Wettability and Flow Rate Effects on Mass Transfer for Simulation of Fractured Reservoirs

Abstract

Successful implementation of a recovery project in a fractured reservoir requires that the matrix fracture mass transfer is well understood. As a consequence, several processes involved in the mass transfer have been widely studied along time on account of its impact on the fractured porous media. Capillary imbibition is one of these significant phenomena and 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 presents simulated results of waterflooding tests in a fractured core-plug model, evaluating the influence of wettability and flow rate alteration on the matrix-fracture mass transfer. The methodology applied is divided into three main parts. Initially, a single-porosity core model with an induced longitudinally fracture at laboratory scale is recreated. Secondly, three synthetically wettability scenarios (water-wet, intermediate-wet, and oil-wet) and two flow rates (0.1 and 1 cm³/min) are selected and applied in the core-plug model to perform, as a third step, a sensitivity analysis in terms of oil recovery factor, water cut and water saturation. Results show that the increase of rock preference for water leads to the highest oil recovery factors at low and high-water injection rate, benefiting mainly from the spontaneous imbibition of water. The spontaneous imbibition in these cases is notably critical in the low-rate scenario, 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 injected pore volumes) needed to get this increase. In contrast, intermediate and oil-wet scenarios exhibit low oil sweep and displacement efficiency at both water injection rates. Accordingly, these scenarios reach water breakthrough quickly and exhibit a less accentuated tendency to water saturation alterations if compared with the water-wet scenario. Results also show a good agreement between the water saturation distributions along the length and the effect of the induced fracture, validating its use. 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.