Preliminary study on depositional and reservoir characteristics of high-saturation gas hydrate worldwide

Natural gas hydrate resources have been a popular replacement object of global energy in the future. High-saturated (S_h>50%) hydrate reservoir is the first choice for industrial exploration and exploitation. However, relationship between saturation of gas hydrate and its reservoir facies lacks of systematic investigation at present. Based on published literatures, five gas hydrate-exploration hotpot areas in the word are systematically summarized, including the Gulf of Mexico, the Nankai Trough in Japan, the Ulleung Basin in South Korea, the Krishna-Godavari basin in India, and the Shenhu area of the South China Sea. The cores and logs of 64 penetrated wells were used to analyze the lithology, sedimentary environment, hydrate saturation and other parameters of the hydrate reservoir in detail. The results show that under suitable temperature and pressure conditions associated with gas sources, the deposits of MTDs (mass transport deposits) and turbidite in deep marine areas are facilitated with good gas hydrate resources. The reservoirs of gas hydrate include fine-grained sandstone, very fine-grained sandstone, siltstone, and silty mud and mud sediments. However, the high saturation hydrate mainly occurs in siltstone and fine-grained sandstone. The porosity and saturation of the gas hydrate reservoir have a relatively positive correlation. The Shenhu area of the South China Sea is mainly composed of fine-grained sediments, including clayed silt or foraminifera-rich silty clay. The sand content is low (less than 10%), but the hydrate saturation can reach a medium-to-high level (20%-48%). This study provides a geological base for large-scale exploration and development of high-quality and high-saturation hydrates gas reservoirs.