Technology Of Decreasing Injection Pressure And Increasing Injection Rate By Surfactant In The Daqing Oilfield

Laminated reservoirs in low permeable oilfields in Daqing are characterized notably by low permeability, low porosity and great effect of microstructure. Flow resistance increases, injection pressure rises and water injection rate decreases quickly with continuous water advancement. Water injection efficiency depends on whether the injection pressure is high or low in water injection wells. High injection pressure will increase the load of formation injection allocation system and injection energy consumption, and meanwhile long-term high-pressure water injection can result in damage to casing. Analysis of reasons for high water injection pressure: the radical reason is the existence of starting pressure gradient, which must be overcome during water injection in low (ultra-low) permeable reservoirs, or else an effective pressue difference cannot be established to achieve the goal of oil displacement. Different from common reservoirs, surface molecule forces, capillary forces and others of low permeable reservoirs have essential effects on fluids through porous media. Surfactant solution can reduce oil-water interfacial tension, decrease capillary resistance of oil-wet reservoir, increase capillary numbers and enhance oil displacement efficiency, as a result, technology of decreasing injection pressure and increasing injection rate by surfactant in low permeable oilfields in Daqing is developed.Research on surfactant at present is mostly for enhancing oil recovery. Surfactant is a kind of chemical agent which can enhance oil recovery greatly and has wide fitness for purpose and development potential. However, results from production performance of field chemical flooding wells and laboratory core physical simulation experiments show that: surfactant can not only improve oil recovery greatly, but can increase filtration rate of reservoirs and decrease injection pressure also, and thus reduce the water injection difficulty under high pressure for lower permeable reservoirs and save production cost.Firstly on the basis of theories of decreasing starting pressure, combined with laboratory experiments of surfactant solution effect on relative permeability, this paper studies the mechanisms of decreasing pressure and increasing injection rate by surfactant. Results show that surfactant solution can reduce oil-water interfacial tension and increase oil flow capacity; change wettabilities of rock surface from oil-wet to water-wet, decrease capillary resistance of water drive; increase water-phase permeability and decrease injection pressure. Then based on analysis of these...