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Apparent Gas Permeability Behaviour in the Near Critical Region for Real Gases
Gas Science and Engineering ( IF 5.285 ) Pub Date : 2020-05-01 , DOI: 10.1016/j.jngse.2020.103245
Tong Wu , Zhejun Pan , Luke D. Connell , Michael Camilleri , Xiaofei Fu

Abstract Gas apparent permeability is an important parameter for gas flow in the reservoir rocks. It is higher than the absolute permeability measured using liquid. The Klinkenberg equation corrects the liquid permeability to the apparent gas permeability allowing for the pressure dependent effects of interactions between gas molecules and pore walls. However, in this paper it is shown that Klinkenberg equation does not apply for gas flow in the near critical region for real gases. This has important implications for a number of reservoir management applications including carbon geosequestration and gas condensate reservoirs. In this paper, a series of permeability measurements with respect to pressure and temperature are presented on sandstone core samples using carbon dioxide (CO2), ethane (C2H6) and helium (He). The experimental results show that the apparent permeability is enhanced in the near-critical region. CO2 apparent permeability at 311 K (critical temperature of 304.25 K) increases about 2.24 times from 7.18 MPa to 8.6 MPa (critical pressure of 7.37 MPa) on the Sandstone Sample M1 and 1.83 times on the Sandstone Sample M2 for the same pressure change. C2H6 apparent permeability at 311 K (critical temperature of 305.35 K) increases 1.83 times from 4.6 MPa to 5.4 MPa (critical pressure of 4.9 MPa) on the Sandstone Sample M1 and 1.59 times on the Sandstone Sample M2 for the same pressure change. These results suggest that the permeability enhancement is stronger for the lower permeability sample. Moreover, the experimental results show that enhancement decreases as temperature increases. Modelling work shows that applying Klinkenberg equation is invalid for describing the apparent gas permeability in near critical region, even with attempts to use different equations to calculate the mean free path required in the Klinkenberg equation. A dual mechanism model, which simultaneously considers convection flow and molecular diffusion, is modified allowing the gas diffusivity to be a function of gas density and it can well describe the gas apparent permeability in the near critical region. It is suggested that the flow is in the viscous flow regime or weak slip flow regime for the near critical gas on the sandstone samples studied in this work, and the enhancement of permeability in the near critical region is attributed to the higher density (concentration) gradient with respect to pressure.

中文翻译:

真实气体近临界区的表观气体渗透行为

摘要 气体表观渗透率是储层岩石中气体流动的重要参数。它高于使用液体测量的绝对渗透率。Klinkenberg 方程将液体渗透率校正为表观气体渗透率,允许气体分子和孔壁之间相互作用的压力相关效应。然而,在本文中,Klinkenberg 方程不适用于实际气体的近临界区域的气体流动。这对包括碳地质封存和凝析气藏在内的许多储层管理应用具有重要意义。在本文中,使用二氧化碳 (CO2)、乙烷 (C2H6) 和氦气 (He) 对砂岩岩心样品进行了一系列与压力和温度相关的渗透率测量。实验结果表明,表观渗透率在近临界区增强。CO2 表观渗透率在 311 K(临界温度为 304.25 K)时,对于相同的压力变化,砂岩样品 M1 的 CO2 表观渗透率从 7.18 MPa 增加到 8.6 MPa(临界压力 7.37 MPa)约 2.24 倍,砂岩样品 M2 的 1.83 倍。对于相同的压力变化,C2H6 在 311 K(临界温度为 305.35 K)下的表观渗透率在砂岩样品 M1 上增加了 1.83 倍,从 4.6 MPa 增加到 5.4 MPa(临界压力为 4.9 MPa),在砂岩样品 M2 上增加了 1.59 倍。这些结果表明渗透率增强对于较低渗透率的样品更强。此外,实验结果表明,增强随着温度的升高而降低。建模工作表明,即使尝试使用不同的方程来计算 Klinkenberg 方程所需的平均自由程,应用 Klinkenberg 方程也无法描述近临界区的表观气体渗透率。修改了同时考虑对流和分子扩散的双重机制模型,使气体扩散系数成为气体密度的函数,可以很好地描述近临界区域的气体表观渗透率。表明本文研究的砂岩样品上的近临界气体流动处于粘性流态或弱滑移流态,近临界区渗透率的增强归因于较高的密度(浓度)压力梯度。
更新日期:2020-05-01
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