水力压裂微地震监测中应力场的复杂性对应力反演的影响
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摘要
在微地震监测过程中,压裂区域的应力状态对于水力压裂的效果有着不可忽视的影响,但是由于压裂区域裂缝形态交错,应力场较为复杂,往往很难有效地获取较为准确的应力状态。本文将探究应力场的复杂程度对于应力反演的影响,通过数值模拟均一应力场条件下和复杂应力场条件下的震源机制解,利用Vavry?uk的迭代联合反演方法进行应力反演,并对反演结果进行误差分析。发现均一应力场作用下震源机制的不确定性对于求解应力模型的影响不大,但是会对滑动方向的误差统计带来一定程度的影响;在复杂应力场的条件下进行应力反演,滑动方向的误差值会随着应力场复杂程度的增加而增大,并且比震源机制的不确定性造成的误差值大得多。此外,当应力场的复杂程度增加到一定水平时,反演得到的单一应力模型将使得相当一部分断层面无法满足摩尔—库伦破裂准则,这种反演结果是不可取的。本文还选择了与数值实验有相似特征的两组实际数据,大庆油田某压裂井和长宁区块的某压裂井监测数据,分别进行应力反演和误差分析,用以验证上述结论。
The regional stress state impacts on the effectiveness of microseismic monitoring of hydrofracturing. But the ideal stress state in the fracturing region is difficult to obtain because of the interlaced distribution form of fractures and complex stress fields. In this paper, the object is to study the impact of complexity of stress field on stress inversion. We first numerically simulate two series of focal mechanisms in a homogeneous stress field and a complex stress field, and then implement stress inversion by utilizing Vavry?uk's iterative joint inversion method and do the error analysis. The results indicate that the uncertainty of focal mechanisms in homogeneous stress field has a slight influence on acquiring a stress model, but does impact on the error statistics of the slip direction. Also the slip deviation increases as the complexity of the stress field rises and the error is much bigger than that caused by uncertainty of focal mechanisms when stress inversion is in a complex stress field. In addition, part of the fault planes cannot meet the Mohr-Coulomb failure criterion with the condition of a single stress model inverted as the complexity of stress field reaches a high level, which means the inversion result is desirable. Two series of actual field data in the Daqing oil field and the Changning Block are chosen in this paper. These agree well with the numerical simulation and are applied to stress inversion and error analysis to verify the conclusions above.
The regional stress state impacts on the effectiveness of microseismic monitoring of hydrofracturing. But the ideal stress state in the fracturing region is difficult to obtain because of the interlaced distribution form of fractures and complex stress fields. In this paper, the object is to study the impact of complexity of stress field on stress inversion. We first numerically simulate two series of focal mechanisms in a homogeneous stress field and a complex stress field, and then implement stress inversion by utilizing Vavry?uk's iterative joint inversion method and do the error analysis. The results indicate that the uncertainty of focal mechanisms in homogeneous stress field has a slight influence on acquiring a stress model, but does impact on the error statistics of the slip direction. Also the slip deviation increases as the complexity of the stress field rises and the error is much bigger than that caused by uncertainty of focal mechanisms when stress inversion is in a complex stress field. In addition, part of the fault planes cannot meet the Mohr-Coulomb failure criterion with the condition of a single stress model inverted as the complexity of stress field reaches a high level, which means the inversion result is desirable. Two series of actual field data in the Daqing oil field and the Changning Block are chosen in this paper. These agree well with the numerical simulation and are applied to stress inversion and error analysis to verify the conclusions above.
引文
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[2]PHILLIPS W S,FAIRBANKS T D,RUTLEDGE J T,et al.Induced microearthquake patterns and oil-producing fracture systems in the Austin chalk[J].Tectonophysics,1998,289(1-3):153-169.
[3]RUTLEDGE J T,PHILLIPS W S,MAYERHOFER M J.Faulting induced by forced fluid injection and fluid flow forced by faulting:An interpretation of hydraulic-fracture microseismicity,Carthage Cotton Valley Gas Field,Texas[J].Bulletin of the Seismological Society of America,2004,94(94):1817-1830.
[4]BAIG A,URBANCIC T.Microseismic moment tensors:A path to understanding frac growth[J].Leading Edge,2010,29(3):320-324.
