不同成熟度页岩干酪根中CO2吸附与孔隙变形的耦合机理

Coupling Mechanism of CO2 Adsorption and Pore Deformation in Shale Kerogen with Different Maturities

  • 摘要: 页岩干酪根中CO2吸附会诱导孔隙变形,同时孔隙变形会影响干酪根吸附能力,CO2吸附与孔隙变形的耦合特征和微观机理尚不明确。针对不同成熟度的干酪根,采用分子模拟方法开展了其在不同应变和压力条件下的CO2吸附模拟;结合多孔介质力学理论确定了干酪根中CO2吸附-孔隙变形耦合系数,并分析了吸附-变形耦合特征;联合干酪根孔隙结构和非键相互作用(包括静电力和范德华力),明确了CO2吸附与孔隙变形的耦合机制。结果表明:页岩干酪根中CO2吸附与孔隙变形的耦合系数受干酪根成熟度影响,不能直接采用煤岩有机质中结果,干酪根吸附-变形能力随成熟度增加而降低。吸附-变形耦合系数在一定压力范围内(>2 MPa)可近似为常数,未成熟干酪根在压缩变形和膨胀变形阶段的耦合系数存在明显差异。CO2与干酪根的吸附作用以范德华力为主,其次为静电力。CO2吸附使得干酪根孔隙度和比表面积增加,孔径分布向更大尺寸偏移。研究结果揭示了页岩干酪根中CO2吸附与孔隙变形的耦合特征及微观机理,可为页岩储层CO2封存效果评价提供理论指导。

     

    Abstract: The adsorption of CO2 in shale kerogen results in the pore deformation, which, in turn, affects the adsorption capacity of kerogen. The coupling characteristics and micro-mechanisms between CO2 adsorption and pore deformation in shale kerogen remain unclear. For kerogen with different maturities, this study systematically simulated CO2 adsorption behavior under various strains and pressures using molecular simulation methods. Building on this, the coupling coefficient between CO2 adsorption and pore deformation in shale kerogen was quantified through poromechanical theory, uncovering its dynamic volution with kerogen maturity. Additionally, the micro-mechanisms of adsorption-deformation coupling were clarified by examining the evolution of kerogen pore structures and their non-bonded interactions (e.g., van der Waals and electrostatic forces) with CO2. The findings show that the coupling coefficient between CO2 adsorption and pore deformation in shale kerogen is maturity-dependent, and results derived from coal organic matter are not directly transferable. Furthermore, the adsorption-deformation capacity of kerogen diminishes as maturity increases. The coupling coefficient is approximately constant within a certain pressure range (>2 MPa), and significant differences are observed in the coupling coefficients for immature kerogen during its compression and expansion stages. The adsorption interaction of CO2 on kerogen is mainly controlled by van der Waals forces, followed by electrostatic forces. The adsorption of CO2 increases the porosity and specific surface area of kerogen and induces a shift towards larger pore sizes in the pore size distribution. The results reveal the coupled characteristics and micro-mechanisms between CO2 adsorption and pore deformation in shale kerogen, which provide theoretical guidance for evaluating the performance of CO2 sequestration in shale reservoirs.

     

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