论文部分内容阅读
页岩气是一种以吸附态和游离态为主,赋存于纳米级多孔介质中的一种非常规气藏,其渗流特征较常规气藏存在较大的差异。前人研究表明,页岩气运移过程存在多种渗流机理,主要包括:达西渗流、滑脱效应和扩散。虽然前人对自由气扩散的渗流机理模型进行了大量的研究,但是大多没有考虑吸附气表面扩散对渗流的影响。针对以往研究的不足,该文采用两区复合概念模型,建立了考虑吸附气表面扩散、达西渗流和滑脱效应的气体渗流模型,将吸附气和自由气运动关系利用修正的滑脱速度边界条件进行耦合,采用等值渗流阻力法对气体在纳米孔隙介质中渗流的关键参数―渗透率―进行了深入研究,获得了适用于任意克努森数范围的页岩气渗透率解析模型。通过对不同尺度、不同压力下的储层在考虑表面扩散等多重机制下的渗透率进行了计算并发现:吸附气表面扩散是页岩气渗流的重要机理,其对渗透率的贡献会对页岩气藏储层评价和开发方案制定以及增产改造施工设计产生重要影响。
Shale gas is a kind of unconventional gas reservoirs mainly in adsorbed state and free state, which occur in nanometer porous media. The seepage characteristics of shale gas are quite different from conventional gas reservoirs. Previous studies have shown that there are many percolation mechanisms of shale gas migration, including Darcy seepage, slippage effect and diffusion. Although predecessors have done a lot of research on the percolation mechanism model of free gas diffusion, most of them do not consider the influence of surface diffusion of adsorbed gas on seepage flow. Aiming at the deficiencies of previous researches, a gas seepage model considering the surface diffusion of adsorbed gas, Darcy flow and slippage effect was established by using the composite concept model of two zones. The relationship between the adsorption gas and free gas movement was established by using the modified boundary conditions of slippage velocity Coupled with the equivalent seepage flow resistance method, the critical parameter of gas permeability in porous media - permeability is studied in depth. An analytical model of shale gas permeability suitable for any Knudsen number range is obtained. By calculating the permeability of reservoirs under different scales and pressures under various mechanisms such as surface diffusion, it is found that the surface diffusion of adsorbed gas is an important mechanism of shale gas seepage, and its contribution to permeability will be on the page Rock gas reservoir evaluation and development plan development as well as stimulation of construction design have a significant impact.