[5]MAXWELL S C,RUTLEDGE J,JONES R,et al.Petroleum reservoir characterization using downhole microseismic monitoring[J].Geophysics,2010,75(5):75A129-75A137.
[6]HUANG W,WANG R,LI H,et al.Unveiling the signals from extremely noisy microseismic data for high-resolution hydraulic fracturing monitoring[J].Scientific Reports,2017,7(1):11996.
[7]HUANG W,WANG R,ZU S,et al.Low-frequency noise attenuation in seismic and microseismic data using mathematical morphological filtering[J].Geophysical Journal International,2017,211(3):1296-1318.
[8]SONG F,TOKS?Z M N.Full-waveform based complete moment tensor inversion and source parameter estimation from downhole microseismic data for hydrofracture monitoring[J].2011,76(6):WC103.
[9]SONG F,WARPINSKI N R,TOKS?Z M N.Full-waveform based microseismic source mechanism studies in the Barnett Shale:Linking microseismicity to reservoir geomechanics[J].Geophysics,2014,79(2):109-126.
[10]VAVRY?UK V,KüHN D,Moment tensor inversion of waveforms:A two-step time-frequency approach[J].Geophysical Journal International,2012,190(3):1761-1776.
[11]STANEK F,JECHUMTáLOVáZ,EISNER L.Reservoir stress from microseismic source mechanisms[J].Leading Edge,2015,34(8):890-893+895.
[12]WARPINSKI N R,SCHMIDT R A,NORTHROP D A.In-situ stresses:The predominant influence on hydraulic fracture containment[J].Journal of Petroleum Technology,1982,34(34):653-664.
[13]严川.小震震源机制与应力场反演方法及其应用研究[D].北京:中国地震局地球物理研究所,2015.[YAN C.Inversion methods for the focal mechanisms of small earthquakes and the stress field and their application[D].Beijing:Institute of Geophysics,China Earthquake Administration,2015.]
[14]WALLACE R E.Geometry of shearing stress and relation to faulting[J].Journal of Geology,1951,59(2):118-130.
[15]BOTT M H P.The mechanics of oblique slip faulting[J].Geological Magazine,1959,96(2):109-117.
[16]ANGELIER J.Determination of the mean principal directions of stresses for a given fault population[J].Tectonophysics,1979,56(3):T17-T26.
[17]ETCHECOPAR A,VASSEUR G,DAIGNIERES M.An inverse problem in microtectonics for the determination of stress tensors from fault striation analysis[J].Journal of Structural Geology,1981,3(1):51-65.
[18]MICHAEL A J.Determination of stress from slip data:Faults and folds[J].Journal of Geophysical Research Solid Earth,1984,89(B13):11517-11526.
[19]GEPHART J W,FORSYTH D W.An improved method for determining the regional stress tensor using earthquake focal mechanism data:Application to the San Fernando earthquake sequence[J].Journal of Geophysical Research Solid Earth,1984,89(B11):9305-9320.
[20]SASAKI S,KAIEDA H.Determination of stress state from focal mechanisms of microseismic events induced during hydraulic injection at the Hijiori Hot Dry Rock Site[J].Pure&Applied Geophysics,2002,159(1-3):489-516.
[21]ANGELIER J.Inversion of earthquake focal mechanisms to obtain the seismotectonic stress IV-a new method free of choice among nodal planes[J].Geophysical Journal International,2002,150(3):588-609.
[22]MAURY J,CORNET F H,DORBATH L.A review of methods for determining stress fields from earthquakes focal mechanisms;Application to the Sierentz 1980 seismic crisis(Upper Rhine graben)[J].Bulletin De La Societe Geologique De France,2014,184(4-5):319-334.
[23]ABERS G A,GEPHART J W.Direct inversion of earthquake first motions for both the stress tensor and focal mechanisms and application to southern California[J].Journal of Geophysical Research Solid Earth,2001,106(B11):26523-26540.
[24]MICHAEL A J.Use of focal mechanisms to determine stress:a control study[J].Journal of Geophysical Research Solid Earth,1987,92(B1):357-368.
[25]VAVRY?UK V,BOUCHAALA F,FISCHER T.High-resolution fault image from accurate locations and focal mechanisms of the 2008swarm earthquakes in West Bohemia,Czech Republic[J].Tectonophysics,2013,590(2):189-195.
