Characteristics Analysis And Application Of Precipitation In CO₂ Flooding Of Low Permeability Reservoir

CO₂ flooding can be used as an effective means to increase oil recovery in low permeability reservoirs.However,when CO₂ is injected into the formation,CO₂dissolves in the formation water and undergoes a series of chemical reactions with the ions in the formation water to form precipitation,which affects the development of the field.In view of the problem of precipitation during CO₂ flooding,this paper has determined the research method of precipitation through literature survey and theoretical analysis.Through the static experiments of high-temperature and high-pressure reactor,the composition and amount of precipitation with CO₂ under different conditions of pressure difference,temperature,and scale ion content were studied.The effects of pressure difference,temperature,and scale ion content were analyzed,and established a corresponding quantitative characterization model.Through CO₂ continuous injection gas core flooding experimental methods,the core permeability and porosity variation characteristics under different pressure conditions were analyzed and compared.The changes of core physical properties under formation water with different scale ion content.The effect of precipitation on the physical properties of the reservoir was obtained.Based on the experiment,a numerical model was established to fit the model and experimental results,and the model parameters were determined to ensure the accuracy of the model.The model parameters were used in the typical area of Jiyuan oil field in Changqing to predict the distribution of precipitation during continuous gas flooding,and the effects on reservoir physical properties and development parameters with and without consideration of precipitation were compared and analyzed.Through experiments,it was found that CO₂ flooding in ultra-low permeability reservoirs is prone to precipitation under conditions of large differential pressure,low temperature,and high scale ion content.The sedimentation laws and the adverse effects on the physical properties and recovery of the reservoirs were summarized through precipitation numerical models.Taking the typical area of the Jiyuan Oil Field in Changqing as an example,it was found that the precipitation was eventually distributed in the production wells and its vicinity.The presence of precipitation would reduce the gas-oil ratio and recovery.The research results have guiding significance for the development of CO₂ flooding in ultra-low permeability reservoirs with high scale ion formation water.