裂缝型储层五维地震有效压力参数预测

Estimation of effective stress parameters in fractured reservoirs based on 5D seismic data

裂缝型储层是目前油气勘探开发的重要领域之一,有效压力预测在此类油气藏的开发中发挥着重要作用。有效压力可由有效压力参数计算得到,具有丰富方位及偏移距等信息的五维地震数据为裂缝型储层有效压力参数预测提供了基础资料。基于各向异性Gassmann方程和线性滑动理论,结合Smith有效压力参数函数和临界孔隙度模型,推导出由有效压力参数、流体体积模量和裂缝法向及切向裂缝弱度参数直接表征的正交各向异性(OA)介质纵波反射系数弱各向异性近似方程。在此基础上,提出了五维地震时频域分步反演方法,即在分步反演策略的基础上,综合利用时间域地震反演的抗噪性和频率域反演的高分辨率优势,提高预测精度。基于五维地震频率和振幅信息及岩石、测井和地质资料,实现了裂缝型储层有效压力参数及流体参数和裂缝法向及切向裂缝弱度参数的直接预测。模型测试和实际数据应用结果表明,反演结果与井上实际数值吻合程度较高,为裂缝型储层五维地震有效压力预测提供了一种可靠的方法。

Fractured reservoirs occupy an important position in the production of oil and gas,and effective stress prediction plays an important role in this type of reservoirs.Effective stress can be calculated using effective pressure parameters.Five-dimensional(5D)seismic data with rich azimuth and offset information lays the foundation for effective pressure seismic prediction of fractured reservoirs.Our goal was to demonstrate a seismic inversion approach to utilize 5D seismic reflection data to predict the effective stress parameters in a fractured reservoir.Based on anisotropic Gassmann equation and linear sliding theory,combined with critical porosity model and Smith effective stress function,we developed an effective stress elastic theory equation for fractured reservoirs and derived a new seismic reflection equation characterized by effective stress,fluid parameters,fracture normal,and tangential weakness directly,avoiding the complicated nonlinear relationship between orthorhombic anisotropy and azimuthal seismic reflection data.In addition,we discussed the applicable conditions of the new equation.A 5D seismic time-frequency domain step-by-step inversion method was proposed by incorporating convolution model and Bayesian step-by-step inversion.The method comprehensively utilized the noise immunity of time domain seismic inversion and high-resolution characteristics of frequency domain inversion to improve prediction accuracy.With frequency and amplitude domain information and petrophysics,logging,and geological data,the effective pressure parameters,fluid parameters,normal and tangential fracture weakness parameters were effectively inverted.The synthetic examples containing a moderate noise demonstrated the feasibility of inversion method,and the real data illustrates the inversion stabilities of effective pressure and fracture parameters in fractured reservoir.