Water-wet three-phase flow micro-CT tomograms

• https://doi.org/10.3997/2214-4609.201800777
• 10.3997/2214-4609.201800777

Abstract — We have used X-ray micro tomography techniques to obtain high quality three-dimensional images of the pore space of a water-wet Ketton carbonate sample and the fluids within it, after the injection of three phases (brine, oil and gas) in a sequence involving oil injection into a fully water-saturated pore space, waterflooding, gas injection and secondary waterflooding. The rock was imaged dry initially, and then again after each injection step, to obtain the saturation of the phases, oil recovery and gas trapping capacity. A maximum ball pore network extraction algorithm was applied on the dry images and used to obtain statistics of pore occupancy. The results are in line with the theories of a uniform water-wet system and with the published outcomes of pore-network simulators: the pore and throat centres of smallest and largest pores are respectively occupied by brine and gas, while the oil resides in the cavities with intermediate size. High resolution images were used to study double displacement and the nature of trapping; the thickness of oil layers were also measured from the images. The results can improve the predicitvity of three-phase flow simulators and improve the efficiency of CO2 storage and utilization.

• https://doi.org/10.1016/j.advwatres.2018.09.010
• 10.1016/j.advwatres.2018.09.010

Abstract — X-ray micro-tomography is used to image the pore-scale configurations of fluid in a rock saturated with three phases - brine, oil and gas - mimicking a subsurface reservoir, at high pressure and temperature. We determine pore occupancy during a displacement sequence that involves waterflooding, gas injection and water re-injection. In the water-wet sample considered, brine occupied the smallest pores, gas the biggest, while oil occupied pores of intermediate size and is displaced by both water and gas. Double displacement events have been observed, where gas displaces oil that displaces water or vice versa. The thickness of water and oil layers have been quantified, as have the contact angles between gas and oil, and oil and water. These results are used to explain the nature of trapping in three-phase flow, specifically how oil preferentially traps gas in the presence of water.