A method for evaluation of water flooding performance in fractured reservoirs

• A methodology is proposed to evaluate water-flooding in fractured reservoir.
• A new revision imbibition model is proposed for the dynamic saturation profile.
• The methodology is tested on laboratory data and applied to some field cases.
• Compared against simulation and other classic methods, the result is reliable.

A mathematical model is developed for evaluation of water flooding performance in a highly fractured reservoir. The model transforms a dual-porosity medium into an equivalent single porosity medium by using a pseudo relative permeability method to normalize the relative permeability. This approach allows both fractures and matrix to have permeability, porosity, endpoint saturation, and endpoint relative permeability by themselves. Imbibition is also taken into account by modifying Chen׳s equation. Some effects, including imbibition and recovery rates are investigated. The investigation shows that imbibition can determine the potential of a fractured reservoir and a low recovery rate can improve the water flooding situation in terms of retarding water breakthrough and controlling the rise of water cut. A new chart composed by water cut vs. recovery curves is protracted to estimate the ultimate water-flooding recovery rate. The water flooding performance of two reservoirs is evaluated. Compared with numerical simulation method, the error of these two cases are not more than 2%, which proved that this method is reliable. Both lab test data and field data are applied to a further discussion of the characteristics of water flooding performance in fractured reservoirs. On comparison with the classical method, such as Tong׳s method and the X-plot method, the reason why the new method is more suitable to fractured reservoirs is addressed by a theoretical analysis. An appropriate application of this method can help the reservoir engineer to optimize the reservoir management with low costs and high efficiency.