Study on Optimization of Methane Hydrate Production System by Using Genetic Algorithm

地下水合物以固体形式存在，与常规油气不同，目前尚无经济开采天然气的方法。在本研究中，我们进行了室内实验来阐明水合物在沉积物中的解离行为，并对水合物生成系统进行了数值评价。为了寻找合适的产气系统，我们采用了一种基于遗传算法的优化方法。(1)水合物形成与解离实验建立了观察沉积物中水合物形成与解离行为的实验装置。通过实验分析了Berea砂岩岩心中CO2水合物形成和解离过程中的压力/温度行为。实验数据分析表明，降压过程中水合物的采收率受环境换热、初始水合物饱和度和沉积物渗透率的影响较大。(2)水合物开采的经济评价。(2)水合物开采的经济评价。结果表明，以下参数对确定水合物产气量非常重要：井构型（井的垂直和水平布置）；水平段长度；以及水合物沉积物附近上下沉积物的导热系数。(3)基于遗传算法的生产系统优化针对日本近海向水合物注入热水的天然气开采过程进行了优化研究。以采气项目净现值为目标函数，对注入水温度、注入水量、生产周期、水平井段长度等生产参数进行了优化。该研究为水合物生产系统的优化提供了指导，但由于现有的水合物产率和数量数据较少，由于地质模型假设简化，计算结果并不精确。少

There is no method established for recovering gas economically from subsurface hydrates because they exist as the solid sate, which is different from conventional oil and gas. In this study, we carried out laboratory experiments to clarify dissociation behavior of hydrates in sediments, and numerically evaluated hydrate production system. For finding appropriate gas production systems, we applied an optimization method using genetic algorithm.(1)Experiments on formation and dissociation of hydratesAn experimental apparatus was built for observing formation and dissociation behavior of hydrates in sediments. Experiments were carried out to analyze pressure/temperature behavior during formation and dissociation of CO2 hydrate in Berea sandstone core. The analysis of experimental data showed that gas recovery rate from hydrates in depressurization was much influenced by heat transfer from the surroundings, initial hydrate saturation, and permeability of sediments.(2)Economic evaluation fo … More r a hypothetical hydrate sedimentSimulation studies were carried out to investigate feasibility of hydrate gas production. The results showed that the following parameters were important to determine gas productivity from hydrates : well configuration (vertical and horizontal settings of well) ; length of horizontal section ; and thermal conductivity of upper and lower sediments adjacent to the hydrate sediment.(3)Production system optimization using genetic algorithmOptimization studies were carried out for a gas recovery process injecting hot water into hydrates in offshore Japan. Production parameters as temperature of injected water, volume of water injected, production period, and length of well horizontal section were optimized by using net present value of the gas recovery project as an objective function. This study showed a guideline for optimization of hydrate production system, although the calculated results were not precise due to a simplified geological model assumption because of little field data available on hydrate occurrence and amounts. Less