Experimental Study Of Surfactants In Depressurization And Augmented Injection Mechanism And Influence Factors For Low-permeability Reservoir In Bonan Oilfield

According to the conditions of low permeability, low porosity and high water injection pressure for low permeability reservoirs inY-34 block of Bonan Oilfield, surfactant system has been used to change the wettability of rock surface, to reduce the seepage ability of injected water and increase the water phase permeability, to achieve the goal of reducing pressure and increasing injection.First the experiments of IFT measurement, emulsification test, solubilization test and wetting angle measurement were carried out to screen the main surfactant G, which has very low interfacial tension, good emulsion stability and soluble oil capacity and can change the wettability of rock surface. The lowest oil water interfacial tension can reach 10-2 mN/m, the water bleeding ratio is almost zero when the concentration is 0.01%, the soluble oil volume fraction is 12.57%. Then butyl alcohol and isopropyl alcohol were optimized to improve solubilization effect, and the optimum ratio is 2:3.The surfactant was compounded with butyl alcohol and isopropyl alcohol to determine the best ratio of system’s main agent and additives. Its best using concentration was also optimized. The best ratio is 1:1 and the best concentration is 0.02%. After cores were dealt with this system, wettability changed from strong water-wet to weak water-wet or neutral wet, which indicated the wettability change effect was remarkable. Then the indoor core simulation displacement experiment was carried out, the results showed that water flooding pressure declined sharply when the injection rate was 1 PV-4PV. The pressure drop rate reached up to 17.3%.The effect was obvious.