Simulation Experiment Research On The Core Displacement Of Residual Gas Formation Process Under The Condition Of Geological Storage

Global warming has been a serious threat to human life and property,one of the culprits who causing global warming is carbon dioxide, How to reduce the CO₂ content of the atmosphere has been a scientific problems of mankind which need to solve immediately. CO₂ geological storage is one of methods which many scientists approved, and CO₂ geological storage in deep saline aquifers is one of the important parts. CO₂ geological storage in deep saline aquifers has many kinds of different storage mechanisms, such as, structural and stratigraphic, hydrodynamic, residual gas, solubility and mineral traps. The formation of trapped gas storage experiences two processes: first, to form residual water in rock pore at the CO₂ injection stage, second, the formation water returns when we stop injecting CO₂, some supercritical CO₂ will residue in rock pore, this is the trapped gas.We used deionized water, 17.5g/L, 35g/L Na Cl solution and 17.5g/L CaCl₂ solution which made in our laboratory by ourselves, to do the flooding experiment and simulated forming process of residual gas, under 40℃8MPa. This process was on the basis of the previous experiment which the residual water had formed. In this study, we used a homogeneous, isotropic, hydrophilic man made core, it is a long cylindrical core, with a permeability of 1.33 mD, porosity of 13.9%, and dimensions of 50*80 mm. when gas flooding water for 6 hours, we could make curves of residual water saturation with time, and know the final residual water saturation.From curves of residual water saturation, we can find that with increasing of the NaCl concentration, the residual water saturation increase, in a certain concentration range, but when the concentration exceed a certain value, the residual water saturation will decrease. The CaCl₂ has a very small effect on the formation of residual water, and its final residual water saturation is very close to the deionized water, the NaCl has a significant effect on the formation of residual water. The results show that between Cl-Na-type water and Cl-Ca-type water, the Cl-Na-type water can trap more residual water at the CO₂ injection stage, inject less CO₂. The results of gas flooding water experiment shows that the NaCl has a significant effect on the formation of residual gas, and with increasing of the NaCl concentration, the residual gas saturation increase, also the CaCl₂ has a significant effect on the formation of residual gas, the residual gas saturation of NaCl concentration is bigger than CaCl₂ concentration. This also means that in deep saline aquifers, the Na⁺、Ca²⁺、Cl^- has a significant effect on the formation of residual gas, storage potential of trapped gas of Cl-Na-type water is bigger than CaCl₂ concentration.