Abstract:

In the Shunbei oilfield, the fault-controlled fractured-vuggy reservoirs are difficult to develop, and particularly in the Shunbei Zone 1, the severely depleted formation energy has induced a sharp rise of the natural decline rate of production, necessitating water injection for energy replenishment. The water flow pathways are predominantly constrained by fault surfaces, leading to severe water channeling and flooding during waterflooding process. Currently, there is a lack of theoretical frameworks for analyzing waterflooding failures. Based on the performance data of production by water injection in the Shunbei oilfield, and by using the K-means clustering algorithm, the classification criteria for energy replenishment via water injection was established. Based on the analysis results of clustering center, the quantitative threshold for injection effectiveness was determined, that is, a well is deemed effective if the pressure increment exceeds 8.7 MPa and the daily oil production increment is not less than 15.2 t; otherwise, it is considered ineffective. Using the established classification criteria, 12 water injection wells in the study area were evaluated, focusing on key influencing factors such as soaking time, cumulative injected water volume per cycle, injection-production ratio per cycle, ratio of oil production increment after water injection to cumulative water injection volume, and water consumption per unit of pressure recovery. A case study of Well SHB5-4H in the Shunbei No.1 fault zone elucidates the causes of waterflooding failure, providing a theoretical foundation for designing water injection strategies and optimizing remediation measures for ineffective wells in the fault-controlled fractured-vuggy reservoirs.

Key words: Shunbei oilfield, fault-controlled fractured-vuggy reservoir, water injection for energy replenishment, evaluation indicator, failure analysis