Experimental study on the effect of enhanced CO2/water alternate flooding in low permeability reservoir
In order to enhance the effect of CO2/water alternating injection(WAG)displacement in low permeability reservoirs,two methods of cone WAG displacement and active WAG displacement were proposed to solve the problem of CO2 viscous fingering.Through heterogeneous core displacement experiment,the change of recovery degree under conical water-gas ratio(5∶1～1∶1 and 1∶1～1∶5)and equal ratio(1∶1)injection is compared and analyzed.Based on the evaluation results of foam properties and interfacial activity,WAG enhanced surfactants were selected and WAG enhanced with active water was evaluated by heterogeneous core displacement experiment.The results show that the recovery degree of cone WAG displacement is higher than that of water gas displacement with equal proportion.L-1 surfactant with good foaming performance and low interfacial tension was selected.When the concentration of L-1 is 0.5％,the foam strength reaches medium strength and the oil-water interfacial tension decreases to 2.91 × 10-2 mN/m.When the concentration of L-1 is 0.4％,the recovery degree of the high permeability layer is increased by 26.82％,mainly to improve the oil washing efficiency.When the concentration of L-1 is 0.6％,the recovery degree of the low permeability layer is increased by 21.48％,and the main effect is foam regulation and displacement.The research results have guiding significance for realizing efficient development of CO2 flooding in low permeability reservoirs.
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