致密砂岩电学各向异性测井评价与声电各向异性一致性分析

Anisotropy interpretation and the coherence research between resistivity and acoustic anisotropy in tight sands

针对致密砂岩各向异性反演问题,提出了从阵列侧向测井和微电阻率扫描成像测井提取电阻率各向异性的新方法,并对电学和声学各向异性的一致性开展研究。阵列侧向测井包含电阻率各向异性信息,但数模表明钻井液侵入是影响其响应特征的主要因素,其次分别是相对倾角θ和电各向异性系数λ。提出在已知θ前提下分步确定侵入半径ri、冲洗带电阻率Rxo、原状地层电阻率Rt初始值的分级反演以确定ri、Rxo、Rt和λ的方法。微电阻率扫描成像测井是对不同方位上电阻率分布特征的刻画,可以通过对比不同方位上电阻率的大小及水平、垂直方向的电阻率差异来提取电各向异性信息。致密砂岩矿物颗粒的定向排列和裂隙发育等因素是决定其各向异性的主要内在因素,由此产生了电各向异性及声各向异性,二者的强弱具有一致性。对多口井的测井资料分析表明,从阵列侧向、微电阻率扫描成像和交叉偶极声波测井分别提取的电、声各向异性强弱程度相互匹配,验证了反演方法的准确性及刻画不同岩石物理各向异性变化趋势的一致性。该研究为致密砂岩的各向异性评价提供了更多的技术手段。

Aiming at the problem of anisotropy inversion of tight sands,a new method for extracting resistivity anisotropy from array laterolog and micro-resistivity scanning imaging logging is proposed,and also the consistency of electric and acoustic anisotropy is discussed.Array laterolog includes resistivity anisotropy information,but numerical simulation shows that drilling fluid invasion has the greatest influence on the response,followed by the relative dip angleθand electrical anisotropy coefficientλ.A new inversion method to determine ri,Rxo,Rt andλis developed with the givenθand initial values of invasion radius ri,flushed zone resistivity Rxo,in-situ formation resistivity Rt.Micro-resistivity image can describe the resistivity distribution information in different directions,and the resistivity from micro-resistivity log in different azimuths,lateral and vertical directions can be compared to extract electric anisotropy information.Directional arrangement of mineral particles in tight sands and fracture development are the intrinsic causes of anisotropy,which in turn brings about anisotropy in resistivity and acoustic velocity,so the resistivity anisotropy and acoustic velocity anisotropy are consistent in magnitude.Analysis of log data of several wells show that the electrical anisotropy and acoustic anisotropy extracted from array laterolog,micro-resistivity imaging and cross-dipole acoustic logs are consistent in magnitude,proving the inversion method is accurate and the anisotropies of different formation physical parameters caused by the intrinsic structure of tight sand reservoir are consistent.This research provides a new idea for evaluating anisotropy of tight sands.