A Study Of Effect Of Biochemical Treatments On Flow Behaviors In Oil Reservoirs

In gas condensate reservoirs, when the flowing pressure of bottom hole goes below the dew-point pressure, condensation starts occurring. With the oil production, traps of condensate oil form at the bottom of wells to hinder the move of gas, which leads to decrease in gas production. In order to avoid the reduction of oil production, an effective solution is to alter wettability of rocks to intermediate gas wetting. In this study, the effects of biological and chemical surfactants on wettability alteration to intermediate gas wetting were analyzed, and the flow characteristics of two phases after wettability alteration to gas wetting were identified. The results could provide a stratagem to reduce the loss caused by the condensate oil blockage. Firstly,15kinds of surfactants were selected; The interfacial tension and the contact angle of water-air-quartz (the quartz surface has been treated by surfactant solution) of each surfactant solution with different concentrations were measured; Coreflooding experiments of water/gas and oil/gas were conducted to test the effects of the surfactants selected on the wettability alteration, and relative permeability curves were obtained. We study the effect of wettability alteration by analyzing and comparing the two phases flow behaviors before and after surfactant treatments.(1) There were4kinds of surfactants which appeared low interfacial tensions with large contact angle:FC-C01was a cationic fluorocarbon surfactant. When the solution concentration was20ppm, the quartz surface after treatment got a contact angle of99°. FC-N01was a fluorocarbon surfactant. When the solution concentration was20ppm, the quartz surface after treatment got a contact angle of93.5°. Both FC-C01and FC-N01got a very low interfacial tension of20mN/m with the solution concentration of100ppm. JST was a biological surfactant, rhamnolipid. When the solution concentration was50ppm, the quartz surface after treatment got an interfacial tension of42.59mN/m, and a contact angle of85.6°. JHEMU is a biological emulsifier. When the solution concentration was500ppm, it got an interfacial tension of37mN/m, and the quartz surface after treatment got a contact angle of107°.(2) The results showed the effects of wettability alteration about FC-C01became better with the raise of the concentration. When the concentration was100ppm, in the water-gas coreflooding experiment, the saturation of connate water, after wettability alteration, decreased by74%, and the final recovery of water increased by44%; In the oil-gas coreflooding experiment, the residual oil saturation after wettability alteration decreased by60%, and the final recovery of oil increased by24%. (3)The results also showed that the effects of wettability alteration about FC-N04became better with the raise of the concentration. When the concentration was100ppm, in the water-gas coreflooding experiment, the saturation of connate water after wettability alteration decreased by60%, and the final recovery of water increased by39%; In the oil-gas coreflooding experiment, the residual oil saturation after wettability alteration decreased by49%, and the final recovery of oil increased by16%. The FC-C01solution had better effect on wettability alteration than the FC-N01solution in the same concentration.(4) When the concentration was100ppm, the JST solution could not alter the wettability of core. However, when the concentration increased to500ppm, the JST solution showed outstanding effect on wettability alterarion. In the water-gas coreflooding experiment, when the concentration was500ppm, the connate water saturation after wettability alteration decreased by48%, and the final recovery of water increased by28%. In the oil-gas coreflooding experiment, the residual oil saturation after wettability alteration decreased by29%, and the final recovery of oil increased by12%.(5) The result showed the JHEMU solution had strong ability of altering wettability in this concentration. The JHEMU solution had better effect on wettability alteration than the JST solution in the same concentration. In the water-gas coreflooding experiment, the connate water saturation after wettability alteration decreased by70%, and the final recovery of water increased by38%. In the oil-gas coreflooding experiment, the residual oil saturation after wettability alteration decreased by60%, and the final recovery of oil increased by21%.The results of relative permeability of oil-gas and water-gas appeared similar tendency before and after wettability alteration:the gas relative permeability decreased while the liquid relative permeability increased. The biological surfactants showed strong abilities to alter wettability when the solution concentrations were high enough. With the advantages of environment friendly and economic, the biological surfactants were substantial for reducing the condensate oil blockage.