A Case Study on Simulation of In–Situ CO2 Huff–‘n’–Puff Process

Abstract

In-situ carbon dioxide (CO2) huff-‘n’-puff (ISCHP) is a promising enhanced-oil-recovery (EOR) technique that could overcome some major drawbacks associated with continuous CO2 flooding such as early CO2 breakthrough, high operation costs, and demand for CO2 source. The application in Jiangsu Oil Field triggered the augmentation of well productivity and indicated the preliminary potential of this technique. Our work is to establish a prediction model for gas generation and to examine the mechanisms of ISCHP/EOR through sandpack tests and reservoir simulation. A salt solution with surfactant additives was selected to be the gas-forming agent, the gas-generating performance was tested in a high-temperature/high-pressure reactor first, and a kinetics-derived equation for gas-volume prediction was then verified by use of the experimental results. The displacement performance and efficiency were determined with sandpack tests with three different concentrations of a gas-forming agent. A reservoir model of ISCHP was established and calibrated on the basis of the sandpack-test results and past-production observations of the candidate well. The sensitivity analysis on the main-operation parameters was conducted to determine the optimal scheme, including injected volume, concentration, and soaking time. The results indicate that gas volume predicted by the theoretical model is well-matched to experimental data of the gas-forming reaction, the sandpack test makes clear the synergy of CO2 and chemical flooding in ISCHP, and a higher concentration of reagent tends to produce more oil than a lower one. Reservoir simulation shows a large amount of CO2 generated near the wellbore, an average growth of 61% in oil production, an regent usage of 0.91 ton/ton of oil, and a temperature decline of 2.5°C in the region of 20 m from the wellbore as a result of the endothermic reaction of reagent. On the basis of the reservoir model, the optimal scheme is achieved with a reagent concentration 16.4 wt%, an injected volume of 250 tons, and a soaking time of 7 days. This study can provide an improved understanding of ISCHP for EOR in Jiangsu Oil Field, including the gas-volume prediction, EOR potential in laboratory, and main operating parameters of ISCHP.