[26]VAVRY?UK V.Iterative joint inversion for stress and fault orientations from focal mechanisms[J].Geophysical Journal International,2014,199(1):69-77.
[27]HARDEBECK J L.Homogeneity of small-scale earthquake faulting,stress,and fault strength[J].Bulletin of the Seismological Society of America,2006,96(5):1675-1688.
[28]HARDEBECK J L,MICHAEL A J.Damped regional‐scale stress inversions:methodology and examples for southern California and the Coalinga aftershock sequence[J].Journal of Geophysical Research Solid Earth,2006,111(B11).
[29]MARTíNEZ-GARZóN P,KWIATEK G,ICKRATH M,et al.MSATSI:A matlab package for stress inversion combining solid classic methodology,a new simplified user‐handling,and a visualization tool[J].Seismological Research Letters,2014,85(4):896-904.
[30]LAY T,WALLACE T.Modern global seismology[M].London:Academic Press,1995.
[31]LUND B,SLUNGA R.Stress tensor inversion using detailed microearthquake information and stability constraints:Application to?lfus in southwest Iceland[J].Journal of Geophysical Research Solid Earth,1999,104(B7):14947-14964.
[32]BYERLEE J.Friction of rocks[J].Pure&Applied Geophysics,1978,116(4-5):615-626.
[33]MARTíNEZ-GARZóN P,VAVRY?UK V,KWIATEK G,et al.Sensitivity of stress inversion of focal mechanisms to pore pressure changes[J].Geophysical Research Letters,2016,43,8441-8450.
[34]CHEN X,WANG R,HUANG W,et al.Clustering-based stress inversion from focal mechanisms in microseismic monitoring of hydrofracturing[J].Geophysical Journal International,2018,215(3):1887-1899.
[2]PHILLIPS W S,FAIRBANKS T D,RUTLEDGE J T,et al.Induced microearthquake patterns and oil-producing fracture systems in the Austin chalk[J].Tectonophysics,1998,289(1-3):153-169.
[3]RUTLEDGE J T,PHILLIPS W S,MAYERHOFER M J.Faulting induced by forced fluid injection and fluid flow forced by faulting:An interpretation of hydraulic-fracture microseismicity,Carthage Cotton Valley Gas Field,Texas[J].Bulletin of the Seismological Society of America,2004,94(94):1817-1830.
[4]BAIG A,URBANCIC T.Microseismic moment tensors:A path to understanding frac growth[J].Leading Edge,2010,29(3):320-324.
[5]MAXWELL S C,RUTLEDGE J,JONES R,et al.Petroleum reservoir characterization using downhole microseismic monitoring[J].Geophysics,2010,75(5):75A129-75A137.
[6]HUANG W,WANG R,LI H,et al.Unveiling the signals from extremely noisy microseismic data for high-resolution hydraulic fracturing monitoring[J].Scientific Reports,2017,7(1):11996.
[7]HUANG W,WANG R,ZU S,et al.Low-frequency noise attenuation in seismic and microseismic data using mathematical morphological filtering[J].Geophysical Journal International,2017,211(3):1296-1318.
[8]SONG F,TOKS?Z M N.Full-waveform based complete moment tensor inversion and source parameter estimation from downhole microseismic data for hydrofracture monitoring[J].2011,76(6):WC103.
[9]SONG F,WARPINSKI N R,TOKS?Z M N.Full-waveform based microseismic source mechanism studies in the Barnett Shale:Linking microseismicity to reservoir geomechanics[J].Geophysics,2014,79(2):109-126.
[10]VAVRY?UK V,KüHN D,Moment tensor inversion of waveforms:A two-step time-frequency approach[J].Geophysical Journal International,2012,190(3):1761-1776.
[11]STANEK F,JECHUMTáLOVáZ,EISNER L.Reservoir stress from microseismic source mechanisms[J].Leading Edge,2015,34(8):890-893+895.
[12]WARPINSKI N R,SCHMIDT R A,NORTHROP D A.In-situ stresses:The predominant influence on hydraulic fracture containment[J].Journal of Petroleum Technology,1982,34(34):653-664.
[13]严川.小震震源机制与应力场反演方法及其应用研究[D].北京:中国地震局地球物理研究所,2015.[YAN C.Inversion methods for the focal mechanisms of small earthquakes and the stress field and their application[D].Beijing:Institute of Geophysics,China Earthquake Administration,2015.]
