Laboratory study to investigate cyclic hysteresis in miscible and immiscible WAG experiments in carbonate reservoir

In this paper, we present the results of a detailed experimental study aimed at understanding three-phase hysteresis in miscible and immiscible WAG injection processes. It has been reported in literature that the two-phase hysteresis models will generally not be able to describe relative permeability obtained in three-phase core floods. The main shortcoming of two-phase hysteresis models is that after imbibition cycle, the relative permeability is reversible. In three-phase flow, a cycle dependent hysteresis was reported which could significantly impact the gas mobility in the different cycles and improves sweep efficiency. In this study, a number of immiscible and miscible gas and WAG injection experiments were performed using limestone reservoir core samples from a carbonate reservoir. The experiments were performed under reservoir conditions using live crude oil. The core wettability was restored by ageing the core in crude oil for several weeks under reservoir conditions. Methane (C1) was used as the immiscible injectant and CO2 was used as the miscible injectant. The main conclusions of this study are: 1-Cyclic hysteresis in gas relative permeability was observed when comparing the first and second gas cycle, however, no further hysteresis was observed in the subsequent cycles, 2-The gas mobility at similar gas saturation for experiments starting with gas is better than that for experiments starting with water, 3-Gas and water relative permeability end points are not dependent on their own saturation alone as assumed in three-phase relative permeability models, significant variation in the relative permeability end points was measured at almost the same saturation, and 4-The water mobility of the experiments starting with water cycle is better than the water mobility of the experiments starting with gas cycle at the same water saturation. This shows the presence of gas before the first water cycle reduces the water mobility.