Gas injection for enhanced oil recovery in two-dimensional geology-based physical model of Tahe fractured-vuggy carbonate reservoirs: karst fault system

Gas injection serves as a main enhanced oil recovery (EOR) method in fractured-vuggy carbonate reservoir, but its effect differs among single wells and multi-well groups because of the diverse fractured-vuggy configuration. Many researchers conducted experiments for the observation of fluid flow and the evaluation of production performance, while most of their physical models were fabricated based on the probability distribution of fractures and caves in the reservoir. In this study, a two-dimensional physical model of the karst fault system was designed and fabricated based on the geological model of TK748 well group in the seventh block of the Tahe Oilfield. The fluid flow and production performance of primary gas flooding were discussed. Gas-assisted gravity flooding was firstly introduced to take full use of gas-oil gravity difference, and its feasibility in the karst fault system was examined. Experimental results showed that primary gas flooding created more flow paths and achieved a remarkable increment of oil recovery compared to water flooding. Gas injection at a lower location was recommended to delay gas breakthrough. Gas-assisted gravity flooding achieved more stable gas-displacing-oil because oil production was at a lower location, and thus, the oil recovery was further enhanced.