Study On Main Controlling Factors Of Air Flooding And WAG Optimization In Ultra-low Permeability Reservoir

During the exploitation for the ultra low permeability reservoir,water flooding is difficult and production capacity declines rapidly.Therefore we carried out research about the main controlling factors of air flooding which has the obvious advantages in both economic cost and injection capacity as well as optimization study of WAG(water alternating gas)which can improve the effect of the air flooding.The main mechanism to enhance oil recovery for the LTO-IAF(low temperature oxination-immiscible air flooding)process is to supplement the energy of the formation,while oxidative heat release is complementary.We established the kinetic model oxidation reaction at low temperature and typical model in accordance with the pilot area,meanwhile key parameters in the numerical simulation of air flooding were determined.Effective thickness,permeability,oil saturation,oil viscosity and injector-producer distance are the most sensitive parameters,which determine the effect of air flooding.We analysed dynamic characteristics and seepage laws for air flooding process with different facorts incluing geological factors,fluid factors and development factors.The evaluation system for the sensitivity was put forward.The sensitivity of dynamic and static parameters was evaluated.Eventually the main controlling factors were selected.Through the geological model of the pilot area,the production performance was tracked and the distribution characteristics of remaining oil were obtained.The pilot test showed that the characteristics of low permeability were prominent: there was a large pressure difference between the producer and injector,the production rate declined rapidly,the formation energy dropped rapaidly;the whole oil saturation was relatively high,so the effect of air flooding will be more obvious.When the heterogeneity of the reservoir is weak,application of WAG method in air flooding is not obvious;however,for the reservoir with strong heterogeneity,the application of WAG method could dramatically improve develop effect of air flooding.Pilot area is in early stage of gas injection,heterogeneity characteristics are not obviously.Thus we evaluated the actual model and the modified model with heterogeneity and analysed the effect and applicability with WAG and optimized the parameters.This paper forms the creative recognizition in the field of quantification of LTO-IAF mechanism and adjustment strategy design for air flooding in ultra deep low permeability reservoir.