基于裂缝柔度和地应力模型的声电测井正、反演方法及应用

电阻率成像探测深度通常为几厘米，超声波成像数据也只能提供井壁的声幅或到时图像。因此，很难评估井壁张开裂缝在地层中的分布情况。声波测井一般应用弹性各向异性表征地应力场和裂缝特性等，通常岩石的固有各向异性、高角度地层层面、裂缝或不平衡应力挤压等都可以导致弹性波表观各向异性，因此往往难以判断各向异性的成因。前人针对单一方位二维裂缝模型进行了声波正演模拟，但不适用于井筒含多组任意方位裂缝介质的弹性波模拟。为此，首先拾取井壁成像测井中导致声波表观各向异性的三类结构特征(天然裂缝、层面缝(或薄层)和钻井应力诱导缝)信息，同时定量化层理结构信息(如倾向、方位等),并将裂缝分层、分组；然后从声波全波列中提取地层的快、慢横波慢度及各向异性方位；接着在岩石和裂缝信息井壁成像建模基础上，通过裂缝附加柔度模型、层面伪裂缝模型和非线性应力场弹性波动理论正演模拟岩石的声波属性；最后通过对比声波速度及各向异性方位等信息的模型预测结果与实测结果，利用最小误差拟合反演确定井壁图像表征的裂缝类型与各向异性的成因，并对比、分析了频散曲线特征。将所提方法应用于花岗岩潜山裂缝型气田生产测试井以验证方法合理性，实际模拟结果表明：...

Forward and inversion methods and application of acoustoelectric logging based on fracture compliance and crustal stress model

The depth of investigation of resistivity images is usually several centimeters,and the ultrasonic imaging data can only provide the sound amplitude or arrival images of the borehole wall. Therefore,it is difficult to eva-luate the distribution of fractures of the borehole wall in the formation. Acoustic logging generally uses elastic anisotropy to characterize the geological stress field and fracture characteristics. Generally,the intrinsic anisotropy of rocks,high-angle strata,fractures,or unbalanced stress compression can lead to the apparent anisotropy of elastic waves. Therefore,it is often difficult to determine the cause of anisotropy. Previous researchers have conducted acoustic forward modeling for a single-azimuth two-dimensional fracture model,but the model is not sui-table for elastic wave simulation of wellbore media with multiple sets of arbitrary azimuthal fractures. To this end,we first collect the information of three types of structural features (natural fractures,bedding fractures (or thin layers),and drilling stress-induced fractures) that lead to acoustic apparent anisotropy in imaging logging of the borehole wall,quantify bedding structure information (such as dip,azimuth,etc.),and separate and group fractures. Then,the slowness of fast and slow shear waves and the anisotropic orientation of the formation are extracted from the acoustic full wave train. Next,on the basis of borehole wall imaging and modeling of rick and fracture information,the acoustic properties of the rock are simulated through the additional fracture compliance model,pseudo layer fracture model,and elastic wave theory of nonlinear stress field. Finally,by comparing the predicted model results and measured results of acoustic velocity and anisotropic orientation,the minimum error fitting inversion is used to determine the fracture types and the causes of anisotropy for characterizing borehole wall images. In addition,the characteristics of dispersion curves are compared and analyzed. In order to verify the rationality of the proposed method,the method is applied to the production test well B in a fractured gas field on a granite buried hill. The actual simulation results show that the sensitivity of wave velocity to the cause of anisotropy is not as high as that of fast shear wave orientation,the fitting error of wave velocity is generally small and easy to converge,and the fast shear wave orientation can better distinguish and judge the anisotropic types of the formation and effectively indicate the fracture types. Well B formation is divided into upper and lower zones,and the lower zone (2950~3000 m) develops pseudo layer fractures,drilling-induced fractures,and a few effective fractures,and the productivity is low,while the upper zone (2900~2940 m) develops effective fractures,and the productivity is high.