注CO_2条件下花岗岩破裂特征的试验研究
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摘要
CO_2增强型采热系统(CO_2-EGS)工程中CO_2作用下岩石的水压破裂行为是目前亟需解决的一个关键科学问题。从福建漳州采取花岗岩露头,利用自主研制的厚壁圆筒式致裂仪进行了不同流体(CO_2、水)的水压致裂试验,研究了CO_2、水入渗致裂后花岗岩的破裂特征及破裂机制。研究表明:随着致裂液黏度的减小,试样破裂过程会形成更多且更曲折的微裂纹分支,这意味着,采用CO_2压裂可能更有利于形成缝网,从而有助于提高增强型采热(EGS)工程中换热效率;试样的破裂压力随着致裂液黏度的减小而降低,而较低的破裂压有助于注入井的安全运行;试验结果可用从对流换热角度分析的流体岩石相互作用机制解释,进而验证了其准确性。
The hydraulic fracturing(HF) behavior under CO_2 condition is a key scientific issue in CO_2-enhanced geothermal system project. The granite specimen was taken from the quarry in Zhangzhou, Fujian province. HF experiments were conducted to investigate the effects of CO_2 and H2 O on the HF process and crack propagation by using a new independently developed hollow cylinder. This study reveals that with the decrease of the viscosity of the fracturing fluid, a greater number and more sinuous microcrack branches form in the fracture process. This indicates that CO_2 fracturing may be more conducive to the formation of the crack network, which helps to increase the heat exchange efficiency in the CO_2-EGS projects. The fracture pressure of the specimen decreases with decreasing the viscosity of the fracturing fluid, which leads to the safe operation of the injection well with a lower value. The experimental results consist with the interaction mechanism of fluid rock from the convective heat transfer perspective,and its accuracy is verified.
The hydraulic fracturing(HF) behavior under CO_2 condition is a key scientific issue in CO_2-enhanced geothermal system project. The granite specimen was taken from the quarry in Zhangzhou, Fujian province. HF experiments were conducted to investigate the effects of CO_2 and H2 O on the HF process and crack propagation by using a new independently developed hollow cylinder. This study reveals that with the decrease of the viscosity of the fracturing fluid, a greater number and more sinuous microcrack branches form in the fracture process. This indicates that CO_2 fracturing may be more conducive to the formation of the crack network, which helps to increase the heat exchange efficiency in the CO_2-EGS projects. The fracture pressure of the specimen decreases with decreasing the viscosity of the fracturing fluid, which leads to the safe operation of the injection well with a lower value. The experimental results consist with the interaction mechanism of fluid rock from the convective heat transfer perspective,and its accuracy is verified.
引文
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[26]LEGUILLON D,QUESADA D,PUTOT C,et al.Prediction of crack initiation at blunt notches and cavities-size effects[J].Engineering Fracture Mechanics,2007,74(15):2420-2436.
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[28]GARAGASH D,DETOURNAY E.An analysis of the influence of the pressurization rate on the borehole breakdown pressure[J].International Journal of Solids&Structures,1997,34(24):3099-3118.
[29]ZHOU X,BURBEY T J.Fluid effect on hydraulic fracture propagation behavior:a comparison between water and supercritical CO2-like fluid[J].Geofluids,2014,14(2):174-188.
[30]WARPINSKI N R,KRAMM R C,HEINZE J R,et al.Comparison of single-and dual-array microseismic mapping techniques in the barnett shale[C]//2005 Annual Technical Conference and Exhibition.Dallas:Spe Technical Conference&Exhibition,2005.
[31]CHAPMAN A J.Heat transfer[M].New York:Macmilan Publishing Company,1989.
[2]MOHAN A R,TURAGA U,SHEMBEKAR V,et al.Utilization of carbon dioxide from coal-based power plants as a heat transfer fluid for electricity generation in enhanced geothermal system(EGS)[J].Energy,2013,57(8):505-512.
[3]XU C,DOWD P,LI Q.Carbon sequestration potential of the Habanero reservoir when carbon dioxide is used as the heat exchange fluid[J].Journal of Rock Mechanics and Geotechnical Engineering,2016,8(1):50-59.
[4]ISHIDA T,CHEN Q,MIZUTA Y.Effect of injected water on hydraulic fracturing deduced from acoustic emission monitoring[J].Pure and Applied Geophysics,1977,150(3-4):627-646.
[5]ZOBACK M D,RUMMEL F,JUNG R,et al.Laboratory hydraulic fracturing experiments in intact and pre-fractured rock[J].International Journal of Rock Mechanics and Mining Sciences&Abstract,1977,14(2):49-58.
[6]ZOBACK M D,POLLARD D D.Hydraulic fracture propagation and the interpretation of pressure-time records for in-situ stress determination[C]//Proceedings of19th US Rock Mechanics Symposium.Reno:American Rock Mechanics Association,1978.
[7]OJALA IRA O.The effect of CO2 on the mechanical properties of reservoir and caprock[J].Energy Procedia,2011,4(4):5392-5397.
[8]MARBLER HERWIG,ERICKSON KIRSTEN P,SCHMIDT MICHAEL,et al.Geomechanical and geochemical effects on sandstones caused by the reaction with supercritical CO2:an experimental approach to in situ conditions in deep geological reservoirs[J].Environmental Earth Sciences,2012,69(6):1981-1998.
