断层岩气体渗透率及Klinkenberg效应  

GAS PERMEABILITY AND KLINKENBERG EFFECT OF FAULT ROCKS

作　　者：段庆宝[1] 杨晓松[1] 陈建业[1] 

机构地区：[1]中国地震局地质研究所地震动力学国家重点实验室,100029

出　　处：《地震地质》2014年第4期964-975,共12页Seismology and Geology

基　　金：地震动力学国家重点实验室自主研究课题(LED2010A03);国家科技支撑计划“汶川地震断裂带科学钻探”(WFSD09)课题;中国地震局地震行业科研专项(200808012)共同资助

摘　　要：在围压2～40MPa变化范围内,以恒流法多次变化上游压力测量了以断层岩为主的样品的气体（N2）渗透率,将实验结果进行了Klinkenberg效应校正.对实验数据的拟合分析表明,滑脱因子b值与绝对渗透率kl存在b=λkl-d形式的幂律关系,断层岩符合b=0.004 6kl-0.4766的变化关系.与沉积岩相比,断层岩的气体滑脱效应更强,采用气体测量渗透率时,其滑脱效应不能忽略.断层岩气体渗透率和绝对渗透率与测量所用的孔隙压力间的关系为kg/kl=1＋（0.0092kl-0.476）/（Pu＋Pdl）.结果表明样品渗透率越低,滑脱效应越强,提高孔隙压力,滑脱效应逐渐减小;对于高渗（10-15m2～10-18m2）的样品,高孔隙压力下（4MPa以上）的气体渗透率与绝对渗透率基本一致,对于超低渗（10-22m2～ 10-20m2）的样品,即使提高孔隙压力亦很难避免滑脱效应.在40MPa有效压力下断层泥样品的绝对渗透率为4.54× 10-199m2～2.43×10-17m2,角砾岩的绝对渗透率较断层泥高出1～2个数量级,为2.25×10-17m2 ～7.94×10-16m2,表明汶川地震断层带具有核部低、破碎带高的渗透结构,断层带核部具备热压作用发生所要求的低渗条件.The nitrogen gas permeabilities of fault rocks were measured under confining pressure ranging from 4 to 40MPa.At each confining pressure step,we changed the upstream pressure several times and measured the permeability.The measured gas results were then corrected by Klinkenberg＇s equation.Relationship between slippage factor b and intrinsic permeability kl can be described by a power law correlation expressed as b =0.004 6kl-0476 Compared with sedimentary rocks,the gas slippage effect of fault rocks is stronger,which should not be ignored when using gas as a medium for permeability experiments.The relationship between gas permeability,intrinsic permeability and pore pressure is expressed as kg/kl =1 ＋ （0.009 2kl-0.476）/（Pu ＋Pd）.Results show that the lower the permeability of rocks is,the stronger the Klinkenberg effect is.Additionally,the slippage effect decreases as pore pressure increases.For the relative permeable （10 15m2～ 10-18m2） samples,their gas permeabilities are almost identical to intrinsic permeabilities under relative higher pore pressure condition（higher than 4MPa）.However,for the ultra-low permeable （10-22m2 ～ 10-20m2） samples,it＇s difficult to avoid the slippage effect although under high pore pressure condition.The intrinsic permeability of fault gouge samples ranges between 4.54×10 19m2 and 2.43×10-17m2,and those of the breccia samples are higher by 1 ～ 2 orders of magnitude which range between 2.25×10-17m2 and 7.94× 10-16 m2.These results demonstrate that the permeability structure of Wenchuan earthquake fault zone is characterized by a low permeable fault core and relative higher permeable damaged zone.The fault zone has the characteristics of low permeability for thermal pressurization.

关 键 词：断层岩 Klinkenberg效应 气体渗透率 绝对渗透率 汶川地震 

分 类 号：P313[天文地球—固体地球物理学]