Experimental study on the minimum miscibility pressure of associated gas injection for oil recovery in low permeability offshore oil fields
To analyze whether mixed phase flooding can be achieved by injecting associated gas in L oilfield,experiments were conducted to determine the minimum miscibility pressure.The minimum miscibility pressure of associated gas flooding in the W31,W32,and W51 oil formations of offshore low-permeability L oilfields was measured using the long and thin tube experimental method,and the variation law of oil and gas compo-nents produced before and after gas breakthrough at the end of the long and thin tube was analyzed using a gas chromatograph.The experimental results showed that in the early stage of gas flooding(0-0.5 PV),the inject-ed gas did not migrate to the end of the long and thin pipe,and the produced fluid was crude oil.The oil dis-placement efficiency and gas oil ratio change law were similar under different pressures.As the pressure in-creased,the phase state of the injected gas and crude oil changed from immiscible to nearly immiscible,and then to mixed.The gas-liquid interface gradually disappeared,and the oil displacement efficiency continued to increase.Under formation pressure,the injection of associated gas into the W31 and W32 oil formations in L oilfield couldn't achieve miscible displacement,while the injection of associated gas into W51 could achieve miscible displacement.During the process of associated gas flooding,the main components of light hydrocar-bons in crude oil were extracted,while CO2 and C5+in associated gas dissolved in the crude oil.
offshore low-permeability oil fieldsCO2 floodingmiscible floodingminimum miscibility pres-sureoil and gas componentsassociated gas
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