天然气水合物稳定带的计算方法与参数选择探讨

天然气水合物稳定带的研究对于认识天然气水合物的成矿与分布规律以及资源评价都具有重要的指导意义。在计算稳定带厚度的不同方法之间, 特别是在参数的选择上存在很大的差异。通过简单评价天然气水合物稳定带计算的几种方法和参数选择, 认为选择压力计算公式时要考虑孔隙水产生的压力、海底以上水柱的压力和大气压; 考虑大气压的压力随纬度变化的二阶方程是最符合实际的深度—压力转换方程; 通过实验得到的方程只适用于纯水或盐度为33 5‰的海水中纯甲烷的预测; 根据热力学理论可以计算不同盐度、不同气体组分的稳定带的温压条件; 用相平衡图的方法最简单, 但误差很大; 通过四阶方程拟合实验数据和热力学数据得到的稳定带厚度更接近实际情况; 不同方法预测的稳定带底界与实际含水合物沉积底界很难一致。

Discussion of the Calculation Methods and Selection of Parameters of the Gas Hydrate Stability Zone

The study of the gas hydrate stability zone has great significance in comprehension of the distribution (features) and the resource assessment of gas hydrates.Many scholars have calculated the thickness of the stability zone by different methods, but there are some big differences among these methods, especially in the selection of parameters. The authors simply evaluate several methods and the selection of parameters for the calculation of the gas hydrate stability zone. The results show that we must consider pore-water pressure, water-column pressure and atmospheric pressure when we select the pressure formula. The second-order polynomial of pressure variation with different latitudes considering atmospheric pressure is best. The obtained equation by experiment is only used to predicting pure methane of pure water or seawater of 33.5‰ salinity. We can calculate the temperature-pressure condition of stability zone with different salinities and gas compositions by the theory of thermodynamics. The phase equilibrium plot is most simple, but its error is great. The calculated thickness of stability zone by the four-order polynomial using the experiment and thermodynamics data is close to practice. The predicted limit of the stability zone by different methods is not always consistent with actual limit of hydrate sediment.