为了在地震资料和裂缝储层特征之间建立联系,对裂缝储层采用了等效介质模型.而传统的等效介质模型未充分考虑非完全弹性介质理论和基于频变各向异性理论的双相或多相流体假设,也不能对实际裂缝储层中的地震波频散和衰减现象提供准确合理的解释,并且储层参数的反演研究对裂缝储层的定性预测和定量描述举足轻重.为此,本文首先根据所提出的黏弹性Chapman-Kelvin动态等效介质模型,该模型考虑了耦合的双相流体假设、黏弹性理论、喷射流以及斑块效应,并在此基础上分析了裂缝储层参数(主要为裂缝密度、裂缝长度、孔隙度和含水饱和度)对地震波频变特征的影响.然后基于黏弹性Chapman-Kelvin模型与Schoenberg和Protazio概括的Zoeppritz方程所计算出的频变反射系数,分析了反射PP波和PS波的频变AVAZ(Amplitude Versus Angle and Azimuth)特性和PP波频变反射系数与裂缝储层参数的关系.同时考虑到发生地震频散时,反射系数和频率产生关系,构建了在角度、方位和时间域内的新型正演方程.最后,基于PP波频变反射系数对裂缝密度、裂缝长度、孔隙度和含水饱和度的变化有较好的敏感性特点,进行了两种反演方法研究:其一是基于贝叶斯理论直接反演方法,其中以对数绝对范数作为似然函数和高斯分布,即L2范数度量作为先验约束;其二是基于频变反射系数的MCMC(Markov Chain Monte Carlo)随机反演方法.通过频变AVAZ进行裂缝储层参数的反演研究,结果表明,MCMC随机反演方法在缺失先验的储层参数信息时,反演结果的不确定性较强.当存在有效且足够的先验信息时,反演结果的可靠性进一步提升.而基于贝叶斯理论直接反演方法,则显示出基于频变AVAZ来区别大尺度裂缝和微尺度裂隙的潜力.
Inversion study of frequency-dependent AV AZ fractured reservoirs based on the viscoelastic Chapman-Kelvin model
To establish a connection between seismic data and fracture reservoir characteristics,an equivalent medium model was used for fractured reservoir.However,conventional equivalent medium models do not fully consider the incompletely elastic medium theory and the assumption of two-phase or multi-phase fluids based on the frequency-dependent anisotropy theory.As a result,they cannot provide accurate and reasonable explanations for seismic wave dispersion and attenuation phenomena in real fracture reservoirs.Moreover,the inversion study of reservoir parameters is crucial for qualitative prediction and quantitative description of fracture reservoirs.Therefore,this paper first analyses the influence of fractured reservoir parameters(mainly fracture density,fracture length,porosity and water saturation)on the frequency-dependent characteristics of seismic waves based on the proposed dynamic equivalent medium model based on the viscoelastic Chapman-Kelvin,which takes into account coupled the two-phase fluid assumption,viscoelastic theory,squirt flow,and patch effects.Then,the frequency-dependent reflection coefficients of reflected PP and PS waves,as well as the AVAZ(Amplitude Versus Angle and Azimuth)characteristics of the reflected PP and PS waves,and the relationship between PP wave frequency-dependent reflection coefficients and fracture reservoir parameters are analyzed based on the viscoelastic Chapman-Kelvin model and the Zoeppritz equation summarized by Schoenberg and Protazio.Considering the relationship between reflection coefficients and frequency during seismic dispersion,a new forward equation is constructed in the angle,azimuth,and time domains.Finally,two inversion methods are studied based on the sensitivity characteristics of fracture density,fracture length,porosity,and water saturation to PP wave frequency-dependent reflection coefficients.One is a direct inversion method based on Bayesian theory,which the logarithmic absolute norm is used as the likelihood function and the Gaussian distribution(L2 norm)is used as the prior constraint.The other is a Markov Chain Monte Carlo(MCMC)random inversion method based on frequency-dependent reflection coefficients.Through the inversion study of fracture reservoir parameters using frequency-dependent AVAZ,the results show that the MCMC random inversion method has strong uncertainty in inversion results when there is a lack of prior information on reservoir parameters.The reliability of inversion results is further improved when there is effective and sufficient prior information.The direct inversion method based on Bayesian theory shows potential for distinguishing large-scale fractures from micro-scale cracks based on frequency-dependent AVAZ.
万方数据
维普
