Carbon dioxide (CO2) injection at supercritical conditions using the huff-n-puff process has been proven to be an effective resource to mitigate the production impairment generated by near wellbore condensate banking in rich gas condensate fields. This approach decreases the density of condensate and at the same time increases the density of the gas, thereby generating a reduction in the interfacial tension between the two co-existing phases. This study evaluates the impact of CO2 injection under the huff-and-puff process on gas recovery enhancement using reservoir simulation.
A compositional reservoir simulator was utilized to perform CO2 injection at supercritical conditions. Several sector models with local grid refinement (LGR) were constructed to evaluate the impact of CO2 injection at supercritical conditions (huff-n-puff) on the condensate banking in wells with rich gas condensate production. The evaluation considered numerous scenarios of injecting supercritical CO2 at different decreasing reservoir pressures in combination with sensitivities of CO2 injected volume, gas production rate, and soaking time duration.
The results indicated a significant reduction of condensate saturation around the wellbore leading to improvements in gas productivity. In addition, an optimum CO2 injection frequency required to maintain low condensate saturation in the near wellbore region was established. Overall, the results indicated that injecting CO2 at supercritical conditions in carbonate reservoirs has the potential to mitigate the condensate banking problem. A positive correlation between reservoir depletion status and gas recovery was also established from the study: optimum treatment results are obtained at condensate saturation above 20%, and at reservoir pressures below the dew point.
Condensate banking around the wellbore can significantly limit gas/condensate production and recovery. The injection of CO2 to overcome this problem has been more commonly used on sandstones while its use on carbonates is still under testing and development. This paper presents a reservoir simulation study using huff-n-puff CO2 injection in a carbonate reservoir to enhance well production and mitigate condensate formation around the wellbore region.