Characteristics of gas hydrate reservoir from resistivity image in the Shenhu area, China

In 2016, logging-while-drilling (LWD) was conducted at 11 sites in the Shenhu area of the South China Sea to characterise the gas hydrate reservoir. The authors used LWD resistivity image from these sites to analyse the hydrate occurrence mode, near-well structure, sedimentary structure, fracture and in situ stress orientation of the gas hydrate reservoir. The analysis revealed the following. (a) Three categories of gas hydrate occurrence mode were identified: thick-bedded, dispersed and thin-bedded. (b) The dip angle of the regional stratigraphic structure is concentrated between 2 and 4 degrees, and the dip direction is mainly south-west. (c) The typical sedimentary structure is deformed bedding and primarily developed in the gas hydrate intervals. It is inferred that the deformed bedding is affected by gas hydrate formation and the drilling process. (d) Based on the borehole breakout, the minimum horizontal principal stress direction was determined to be north-east-south-west, which provides valuable information for the design of the gas hydrate production. (e) Two categories of fracture were identified: conductive fracture and resistive fracture. Conductive fracture developed in the gas hydrate zone and contributed to higher gas hydrate saturation. High-resolution resistivity images provide extensive visual geological information and are particularly important in future exploration plans.