超临界二氧化碳驱替页岩气动态竞争吸附传质机理研究

CO2 enhanced shale gas recovery (CO2-ESGR) is a key technology to extract the resources from shale gas reservoirs which are very tight and low permeability. It is vital to CO2-ESGR to reveal the mass transfer mechanism of dynamic competitive adsorption in the miscible displacement of shale gas by supercritical CO2. This research proposal will carry out the experimental and theoretical study on the dynamic competitive adsorption of CO2 and CH4 in the miscible displacement. The influences of shale mineral composition, fracture/pore structure and component contents of CO2-CH4 mixtures on the adsorption/desorption characteristics of CO2-CH4 mixtures in the fractured shale will be analyzed, and an adsorption/desorption kinetic model for will be established for the adsorption/desorption characteristics prediction of CO2-CH4 mixtures and its components. Simultaneously, the adsorption selectivity of CO2 and CH4 will be quantitatively analyzed to clarify the mechanism of the competitive adsorption of CO2 to CH4. Moreover, this proposal will conduct the miscible displacement experiments of CH4 by CO2 in the fractured shale. The CO2-CH4 dispersion/miscibility and dynamic adsorption/desorption characteristics will be quantitatively described by measuring the CO2 and CH4 concentration of the outlet gas in the displacement in real time. The interactions between the CO2-CH4 dispersion/miscibility characteristics and the dynamic competitive adsorption will be analyzed with considering the different temperatures, confining pressures, pore pressures and CO2 injection parameters. Correspondingly, a model will be built to predict this dynamic adsorption/desorption and competitive adsorption characteristics of CO2 and CH4 in the miscible displacement in the fractured shale. Moreover the mass transfer mechanism of the dynamic competitive adsorption of CO2 and CH4 in the miscible process will be indicated. The outcomes will provide a theoretical basis and technical support for the application of CO2 enhanced shale gas recovery and Chinese shale gas resources exploitation.

CO2增强页岩气开采是开发储层低渗、致密的页岩气藏资源的关键技术，压裂页岩内超临界CO2驱替CH4混相流动中的动态竞争吸附特性及传质机理，对CO2增强页岩气开采具有重要意义。本项目通过实验与理论分析，研究页岩矿物成分、裂缝孔隙结构和气体组分含量等因素对压裂页岩内CO2-CH4混合体系吸附解吸特性的影响，建立吸附解吸模型与吸附选择性评估准则，揭示混合状态下CO2、CH4竞争吸附机制；基于压裂页岩内CO2驱替CH4流动传质实验，实时追踪驱替过程中的气体组分动态变化，定量描述驱替中对流扩散作用下的CO2/CH4弥散混相特性与动态吸附解吸特性；探明多因素条件下裂缝孔隙内弥散混相与动态竞争吸附的相互作用，建立压裂页岩内CO2驱替CH4混相流动中的动态吸附解吸与竞争吸附预测模型，揭示其动态竞争吸附传质机理，完善CO2驱替页岩气流动传质基础理论体系，为我国页岩气资源优质高效开发提供支撑。

注CO2提高页岩气采收率技术既能够强化页岩气开采又可以实现碳封存，有助于清洁天然气生产和实现碳中和，CO2驱替页岩气过程中涉及复杂的混相流动和动态竞争吸附传质。本项目以此为背景，开展了页岩内CO2-CH4混合体系气体吸附特性及多因素影响规律研究，综合考虑了温度、压力、TOC、黏土含量、CO2含量等因素影响，分别基于Langmuir模型和神经网络建立了页岩内CO2-CH4混合体系吸附预测模型，引入竞争吸附选择系数研究了页岩内CO2-CH4混合状态吸附过程的CO2/CH4竞争吸附规律，建立了相应的竞争吸附选择系数预测评估模型，揭示了混合状态下的竞争吸附机制，基于对流弥散理论，考虑页岩基质气体吸附形成滞留区域的作用，探明了CO2驱替页岩气对流弥散混合与动态竞争吸附的相互作用，提出了改进型CSDCM方法用于描述CO2驱替页岩气流动传质规律，揭示了动态竞争吸附与对流弥散耦合传质机制。