页岩气渗流数学模型

Gas flow in shale reservoirs

针对页岩气藏流体运移机理复杂、传统模型难以准确描述的难题,本文综合考虑页岩气在孔隙中的黏性流动、Knudsen扩散以及吸附气的表面扩散和因岩石变形引起的滑移分别建立自由气和吸附气扩散方程,建立页岩气在基质与裂缝中的渗流数学模型,并采用非线性非平衡Langmuir吸附理论分析页岩气渗流过程中的解吸附机理.通过数值模拟方法研究了不同流动机制对页岩气产量的影响,结果表明,吸附气的表面扩散与滑移对页岩气产量的影响均在0.1%以下,可以忽略;黏性流动与Knudsen扩散主导页岩气的渗流;非平衡吸附速率对页岩气产量影响较大,吸附速率越大,产量越大.本文建立的模型能较好地揭示页岩气的复杂渗流机理,并为页岩气藏的开发提供了科学基础.

This study incorporates various gas transport mechanisms in shale nanopores with nonlinear and non-equilibrium gas adsorptiondesorption kinetics. We formulate a simplified model for matrix and hydraulic fractures to study the dynamic production performance of multi-stage fractured horizontal wells in shale gas reservoirs. The gas transport mechanisms include viscous flow, Knudsen diffusion of free gas, surface diffusion, and slippage of adsorbed gas whilerock deformation is coupled in the flow equations. The sensitivity of the production rate to key physical parameters is examined through numerical simulation. Our results indicate that the viscous flow and Knudsen diffusion dominate the production of shale gas. The production rate was sensitive to the desorption rate while largely unaffected by the surface diffusion and slippage of the adsorbed gas, given that the transport process of adsorbed gas is a much slower process than the diffusion of free gas.