An accurate understanding of the matrix-fracture mass transfer is fundamental to the modeling of fractured reservoirs. Nevertheless, the difficulty in an appropriate representation of this process comes from the fact that matrix and fracture interact in a particular manner depending on physical mechanisms as capillary imbibition. Capillary imbibition is considered through wettability in several mass transfer formulations (also called transfer functions) as the main mass driving force between matrix and fracture. This paper provides simulation results of waterflooding in two different scales of fractured models: Core plug models and extended models (a quarter of 5-spot), aiming to evaluate the influence of wettability and flow rate alteration on the matrix-fracture mass transfer. The methodology applied is based on sensitivity analyzes of wettability and flow rates scenarios, comparing parameters involved in matrix-fracture mass transfer: capillary continuity, fluid transfer rate, and hydraulic conductivity of the fracture system.
The methodology is divided into three main parts. Initially, single-porosity models with an induced longitudinally fracture at laboratory scale are simulated, to obtain accurate models in terms of representative responses for wettability and flow rate changes. Secondly, dual-porosity/permeability models are constructed also at laboratory scale to analyze and compare answers to mass transfer. As a third stage, extended models are created attempting to analyze the impacts of sensitivity parameters of mass transfer on a larger scale. Results show that the increase of rock preference for water leads to highest oil recovery factors at low and high-water injection rates, benefiting mainly from the water spontaneous imbibition. Notably, the spontaneous imbibition in these cases is more considerable in low-rate scenarios, due to its larger contact time with water and rock. However, the increment on production may not be economically feasible, because of the long time (high pore volumes injected) needed to get this increase. In contrast, intermediate and oil-wet scenarios exhibit low oil sweep and displacement efficiency at low and high-water injection rates. Accordingly, these scenarios reach water breakthrough quickly and exhibit a less accentuated tendency to water saturation alterations if compared with a water-wet scenario.
Results from single-porosity models show a good agreement between the water saturation distributions along the length and the effect of the induced fracture, validating its use. Results also reflect the effects of the fractured porous media formulations at both model scales as well as the effects of the shape-factors. In a numerical simulation study, this work shows the importance of close interaction between the wettability, flow rate changes, and the parameters that control matrix-fracture mass transfer. At last, the significance of these sensitive parameters is also demonstrated.