[9]MORITA N,BLACK A D,FUH G F.Theory of lost circulation pressure[C]//Annual Technical Conference and Exhibition.New Orleans:Spe Technical Conference&Exhibition,1990.
[10]OORT VAN E,RAZAVI S O.Wellbore strengthening and casing smear:the common underlying mechanism[C]//Drilling Conference and Exhibition.Fort Worth:Society of Petroleum Engineers,2014.
[11]HUBBERT M KING,WILLIS DAVID G.Mechanics of hydraulic fracturing[J].Developments in Petroleum Science,1957,210(7):369-390.
[12]HAIMSON B,FAIRHUST C.Initiation and extension of hydraulic fractures in rocks[J].Society of Petroleum Engineers Journal,1967,7(6):310-318.
[13]HAIMSON B,FAIRHURST C.Hydraulic fracturing in porous-permeable materials[J].Journal of Petroleum Technology,1969,21(7):811-817.
[14]MORITA N,BLACK A D,FUH G F.Borehole breakdown pressure with drilling fluids-I.Empirical results[J].International Journal of Rock Mechanics&Mining Sciences,1996,33(1):39-51.
[15]HU SHAOBIN,LI XIAOCHUN,BAI BING.Effects of different fluids on microcrack propagation in sandstone under true triaxial loading conditions[J].Greenhouse Gases:Science and Technology,2017,8:9-11.
[16]LI Q,WU Z,LEI X,et al.Experimental and numerical study on the fracture of rocks during injection of CO2-saturated water[J].Environmental Geology,2007,51(7):1157-1164.
[17]LEI X L,NISHIZAWA O,XUE Z.Experimental study on the fractures of sandstone and andesite during injection of CO2-saturated water by monitoring acoustic emission and velocity[C]//EGS-AGU-EUG Joint Assembly.[S.l.]:[s.n.],2003.
[18]ISHIDA T,CHEN Q,MIZUTA Y,et al.Influence of fluid viscosity on the hydraulic fracturing mechanism[J].Journal of Energy Resources Technology,2004,126(3):190-200.
[19]ISHIDA T,AOYAGI K,NIWA T,et al.Acoustic emission monitoring of hydraulic fracturing laboratory experiment with supercritical and liquid CO2[J].Geophysical Research Letters,2012,39(16):16309.
[20]ISHIDA T,CHEN Y,BENNOUR Z,et al.Features of CO2 fracturing deduced from acoustic emission and microscopy in laboratory experiments[J].Journal of Geophysical Research Solid Earth,2016,11(121):8080-8098.
[21]CHEN YOUQING,NAGAYA Y,ISHIDA T.Observations of fractures induced by hydraulic fracturing in anisotropic granite[J].Rock Mechanics&Rock Engineering,2015,48(4):1455-1461.
[22]BIENIAWSKI Z T,HAWKES I.Suggested methods for determining tensile strength of rock materials[J].International Journal of Rock Mechanics&Mining Sciences,1978,15(15):99-103.
[23]李小春,鲁建荣,白冰,等.厚壁圆筒式两相流体致裂仪研制[J].岩石力学与工程学报,2012,31(8):1537-1544.LI Xiao-chun,LU Jian-rong,BAI Bing,et al.Development of hollow-cylinder tensile tester in two-phase fluids[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(8):1537-1544.
[24]刘明泽,白冰,李小春,等.CO2-水两相条件下砂岩致裂特征与有效应力模型的试验研究[J].岩石力学与工程学报,2016,35(2):250-259.LIU Ming-ze,BAI Bing,LI Xiao-chun,et al.Experimental study of fracturing characteristics of sandstone under CO2-water two-phase condition and effective stress model[J].Chinese Journal of Rock Mechanics and Engineering,2016,35(2):250-259.
[25]马峰,孙红丽,蔺文静,等.中国EGS示范工程靶区选址与指标矩阵评价[J].科技导报,2015,33(8):41-47.MA Feng,SUN Hong-li,LIN Wen-jing,et al.Target site selection and index matrix evaluation of EGS trial project in China[J].Science&Technology Review,2015,33(8):41-47.
[26]LEGUILLON D,QUESADA D,PUTOT C,et al.Prediction of crack initiation at blunt notches and cavities-size effects[J].Engineering Fracture Mechanics,2007,74(15):2420-2436.
[27]SCHMITT D R,ZOBACK M D.Poroelastic effects in the determination of the maximum horizontal principal stress in hydraulic fracturing tests a proposed breakdown equation employing a modified effective stress relation for tensile failure[J].International Journal of Rock Mechanics&Mining Sciences,1989,26(6):499-506.
[28]GARAGASH D,DETOURNAY E.An analysis of the influence of the pressurization rate on the borehole breakdown pressure[J].International Journal of Solids&Structures,1997,34(24):3099-3118.
[29]ZHOU X,BURBEY T J.Fluid effect on hydraulic fracture propagation behavior:a comparison between water and supercritical CO2-like fluid[J].Geofluids,2014,14(2):174-188.
[30]WARPINSKI N R,KRAMM R C,HEINZE J R,et al.Comparison of single-and dual-array microseismic mapping techniques in the barnett shale[C]//2005 Annual Technical Conference and Exhibition.Dallas:Spe Technical Conference&Exhibition,2005.
[31]CHAPMAN A J.Heat transfer[M].New York:Macmilan Publishing Company,1989.