| The energy structure has given priority to coal for a long time in China and the contradiction between supply and demand of oil needs have to be eased by increasing domestic oil production. In the meantime the environmental problems caused by the burning of a large amount of fossil fuel for industrial production are gripping attention around the world. Effective usage of CO2 in enhancing oil recovery and storage of industrial emission is one of the efficient measure to cope with the energy and environmental problems. We can achieve emission reduction directly and effectively by burying captured CO2 in deep saline aquifer with lots of basin structure layers or inject CO2 to the oilfield with low production for enhancing oil recovery. The injection of CO2 into layer will cause two phase or multiphase fluid flow in the caprock pore space. Interaction between fluid-fluid and core-fluid in reservoir can affect the distribution of the fluid on the caprock surface as well as on the direction and size of the capillary force, which would impact the fluid flow in the caprock. To estimate storage capacity of saline aquifer, interfacial tension between fluids and wettability of caprocks related to reservoir temperature and pressure should be measured thoroughly. Thus, a large number of experimental results of the interfacial tension (IFT) of fluid-fluid and wettability of caprocks at reservoir condition will provide data base for the oil recovery research and safe & long-term capillary trapping of CO2. In this paper, to enhance oil recovery and achieve CO2 geological storage following research is carried on:In this study, IFT valves of CO2-brine and decane-water were obtained via Pendant-Drop shape analyze method. The detailed analysis of the relationship among interfacial tension, temperature, pressure and salinity were processed. Then, we get the corresponding correlations to predict CO2-brine interfacial tension at constant temperature and pressure and certain salinity. The contact angles of different Berea sandstones in the presence of supercritical, liquid and gas CO2 were measured through Sitting-Drop method and the wettability alteration of Berea core surfaces in the presence of supercritical CO2 was systematically investigated at elevated temperatures and pressures. According to the research, IFT of the decane-water is independent of pressure but it will show the tendency to increase with temperature, however interfacial tension for CO2-brine systems decreases with pressure and increases with temperature and salinity. And for CO2-brine system, the linear relationship between IFT growth and salinity was observed. On the other hand, contact angles of different Berea sandstones exhibited different response to the temperature and pressure change, which may be caused by difference in surface roughness and component. Whereas, in the presence of supercritical CO2, both Berea cores become less water-wet.After the experiment process, pore network of Berea sandstones were obtained via Maximal Ball (MB) method. Then flow simulation of oil-water and CO2-brine two phase flow simulation based on pore network modeling were carried out to study the corresponding oil/gas-water two-phase relative permeability curves and capillary force curve, thus the input parameters, such as rock wettability and interfacial tension have been obtained from the experiment. Estimation of seepage characteristics showed good agreement with the results available in literatures. It indicates that pore network model can not only be used to predict oil-water percolation features, but also for CO2- brine seepage characteristics study in reservoir, that will provide a powerful technical guidance for predicting CO2 storage capacity of saline aquifer. Moreover, according to the simulation results, we observed that CO2 sequestration efficient in saline aquifer will be greatly affected while CO2 is in its supercritical state. |
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