Semi‐quantitative Analysis of Factors Affecting Gas Hydrate Formation Conditions and Its Fractions

Gas hydrate formation conditions and its fraction out of pore space are two important issues. Based on the theoretical thermo-dynamic model of gas hydrate formation and accumulation, the semi-quantitative analysis on various intrinsic factors (such as temperature, pressure, gas composition, pore-water salinity, sediment pore size) is conducted to characterize their effects on gas hydrate formation conditions and its fraction out of pore space. The analytical results indicate that gas composition plays a significant role in affecting gas hydrate formation conditions of temperature and pressure; comparatively the effect of the mixture of methane and propane is the largest and that of the mixture of methane and hydrogen sulphide is secondary, and effects of the mixture of methane and ethane and the mixture of methane and carbon dioxide follow in turn with respect to pure methane. Pore-water salinity also greatly affects gas hydrate formation conditions. Sediment pore size within a certain range (1 × 10–6 ~ 4 × 10–8m) has a small effect on gas hydrate formation conditions; beyond this range when sediment pore size becomes smaller and smaller, its effect gets more and more evident on inhibiting gas hydrate formation and especially when sediment pore size is smaller than 1×10–9m, it seems impossible for pure methane and pure water to form gas hydrate; contrarily when sediment pore size is bigger than 1 × 10–3m, it nearly has no effect on gas hydrate formation conditions. Gas hydrate fraction out of pore space is little affected by pore size and pore-water salinity, but is strongly dependent on gas supply.