置换减压法开发天然气水合物工艺及数值模拟

天然气水合物是能源领域尚未开发的领域之一，有巨大的潜力来满足未来的能源需求，降压、热刺激、碳交换和抑制剂注入是其生产过程中涉及的四种开采方法。文章提出了采用双水平井降压 ＋二氧化碳置换法开采天然气水合物，应用油藏模拟器 ＣＭＧ对矿藏条件下水合物进行数值模拟分析，模拟了多组分、多相流体和热流在地下的流动和传输，以及甲烷饱和度和温度分布，估算了水合物解离产气量和出砂量。模拟结果表明，随着开采的进行，甲烷饱和度降低，顶部的水合物优先开始分解，二氧化碳置换区域地层温度提高 ２～５℃，温度升高促进甲烷持续解离，形成了一个连续交换和生产的循环过程；同时随着甲烷产量的增加，生产井出砂量也随之增加。采用双水平井开采技术，扩大了水合物储层的波及面积，有效增加了产气量，达到商业开采价值规模。研究结果为科学评价天然气水合物开采技术的可行性、经济性提供了理论依据。

Process and Numerical Simulation of Gas Hydrate Development by Displacement and Decompression Method

Natural gas hydrate in shale gas platform in Weiyuan block is one of the untapped areas in the energy field and has great potential to meet future energy demand. Depressurization, thermal stimulation, carbon exchange and inhibitor injection are the four extraction methods involved in its production. In this paper, the method of dual horizontal well depressurization and carbon dioxide replacement is proposed to exploit the natural gas hydrate. Exploitation of natural gas hydrate reservoir simulator CMG numerical simulation analysis was carried out on the mineral deposits under the conditions of hydrate, simulating the underground flow and transportation of the multicomponent and multiphase fluid and heat flow, as well as methane saturation and temperature distribution, calculating the gas hydrate dissociation and sand production. The simulation results show that with the development of mining, methane saturation decreases, and the hydrate at the top begins to decompose preferentially. The formation temperature in the CO2 replacement area is increased by 2～5 ℃, which promotes the continuous dissociation of methane, forming a cycle of continuous exchange and production. Meanwhile, with the increase of methane production, the production of sand also increases. Double horizontal well exploitation technology expands the affected area of hydrate reservoir, which effectively increases the gas production and achieves the commercial exploitation value scale. The research results provide a theoretical basis for scientific evaluation of the feasibility and economy of gas hydrate extraction technology.