基于微电阻率成像测井的地层各向异性表征方法

Formation Anisotropy Characterization Method Based on Micro-Resistivity Imaging Logging

各向异性是地层固有的属性,在大斜度井、水平井中,可利用随钻电磁波测井曲线的差异信息进行各向异性系数计算;在井斜角较小的井中,各向异性对电阻率的影响较小,利用差异信息来计算地层各向异性系数的方法不再适用。为此,利用微电阻率成像测井的高分辨率特征和不同方位局部测量特性来划分图像灰度等级,并建立等效电阻率体积模型,进一步计算等效水平电阻率和垂直电阻率,从而获得储层的各向异性系数。与实钻井随钻电阻率计算的各向异性系数对比,一致性好,并且微电阻率成像计算的各向异性系数分辨率更高,能够很好地反映裂缝、孔洞、非均质井段的各向异性特征,为评价地层的各向异性提供新手段。

Anisotropy is an inherent property of the formation.In highly deviated wells and horizontal wells,the anisotropy coefficient can be calculated by using the difference information of electromagnetic wave logging curves while drilling.In slightly deviated wells,anisotropy has no obvious influence on resistivity.The traditional method of calculating formation anisotropy coefficients by using difference information is no longer applicable.In this paper,the high-resolution characteristics of micro-resistivity imaging logging and local measurement characteristics in different directions were used to divide the image gray scale,and the equivalent resistivity volume model was established to further calculate the equivalent horizontal resistivity and vertical resistivity,so as to obtain the anisotropy coefficient of the reservoir.The obtained anisotropy coefficient was compared with the anisotropy coefficient calculated with the resistivity while drilling of drilled wells,and the two were in good agreement.In addition,the resolution of the anisotropy coefficient calculated by the micro-resistivity imaging was higher,which could well reflect the anisotropy characteristics of fractures,holes,and heterogeneous well sections,and provide a new method for evaluating the formation anisotropy.