The effect of matrix-fracture permeability contrast on hydrocarbon foam performance in oil-wet carbonate

Foam-based enhanced oil recovery methods are becoming instrumental in increasing hydrocarbon production from unconventional reservoirs. However, the efficacy of such techniques is significantly affected by reservoir heterogeneity and adverse wettability conditions. This experimental study addresses such challenges by investigating the effect of fracture-matrix permeability contrast on the effectiveness of foam-based enhanced oil recovery in fractured oil-wet porous systems under reservoir conditions. Fractured oil- wet Minnesota Northern Cream Buff carbonate core samples were employed and fracture permeability was varied using four different mixtures of proppants with varying mesh sizes. An amphoteric surfactant was used as the foaming agent and the aqueous solution was prepared in a synthetic brine of 200,000 ppm salinity. The results showed that foam reduced gas mobility in fractures, diverting gas to the matrix and mobilizing oil toward fractures. The permeability of the fracture showed a significant impact on foam behavior in oil-wet porous systems. It was noted that as the fracture-matrix permeability contrast decreased to a certain ratio, the apparent viscosity of the foam increased, resulting in the enhancement of fracture-matrix interactions and, therefore, higher oil recovery. However, further reduction in this ratio resulted in a significant decline in foam strength. The optimal fracture-matrix permeability contrast was determined when using 100 wt.% of 100 mesh sand, enabling the creation of small and durable bubbles, which notably restricted gas movement and led to higher oil recovery. The results confirm that foam can be a viable and effective alternative to traditional gas injection methods in fractured carbonates with oil-wet characteristics.