An experimental investigation of the effect of temperature on recovery of heavy oil from diatomite

An X-ray computed-tomography (CT) scanner, in combination with a novel high-temperature and high-pressure core holder, was used to investigate systematically heavy oil recovery from outcrop diatomite and field core. Temperatures ranged from 20 to 180degreesC, and all experiments are isothermal. Decane, two viscous white mineral oils, and heavy crude oil from the field were used as oil phases. In reservoir core filled with crude oil, oil recovery by spontaneous imbibition of water increased from 3% at 40degreesC (reservoir temperature) to 40% of oil in place at 180degreesC. Forced displacement brought total recovery to more than 50%. Thermal methods are effective at improving oil recovery from low-permeability, fractured oil-rock systems filled with moderate to viscous oil, whereas waterflood is not. Recovery increases with temperature because oil viscosity decreases and wettability is altered toward water wetness. Increased imbibition rate and oil recovery corresponded with production of oil-wet fines at elevated temperature. A mechanism for increase in water wettability is proposed whereby fines detachment from pore surfaces increases the water-wet surface area.