页岩气渗流机理与产能研究

Study on seepage mechanism and productivity of shale gas

李亚洲 李勇明 罗攀 赵金洲

西南石油大学油气藏地质及开发工程国家重点实验室，四川 成都 610500

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University,
Chengdu 610500, China

页岩气储存和运移的特殊性导致了其渗流过程描述的复杂性。很多学者按照双重介质渗流研究页岩气渗流，认为吸附气解吸后直接扩散到裂缝中；但由于其忽略了基质颗粒间存在的游离气，使得渗流过程的描述不完整。在前人研究的基础上，文中引入了一个新的流动过程——基质孔隙系统中的流动，建立了相应的页岩气渗流方程；通过空间变换及数值求解，得出了圆形封闭地层中页岩气井定压生产时无因次拟压力的Laplace空间解；在此基础上绘制了产能随时间的变化关系图，分析了吸附系数、封闭边界半径、弹性储容系数等页岩气特征参数对产能曲线的影响。研究结果表明：页岩气井的产能曲线呈初期产能快速下降—稳产—产能缓慢下降的“三段式”特征；封闭边界半径越大，稳产时间越长；吸附系数越大，初期产能下降越慢，稳产时间越长；裂缝弹性储容系数越大，初期产能下降越快。

The storage and migration process of shale gas is particular. It leads to the complexity of the description about seepage process. Lots of people research on the flow of shale gas according to the flow through dual medium. It is considered that the adsorbed gases diffuse into fractures directly after desorption with ignoring the free gas which exists in the interspaces between matrix grains. It makes the incompleteness of seepage process. Based on the works previously, this paper introduced a new flow process, which is the flow in matrix pore system, and correspondingly established the seepage equation of shale gas. By means of space transformation and numerical solution, the solution of non-dimensional pseudo-pressure in Laplace space was founded when a well is producing with constant pressure in closed circular formation. On these bases, The relation curve of productivity and time was drawn. And the influence of characteristics parameters of shale gas such as absorption coefficient, closed boundary radius, elastic storativity coefficient on the productivity was analyzed. Results show that the productivity curve of shale gas well presents tripartite feature of sharp dropping in the early days, maintaining stable production for a period of time and then slowly dropping. The greater the closed boundary radius is, the longer the stable production time is. The greater the absorption coefficient is, more slowly the productivity drops in the early days, and  the longer the stable production time is. The greater the elastic storativity coefficient of the frature is, more quickly the productivity drops in the early days.

10.6056/dkyqt201302013