Dimethyl Ether DME Solvent Based Enhanced-Oil-Recovery Technology - A Laboratory and Subsurface Study

Abstract

DME as a water-soluble solvent for enhanced oil recovery has been introduced and some study results of DME enhanced waterflooding have recently been reported. However, DME-based EOR has not yet been implemented because of high prices of DME, the consequent need to recycle and reinject DME, and uncertain incremental oil per injected DME. This paper describes new insights into the different aspects (lab, subsurface, and economic) of DME-based EOR technology. An experimental protocol was defined to study the IFT, viscosity, and density of DME-Oil-brine mixtures as a function of T, P, and salinity, and DME compatibility with heavy components (e.g., asphaltenes), and adsorption on minerals. A compositional fractured-reservoir dynamic model that honors the PVT characteristics of DME was developed to investigate the performance of DME flood into fractured and unfractured reservoirs with light and heavy crudes. A business case as a function of DME recycling efficiencies, incremental oil, and phase implementation was discussed. The experimental results revealed that the oil viscosity 31 cP is significantly reduced to below 2 cP when mixed with DME in small volume ratios. No asphaltene precipitation (asphaltene content = 6.4 wt%) was observed when the oil was mixed with DME at increasing ratios up to 80 v/v%. Compatibility tests with formation water (total salinity 9.2 wt%) showed that DME is soluble in the formation water without any incompatibility or salting-out effect. The DME partitioning into oleic phase improves when temperature and brine-salinity increase. Imbibition tests at 5 bars and 50°C with DME-saturated formation water and limestone core plugs (permeability: 1.3–2.2 mD) increased the ultimate recovery to 70%. The simulation results indicate that DME injection into unfractured reservoirs does not improve the displacement efficiency, but it accelerates oil production because of improved injectivity up to 30%. However, DME injection into heavy-oil fractured reservoirs can improve displacement efficiency initially by enhancing imbibition rates from the matrix to the fracture system. However, this improved displacement efficiency decreases as DME injection continues because of DME breakthrough and there will be a point at which the DME displacement efficiency becomes the same as water. Nonetheless, DME significantly increases the recovery factor from heavy-oil fractured reservoirs (up to 200%). The economic results demonstrate that to have an economic DME-based EOR technology, the DME-recycling efficiency must be higher than 80%, incremental oil must be higher than 15%, and development must be a phased development plan.