双相不混溶流体饱和裂缝—孔隙岩石依赖频率的地震响应数值分析

裂缝—孔隙岩石中流体类型及其分布特征是影响弹性参数的重要因素，实际储层中流体大多不是单一流体，且在数值模拟过程中很少考虑流体间饱和状态的影响。为此，基于Chapman模型，针对饱含双相不混溶流体的裂缝—孔隙岩石，研讨了饱和度和毛细压力参数变化对砂岩储层频散衰减和地震响应的影响。数值分析结果表明：随着油气饱和度的增加，特征频率（不同于于单一流体介质情形）呈先减后增趋势，且在中间频段的变化最明显，地震响应存在时间延迟和波形畸变现象；当双相流体中存在气体时，频散衰减和地震响应对饱和度的变化更敏感；随着衡量流体间毛细压力的参数q值的增加，双相流体间由“斑块饱和”趋向“均匀饱和”状态，特征频率向着“高频低饱”方向移动。该数值模拟结果为储层流体识别提供了有效依据。

Numerical analysis of frequency-dependent seismic responses from fractured-porous rock saturated with two-phase immiscible fluids

Types and distribution of fluids in fractured-porous rock are important factors affecting the elastic parameters of the rock. In most cases,fluids in actual reservoirs are not single components,and the influences of their saturation states are rarely considered in numerical simulation. Based on the Chapman model,this paper discusses how saturation and capillary pressure affect the dispersion attenuation and seismic response of fractured-porous sandstone reservoirs saturated with two-phase immiscible fluids. The numerical results show that with the increase of oil or gas saturation,the characteristic frequency is different from that of the medium saturated with a single fluid,and it decreases first and then increases. Especially in the intermediate frequency band,such variation is the most outstanding,and the seismic responses are suffered from travel-time delay and distortion of the seismic waveform. When there is gas in the two-phase fluids,the dispersion,attenuation and seismic response are more sensitive to changes in saturation. As the parameter q measuring the capillary pressure between fluids increases,the state of two-phase fluids changes from "patchy saturation" to "uniform saturation",and the characteristic frequency moves toward the direction with "high frequency and low saturation". The results of numerical simulation provide an theoretical basis for reservoir fluid identification.