Fractured Buried Hill Reservoir Gas Injection Eor Research

Fractured buried hill reservoir belongs to the typical dual porosity reservoir. The main storage and permeable media are the fissure system and matrix system. Fractured buried hill reservoir has the properties of serious heterogeneity due to the big discrepancy between fissure system and matrix system in storage and permeable capacity. It's really difficult to get a ideal recovery factor in both primary recovery and waterflooding development. The application of gas injection EOR technologies keep on the trend of fast increasing and good application results have been achieved in recent years. Many successful field applications in overseas fracture buried hill reservoir has been reported. Plenty of fractured buried hill reservoirs are discovered in China as the advancement of exploration technology in recent years. Based on the good knowledge of the geological properties and development characteristic, it's significantly important for conducting gas injection EOR technologies and numerical simulation study.The main geological properties, development features as well as gas injection displacement mechanism have been summarized for naturally fractured buried hill reservoirs by literatures review. The feasibility study for gas injection has been conducted in XingGu 7 (XG7) naturally fractured buried hill reservoir. Moreover, numerical simulation was conducted to evaluate the feasibility of consecutive gas injection and water alternate gas (WAG) injection in XG7 reservoir.The main storage media are structural fractures and fragmented interparticle pores. The decline curve analysis for single well shows moderate decline rate due to lack of natural energy. Moreover, the waterflooding pilot test doesn't give us any encouraging results for water injection development. According to the screening criterion for gas injection EOR technologies, the reservoir properties of XG7 reservoir comply with this criterion. CO2 injection belongs to miscible flooding and dry gas injection is immiscible flooding. The long core experiment study shows gas injection displacement efficiency is the highest one. XG7 reservoir has good potential for gas injection study.The numerical simulation results for consecutive gas injection have shown the following observation. First, the optimized gas injection rate for CO2 is 200-300t/d. Second, the oil displacement efficiency is higher than that of dry gas. Third, the result of CO2 injection is much better than that of dry gas.The numerical simulation for WAG injection shows the following findings. Gas injection rate has the biggest impact on the final recovery factor. Then the weight factors from high to low are alternating time, injection pattern as well as gas/water injection duration ratio.The result of the gas injection evaluation in XG7 reservoir is as follows. The incremental recovery factors for consecutive gas injection and WAG are 2.9% and 3.3% respectively after 10 years injection, while for the main production zones are 6.5% and 9.3% respectively. WAG injection is much better than that of consecutive gas injection. The incremental recovery factor is bigger than that of the whole reservoir. Thus, the producers have good response to WAG injection in the swept area. Gas injection has good potential in XG 7 reservoir.