Influence of wettability on residual gas trapping and enhanced oil recovery in three-phase flow: a pore-scale analysis using micro-computed tomography

We imaged two enhanced oil recovery processes in a mixed-wet sandstone plug at high resolution (3.4µm)3 with a micro-computed tomograph. In the first process, gas was directly injected into an oil reservoir which was subsequently waterflooded (Sogb process). In the second process, the oil reservoir was first waterflooded, then gas-flooded and finally waterflooded again (Sobgb process – typically referred to as water-alternating-gas process). We qualitatively found that during immiscible gas/brine/oil displacements a) similar amounts of gas can be stored in a mixed-wet reservoir with the Sogb and the Sobgb processes compared with the Sogb process in a water-wet reservoir (note that less gas can be stored in a water-wet reservoir with the Sobgb process), and b) more oil can be produced with a Sobgb process compared to Sogb in a mixed-wet reservoir, contrary to the situation in a water-wet reservoir, where the Sogb process is more efficient. In addition, we identified several pore-scale fluid configurations, which ultimately determine reservoir flow properties