利用频变地震反射系数识别含气储层

Frequency-dependent seismic Reflection Coefficient for Discriminating Gas Reservoirs

地震波在孔隙介质中传播的渐进方程可用于在地震频带内计算法向入射反射系数,这个频变的反射系数可用一个无量纲的参数ε来表示,ε可表示为储层流动性参数(即粘滞性的倒数)、流体密度和信号频率的乘积。利用该表达式,对中国新场气田的实际数据进行了计算,新场气田的储层大多为超致密的砂岩并且渗透率很低。在计算结果上观测到了砂岩储层内过渡区的气水界面上反射系数在地震频带内随频率变化的现象。利用该研究结果指导了地震反演并提取了相应的地震属性,这些属性被首先用于进行的流体(气或水)辨别,最后,在此基础上进行了含气和含水储层的识别。

The asymptotic equation of wave propagation in fluid-saturated porous media is available for calculating the norma/ reflection coefficient within seismic frequency band. This frequency-dependent reflection coefficient is expressed in terms of a dimensionless parameter, which is the product of the reservoir fluid mobility （i.e. inverse viscosity）, fluid density, and the frequency of the signal. In this paper, we apply this expression to Xinchang gas-field, China, where reservoirs are super in tight sands with very low permeability. We demonstrate that the variation in reflection coefficient at gas/water contacts is as a transition zone within a sand formation observable within seismic frequency band. Then we conduct seismic inversion to generate attributes which first indicate the existence of fluid （either gas or water）, and then discriminate a gas reservoir from a water reservoir.