基于局部平衡反应的海底甲烷水合物形成及富集机制数值模拟

针对具有开发潜力的渗漏型天然气水合物藏，尝试采用油藏数值模拟方法，建立海底甲烷水合物形成及富集机制模型。基于水合物的相平衡和动力学特征，通过对水合物反应的局部平衡设置和对海底浅层高压低温环境的精确描述，实现对深部甲烷气运移至海底水合物稳定区、触发形成水合物过程的模拟，分析海底低渗层遮挡和海底冷泉两种情形下甲烷水合物富集成藏过程及其影响因素。结果表明：在深水海底浅层中，深部甲烷气以较小通量且不发生泄漏至海水情形下，长时间、持续的运移至海底水合物稳定区，则有利于形成大厚度、高丰度的水合物藏；油藏数值模拟方法可作为种研究海底水合物成藏动力学的有效手段，值得开发利用。
Aiming at subsea gas hydrate reservoirs formed via a seepage-type gas migration, a hydrate formation and accumulation model in subsea sediments was established using a reservoir simulation method. Based on the phase equilibrium and reaction kinetics of methane hydrate in sea water, the process of hydrate formation during methane migrating into the upper hydrate stability zone from a deep gas reservoir was realized, in which a partial-equilibrium setting of the hydrate reaction model and high-pressure and low-temperature of the subsea sediments were considered. The effects of different influence factors on methane migration and hydrate formation are analyzed, and a low-permeability barrier case and a leakage case were considered. The simulation results show that low flux of methane gas, cap rock barrier, large water depth, and small geothermal gradient below the mud line are beneficial to the formation of large and thick hydrate reservoirs with high hydrate saturation. It has been also proved that conventional reservoir simulation method can be used as an effective tool to study the hydrate accumulation mechanisms, which deserve for further development and utilization