A Fundamental Study On The Underground Sequestration And Ehanced Oil Recovery Utilization Of Carbon Dioxide

It has been widely concerned about the impacts on global climate and environment caused by carbon dioxide (CO2) green-house gas emission. Mitigation of CO2 emission to the atmospere has great importance to the sustainable development of mankind. CO2 underground sequestration and enhanced oil recovery are the two main options of many mitigation metods. Underground sequestration based on mature techniques and appropriate locations is a method with the most potential capacity. On the other hand, enhanced oil recovery is considered to be a win-win method for both economic and environmental benefits because it may not only storage CO2 underground but also improve oil recoverable reserves. This project is proposed against the background of long term and safe storage of CO2. Experiments for CO2 storage in artificial sediments were inducted at laboratory scale. Fundamental studies on CO2 hydrate storage in ocean sediments, storage in saline aquifer and enhanced oil recovery were carried out for obtaining basic data and mechanism in expectation of theoretical support for CO2 sequestration.A high precision and maneuverable experimental system for CO2 hydrate equilibrium study in simulated ocean sediments was developed. Ocean sediment environment with different pore size and salinity was built up using glass beads with different grain size and brine with different concentration.Experimental studies on the effect of pore size, salinity and nitrogen fraction on CO2 hydrate equilibrium were carried out using the experimental system of hydrate equilibrium. Results showed that equilibrium of CO2 hydrate moves toward high pressure and low temperature direction as pore size decreses as well as salinity and nitrogen faction increases. It needs higer pressure and lower temperature for the stability of CO2 hydrate in ocean sediments than in pure water. It was also shown that permeability decreases exponentially with hydrate saturation as hydrate grows in porous media.Another experimental system based on a 400 MHz magnetic resonance imaging (MRI) device and its peripheral equipments was also developed which can be applied to the visualization of CO2 hydrate and CO2-water-oil multiphase flow in porsous media.Induction time and saturation were measured and growth pattern was visualized as hydrate formed in porous media. Results showed that induction time decreases greatly as super cooling temperature and initial pressure increase. Final saturation of hydrate was linear relation with super cooling temperature and initial pressure. Hydrate grows in a pattern of cementing with glass beads pack-simulated sediments in our experiments.Porosity obtained using MRI intensity analysis was shown to be identical with tradition methods and local porosity was also obtained. Channeling and fingering phenomenon arose by buoyancy was obviously detected in CO2 flooding through water saturated sediments. Experiment results showed that paths with higher permeability are the main reasons which make CO2 become lazy in saline aquifer storage. Phase velocities of water and CO2 flowing in porous media were also obtained by using MRI pahse shift imaging and MRI saturation analysis combined with Darcy’s theory.Miscible status of CO2 with oil was detected and minimum miscibility pressure (MMP) was quantified exactly using MRI intensity analysis. Water flooding experiments in simple channels showed that wettability has great effect on oil displacement. Results showed that isolated oil drops trend to form in bifurcate channels which is a main inducement of oil trap after water flooding.Comparison of immiscible and miscible displacement of CO2 showed that pistion-like miscible zone of CO2 and oil can improve the sweep coefficiency and enlarge the breakthrough time during CO2 flooding. It showed that a much higher displacement coefficient can be obtained in CO2 miscbile displacement than in immiscible displacement.