Experimental Study On Surfactant Flooding In Low Permeability Reservoirs

The Area a of Saertu oilfield belongs to a typical low permeability reservoir.After nearly fifty years of water injection development,the oil production in this area is very high.For the low permeability reservoirs in this area,water injection development is difficult to meet the economic requirements of development.For the block to the three oil recovery measures,but the effect on the block of low permeability reservoir rock and surface active agent is not clear,therefore,this paper carried out the experimental study on the block surface activity of low permeability reservoir oil displacement agent,effects of surfactants on the aim to master the area of low permeability reservoir oil displacement effect,which lays the foundation for the displacement of surface active agent.In this paper,we have analyzed and determined the rule and mechanism of surfactant flooding for improving the recovery efficiency of low permeability reservoirs in the study area by means of macro displacement experiments,microscopic visualization experiments and microscopic observation.Four understandings are summed up:A sophisticated single-phase and two-phase start-up pressure gradient method for the determination of low-permeability cores was developed,and the effect of different interfacial tension activator solutions on the starting pressure was investigated.The study shows that in the case of formation water or surfactant,the core of low permeability has a start-up pressure gradient,but the minimum start-up pressure and quasi-start-up pressure of low permeability core decrease significantly when the surfactant solution is injected.And the greater concentration of surfactant solution,affecting the starting pressure and non-Darcy flow more obvious.In low permeability cores,when oil encounters two types of fluid migration in the water phase,the oil-water displacement rate ratio is proportional to the pressure gradient of the two-phase start-up and inversely proportional to the water saturation.Under the same oil-water ratio,the interfacial tension is in direct proportion to the pressure gradient of two-phase start-up and inversely proportional to the water saturation.And as the amount of surfactant solution increases,the effect on the two-phase activation pressure and water saturation is increased.The relationship between interfacial tension of oil and water and the effect of core flooding with low permeability was studied.The surfactant solution can emulsify the simulated oil into droplets,and the average diameter of the droplets decreases as the interfacial tension decreases.The core permeability experiments with low permeability values were carried out under different interfacial tension values.The experimental results show that the core with low permeability values have very high irreducible water saturation and high residual oil saturation.However,the seepage zone of oil-water two-phase is very narrow,and the recovery rate of primary water-driven core is very small.When the interfacial tension of injected water decreases,the area of oil-water two-phase seepage becomes larger and the relative permeability of oil phase becomes larger.The relative permeability of the aqueous phase in the residual oil state also becomes larger,so that the oil recovery rate is improved.The experimental results of core recovery by displacing crude oil with surfactant solution slug show that the core recovery rate is small when a low permeability core is flooded once.After the injection of the surfactant solution slug.Waterflood recovery increased.When the oil-water interfacial tension decreases,the use of surfactant solution to make the recovery rate increases slowly.Surfactant Solution Sludge Decreasing Injection Pressure Experimental results show that when a low permeability core undergoes a waterflood,the pressure at steady state is very high.After injection of the surfactant slug,the injection pressure of the waterflood decreases small.With the decrease of interfacial tension,the pressure drop of surfactant solution increases and the pressure of injection decreases slowly.Low permeability cores with different wetting but similar permeability,cores analyzed for different wetting effects have a primary waterflood effect,and the effect of enhanced oil recovery and reduced pressure amplitude when surfactants are used.The experimental results show that the cores with weak wet-wet property have the highest recovery rate of water flooding once,the lithologies with neutral wettability are the second,and the cores with lipophilicity are the smallest.Low permeability cores with different wettability properties,when injected with surfactant slug,depressurize the amplitude differently.The cores with neutral nature have the largest pressure drop and the cores with weak water and wet property are the second.The total recovery of water flooding,surfactant flooding and secondary waterflooding shows that the cores with weak wet and wet properties have the highest oil recovery,the cores with neutral properties are the second,and the cores with lipophilic properties are the smallest.