Numerical analysis of frequency-dependent seismic responses from fractured-porous rock saturated with two-phase immiscible fluids
LIU Yunfei1, CHEN Xuehua1,2, LUO Xin2, ZHANG Jie2, NI Hui2
1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China; 2. Key Laboratory of Earth Exploration and Information Technology, Ministry of Education, Chengdu University of Technology, Chengdu, Sichuan 610059, China
Abstract：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.
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