Estimation of AVO response of methane-hydrate bearing layer

摘要

Three phases model of Leclaire et al. is established as three phases extended Biot model. It is confirmed by experimental studies using glass beads, kerosene and ice, which is simulated a methane hydrate. The emulsification of kerosene into water at room temperature turns to ice and liquid kerosene at -20 degree Celsius. Thus, the change of kerosene contents in water brings wide range of ice contents in pore spaces generated by glass beads packing. Elastic velocity measurements of the three phases, i.e. glass beads, kerosene and ice, at ultra sonic frequency are carried out in range of 72-95 percent of ice saturation in pore space. Using the three phases extended Biot model, the velocities at ultra-sonic are converted into a reflection seismic frequency of less than 100 Hz. We study amplitude and AVO response at bottom simulating reflector (BSR), which normally might indicate the existence of methane hydrate and gas bearing sandstone below it. We show amplitude and AVO response that can be generated at the reflection from the interface between methane hydrate bearing sandstone and brine sandstone. Thus, no gas zone below methane hydrate is required to generate amplitude anomaly or AVO. This evidence may explain the BSR, by which no gas trap structure is formed, as well.