Investigation on hydrate exploitation in submarine slope: Insights from discontinuous pillar exploitation

Abstract

The decomposition of natural gas hydrate (NGH) will cause a decrease in reservoir strength, which can easily induce submarine landslides when hydrate reservoirs are located on a submarine slope. Although there have been several studies on the stability of hydrate-bearing submarine slopes (HBSS), little attention has been paid to minimizing the risk of landslides due to NGH exploitation. The “multistage reduction method” based on strength reduction was described in this paper. Subsequently, “discontinuous pillar exploitation” was proposed to achieve safe extraction of NGH and avoid submarine landslides. Finally, the “discontinuous pillar exploitation” was analyzed using the “multistage reduction method”. The results show that NGH decomposition has a far-reaching impact on the HBSS; it reduces the stability of HBSS and can trigger submarine landslides. The “discontinuous pillar exploitation” can divide the continuous plastic failure zone into short discontinuous plastic zones through the setting up of pillars, which significantly improves the stability of HBSS. With the decrease in the exploitation ratio, the safety factor of the submarine slope increases continuously. When the “discontinuous pillar exploitation” is adopted for NGH production on a submarine slope, there are two positions that require special attention: the junctions between the pillars and the exploitation area (peak area of shear stress); the side of exploitation area near the top of the slope (peak area of tensile stress).