差应变法地应力测量——以汶川地震断裂带科学钻探WFSD-1钻孔为例
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摘要
岩心差应变分析法是汶川地震断层科学钻探(WFSD)项目地应力测量的主要手段之一,该技术通过高压容器对取之于钻孔不同深度的实验样品施加围压,观察先前由于失去地层应力而膨胀产生的裂纹重新闭合,并通过裂纹闭合过程差应变曲线分析,确定主应力大小和方向。WFSD-1孔12个岩心样品的DSA测试结果表明:断层上下盘的应力状态有明显差异,区域地应力不仅随深度增加,还与地质结构和岩石的物理性质等因素有关。
Core differential strain analysis method is one of the primary means of in-situ stress measurement in WFSD.Through the pressure vessel,the experimental samples taken from different depths are pressured.And it is observed that the produced cracks are re-closed due to the previously loss stratum stress.The technology is that the size and direction of principal stress are determined by differential stain analysis in the process of crack closure.This article describes the principle and data processing method of in-situ stress measurement by differential strain analysis(DSA) in WFSD-1.And the stress profile is established with depth in the hole.Test results show that the stress states of the upper and lower plate in the Yingxiu-Beichuan fault are significant differences.Regional in-situ stress not only increases with depth,but also concerns with the geological structure,rock physical properties and other factors.
Core differential strain analysis method is one of the primary means of in-situ stress measurement in WFSD.Through the pressure vessel,the experimental samples taken from different depths are pressured.And it is observed that the produced cracks are re-closed due to the previously loss stratum stress.The technology is that the size and direction of principal stress are determined by differential stain analysis in the process of crack closure.This article describes the principle and data processing method of in-situ stress measurement by differential strain analysis(DSA) in WFSD-1.And the stress profile is established with depth in the hole.Test results show that the stress states of the upper and lower plate in the Yingxiu-Beichuan fault are significant differences.Regional in-situ stress not only increases with depth,but also concerns with the geological structure,rock physical properties and other factors.
引文
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[2]Hardy H R Jr,Zhang D,Zdlanko J C.Recent studies of the Kaiser effect in geologic materials[C]//Drnevich V P,GrayR E.Proceedings of the 4th Conference on Acoustic Emission:Microseismic Activity in Geologic Structures and Materials.American Society for Testing and Materials,1989:27～55.
[3]Yoshikawa S,Mogi K.Experimental studies on the Kaiser effect of stress history on acoustic emission activity:A possibilityfor estimation of rock stress[J].Journal of Acoustic Emission,1990,8(4):113～123.
[4]Michadl J F.Stress determination in rock using the Kaiser Effect[M].Washington:Bureau of Mines,United StatesDepartment of the Interior,1990.
[5]石林,张旭东,金衍,等.深层地应力测量新方法[J].岩石力学与工程学报,2004,23(14):2355～2358.SHI Lin,ZHANG Xu-dong,JIN Yan,et al.New method for measurement of in-situ stresses at great depth[J].ChineseJournal of Rock Mechanics and Engineering,2004,23(14):2355～2358.
[6]邓金根,黄荣撙,田效山.油田深部地层地应力测定的新方法[J].石油大学学报:自然科学版,1997,21(1):32～35.DENG Jin-gen,HUANG Rong-zun,TIAN Xiao-shan.A new method for measuring in-situ stresses in deep formation[J].Journal of Petroleum University:Natural Science Edition,1997,21(1):32～35.
[7]张广清,金衍,陈勉.围压下利用凯泽效应测量地应力[J].岩石力学与工程学报,2002,21(3):360～363.ZHANG Guang-qing,JIN Yan,CHEN Mian.Measurement of in-situ stresses by Kaiser Effect under confining pressures[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(3):360～363.
[8]刘建中,张金珠,张雪.油田应力测量[M].北京:地震出版社,1993.LIU Jian-zhong,ZHANG Jin-zhu,ZHANG Xue.In-situ stress measurement in oilfield[M].Beijing:SeismologicalPublishing House,1993.
[9]White J E.The hula log:A proposed acoustic tool[C]//Proceedings of the 8th Annual Logging Symposium.Houston:Society of Professional Well Log Analysts,1967:125.
[10]Sinha B K,Kostek S.Stress-induced azimuthal anisotropy in borehole flexural waves[J].Geophysics,1996,61(6):1899～1907.
[11]Sinha BK,Plona T J.Wave propagation in rocks with elasto-plastic deformations[J].Geophysics,2001,66(3):772～785.
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