Physical characteristics of high concentrated gas hydrate reservoir in the Shenhu production test area, South China Sea

High concentrated and heterogeneous distribution of gas hydrates have been identified in the gas hydrate production test region in the Shenhu area, South China Sea. The gas hydrate-bearing sediments with high saturation locate at two ridges of submarine canyon with different thickness and saturations just above the bottom simulating reflection. The crossplots of gamma ray, acoustic impedance (P-impedance) and porosity at four sites show that the sediments can be divided into the upper and lower layers at different depths, indicating different geotechnical reservoir properties. Therefore, the depositional environments and physical properties at two ridges are analyzed and compared to show the different characteristics of hydrate reservoir. High porosity, high P-wave velocity, and coarse grain size indicate better reservoir quality and higher energy depositional environment for gas hydrate at Sites W18 and W19 than those at Sites W11 and W17. Our interpretation is that the base of canyon deposits at Sites W18 and W19 characterized by upward-coarsening units may be turbidity sand layers, thus significantly improving the reservoir quality with increasing gas hydrate saturation. The shelf and slope sliding deposits compose of the fine-grained sediments at Sites W11 and W17. The gas hydrate production test sites were conducted at the ridge of W11 and W17, mainly because of the thicker and larger area of gas hydrate-bearing reservoirs than those at Sites W18 and W19. All the results provide useful insights for assessing reservoir quality in the Shenhu area.