Volume 52

Characteristics and Key Controlling Factors of Impure CO2 Huff-n-Puff and Storage in Shale Oil Reservoirs with Complex Fracture Networks Lufei Bi, Jing Li, Fuhao Guo, Shuyi Zhou

Abstract

In the current context where the cost of obtaining pure CO2 is high, using impure CO2 gas for huff-n-puff is a more practical approach. The effects of impure CO2 huff-n-puff and storage in shale reservoirs with complex fracture networks, as well as the characteristics and main controlling factors of injecting CO2 of different purities for huff-n-puff and storage, are not yet well understood. This study considers the fracture extension mechanism in horizontal well fracturing and establishes an unstructured grid numerical model to depict fracture morphology. Using actual physical experiment results, a fluid model is fitted. By analyzing the impacts of huff-n-puff and storage under various production parameters and utilizing statistical methods, the key controlling factors of impure CO2 huff-n-puff and storage in complex fracture well networks are identified and their characteristics are summarized. The results indicate that, compared to injecting pure CO2 for huff-n-puff, injecting impure CO2 can still significantly enhance the recovery rate of shale reservoirs. Furthermore, the effectiveness of huff-n-puff and storage increases with the enhancement of production parameters such as soaking time, injection rate, and cyclic cumulative injection rate. Among these factors, Injection rate has the greatest impact on huff-n-puff effectiveness, while the timing of huff-n-puff has the greatest impact on storage effectiveness. This research provides a robust theoretical foundation and practical guidance for improving the development efficiency of shale oil using impure CO2 huff-n-puff technology.

Keywords shale reservoirs, impure CO2 huff-n-puff, complex fracture networks, CO2 storage