Laboratory Evaluation Of CO₂ Injection Development In XX Oilfield

The target block XX oilfield is located in the Beibu Gulf Basin in the northern South China Sea,which is a fault block structure with complex faults.At present,the contradiction of water injection development in this block is increasingly serious,the water cut is rising rapidly,and the production is obviously reduced.From the perspective of the development trend of EOR technology in low permeability reservoir,the research and application of gas injection development technology have been developed year by year and achieved remarkable results.According to the actual situation of the target block,the feasibility analysis and injection mode research of CO₂flooding have been carried out to lay the foundation for the next development and adjustment of the reservoir.This paper analyzes the characteristics of the target block After comparing and analyzing the reservoir and fluid characteristics with the cases of CO₂flooding at home and abroad,it is proposed to analyze the phase state characteristics of CO₂flooding and determine the minimum miscible pressure of the target reservoir by the method of thin tube experiment.Finally,based on the long core displacement experiment,by changing the injection mode?continuous CO₂flooding,intermittent CO₂flooding,water/CO₂co injection flooding,water?/CO₂alternate flooding),the comprehensive recovery rate,gas breakthrough time and average injection capacity corresponding to each injection mode are compared and analyzed,and the injection mode and injection parameters suitable for the target block are optimized.The results show that there are gas sources in the target block,and the reservoir and fluid properties meet the CO₂flooding screening standard.The minimum miscible pressure measured by the thin tube test method is 29.49mpa,which is less than the original formation pressure,which means that the target reservoir can achieve miscible displacement of CO₂injection.After a certain amount of CO₂is injected,the viscosity of crude oil changes greatly.Finally,the volume expansion of crude oil in the formation is about 1.57 times,and the viscosity is reduced by about 2 times.It shows that the fluidity of crude oil is improved to some extent after gas injection.And through the simulated calculation of the pseudo ternary phase diagram,it can be seen that the target block can achieve multiple contact miscibility under the stratigraphic conditions,but not one contact miscibility.Through the long core displacement experiment,it is determined that the best injection mode of the reservoir is intermittent CO₂injection,the injection pressure is kept above the minimum miscible pressure,and the slug size is0.02PV.This study is of great significance for improving oil recovery of target reservoir,and can provide guidance for CO₂flooding of similar low permeability reservoir.