含气页岩储层脆性及裂缝参数方位地震反演方法研究与应用

Azimuthal variation of seismic amplitude for brittleness and fracture parameter of gas-bearing shale reservoir

工程甜点评价是页岩等非常规油气储层勘探开发的重要环节,其中脆性和裂缝密度预测是工程甜点评价中非常关键的要素.宽方位地震反演技术是研究裂缝储层的重要手段.然而针对脆性和裂缝密度预测的储层模型参数化,正、反问题的构建与求解依旧存在挑战.所以本文将聚焦各向同性背景中发育一组垂直定向裂缝的岩石,基于Schoenberg线性滑动理论和Hudson模型,推导杨氏模量、泊松比及裂缝密度参数直接表征的岩石刚度矩阵,然后在界面弱对比、弱各向异性假设下,求解裂缝岩石刚度矩阵的差分形式,并将所得的差分表达写为杨氏模量、泊松比和裂缝密度扰动量之和的形式,以直观地展示不同参数扰动的贡献度.在此基础上,采用散射函数与地震反射系数之间的关系,推导裂缝储层纵波反射特征方程.并提出了方位各向异性弹性阻抗方程以提高工程甜点描述精度.最后,发展了一套模型低频信息正则化约束的Bayesian反演方法.将该方法应用到裂缝型工区,应用结果表明本文所提出的方法是合理的.

Engineering dessert evaluation is an important role in the exploration and development of unconventional oil and gas reservoirs such as shale.Brittleness and fracture parameter prediction are very key elements in engineering dessert evaluation.AVAZ(seismic amplitude variation with the angle and azimuth)inversion technology is an important means to study fractured reservoir.However,for brittleness and fracture parameter prediction,there are still challenges in the model parameterization,construction and solution of forward and inverse problems.Therefore,this paper will focus on the rocks with a group of vertically oriented fractures in the isotropic background.Based on the Schoenberg linear sliding theory and Hudson model,the stiffness matrix directly characterized by Young's modulus,Poisson's ratio and fracture density parameters is derived.Then,we deduce the differential form of the stiffness matrix and write it in the form of the summation of perturbations of Young's modulus,Poisson's ratio and fracture density,which visually demonstrates contributions of different parameters perturbations.On these bases,using the relationship between perturbations in stiffness coefficients and seismic reflection coefficient,the P-P wave reflection equation of fractured reservoir is deduced under the assumptions of weak interface contrast and weak anisotropy.Besides,for the more stable and feasible inversion result of the fracture density,we give a new definition of the quasi fracture density andparameterize the P-P wave reflection equation in terms of the Young's modulus,Poisson's ratio,mass density and quasi fracture density.Furthermore,the azimuthal anisotropic elastic impedance equation is proposed to improve the prediction accuracy of engineering dessert.Finally,within the Bayesian inversion framework,a seismic inversion method with regularization constraints of model low-frequency information is developed for the Young's modulus,Poisson's ratio and quasi fracture density.The weighted summation of the Young's modulus and Poisson's ratio is used to evaluate the reservoirs brittleness and the quasi fracture density is employed to characterize fracture distribution.The application case shows that the method proposed in this paper is reasonable.