Property Evaluation of Metamorphic Rocks Using a New Metamorphic Reservoir Quality Index: Buried Hill of Bozhong 19-6 Area, Bohai Bay Basin, China

Metamorphic buried hills are characterized as fractured reservoirs with immense potential for hydrocarbon exploration and exploitation. Identifying their effective reservoirs is crucial for prioritizing exploration and development efforts. However, current methods are inadequate for such reservoirs. In this study, we established a new evaluation method, the metamorphic reservoir quality index (MRQI), based on analyses of wallrock cores, cuttings, well logs, and test data in the Bozhong (BZ) 19-6 area. The MRQI method integrates three main control factors for the formation of metamorphic buried hill reservoirs, namely lithology, tectonism, and weathering. Our results indicate that exploratory wells in the BZ19-6 area have MRQI values ranging from 29.91 to 86.47, with average of 56.45, showcasing the wide distribution of metamorphic rocks with moderate reservoir quality. We also observed a significant increasing trend between fracture development and MRQI values, suggesting that MRQI can effectively characterize reservoir development. Moreover, individual well production displays an exponentially increasing trend with higher MRQI, with a clear turning point at MRQI of 65, representing the lower limit of an effective reservoir. Finally, we applied the MRQI method to classify the reservoir through depth in two exploration wells, demonstrating its effectiveness. The MRQI method enables quick and effective decision-making on exploratory and developmental projects in metamorphic buried hills. Hence, this method provides a valuable tool for reservoir management and enhancing the economic benefits of exploration and exploitation in such reservoirs.