[14]WALLACE R E.Geometry of shearing stress and relation to faulting[J].Journal of Geology,1951,59(2):118-130.
[15]BOTT M H P.The mechanics of oblique slip faulting[J].Geological Magazine,1959,96(2):109-117.
[16]ANGELIER J.Determination of the mean principal directions of stresses for a given fault population[J].Tectonophysics,1979,56(3):T17-T26.
[17]ETCHECOPAR A,VASSEUR G,DAIGNIERES M.An inverse problem in microtectonics for the determination of stress tensors from fault striation analysis[J].Journal of Structural Geology,1981,3(1):51-65.
[18]MICHAEL A J.Determination of stress from slip data:Faults and folds[J].Journal of Geophysical Research Solid Earth,1984,89(B13):11517-11526.
[19]GEPHART J W,FORSYTH D W.An improved method for determining the regional stress tensor using earthquake focal mechanism data:Application to the San Fernando earthquake sequence[J].Journal of Geophysical Research Solid Earth,1984,89(B11):9305-9320.
[20]SASAKI S,KAIEDA H.Determination of stress state from focal mechanisms of microseismic events induced during hydraulic injection at the Hijiori Hot Dry Rock Site[J].Pure&Applied Geophysics,2002,159(1-3):489-516.
[21]ANGELIER J.Inversion of earthquake focal mechanisms to obtain the seismotectonic stress IV-a new method free of choice among nodal planes[J].Geophysical Journal International,2002,150(3):588-609.
[22]MAURY J,CORNET F H,DORBATH L.A review of methods for determining stress fields from earthquakes focal mechanisms;Application to the Sierentz 1980 seismic crisis(Upper Rhine graben)[J].Bulletin De La Societe Geologique De France,2014,184(4-5):319-334.
[23]ABERS G A,GEPHART J W.Direct inversion of earthquake first motions for both the stress tensor and focal mechanisms and application to southern California[J].Journal of Geophysical Research Solid Earth,2001,106(B11):26523-26540.
[24]MICHAEL A J.Use of focal mechanisms to determine stress:a control study[J].Journal of Geophysical Research Solid Earth,1987,92(B1):357-368.
[25]VAVRY?UK V,BOUCHAALA F,FISCHER T.High-resolution fault image from accurate locations and focal mechanisms of the 2008swarm earthquakes in West Bohemia,Czech Republic[J].Tectonophysics,2013,590(2):189-195.
[26]VAVRY?UK V.Iterative joint inversion for stress and fault orientations from focal mechanisms[J].Geophysical Journal International,2014,199(1):69-77.
[27]HARDEBECK J L.Homogeneity of small-scale earthquake faulting,stress,and fault strength[J].Bulletin of the Seismological Society of America,2006,96(5):1675-1688.
[28]HARDEBECK J L,MICHAEL A J.Damped regional‐scale stress inversions:methodology and examples for southern California and the Coalinga aftershock sequence[J].Journal of Geophysical Research Solid Earth,2006,111(B11).
[29]MARTíNEZ-GARZóN P,KWIATEK G,ICKRATH M,et al.MSATSI:A matlab package for stress inversion combining solid classic methodology,a new simplified user‐handling,and a visualization tool[J].Seismological Research Letters,2014,85(4):896-904.
[30]LAY T,WALLACE T.Modern global seismology[M].London:Academic Press,1995.
[31]LUND B,SLUNGA R.Stress tensor inversion using detailed microearthquake information and stability constraints:Application to?lfus in southwest Iceland[J].Journal of Geophysical Research Solid Earth,1999,104(B7):14947-14964.
[32]BYERLEE J.Friction of rocks[J].Pure&Applied Geophysics,1978,116(4-5):615-626.
[33]MARTíNEZ-GARZóN P,VAVRY?UK V,KWIATEK G,et al.Sensitivity of stress inversion of focal mechanisms to pore pressure changes[J].Geophysical Research Letters,2016,43,8441-8450.
[34]CHEN X,WANG R,HUANG W,et al.Clustering-based stress inversion from focal mechanisms in microseismic monitoring of hydrofracturing[J].Geophysical Journal International,2018,215(3):1887-1899.