The influence of submarine landslides on the distribution and enrichment of gas hydrate and free gas

Submarine landslides, gas hydrate and free gas are identified from the three dimensional (3D) seismic data and logging while drilling (LWD) data in the southern Pearl River Mouth Basin. It is a typical area to study the influence of submarine slides on the distribution and enrichment of gas hydrate and free gas. Based on the effective medium model and Archie equation, the P-wave velocity and resistivity of water-saturated sediments are calculated and compared with the measured P-wave velocity and resistivity from LWD data, and gas hydrate-bearing layer and multiple free gas-bearing layers are identified from the anomalies. The differences of the spatial distributions of gas hydrate, free gas and faults in different submarine landslide zones are shown from the coherence and amplitude attributes generated from 3D seismic data. The base of gas hydrate stability zone (BGHSZ) shifts downward due to seafloor erosion caused by submarine landslides. Gas hydrates are widely distributed if the modified BGHSZ is located beneath the sand-rich sediments and the locally developed faults connect free gas-bearing layers to BGHSZ. However, gas hydrate will not be formed where faults cannot arrive at the BGHSZ and free gas is just trapped in local strata due to the lack of fluid flow conduits. This study provides direct evidence to reveal the relationship between the distributions of gas hydrate, free gas and submarine landslides, and also provides the suggestions to find the joint exploitation target of gas hydrate and free gas in the future.