热力法开采天然气水合物的数学模拟

MATHEMATIC MODELING ON THERMAL RECOVERY OF NATURAL GAS HYDRATE

将天然气水合物在热力作用下的分解过程看作一个移动界面问题,即热力开采过程中整个水合物藏可分为分解区和水合物区。通过适当简化,建立了分解区和水合物区的传热模型,并严格推导了模型的解析解。使用模型分别模拟注入蒸气和热水条件下开采天然气水合物的两个实例,得到分解区和水合物区温度场随时间变化的规律。在此基础上,分析了水合物热力开采过程中热量的有效利用率,即用于水合物分解的热量与输入的总热量的比值。模型计算结果表明,在相同条件下,注入热水比注入蒸气将能获得更高的热量有效利用率。在给定的条件下,注入蒸气和热水开采过程的热量的有效利用率分别为0.349和0.465。另一个方面,该比值与水合物地层的物性参数(如水合物的饱和度、分解区域的热传导系数等)有很大的关系,地层水合物饱和度越高,分解区的热传导系数越小,则热量的有效利用率越高。

It is regarded the decomposition process of gas hydrate under heat as essentially interface movement, i.e., hydrate reservoir could be divided into decomposition zone and hydrate zone during thermal recovery. Via proper simplification, heat transfer model of both zones are established and analytic solutions of the model are strictly derived. Through running the model for two different cases of recovering hydrate: by steam injection versus by hot water injection, it is established the rule of temperature field changed by the time of both decomposition zone and hydrate zone. Heat efficiency during hydrate thermal recovery, i.e., hydrate decomposition heat to total heat input ratio, has also been analyzed based on the model. Simulation shows under the same conditions that hot water injection produces higher heat efficiency than steam injection does. Heat efficiency of steam injection and hot water injection was 0.349 and 0.465 under the given condition. On the other hand, hydrate decomposition heat to total heat input ratio is closely related to hydrate formation properties such as hydrate saturation and decomposition zone heat transfer coefficient: the higher hydrate saturation is, the lower heat transfer coefficient is in decomposition zone, and the higher heat efficiency will be.