Characterizing fluid contacts by joint inversion of seismic P-wave impedance and velocity

Abstract

In the past, seismic exploration technique was mainly used for gathering information about subsurface rock structures and fluids by analyzing the travel time, reflection amplitude, and phase variations. However, nowadays, many additional seismic attributes have been introduced by the seismic interpreters, which aid in the visualization of subsurface geological structures, facies, and lithologies. This research aims to identify the pore fluids in the reservoir using post-stacked seismic data without requiring well log data. Gassmann’s equation, a well-known equation for fluid substitution, has been used for fluid substitution in this research. To test the proposed technique, a three-layer geological anticline model has been used. The third layer of the model represents a reservoir which is saturated with water, except its top part which is fully saturated with petroleum. Fluid identification is achieved by using fluid density, velocity changes, and acoustic impedance (AI). P-wave velocity and AI are measured from post-stacked seismic data and its inversion, from which the saturated rock density and compressional modulus (M) are calculated. Using this information, saturated rock density and compressional modulus are inverted for fluid velocity and density, respectively, to identify the pore fluid.