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

The types of fluids and their distribution characteristics in fractured-porous rocks are important factors affecting elastic parameters. In actual reservoirs, most fluids are not single fluids, and the influence of the saturation state between fluids is rarely considered in the numerical simulation process. For this reason, based on the Chapman model, for fractured-porous rocks saturated with two-phase immiscible fluids, the influence of changes in saturation and capillary pressure parameters on the dispersion attenuation and seismic response of sandstone reservoirs is discussed. The results of numerical analysis show that: with the increase of oil and gas saturation, the characteristic frequency (different from the case of a single fluid medium) first decreases and then increases, and the change is most obvious in the intermediate frequency band, and there are time delay and waveform distortion phenomena in the seismic response; when there is gas in the two-phase fluid, the dispersion attenuation and seismic response are more sensitive to changes in saturation; with the increase of the parameter q value that measures the capillary pressure between fluids, the two-phase fluids tend from "patch saturation" to "uniform saturation" state, and the characteristic frequency moves in the direction of "high frequency and low saturation". The results of this numerical simulation provide an effective basis for reservoir fluid identification.

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。