A Novel Enhanced Oil Recovery Technology Using Dimethyl Ether/Brine: Spontaneous Imbibition in Sandstone and Carbonate Rocks

Abstract

Abstract Dimethyl Ether (DME) - augmented brine injection is a novel Shell proprietary enhanced oil recovery (EOR) method. An experimental and numerical study of the enhancement and the acceleration of spontaneous imbibition using DME is carried out, both in sandstone and carbonate limestone cores. The experiments were performed under different boundary conditions using a modified high-pressure Amott cell. The primary recovery with brine from four (weakly water-wet to mixed-wet) sandstone cores, with the top-end, bottom-end, both-ends and all sides open to brine imbibition, was 38-46% of the OIIP. By adding DME, an additional oil recovery of 11-16% of the OIIP was obtained. The primary recovery with brine from the tight limestone cores was only 1-2% of the OIIP. By adding DME to the imbibing brine an additional oil recovery of 43-55% of the OIIP was obtained, which was much higher than the additional recovery from the sandstone cores. A workflow was considered to model DME-enhanced spontaneous imbibition experiments. The model comprises Darcy's law and the simplified phase behavior of the DME-brine-crude oil system. The model parameters were optimized to match the experimental results. Numerical simulation shows that the oil recovery is more sensitive to the molecular diffusion coefficient and to the partition coefficient, than to the relative permeability and capillary pressure. In the presence of a higher oil saturation in the core, a higher partition coefficient and a higher DME concentration in the aqueous phase, DME/brine imbibition leads to a higher oil recovery.