Low Permeability Reservoirs Co <sub> 2 </ Sub> Enhanced Oil Recovery Technology And Application

In recent years, more and more low-permeability reservoirs were discovered, and occupied so large proportion. But the development of low-permeability reservoirs is very difficulty with a very low depletion recovery and a very high injection pressure of waterflooding. So, how to develop the low-permeability reservoirs economically and efficiently becames a quite difficult and significant project. It is known that gas possess easy flow, volume expansion, reduce viscosity and interfacial tension when injection to formation oil, and CO₂ is a optimise solvent during gas injection displacement. Therefore CO₂ injection has a unique predominance at solving low-permeability reservoir development. So, it is very significant to investgate the displacement mechanism and displacement effect as well as how to practise CO₂ gas injection in field effectly.In this dissertation, Daqing Fang 48 fault block Fu Yu reservior is the research object. Reservoir fluid-CO₂ expansion experiment, slim-tube tests and long core displacement experimental were conducted in door. The results of experiments also were modled with Winprop EOS package. The test aear CO₂ injection dynamic performance was analysesed, from which we fould the exit problem of gas injecton. Based on the geologic characeristic of the test field, simulation model was established for gas injection displacement. After matching CO₂ injection dynamic performance by using GEM component simulator, development progrom such as water flooding, gas injection and WAG were designed and predicted. At the end, the optima program fit to this test aera was selected.The results show that the CO₂ injection makes coefficient of expansion, volume coefficient and gas-oil ratio of the formation fluid be increased, and the oil viscosity be reducted. The MMP (Minimine Misible pressure) of CO₂ injection measured by slim-tube tests is 47 MPa. Considered practical conditions of formation pressue and fructure pressure of formation, it is proctical to perform CO₂ injection immiscible displacement. The study results also show that low-permeability reservoir gas injection has a threshold pressure, and the value of this experiment is 2.48 MPa. The recovery of CO₂ injection core displacement is 48.15% at 22.64MPa. From gas injectiong performance, we fould that the gas injection presure was low, it state that gas injection has solved the problem of water injection pressure too high. The resean may be that the injected CO₂ has improved the permibility of near wellbore formation. The simulation results show that water drive will be a best choic after CO₂ breakthrough if injected gas formed an oil-gas mass transfer transition zone. And wells should open and shutin intervally after the gas-oil ratio of the produced well rose to a certainty degree.