REVIEW ON CO₂/CH₄ ADSORPTION AND DISPLACEMENT CHARACTERISTICS OF MICRO-NANO PORES IN SHALE RESERVOIR

Using CO₂ to produce shale gas can not only improve shale gas recovery, but also save water resources and carry out geological storage of CO₂, which is helpful to achieve carbon neutrality in shale gas production process. The gas migration mechanism in micro-nano pores of organic-rich shale reservoir is different from that of conventional reservoir. CO₂ has supercritical properties in the reservoir, which makes the exploitation mechanism complicated and it is impossible to obtain an accurate understanding of the microscopic mechanism of CO₂ exploitation of shale gas. Therefore, it is very important to study the adsorption and displacement characteristics of CH₄, CO₂ and their binary mixtures in micro-nano pores of shale reservoir for accurate evaluation and efficient exploitation of shale gas. In this paper, review on the adsorption properties of CH₄, CO₂/CH₄ binary mixture competitive adsorption and displacement properties in micro-nano pores of shale reservoir were carried out from three aspects: experiment, basic theory and numerical simulation. The key question and research trend on the CO₂/CH₄ adsorption and displacement characteristics of micro-nano pores in shale reservoir has been discussed. The results show that CH₄ is physically adsorbed in shale reservoirs, and the characteristics of organic matter (abundance, maturity and type), pore structure, inorganic mineral composition, temperature and pressure, and water content all have a certain degree of influence on CH₄ adsorption capacity of shale. Under the same conditions, CO₂ is more easily adsorbed by shale reservoir than CH₄. Injecting CO₂ into shale reservoir can promote the desorption of CH₄ and facilitate the geological storage of CO₂. The deployment of the production plan can adopt the injection production method in the form of well pattern. The production plan can be optimized by adjusting the location, number and CO₂ injection rate of injection wells.