高精度方位各向异性反演在顺北8号带裂缝检测中的应用

目前, 基于AVAZ反演方法的方位各向异性反演大都采用Rüger两项式, 基于椭圆拟合方法的方位各向异性反演大多使用分扇区叠加振幅等属性亦或各向同性叠前弹性反演成果数据, 这两类方法都存在局限性。而Rüger三项式方程中B项(B^iso+B^anicos²φ)包含方位各向异性强度项B^ani, 因此, 将其用于方位各向异性椭圆拟合更合理。基于全方位角度域(FAA)叠前偏移道集数据, 首先, 将FAA域道集划分为5个方位扇区, 对每一个方位扇区求解Rüger三项式方程B项属性(B1~B5), 利用5个扇区求解的B项属性成果数据开展椭圆拟合处理以确定椭圆长轴方向、长轴与短轴比值, 进而得到裂缝方向和裂缝密度。与直接求取方位各向异性强度B^ani的AVAZ反演方法相比, 该方法显著减少了计算量。研究区目的层鹰山组上段裂缝预测成果被4口后钻井所证实。

Most of azimuthal anisotropy inversion methods based on AVAZ use the Rüger two-term equation, and most of ellipse fitting methods use the attributes such as poststack seismic amplitude/isotropic prestack inversion results.Both methods have certain limitations.The B term (B^iso+B^anicos²φ) in the Rüger three-term equation contains azimuthal anisotropy intensity (B^ani), and can therefore be used for the ellipse fitting of azimuthal anisotropy.Seismic gathers in the full azimuth angle (FAA) domain are divided into 5 azimuth sectors, and B (B1—B5) attributes are obtained by using the prestack elastic inversion based on the Rüger three-term equation for each azimuth sector.The ellipse fitting is carried out by using five B attributes to determine the major axis direction of the ellipse and major-minor axis ratio, based on which fracture orientation and fracture density could be obtained.Compared with the AVAZ inversion to yield B^ani directly, this method reduces the calculation amount.The prediction results of fractures in the upper Yingshan Formation in the study area were confirmed by four wells drilled later.