Research progress on influence mechanism and control method of wettability on CO2 dissolution storage
Dissolution storage is an important mechanism of CO2 storage,and it is influenced significantly by reservoir wettability.So far,however,the influence mechanisms of wettability on CO2 storage efficiency and safety have not been understood.In this paper,the relationships between reservoir wettability and seepage are analyzed,the influence mechanisms of wettability on CO2 dissolution storage are summarized comprehensively,and thus the control method to optimize reservoir wettability is proposed.The following results are obtained.First,reservoir rocks are generally hydrophilic,and the wettability is mainly under the influence of pressure,temperature,formation water salinity,and rock surface roughness.The CO2-water and rock interaction and the organic acid in reservoirs can decrease the water wettability of the reservoir,and change it into CO2 wettability,which is not beneficial to safe CO2 storage.Second,CO2 dissolution storage process includes three key steps,i.e.,dissolution,diffusion and convection,among which,convection plays an important role and can enhance gas molecule transport,improve gas-liquid contact effect and increase the dissolution rate,so as to increase the amount of dissolved CO2.Third,wettability has an important influence on CO2 migration and dissolution amount.In CO2 wet reservoirs,the gas diffusion intensity in pores is higher,and the gas-liquid contact area is larger,which increases CO2 migration distance and dissolubility,but it is not beneficial to safe storage.However,water wet rocks can decrease CO2 flowability,thus diminishing CO2 leakage risks.Fourth,surfactant plays a significant role in optimizing the wettability,while nano-particle fluid can reverse the action of organic acid on rock surface,so as to turn CO2 wettability to water wettability or weak water wettability.In conclusion,it is indicated by considering CO2 dissolution storage amount and storage safety comprehensively that water wet reservoirs are more favorable safe CO2 storage.What's more,increasing the water wettability of a reservoir by controlling and optimizing the wettability can reduce CO2 leakage risks and improve CO2 storage capacity,so as to ensure the stability and safety of long-term CO2 storage.
CO2 dissolution storageWettabilityFormation migrationStorage safetyWettability controlSurfactantNano-particle
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