Pore level investigation of oil depressurisation in pores with different Wettbility - Critical gas saturation

We have conducted a series of flow visualisation tests at the pore level using high-pressure glass micromodel to identify the key features of the depressurisation process. A series of experiments were conducted to investigate the effect of fluid properties, depletion rate, saturation conditions, wettability and saturation history on the depressurisation process. This paper presents the experimental results of this research on gas evolution, critical gas saturation and hydrocarbon movement. Our observation highlighted the effect of gravity on gas movement. Fluids properties affected the mobilisation point of the gas bubbles. A very low value of critical gas saturation was measured for a low oil/gas interfacial tension. Critical gas saturation and subsequent oil production were strongly affected by the critical value of supersaturation and the number of bubbles that were formed during the depressurisation. The results showed that the oil production was affected by the oil/water wettability; oil production was higher in the mixed-wet system compared to that in the oil-wet one. To study the possibility of improving oil recovery by pressurisation and second depressurisation cycle, a few tests were continued at high gas saturation and the effect of pressurisation rate and water presence on the second depressurisation were studied.