二氧化碳开采页岩气过程储层物性变化机制研究

Unconventional energy (e.g. coal bed methane, shale gas) now is playing more important roles in the whole energy system. The utilization of CO2 for shale gas extraction can reduce the emission amount of green house gas and mitigate global warming, which not only brings economic benefit but also brings significant social benefits. Understanding the adsorption capacity and deformation change during adsorption of methane and CO2 on shale, may help the exploitation and resource evaluation. This project mainly focus on the laboratory experiments on shale samples to explore their adsorption desorption ability for CO2 and nature gas during CO2 flooding, investigating the volume deformation of shale samples and the variation of porosity and permeability. The influencing factors on physical properties of shale reservoir will be studied as well. Based on the experiment results, the variation rules of physical properties of shale reservoir will be investigated and the variation mechanisms will be clarified which can provide accurate information to build simulation model to describe the process for CO2 flooding and storage. Meanwhile the mechanisms of CO2 flooding for shale gas will also be studied.

随着常规油气资源勘探难度的增加，页岩气等非常规油气资源在能源结构中的地位越来越重要。利用CO2驱替页岩气，可以减少温室气体的排放，缓解全球气候变暖，不仅有很好的经济效益，而且具有重要的社会效益。认识和了解页岩孔隙中甲烷和CO2的吸附特征及岩石形变规律，对于页岩气的资源评价和开发有着十分重要的意义。本项目主要针对CO2开采页岩气过程中，页岩孔隙对CO2、天然气的吸附性能及解吸性能，考察驱替过程中页岩岩石体积形变，研究CO2驱替过程储层的孔隙结构、渗透率发生的变化，考察影响储层物性变化的因素。在实验研究的基础上，揭示CO2开采页岩气过程储层物性的变化规律，阐明CO2开采过程储层物性变化机制，为CO2开采页岩气技术的优选及CO2的地下埋存提供准确的气藏信息和储层物性变化的物理化学模型奠定数据基础，同时揭示CO2驱替页岩气的相关机理。

利用页岩对于CO2强的吸附能力，将CO2注入页岩层中，通过竞争吸附机理可以促进页岩中CH4的解吸，从而实现页岩气的增产。实验采用静态容量法研究了页岩对于CH4、CO2和N2纯组分的吸附规律以及页岩对于CH4和CO2混合组分的吸附解吸规律并利用GRI(粉碎岩心渗透率测量)方法和SEM、液氮吸附法分别研究了CO2对于页岩渗透率和储层孔隙结构的影响。实验结果表明，页岩对于三种纯组分气体的吸附能力大小依次为：CO2＞CH4＞N2。温度升高会降低页岩对于气体的吸附能力。Langmiur吸附公式可以用来准确描述CH4的吸附过程，CO2和N2的吸附过程符合Henry吸附公式。与纯组分吸附实验中页岩优先吸附CO2的规律不同，页岩对于CH4和CO2混合气体的吸附过程则呈现优先CH4的规律。而混合气体的解吸过程又呈现出优先吸附CO2的规律。由于页岩气的增产评价取决于混合气体的解吸过程，CO2凭借着解吸过程中表现出来的吸附优势促进了CH4的解吸，使得CH4的解吸率增加。因此利用CO2开采页岩气具备一定的可行性。GRI测试结果表明CO2对于页岩渗透率没有明显的影响。SEM和液氮吸附的结果显示，CO2对于页岩样品中的孔隙大小和结构特征均没有明显影响。