考虑页岩基质不同孔隙特征的表观渗透率模型

Apparent Permeability Model Considering Different Pore Characteristics of Shale Matrix

李荷婷 曾杰 李真祥 路千里

LIHeting ZENGJie LIZhenxiang LUQianli

中国石化西南油气分公司科技部, 四川 成都 610041 油气藏地质及开发工程全国重点实验室·西南石油大学, 四川 成都 610500 中国石化勘探分公司, 四川 成都 610041

Science and Technology Department, Southwest Petroleum Branch, SINOPEC, Chengdu, Sichuan 610041, China National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China SINOPEC Exploration Company, Chengdu, Sichuan 610041, China

页岩基质含气量大、供气时间长，其渗透率随地层孔隙压力变化的演化直接影响气藏的长效产气能力。基质中微纳米孔隙发育，有机孔隙和无机孔隙的力学性质和流体传输机理各异，有效应力和流态变化都将影响其表观渗透率。此外，有机质中的吸附气使岩体发生吸附变形也不同程度地影响表观渗透率。基于孔弹性理论，考虑有机孔隙和无机孔隙中不同岩石力学参数、流体流动机理以及有机孔隙吸附变形的特点，建立了适用于页岩基质的表观渗透率模型，分析了不同孔隙参数对表观渗透率的影响，揭示了表观渗透率演化的主控因素。结果表明，在定压注气和采气过程中，页岩基质表观渗透率的演化均与时间有关，主要受稀薄气体效应、有效应力变化以及有机孔隙周围局部吸附膨胀或解吸附收缩影响。表观渗透率演化过程的主控因素随时间变化，同时与有机孔隙、无机孔隙的体积占总孔隙体积的比例有关。

Shale matrix stores a larger amount of gas and provides a long-term gas supply for shale gas production. Therefore, matrix permeability variation with the change of pore pressure directly affects long-term productivity. Micro- and nano-pores are well developed in shale matrix. These organic and inorganic pores involve different mechanical properties and gas transport mechanisms, the variation of effective stress and flow regimes all affects their apparent permeability. Moreover, gas-adsorptioninduced organic matter swelling also influences the apparent permeability to varying degrees. Based on the poroelasticity theory, this paper establishes an apparent permeability model suitable for shale matrix with consideration of different mechanical properties and fluid flow mechanisms in organic and inorganic pores and gas-adsorption-induced deformation. The impacts of different pore properties are analyzed, and the controlling factors for apparent permeability evolution are figured out. Results indicate that shale matrix apparent permeability evolution is time-dependent during constant-pressure gas injection and depletion. The evolution process is mainly dominated by gas rarefaction effects, effective stress variation, and localized sorption-induced swelling or desorption-induced shrinkage near organic pores. These factors control apparent permeability at different times. The evolution process is also related to the ratios of the volume of organic and inorganic pores to the total pore volume.

10.11885/j.issn.1674-5086.2022.10.08.02