Dimethyl-ether (DME) -enhanced waterflood (DEW) is a process in which DME is added to injection water and, upon injection, preferentially partitions into the remaining oil. As a result, it swells the oil and reduces the oil viscosity, significantly improving oil mobility. Several coreflood experiments conducted in tight-carbonate plugs have shown incremental recoveries of up to 20% post-waterflood. A field trial has been designed to derisk this technology, which, if successful, would add significant reserves.
Enhancing oil recovery from low-permeability formations has been challenging. DEW presents the advantages of a miscible flood without the negative effects of density differences. DME is a slightly polar hydrocarbon that is miscible with most known crude oils. As a result, upon contact with crude oil, the DME will swell the oil and reduce its viscosity, after which the oil will be effectively displaced. DME is soluble in water and, therefore, can be injected with any existing waterflood. Because the molecule is small, there are no limitations on formation type or permeability. Its water solubility enables efficient recovery of the DME with a clean-brine chase. Because it does not interact with the formation, recovery efficiencies of DME are found to be close to 100% in laboratory core experiments. Depending on the injected-slug size and the crude-oil composition, oil recovery could be enhanced by 10 to 25% in field application.
In a DEW, DME is dissolved in the injection brine and injected into the formation. The DME solubility is dependent on salinity and temperature but can be up to 38 wt% for fresh water. Upon contact with the oil in the reservoir, the DME will partition to the oleic phase, where it will swell the oil, reduce its viscosity, and mobilize the oil to the producer wells. The process is schematically presented in Fig. 1....
A Field Trial in a Carbonate Reservoir Using a Solvent-Based Waterflood Process
25 December 2016