Matrix Heterogeneity Effects on Gas Transport and Adsorption in Coalbed and Shale Gas Reservoirs
Matrix Heterogeneity Effects on Gas Transport and Adsorption in Coalbed and Shale Gas Reservoirs
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DOI：
10.1007/s11242-009-9359-4
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发表时间：
2009-11-01
影响因子：
2.7
通讯作者：
Akkutlu, I. Yucel
中科院分区：
文献类型：
--
作者：
Fathi, Ebrahim;Akkutlu, I. Yucel
在煤层和页岩中，天然气运输和储存对于准确预测产量和考虑地下温室气体封存非常重要。它们涉及多孔介质中的耦合流体现象，包括粘性流动、扩散输运和吸附。描述气-基质相互作用的标准方法是确定性的，忽略了孔隙度和基质材料含量的局部空间非均质性的影响。在本研究中，采用弱噪声和平均场近似，并在谱域采用统计方法，研究了随机分配系数存在非平衡吸附时基质的非均质性效应。研究发现，局部非均质性会产生重要的输运效应和动力学效应，从而阻碍气体从基质中释放出来，并对最终气体采收率产生不利影响。宏观输运表现为1/[1 + N (Pe) /(1 + N (Pe))]依赖于P、cllet数，并维持在扩散超低渗透率极限。宏观动力学与Thiele模量的直接关系为：N (Th) /(1 + 2N (Pe))。它导致气体从基质中释放时在吸附相中被捕获，并且在气体被基质吸收期间产生吸附阈值。这两种效应都与初始可用吸附气量成正比，并随着孔隙度场方差的增加而变得更加明显。在此基础上，提出了一种具有实际应用价值的新型确定性气体质量天平。数值结果显示了单孔煤基体的自由气体和吸附气体的分布以及分数气体的吸附曲线，均表现为高斯孔隙度分布。该研究为进一步认识煤层气和页岩提供了一条独特的途径，对建立完善的产气和封存数值模型具有重要意义。
In coalbeds and shales, gas transport and storage are important for accurate prediction of production rates and for the consideration of subsurface greenhouse gas sequestration. They involve coupled fluid phenomena in porous medium including viscous flow, diffusive transport, and adsorption. Standard approach to describe gas-matrix interactions is deterministic and neglects the effects of local spatial heterogeneities in porosity and material content of the matrix. In this study, adopting weak-noise and mean-field approximations and using a statistical approach in spectral domain, matrix heterogeneity effects are investigated in the presence of non-equilibrium adsorption with random partition coefficient. It is found that the local heterogeneities can generate non-trivial transport and kinetic effects which retard gas release from the matrix and influence the ultimate gas recovery adversely. Macro-transport shows 1/[1 + N (Pe) /(1 + N (Pe) )] dependence on the P,clet number, and persists at the diffusive ultra-low permeability limit. Macro-kinetics is directly related to Thiele modulus by the following expression: N (Th) /(1 + 2N (Pe) ). It leads to trapping of gas in the adsorbed phase during its release from the matrix, and to an adsorption threshold during the gas uptake by the matrix. Both effects are proportional to the initially available adsorbed gas amount and becomes more pronounced with the increasing variance of the porosity field. Consequently, a new upscaled deterministic gas mass balance is proposed for practical purposes. Numerical results are presented showing free and adsorbed gas distributions and fractional gas sorption curves for unipore coal matrix exhibiting Gaussian porosity distribution. This study is a unique approach for our further understanding of the coalbeds and gas shales, and it is important for the development of sound numerical gas production and sequestration models.