Fig. C.1 of Annex Cd)Fracture orientation The fracture azimuth is determined as the azimuth of straight lines parallel with theborehole axis, which approximate the fracture trace on the borehole wall.Note11: An example of applying the method for detecting the fracture azimuth is shown in Fig. D.1 of Annex D.© JGS 2018 – All rights reserved 6CalculationThe initial stresses are calculated by the following procedure, where the compressive stress is taken aspositive. The maximum and minimum principal stresses SH and Sh in a plane perpendicular to the borehole axisare given by following equations.Sh = Ps(1)SH = 3Sh – 2Pr(2)The azimuth of the maximum principal stress is given as the mean azimuth of the induced fractures determinedby the test for obtaining the fracture imprint.7ReportThe report includes the followings.a)Outline of the measurements such as the drilling direction, the diameter of the borehole, and themeasurement depths.b)Time variation of the injection pressure and the injection rate, and the packer pressure.c)Methods used to detect the breakdown, reopening and shut-in pressures and the results.d)Image of the fracture trace and the determined fracture azimuth.e)Calculated results of initial stresses, i.e. magnitudes and orientation of principal stresses.f)Description of any method different from this standard, if used.g)Other remarks, if necessary. JGS 3761-2018Annex A(Reference)Example of test recordA.1 Example of test recordAn actual record of hydraulic fracturing test is shown in Fig. A.1.Fig. A.1An actual record of hydraulic fracturing test.© JGS 2018 – All rights reserved Annex B(Reference)Example of analysis the methods to detect the shut-in pressureB.1 Example of applying the ISIP methodAn example of applying the ISIP method for detecting the shut-in pressure is shown in Fig. B.1Pressurein test interval試験区間の圧力(MPa) (MPa)8765432Fig. B.1き裂閉口圧Shut-inPressure Ps060120180240経過時間Time (s)(s)300360420An example of applying the ISIP method for detecting the shut-in pressure.B.2 Example of applying the dt/dP-P methodAn example of applying the dt/dP-P method for detecting the shut-in pressure is shown in Fig. B.2.-50-100-150Interval for getting the timederivative of pressure-200-250-300-350-400Fig. B.2Shut-in Pressure PsPressurein test interval試験区間の圧力(MPa) (MPa)Inverse of thetime derivative of(s/MPa)pressure (s/MPa)圧力の時間微分の逆数05.05.587654320606.0120180240経過時間Time(s)(s)6.5300Pressure in 圧力test (MPa)interval (MPa)3604207.0An example of applying the dt/dP-P method for detecting the shut-in pressure. JGS 3761-2018Annex C(Reference)Example of applying the method to detect the reopening pressureC.1 Example of applying the method to detect the reopening pressureAn example of applying the method to detect the reopening pressure is shown in Fig. C.1.Fig. C.1An example of applying the method to detect the reopening pressure.© JGS 2018 – All rights reserved Annex D(Reference)Example of applying the method to detect fracture azimuthD.1 Example of applying the method to detect fracture azimuthAn example of applying the method to detect fracture azimuth is shown in Fig. D.1.Fig. D.1An example of applying the method to detect fracture azimuth. Japanese Geotechnical Society Standard (JGS3761-2017)Method for initial stress measurement by hydraulic fracturing techniquePublished byThe Japanese Geotechnical Society4-38-2 Sengoku, Bunkyo-ku, Tokyo 112-0011, JapanE-mail: jgs@jiban.or.jpURL: https://www.jiban.or.jp/e/C 2020 The Japanese Geotechnical Society○All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means electronic ormechanical, including photocopying, recording or any information storage and retrieval system now known or tobe invented, without written permission from the publisher.ISBN978-4-88644-113-3
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