Numerical simulation of methane plumes based on effective medium theory

Abstract

Because they offer direct evidence of seafloor seeps and may indicate the presence of gas hydrates, methane plumes have attracted increasing research attention. Here, we attempt to understand the seismic response of methane plumes through simulation and analysing the characteristics of the seismic scattering wave field caused by methane plumes. Through forward modelling, stochastic medium theory was used to set the random distribution of bubbles, and effective medium theory is applied to create a bubble velocity model. We then used the finite-difference method to calculate the common shot gather. To achieve true amplitude migration of methane plumes, reverse-time migration method is introduced to perform it. To study the differences in seismic response to variable methane gas content and to establish the relationship between various attribute parameters and gas content, we create five models with gradually increasing gas contents. After imaging these five models, amplitude class attributes, frequency class attributes and phase class attributes are computed from the migration section, and a theoretical model between attributes and gas content is built. Through quantitative analysis of the change of attributes as a function of gas content, we find that amplitude class attributes vary more linearly with methane gas content than do the other two attribute classes. Therefore, we conclude that amplitude class attributes have most potential application for inversion of gas content in further exploration of bubble plumes.