Basic Research Of Adaptability Between Oil-displacing Agent And Heterogeneous Reservoir

At present,salt resistance or ultralow interfacial tension were usually regarded as major indicators in oil-displacing agent performance evaluation.Due to the blind pursuit of salt resistance and ultralow IFT,the cost increased and the oil-displacing agent with poor adaptability can't meet the actual needs.Based on the present achievements and from two facets of macroscopic and microscopic,the flow properties of four oil-displacing agents(HPAM solution,alkali/surfactant/HPAM solution,surfactant/HPAM solution,and poly-surfactant solution)were studied,the displacing effect of agent types and its combination were evaluated,and the contribution generated from mobility control was verified.The researches were guided by physical chemistry,macromolecular materials,and reservoir engineering and based on chemical analysis,instrument detection,and physical simulation.The experimental subjects were reservoirs and fluids of Daqing Oilfield,Liaohe Oilfield,and Dagang Oilfield.The major indicators were regarded as viscosity,IFT,molecular clew dimension,molecular structure,resistance coefficient,residual resistance coefficient,and recovery efficiency.The results indicated that HPAM was the type of linear chains.But the HPAM was the type of flaky-reticulation network with the action of alkali and petroleum sulfonate.The poly-surfactant presented a flaky-reticulation network and it was of a considerably larger molecular clew dimension than that of HPAM solution prepared with same polymer concentration.The results of permeability limit and molecular clew dimension tests indicated that the relation of adaptability between reservoir rock pore and molecular clew dimension was that the ratio of pore diameter mid-value to Dh,was between 4 and 7.Of all the four kinds of oil-displacing agents,the high concentration HPAM solution,poly-surfactant,alkali/surfactant/HPAM solution,and surfactant/HPAM solution,not only can the surfactant/HPAM solution expand swept volume effectively,but also it was of high displacement efficiency and large increment in recovery efficiency.The high concentration HPAM solution was of larger slug size,stronger ability in enlarging swept volume,and larger increment in recovery efficiency,when the agents were of same costs.The physical simulation results indicated that the mobility control ability can make more contribution to the recovery efficiency than that of displacement efficiency.Not only can the overemphasizing recovery efficiency increase the agents costs,but also it was bad for enlarging swept volume.Two aspects of the evaluation of adaptability between oil-displacing agent and reservoir must be included.One was that the molecular clew dimension must be adjusted with reservoir rock pore size.The other was that the mobility control ability of oil-displacing agents can adapt to reservoir average permeability and its heterogeneity.