裂隙发育对低孔低渗含气地层声传播特征的影响
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摘要
在含孔、裂隙介质弹性波动统一理论的基础上,研究裂隙发育对低孔含气地层弹性波速度的影响。针对岩心测量的纵横波速度,探讨估算岩心裂隙密度的方法。结果表明:随着裂隙密度的增加,弹性波的速度降低明显;地震、测井和实验室岩心测量频率下的波速变化明显,显示出了较强的频散特性;在孔隙度为1.1%时,裂隙发育岩石在饱含气时的纵波速度与饱含水相比明显降低,裂隙密度为0.15和0.35时,500 kHz下的纵波速度分别下降了7.6%和27%;井孔模式波的衰减与速度相比对含气的敏感性更高,这为利用声波测井方法识别孔隙流体性质提供了思路。
Based on the unified elastic wave theory which describes the effect of both pores and cracks,the influence of crack strength on the acoustic velocity of cracked low-porous gas reservoir was studied. According to the compressional and shear wave velocity obtained by measuring the core samples,the estimation method of formation crack density was investigated. The results of numerical calculation show that the elastic wave velocities decrease with the crack density increasing,and the velocity dispersions become obvious. When the porosity is 1.1%,the compressional velocity of gas-saturated rock is lower than that of water-saturated rock. When the crack density is 0.15 and 0.35,the compressional velocity for 500 kHz decreases by 7.6% and 27% respectively. The attenuation of borehole mode waves is more sensitive to gas saturation than the velocity,which provides a new way of identifying pore-fluid nature by acoustic logging technology.
Based on the unified elastic wave theory which describes the effect of both pores and cracks,the influence of crack strength on the acoustic velocity of cracked low-porous gas reservoir was studied. According to the compressional and shear wave velocity obtained by measuring the core samples,the estimation method of formation crack density was investigated. The results of numerical calculation show that the elastic wave velocities decrease with the crack density increasing,and the velocity dispersions become obvious. When the porosity is 1.1%,the compressional velocity of gas-saturated rock is lower than that of water-saturated rock. When the crack density is 0.15 and 0.35,the compressional velocity for 500 kHz decreases by 7.6% and 27% respectively. The attenuation of borehole mode waves is more sensitive to gas saturation than the velocity,which provides a new way of identifying pore-fluid nature by acoustic logging technology.
引文
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[2]DVORKIN J,NUR A.Dynamic poroelasticity:a unified model with the squirt and the Biot Mechanisms[J].Geophysics,1993,58(4):524-533.
[3]ESHELBY J D.The determination of the elastic field of an ellipsoida inclusion,and related problems[J].Pro Roy Soc of London,1957,A241(1226):376-396.
[4]O'Connell R J,BUDIANSKY B.Seismic velocities in dry and saturated cracked solids[J].J Geophys Res,1974,79(1):4626-4627.
[5]杨文采,金振民,于常青.结晶岩中天然气异常的地震响应[J].中国科学D辑:地球科学,2008,38(9):1057-1067.YANG Wen-cai,JIN Zhen-min,YU Chang-qing.Seismic response of gas abnormality in crystalline rock[J].Sci China Earth Sci,2008,38(9):1057-1067.
[6]陈雪莲,唐晓明.孔、裂隙并存地层中的声波测井理论及多极子声场特征[J].地球物理学报,2012,55(6):2129-2140.CHEN Xue-lian,TANG Xiao-ming.Numerical study on the characteristics of acoustic logging response in the fluid-filled borehole embedded in crack-porous medium[J].Acta Geophys Sinica,2012,55(6):2129-2140.
[7]XU Shi-yu,MICHAEL A P.Modeling elastic properties in carbonate rocks[J].The Leading Edge,2009(1):66-74.
[8]张海澜,王秀明,张碧星.井孔中的声场和波[M].北京:科学出版社,2004.
[9]唐晓明,郑传汉.定量测井声学[M].赵晓敏,译.北京:石油工业出版社,2004:20-39.
[10]杨少春,王惠娟,罗海宁,等.胜利油区碎屑岩纳米尺度孔隙结构特征[J].中国石油大学学报:自然科学版,2012,36(1):8-12.YANG Shao-chun,WANG Hui-juan,LUO Hai-ning,et al.Nanoscale pore structure characteristics of clastic rock in Shengli Oilfield[J].Journal of China University of Petroleum(Edition of Natural Science),2012,36(1):8-12.
[11]TANG Xiao-ming,CHEN Xue-lian,XU Xiao-kai.A cracked porous medium elastic wave theory and its application to interpreting acoustic data from tight formations[J].Geophysics,2012,77(6):D245-D252.
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