Main Controlling Factors Of Displacement Efficiency Based On Dynamic Migration In Chemical Combination Flooding

As one of the leading technologies of tertiary oil recovery in China,alkali-surfactant-polymer(ASP)combination flooding technique improves displacement efficiency significantly by forming ultra-low interfacial tension(IFT)between oil and water.However,ultra-low IFT is difficult to achieve,which needs high concentration of strong alkali.And the impact factors of ultra-low IFT are complicated,in particular chemical agent loss.In consideration of the technical limitations of the traditional ASP flooding,and aiming at reevaluating the main controlling factor of displacement efficiency in chemical combination flooding,developing chemical flooding theory and optimizing combination flooding technology,physical experiments and theoretical calculation are conducted to study the displacement mechanics and application effect.Firstly,the distribution rule of displacement agent component and residual oil between injection and production wells are obtained.A 30-meters long sand-packed model is built in laboratory for the investigation of system property changes during long distance migration.Oil displacement experiments are conducted with the model to simulate combination flooding using typical formula in Daqing Oilfield.The residual oil saturation is measured with modified colorimetric method,and the distribution characteristics of residual oil at different flooding stage with different EOR method are obtained.With the analysis of chemical content of liquid samples collected along the model,the relationship of component retention and migration distance is obtained.The parameters,e.i.,accumulative retention amount and mass distribution deviation are created to describe the uneven distribution degree of chemicals in the displacing direction.Besides,the invalid retention of chemicals and its effect on displacement efficiency are discussed.Secondly,the effect on the development of different area between injection and production well by main controlling factors of displacement efficiency is investigated.laboratory experiments are carried out to obtain the effective range of ultra-low IFT and its functional relationship with well spacing.The ultra-low IFT area and the oil enrichment area are non-overlapping and the contradiction is difficult to weaken.In view of the impact factors of emulsion properties,an evaluation method for emulsification of effluent,e.i.,Synthetical Dispersion Number(SDN)Method is established.The effective range of emulsification in combination flooding is then analyzed.In addition,the result is confirmed that injecting ASP slug in advance is beneficial to oil emulsification.The changing relationship of viscoelasticity and migration distance is analyzed,and the result indicates that the loss of elasticity is the mainly reason of the significant decrease of displacement efficiency in the in-depth reservoirs.Thirdly,the energy stabilization mechanism of oil-water disperse system during dynamic migration is analyzed.Experiments on etched microscopic pore models are implemented to investigate the residual oil tapping mechanism by emulsification and its triggering condition.The relationship of emulsion conductivity and activation energy of oil particle coalescence is analyzed,and the controlling factor of coalescence rate is discussed.The result shows that IFT has little impact on the control of particle coalescence.The effect on the total interfacial energy by dispersion and IFT is analyzed by means of chemical thermodynamics.Then,the total work by electrical repulsion of particles and shear force of pore is calculated respectively,to study the forces which resist the particle cohesion during the migration of dispersion system.The result also confirmes the spontaneity of demulsification during migration.Further analysis is carried out to ascertain the main controlling factor of displacement efficiency in chemical combination flooding during migration.Finally,basing on the main controlling factor of displacement efficiency,with the evaluation method for emulsifying ability of ASP solution,e.i.,CPI(Comprehensive Property Index)Method,the new type ASP formula is decided.Besides,the injection timing is optimized.With the 30-meters long sand-packed model and 3D models with a five spot well spacing pattern,the production performance of new type ASP formula is evaluated by flooding experiments.The contribution to the total incremental displacement efficiency by combination flooding in the effective range of ultra-low IFT,emulsification and viscoelasticity is calculated.And the superiority of new type ASP system is analyzed by contrast with traditional ASP system.New type ASP system can improve displacement efficiency by the residual oil tapping capacity from its emulsification property,which has fewer restrictions on the ASP formula.The low dosage of strong alkali reduces the chemical cost and formation damage.Hydrophobic associated polymer increases the salt and alkali tolerance of the combination system,protects its mobility modification ability and save the dosage of polymer.Injecting ASP slug in advance increases the emulsifying effect and shortens the period of tertiary recovery.The superiority on emulsification and viscoelasticity of new type ASP flooding leads to a better development effect in the in-depth reservoirs,and achieves a superior displacement efficiency to traditional ASP flooding.The research enhances understanding of displacement efficiency under a dynamic condition.It also clarified the changing of a multi-phased dispersion system from the perspective of energy.The achievements can supplement chemical flooding mechanism and provide guidance for the optimization of combination flooding and innovation of EOR technology.