Synthetic model for evaluating CO2 flooding in tight oil reservoir

With the increasing energy consumption and the exhaustion of conventional oil reservoir, CO2 flooding is becoming one of the key technologies to improve the oil production of tight reservoirs. Not only oil production of CO2 flooding but also its main influencing parameters and quantitative evaluation have attracted people’s attention in recent years. The experimental and numerical techniques are the main approach to evaluate the production and influencing parameters. However, it is expensive and costs a lot of time to use those approaches. To solve the above problems, in this paper, a comprehensive integrated hierarchy and correlation model is initially established to evaluate the production of CO2 flooding and confirm the main influencing parameters. Specifically speaking, the Analytic Hierarchy Process (AHP) and Grey Relationship Analysis (GRA) are used to evaluate the main influencing parameters of oil production for the CO2 flooding process in tight oil reservoirs, respectively. Subsequently, the Rank-Sum Ratio (RSR) is adopted to combine the Analytic Hierarchy Process with Grey Relationship Analysis to acquire the comprehensive weight and ensure the main influencing parameters. The results show that the comprehensive weight of permeability, variation coefficient, sand injection, and reservoir thickness is 0.1157, 0.0937, 0.0914, and 0.0895 and those parameters play a extremely important role in the production of CO2 flooding. The model is applied to eight production wells and the rank–sum ratio is 2.3 to 6.6. The arrange regular of comprehensive results evaluated by the rank–sum ratio has a very consistent relationship with that of production. It is convenient and accurate to evaluate the production-related parameters by using the comprehensive integrated-hierarchy model, and this study provides a functional method to analyze the production performance.