天然气水合物储藏降压开采产量流固耦合模拟

Fluid-solid coupling simulation of gas deliverability in the depressurization production of gas hydrate reservoirs

针对当前天然气水合物储藏降压开采产能模型局限于水合物分解引起的储集层孔隙度及渗透率变化、忽视流固耦合作用等问题,提出了考虑"水合物分解效应"、流固耦合作用以及储集层应力敏感性,建立了水合物储藏气、水两相非等温流固耦合数学模型并进行程序开发.以墨西哥湾某水合物储藏为例,进行了水合物储藏降压开采产能模拟,剖析了流固耦合作用对水合物储藏开采动态的影响机制.结果表明,流固耦合作用引起的岩石孔隙收缩虽有助于提高储集层弹性驱动能,但岩石孔隙收缩导致储集层孔渗能力降低的影响居主导地位,故流固耦合的总体效果导致水合物储藏产气速率以及累积产气量等生产指标较不考虑流固耦合时偏低.

In the present gas deliverability models for the depressurization production of gas hydrate reservoirs,only the variation of the reservoir porosity and permeability caused by the decomposition of gas hydrate is considered,and the fluid-solid coupling is ignored.For this reason,a gas-water two-phase non-isothermal fluid-solid coupling gas deliverability model is established in which gas hydrate dissociation,fluid-solid coupling and stress sensitivity are comprehensively considered,and the corresponding finite element program is developed. Taking Gulf gas hydrate reservoir in Mexico as an example,the depressurization production of the reservoir is simulated and the influence mechanism of fluid-solid coupling on the gas production of gas hydrate reservoirs is analyzed. The results show that the pore reduction in the reservoir caused by fluid-solid can increase reservoir elastic driving energy,and meanwhile the pore reduction will lead to the decrease of the porosity and permeability. Generally,the latter is the dominant factor so the actual gas deliverability and cumulative gas when the fluid-solid coupling is considered are lower than those without considering the fluid-solid coupling.