Understanding Oil and Gas Flow Mechanisms in Shale Reservoirs Using SLD–PR Transport Model
Understanding Oil and Gas Flow Mechanisms in Shale Reservoirs Using SLD–PR Transport Model
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DOI：
10.1007/s11242-017-0884-2
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发表时间：
2017-06
影响因子：
2.7
通讯作者：
Xiukun Wang;J. Sheng
中科院分区：
文献类型：
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作者：
Xiukun Wang;J. Sheng
页岩油气藏的渗流机理越来越受到人们的重视。当气孔尺寸为纳米级时，固-液相互作用变得明显。这种相互作用改变了流体的物性，导致页岩油藏不同于常规油藏的渗流机制。利用简化的局域密度-Peng Robinson输运模型，我们考虑了固液相互作用产生的密度和粘度分布。气体稀薄效应在高压下可以忽略不计，因此我们假定它是粘性流动。考虑密度和粘度变化的影响，提出了缝隙渗透率模型。利用这一新建立的模型得到了速度剖面。通过对分子动力学模拟得到的密度分布和速度分布进行匹配，验证了该模型的有效性。在此基础上，本文还研究了压力和孔径对油气流动机理的影响。结果表明，天然气和石油在纳米孔中的流动速度都有所提高。纳米孔内的气相流动主要受密度变化效应(吸附)的控制，而油相流动主要受粘度变化效应的控制。当缝隙开度变大时，油气渗透率都迅速下降到达西渗透率。这项工作的结果具有代表性，将有助于我们理解页岩油气藏中的油气流动机制。
More and more attention has been paid to the oil and gas flow mechanisms in shale reservoirs. The solid–fluid interaction becomes significant when the pores are in the nanoscale. The interaction changes the fluid’s physical properties and leads to different flow mechanisms in shale reservoirs from those in conventional reservoirs. By using a Simplified Local Density–Peng Robinson transport model, we consider the density and viscosity profiles, which result from solid–fluid interaction. Gas rarefaction effect is negligible at high pressure, so we assume it is viscous flow. Considering the density- and viscosity-changing effects, we proposed a slit permeability model. The velocity profiles are obtained by this newly established model. This proposed model is validated by matching the density profile and velocity profile from molecular dynamic simulation. Then, the effects of pressure and pore size on gas and oil flow mechanisms are also studied in this work. The results show that both gas and oil exhibit enhanced flow rates in nanopores. Gas-phase flow in nanopores is dominated by the density-changing effect (adsorption), while the oil-phase flow is mainly controlled by the viscosity-changing effect. Both gas and oil permeability quickly decrease to the Darcy permeability when the slit aperture becomes large. The results reported in this work are representative and should significantly help us understand the mechanisms of oil and gas flow in shale reservoirs.