Identifying Method And Distribution Rule Of Remaining Oil After Polymer Flooding

By the end of 2007, there are already more than 30 polymer flooding areas in Daqing oilfield, 14 of which have completed polymer injection. In the future, there will more and more areas adopting polymer flood and then facing the problem of potential tapping. There is more than 40% of OOIP still remained in reservoir after polymer displacement. In order to effectively recover this amount of remaining oil, this paper demonstrated a study on the identifying method and distribution rule of the remaining oil after polymer flooding.This paper developed a set of method for identifying and evaluating potential and distribution rule of the remaining oil after polymer flooding, which incorporates laboratory experiment, nuclear magnetic resonance, fluorescence of slice of core, natural core analysis, log interpretation and numerical simulation as a whole and capable system. For the second, current situation of areas completed polymer flooding was evaluated, including water cut, recovery percent and remaining potential, etc.. For the third, this paper investigated influence of permeability variation coefficient, molecular weight of polymer, concentration of polymer solution and polymer slug size on flooding effect and remaining potential. For the fourth, mechanism of polymer enhancing recovery was studied. For the fifth, this paper defined 3 types of relative permeability curve, i.e., I-, II- and III-type, constructed eigen curve and corresponding equation and proposed a method for calculating relative permeability curve for every grid block in reservoir simulation. For the sixth, numerical simulation of remaining oil distribution after polymer flooding was made for western Beiyierpai area. For the last, this paper concluded microscopic and macroscopic distribution rule of remaining oil and proposed suitable potential tapping measures for different type of remaining oil.Evaluation shows that recovery percent of the 14 areas is 52.8%, a great deal of oil remained underground, and so continuous potential tapping is very necessary. The greater variation coefficient, molecular weight, concentration and polymer slug size, the larger recovery efficient and the lower remaining oil saturation. Polymer flooding can increase both displacing and sweeping efficiency and thus enhance oil recovery. Method for calculating relative permeability curve for every grid block can help increase the art and efficiency of numerical simulation. Microscopic remaining oil after polymer flooding mainly includes cluster, dead-end, cant and film type. Macroscopic remaining oil includes the upper part of rhythmic interval, poor connection, imperfect injection-production, branch stream line, near producing well, the second row of producing wells, imperfect perforation, near fault, large area of poor layer and ineffective displacement, etc.. For remaining oil in different layer unit, location, facies and of type, we should take different suitable measures to tap potential and futher enhance recovery after polymer flooding. Macroscopic remaining oil should be tapped mainly by globally optimized adjustment and microscopic oil by chemical processes such as polymer/surfactant, polymer/surfactant/alkaline and foam combination flooding.This study is of certain theoretical significance and value of field-scale application.