EXPERIMENTAL STUDY TO IMPROVE CRUDE OIL RECOVETY EFFICIENCY IN LOW PERMEABILITY RESERVOIRS——TAKING THE FANG48 BLOCK IN THE NORTH OF THE SONGLIAO BASIN AS AN EXAMPLE

Taking the Fang48 Block in the Daqing Oil Field as an example,it is studied the relationship between crude oil recovery efficiency and pressure when displaced by CO₂,N₂ and natural gas respectively through slim tube experiment.The minimum miscible pressures(MMP) of CO₂,N₂,natural gas and crude oil are measured.In the Fang48 Block,the MMP of CO₂ is 29 MPa and that of natural gas is 40 MPa.N₂ is not miscible from crude oil at the highest experiment pressure(44 MPa).Gas injection has been carried out in the Fang48 Block.Below the formation fracture pressure(31 MPa),CO₂ is miscible while natural gas and N₂ are not.When immiscible,the recovery efficiency with CO₂ displacing is the highest,natural gas the second and N₂ the lowest under the same condition.