Integration of Visualization Experiment and Advanced Simulation for Flow Dynamic Evaluation and Development Scheme Optimization in the Water and Gas Flooding Process: A Case Study in a Fractured Reservoir in Bongor Basin

Abstract

Abstract A fractured reservoir in Bongor Basin has been in production by natural energy for almost a decade. However, its production performance has deteriorated over time, as evidenced by the declining pressure levels, a significant drop in oil production rates, and a rapid increase in water cut in the edge part. To enhance the reservoir’s productivity, this paper aims to characterize the flow pattern under water and gas flooding to clarify the mechanisms of energy recovery, and optimize injection-production parameters for field application. In this paper, development effect of the reservoir is comprehensively evaluated, with a particular focus on understanding the key production performance features. The study considers subsurface fracture distributions and employs a two-dimensional visualization model to investigate the flow characteristics of water and gas in fracture and matrix paths. Furthermore, discrete fractured models are employed to simulate water and gas flooding, followed by sensitive analysis and history match to reveal the influence of fracture on production performance. The simulations, coupled with improved genetic algorithm, create optimal production schemes that can be directly applied in the field. The results indicate that as depletion progresses, pressure levels and oil rates in the areas with developed fractures decline apparently. Fractures have distinct roles in production performance and are essential to improve development. The visualization model reveals the sweep characteristics of water and gas flooding in various fracture distributions. It is evident that water flows preferentially through extensive fracture networks to extend overall sweep but with lower displacement efficiency, while gas can access thinner fractures and even certain matrix regions. The sweep and displacement of water and gas are quantified using standardized curve methods. Core flooding experiments demonstrate that water and gas flooding can extract additional oil after depletion, while improper injection can result in channeling or lower recovery. Based on the collaborations of water and gas flooding, the controlling factors on flow characterization under various fracture distribution and development conditions are screened using discrete fracture models, indicating fracture density, azimuth and production parameter combination posing evident influence. By using a multi-objective fitness function, the traditional genetic algorithm is improved, and in combination with models, the injection volume, timing, and mode are optimized, resulting in the optimal development parameter combinations. The field has implemented injection of water in edge and gas in top, which has appeared favorable signs in production. This study demonstrates the advancement of using visualization experiments to in depth analyze the flow mechanism in fractured reservoirs, and highlights its innovation by optimizing development schemes using an improved genetic algorithm, which significantly enhances work efficiency. It provides valuable insights for the design and operation of water and gas injection in the reservoirs.