Experimental investigation of the use of the dimethyl ether/polymer hybrid as a novel enhanced oil recovery method

Injection of dimethyl ether (DME) dissolved in water can enhance the recovery efficiency with respect to water flooding. In this Shell Proprietary Technology, DME partitions from water into the oil; decreases oil viscosity and increases its volume, and mobilizes the trapped oil again. In this work, DME-enhanced water flooding is combined with polymer and considered for cases in which a favorable mobility control between water and oil does not exist. In order to reduce the remaining oil, slugs of the mixed solution of DME and polymer were injected into the cores containing oil and then followed by injection of a chase fluid. This recovery method benefits both (a) from the presence of polymer, and the oil viscosity reduction caused by DME dissolution and (b) from oil swelling due to DME dissolution. It appears from experimental data that the injectivity of a DME/polymer (DMEP) solution is higher than the injectivity of a polymer solution without DME; this indicates the presence of DME can reduce the viscosifying effect of the polymer. The main experimental observations are: (1) a higher oil recovery is obtained from continuous DMEP flooding than from continuous DME-brine flooding, (2) the presence of polymer in the DME slug and in the chase phase reduced the remaining oil after a finite slug injection, and (3) a larger DME slug and mobility control of the chase phase can improve the oil recovery after a finite slug injection. In summary, the experiments show that combining polymer and DME improves the ultimate recovery significantly and shortens the duration of oil production.