井孔周围轴对称声电耦合波:声电效应测井数值模拟(Ⅱ)  

Coupled Acoustic and Electromagnetic Waves Around A Borehole Embedded in A Porous Formation: Numerical Simulation of Acoustically Induced Fields (Ⅱ)

作　　者：胡恒山[1] 王克协[1] 

机构地区：[1]吉林大学物理系

出　　处：《测井技术》2000年第1期3-13,共11页Well Logging Technology

基　　金：国家自然科学基金!(批准号 49674226)资助项目 ;中国石油天然气集团公司科研项目

摘　　要：胡恒山 ,王克协 .井孔周围轴对称声电耦合波 :声电效应测井数值模拟 ( ) .测井技术 ,2 0 0 0 ,2 4(1) :3～ 13在流体饱和的孔隙介质中存在声电耦合现象。作者已导出了井中点声源激发时井内、外声场和电磁场的表达式 [1 ] ,在此基础上给出数值算例 ,说明转换电磁场的基本特性 ,分析部分介质参数对声电转换波的影响。当位于井轴上的声源激发声波时 ,在流体饱和的孔隙地层中将不仅产生声波 ,而且产生与之耦合的电磁场。在井中 ,不仅可以接收到来自地层的声波 ,还可以接收到以电磁波速度传播、几乎同时达到不同源距的接收器的“电磁首波”和伴随声波的电磁场。井中接收到的转换电场的强弱 ,不仅取决于地层动电耦合系数 ,还取决于波的传播特性 ,特别是井孔的波导效应。文章考察了电声比与频率、接收位置、孔隙度、渗透率、井内外矿化度等的关系。当从接收声压曲线上可分辨出纵波、横波、斯通利波时 ,从转换电磁场也可以分辨出相应的波包。就电声比而言 ,纵波最大 ,斯通利波次之 ,横波最小。由于低频时动电耦合系数较大 ,更由于低频时斯通利波的激发强度显著增大 ,频率为 1k Hz时斯通利波转换电场的幅度约等于频率为 10 k Hz时幅度的 10 0倍 ,频率为 1k Hz时斯通利波的电声比约等于频率为 10 k Hz时的 5倍。When an acoustic point source on the borehole axis emits an acoustic wave,an electric field as well as an acoustic field is generated in the porous formation around the borehole due to electrokinetic effect.Two kinds of electric fields can be received on the borehole axis.The propagating electromagnetic wave arrives at different receivers almost at the same time,and appears as the first wave packet in each full electric field waveform.Another kind of electric fields accompanies the acoustic wave,and consists of the same component waves as that of the acoustic waveforms,so they are electric fields induced by the acoustic wave in the proximity of the borehole wall near the receiver. A study of the ratio of the magnitude of electric field strength Ez to the magnitude of pressure P,or REP,shows that the compressional wave has the largest REP value,Stoneley wave the next,while the value for the shear wave is the smallest. The electric field in the borehole is not only affected by the coupling coefficient L ,butalso by the wave propagation properties,especially by the waveguide effectof the borehole.The peak value of Ezat1k Hz is about10 0 times as large as thatat10 k Hz,while REP is about5times.Off the borehole axis,there are radial electric component Erand circumferential magnetic component Hθas well as axialelectric component Ez.WhenΛ2 =8K0 α∞ /  is assumed,REP increases rapidly with porosity, decreases with tortuosity,and changes little with permeability.The electric field strength decreases with the borehole fluid salinity and the formation water salinity.

关 键 词：井眼 声电耦合波 声电效应 数值模拟 测井 

分 类 号：P631.819[天文地球—地质矿产勘探]