Investigation On The Influence Of Reservoir Heterogeneity On CO₂ Flooding

Most of China's oilfields with low permeability are mainly terrestrial clastic reservoirs,with complex geological conditions,and remarkable heterogeneity.Due to factors such as reservoir geological conditions,especially different geology under the conditions of different reservoir factors and gas injection factors,it will have a significant impact on the CO₂ flooding effect.At present,there are some studies on the effects of heterogeneity on the effect of CO₂ flooding based on actual reservoir models.However,the effects of heterogeneity of different reservoirs on CO₂ flooding efficiency and oil displacement efficiency are still lack of systematic research.In this paper,the typical low-permeability reservoirs in the periphery of Daqing Oilfield are studied,and the effects of reservoir heterogeneity on CO₂ flooding are systematically analyzed.Firstly,the research status of reservoir heterogeneity on CO₂ flooding is investigated,and the heterogeneous characteristics of reservoirs in typical low-permeability reservoirs around Daqing are analyzed.Then,In order to study the influence of permeability difference on CO₂ flooding,the physical simulation experiment of CO₂flooding and double core parallel CO₂ flooding was carried out.Finally,establish a conceptual model to describe the heterogeneity of different reservoirs.Through reservoir numerical simulation,study the influence of different types of reservoir heterogeneity on CO₂ flooding and optimize the well pattern and injection-production parameters of CO₂ flooding in different heterogeneous reservoirs,The technical methods for improving the CO₂ flooding effect of different types of heterogeneous low permeability reservoirs are given,which provides guidance for the engineering design of CO₂ flooding reservoirs in heterogeneous reservoirs.The results of parallel core flooding experiments show that when the grade difference is greater than 17.74,the low permeability core will not be affected,and the oil displacement efficiency is zero.Reservoir numerical simulation results show that channel permeability is the main influencing factor of CO₂ flooding in single channel sand body model.For different reservoir heterogeneity conceptual models,the greater the permeability homogeneity coefficient,the weaker the reservoir heterogeneity,the higher the CO₂ flooding recovery rate and the greater the oil change rate.Optimization results of mining strategy show that the final recovery degree of the rectangular five-point well pattern is about 2%?3.5%higher than the diamond-shaped nine-point well pattern.In addition to the delta phase model,the square anti-nine-point well pattern and the diamond-shaped anti-nine-point well pattern have little difference in the degree of recovery.In other models,the final recovery degree of the diamond-shaped anti-nine-point well network is higher than that of the square anti-nine-point well network by2.8%?5.5%.The reasonable well pattern for CO₂ flooding in heterogeneous low-permeability reservoirs is as follows:the first diamond-shaped anti-nine-point and then corner wells are converted into a five-point well network with oblique rows.The effect of CO₂flooding is seriously affected by reservoir heterogeneity.The bottom well flow and the bottom hole flow pressure of the production well located in the high permeability zone can be adjusted according to the actual situation.The increase in the degree of recovery before and after the optimization of bottom hole flow pressure is from 0.28%to 5.79%.