超临界CO2作用下页岩油储层孔隙变形及渗流特性演化

The technology of developing shale oil enhanced by supercritical CO2 is a new method in China. The impact of treating shale oil reservoirs with supercritical CO2 on the seepage characteristics of shale oil is a key scientific issue for this new method. However, to my best knowledge, there have been very few studies on it. In this project, on the basis of the identification of the adsorption and dissolution of supercritical CO2 in shale oil reservoirs, the adsorption-strain, pore pressure-strain and corrosion-strain are measured under the treatment of supercritical CO2 through a gas—deformation experiment with the combined influence of multiple factors, and to establish a deformation model of oil-bearing shale under the action of supercritical CO2 on account of the energy conservation principle, thereby revealing the evolutionary mechanism of pore deformation of shale oil reservoirs by supercritical CO2. And on this basis, the experiment of viscosity and volume variations of supercritical CO2—shale oil system under multiple conditions will be carried out, so that to clarify the dissolution of supercritical CO2 in shale oil and the effect of supercritical CO2 on the viscosity and volume of shale oil. After understanding the interactive mechanism between the shale pore deformation, the adsorption of supercritical CO2 and the dissolution of supercritical CO2, a shale oil seepage model, concerning the reduction of shale oil viscosity and the volume deformation by dissolution of supercritical CO2 /pore deformation of shale, can be established. And then the model will be verified by a nuclear magnetic resonance experiment based on supercritical CO2—shale oil miscible displacement, so as to discuss the evolutionary mechanism of shale oil seepage characteristics under the treatment of supercritical CO2, as well as to provide a theoretical basis for enhancing the development of supercritical CO2 in shale oil.

超临界CO2吞吐是我国页岩油开发的新方法。其中，超临界CO2作用下页岩油储层孔隙变形及渗流特性的改变是这一新方法的关键基础问题。然而有关这方面的研究却鲜有报道。本项目旨在超临界CO2在页岩油储层吸附和溶解识别的基础上，通过多因素综合影响下气体—变形实验，明确超临界CO2作用下含油页岩的吸附—变形、孔隙压力—变形与腐蚀劣化—变形，建立含油页岩超临界CO2作用下的变形模型，揭示超临界CO2作用下储层孔隙变形；在此基础上，开展多条件下超临界CO2—页岩油体系粘度与体积变化实验，明确超临界CO2在页岩油中的溶解、及对页岩油粘度和体积膨胀的影响，在明确页岩孔隙变形—吸附—溶解过程相互作用机制的前提下，建立考虑超临界CO2溶解后页岩油降粘和体积变形/页岩孔隙变形的页岩油渗流模型，并以驱替核磁共振实验为验证，探讨超临界CO2作用下页岩油渗流特性演化，为超临界CO2吞吐开发提供页岩油运移的理论基础。

我国页岩油储量较大，但因页岩油储层地质特征及超临界CO2对油页岩的影响复杂性，近些年部分专门针对CO2开采页岩油的效果并不理想，以致产能不具备商业开发的经济效益，而随着“碳中和”政策的出台，CO2应用于非常规资源开采的问题越来越受到大家的关注。为此，本项目针对超临界CO2强化页岩油高效开发，对超临界CO2强化页岩过程中页岩在两相流体中的变形、孔隙演化以及超临界CO2压裂页岩裂缝扩展数值仿真进行了研究。通过XRD、N2GA、MIP、FE-SEM等相关实验，结合分形理论，确定含液相页岩超临界CO2处理前后页岩孔隙结构变化特征；结合页岩在不同温度、压力的超临界CO2和He中的气体—变形规律研究，根据能量守恒、热力学和表面物理化学原理建立了基于CO2吸附密度的页岩吸附-变形计算模型，明确页岩吸附超临界CO2的膨胀变形机理；在此基础上开展含液相页岩在不同压力的超临界CO2和He中的气体—变形规律研究，考虑有效应力原则和力学弱化，揭示了超临界CO2与液相体系作用下页岩膨胀变形机理；最后基于Griffith断裂准则对页岩储层损伤情况进行识别，并通过相场法和变分的裂缝扩展能量守恒定律，明确超临界CO2压裂页岩储层的裂缝扩展情况，继而为强化页岩油开发、提高非常规资源采收率提供理论支撑。不仅能够弥补CO2强化页岩油开发的相关研究的不足，还能够打破开发常规能源资源的传统观念，实现创新，为非常规能源的开发研究注入新的力量。