Based on gas composition and temperature measurements in the course of field drilling, the upper and lower depths of gas hydrate stability zone are calculated by modeling in the Muli permafrost, Qinghai, then the modeling results are compared with the drilling results. The modeling results show that the upper depth of gas hydrate stability zone is 148.8~122.7 m and the lower depth of gas hydrate stability zone is 324.6~354.8 m, with the thickness of gas hydrate stability zone of 175.8~232.2 m; the drilling results indicate that gas hydrate and its related indications occur at the interval of 133~396 m. These two types of results are comparable and thus are basically accordant, suggesting that the modeling can serve as a prediction of the upper and lower depths of gas hydrate stability zone. Gas composition, depth of permafrost, thermal gradients above and below the base of permafrost are sensitive factors affecting the upper and lower depths of gas hydrate stability zone in the Muli permafrost.
Based on the analysis of sea‐bottom temperature and geothermal gradient, and by means of the phase boundary curve of gas hydrate and the sea‐bottom temperature versus water depth curve in the South China Sea, this paper studies the temperature and pressure conditions for gas hydrate to keep stable. In a marine environment, methane hydrate keeps stable at water depths greater than 550 m in the South China Sea. Further, the thickness of the gas hydrate stability zone in the South China Sea was calculated by using the phase boundary curve and temperature‐depth equations. The result shows that gas hydrate have a better perspective in the southeast of the Dongsha Islands, the northeast of the Xisha Islands and the north of the Nansha Islands for thicker stability zones.
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