基于衰减各向异性理论的叠前裂缝预测技术及应用

Prestack fracture prediction based on attenuation anisotropy

1.中国石油化工股份有限公司勘探分公司,四川成都610041;
2.成都理工大学,四川成都610059

1. Sinopec Exploration Company,Chengdu 610041,China;
2. Chengdu University of Technology,Chengdu 610059,China

天然裂缝对致密气和页岩气气藏的富集和高效开发有重要的支撑作用,地震裂缝预测则是部署钻井前的关键环节之一。然而,受地表复杂的采集条件、多变的处理流程和目的层岩性突变等因素影响,地震波在振幅和速度上可能表现出“伪方位各向异性”,导致传统的OVT域叠前各向异性裂缝预测的精度下降。在传统方位各向异性理论的基础上,从储层和裂缝对地震波的衰减出发,基于等效介质理论推导了衰减各向异性反射系数近似公式和方位衰减弹性阻抗(QVAZ)方程;结合贝叶斯和组稀疏反演方法建立目标函数,经过求解弹性矩阵获得相应流体项和裂缝弱度等参数,并实现三维裂缝密度高精度预测。利用单井数据进行试算,明确了衰减各向异性对裂缝的敏感性;结合实际钻井和OVT宽方位地震数据,反演分方位衰减弹性阻抗得到裂缝密度等关键参数,这些参数与钻井FMI成像测井解释的结果吻合度较高,证实了方法的可靠性,一定程度上避免了“伪方位各向异性”的现象。

Natural fractures are crucial to tight gas and shale gas production.Therefore,seismic prediction of fractures is a key step in drilling deployment.Due to complex surface conditions,improper processing flow,and the abrupt change of subsurface lithologies,seismic waves may exhibit “pseudo-anisotropy” of amplitude and velocity,resulting in inaccurate prestack fracture prediction based on the anisotropic signatures in the OVT domain.In view of the attenuation of seismic waves by reservoirs and fractures,we derive the approximation formula of reflection coefficient for attenuation anisotropic media and the QVAZ equation for azimuthal attenuation elastic impedance from the equivalent medium theory.The Bayesian method and sparse group inversion are combined to establish the target function,and corresponding parameters of fluids and fracture weakness are obtained by solving the elasticity matrix for 3D high-precision prediction of fracture density.A test using well data confirms the sensitivity of proposed attenuation anisotropy to fractures.We also use well and OVT seismic data for the azimuthal attenuation elastic impedance inversion to obtain key parameters such as fracture density,which is in good agreement with FMI interpretation results.This verifies the reliability of the method and its ability to avoid “pseudo-anisotropy” to a certain extent.

10.12431/issn.1000-1441.2025.64.01.013