页岩储集层微观渗流的微尺度效应

Microscale effect of microvadose in shale reservoirs

页岩有机质中存在大量纳米孔隙,气体在纳米孔隙中的流动存在微尺度效应,宏观流体流动规律难以准确描述其流动行为。考虑气体分子在有机质孔隙中的滑脱效应、扩散和吸附解吸作用,用格子Boltzmann方法模拟气体在有机质纳米孔道中的流动。结果表明:气体在有机质纳米孔道中存在压缩效应,压缩效应导致压力沿纳米孔道呈非线性分布,且孔道两端的压差越大,非线性程度越大。随着Knudsen数增大,稀薄效应增强,减弱了由压缩效应引起的非线性程度。气体在纳米孔道中的边界滑移速度随着进出口压力比和Knudsen数的增大而增大,并且在垂直于孔道方向上的速度不为零,加剧了孔道中气体分子与边界分子的动能交换。滑移效应和吸附解吸效应均对气体在页岩有机质孔道中的质量流量有重要影响。

Gas flow in nano-pores which are abundant in the organic matter of shale can lead to micro-scale effect that can＇t be described by flowing law of macro fluid. The Lattice Boltzmarm Method was applied to simulate gas flow in the nano-channels of organic matter and to investigate the slippage effect, diffusion effect and adsorption/desorption effect. The simulation result shows that the compressibility effect of gas leads to the nonlinear pressure distribution along the channels, and the larger the pressure difference, the more serious the nonlinear distribution. To some extent, the enhancement of rarefaction effect weakens nonlinear degree caused by the compressibility effect. With the increase of Knudsen number and the pressure differential on the two ends, the slip velocity on the boundary increases, and the velocity vertical to the channel is not zero, increasing the exchange of kinetic energy between gas molecules in channels and molecules at boundary. Slippage effect and adsorption/desorption effect have a significant contribution to the gas mass flow in nano-channels of organic matter.