Modelling Water Flooding Scheme in Dual Porosity Reservoirs: An Integrated Approach

Abstract

Water flooding is one of the most widely used secondary recovery techniques in petroleum reservoirs to enhance oil recovery. However, its application in naturally fractured reservoirs (NFRs) presents significant challenges due to the complex dual-porosity and dual-permeability nature of such formations. In NFRs, the high-permeability fracture network provides rapid fluid flow paths, leading to early water breakthrough and bypassing a significant portion of the oil trapped in the low-permeability matrix; this results in inefficient sweep efficiency and poor overall recovery, making conventional water flooding strategies less effective. BOAST (Black Oil Applied Simulation Tool) is a well-established reservoir simulator used for modelling black oil. However, BOAST may require modifications or integration with empirical models to improve water flooding performance in NFRs. The research team modelled a naturally fractured reservoir as a single-layer formation using a 15×1×1 parallel Cartesian grid in MATLAB. They then integrated the developed model into BOAST. They performed a water-flooding simulation to predict pressure distributions within each grid block, as well as production data (oil, gas, and water volumes), and well pressure and shut-in pressure. The simulation results indicate that cumulative oil production reached 1.3 MMSTB after 2000 days, corresponding to a recovery factor of approximately 25%. The reservoir, however, experienced early water breakthrough in the fracture system, leading to increased water cut and reduced oil production after year four. The operators initially maintained pressure support through water injection, but its effectiveness declined as water saturation in the fractures increased. Gas-Oil Ratio (GOR) remained stable throughout, indicating no significant gas breakthrough or solution gas drive. The results of this study show that BOAST faces uncertainty in accurately simulating and predicting performance in fractured systems due to complex fracture–matrix interactions, early water breakthrough, and poor sweep efficiency. However, researchers can use BOAST as a rapid real-time screening tool for dual-porosity reservoirs when selecting candidates for a water-flooding program, provided the model fully captures fracture–matrix interactions.