最新国际天然气水合物研究现状与资源潜力评估(上)

地层骨架孔隙中水合物的高质量形成是开展水合物实验研究的前提和物质基础，可为我国深水油气及水合物资源开发提供理论指导。依据南海GMGS2-07井水合物层地质条件，利用TOUGH+HYDRATE数值模拟软件和自主研制的水合物反应生成装置开展数值模拟和实验研究，在验证数值模拟方法准确性和可靠性的基础上，通过控制变量法分别开展不同地层导热系数和含水饱和度条件下水合物生成质量的影响研究。结果表明：(1) 数值模拟与室内实验过程中，水合物形成时温度、压力与三相物质变化趋势一致且特征值十分接近，验证了数值模拟方法的准确性和可靠性。(2) 导热系数越大，水合物生成越快，最终形成的水合物饱和度越大，分布也更加均匀。但导热系数与最终形成水合物的饱和度的正负相关性，存在临界边界。本次所选用的反应釜尺寸，临界边界距上、右边界距离为1.8 cm，临界边界内导热系数与水合物饱和度呈正相关性，临界边界外呈负相关性。临界边界随着反应釜尺寸的增大而增大，但临界边界位置不受地层渗透率的影响。(3) 随地层含水饱和度增加，最终形成的水合物饱和度先增大后减小，峰值处含水饱和度小于初始压力条件下的理论气水比。当初始压力为7.8 MPa，含水饱和度约22.23%时，所形成的水合物饱和度最大且分布最不均匀。由此可知，选用高导热系数材料制备地层骨架、使初始含水饱和度低于气水理论比以及调整初始温压条件使之偏向相平衡曲线左方有利于形成分布均匀的高饱和水合物。研究认为深水油气含水合物固井和水合物资源钻采提供依据，为水合物商业化开采提供技术储备。

Formation & dissociation of methane gas hydrates in sediments: A critical review

The formation of high-quality gas hydrates in the pores of the sediment matrix serves as the premise and material basis for experimental research on gas hydrates, thus providing theoretical guidance for the exploration of deep-water hydrocarbons and gas hydrates in China. Based on the geological conditions of gas hydrate-bearing sediments in well GMGS2-07 in the South China Sea, this study conducted numerical simulations and laboratory experiments using the TOUGH+HYDRATE code and a self-developed device for gas hydrate reactions and generation, respectively. Firstly, this study verified the accuracy and reliability of the numerical simulation method. Then, it investigated the quality of gas hydrates generated under different thermal conductivities and water saturation of sediments to determine their influencing mechanisms. The results are as follows: (1) Both numerical simulations and laboratory experiments yielded consistent variation trends and nearly identical characteristic values of the temperature, pressure, and three-phase materials in the process of gas hydrate formation. Therefore, the numerical simulation method used in this study is accurate and reliable; (2) A higher thermal conductivity was associated with faster gas hydrate formation, as well as the higher saturation and more uniform distribution of the final gas hydrates. However, the correlation between the thermal conductivity and the final gas hydrate saturation depended on the position relative to critical boundaries, which were determined at a distance of 1.8 cm from the upper and right boundaries of the tank reactor used in this study. There was a positive correlation between the thermal conductivity and the gas hydrate saturation within the critical boundaries. Otherwise, they were negatively correlated. The distances between the critical boundaries and the boundaries of the water bath increased with an increase in the tank reactor size but were not affected by the formation permeability; (3) As the formation water saturation increased, the saturation of the final gas hydrates first increased and then decreased, and the peak water saturation was less than the theoretical gas-water ratio under the initial pressure. The gas hydrates showed the highest saturation and the most ununiform distribution when the initial pressure was 7.8 MPa and the water saturation was about 22.23%. Therefore, the sediment matrix prepared using high-thermal-conductivity materials, the initial water saturation lower than the theoretical gas-water ratio, and the initial temperature and pressure falling to the left of the phase equilibrium curve are conducive to the formation of high-saturation, uniformly distributed gas hydrates. This study will provide a sound material basis for well cementing in deep-water sediments bearing hydrocarbons and gas hydrates, as well as the drilling and exploitation of gas hydrate resources. Moreover, it will contribute to the technical preparation for the commercial recovery of gas hydrates.