Theory and application of DME enhanced waterflooding in low permeable heterogeneous reservoirs

Dimethyl Ether Waterflooding (DEW) is a promising water-soluble solvent-based EOR technique. Here, we study DEW mechanisms by developing a mathematical model taking into account the swelling and viscosity reduction of oil. Our analyses show that the swelling and viscosity reduction of oil cannot explain the observed increased recovery of DEW in the published core flooding data.

Therefore, we define the residual oil saturation as a linear function of DME concentration in the oil phase to fit the model to the experimental data. After model validation against a 1D core flooding experiment, we utilize the model to study the effect of permeability heterogeneity and the injected DME slug size on the recovery of oil from a water-flooded chalk reservoir.

We observe a sharp increase in the ultimate recovery when the DME slug size increases from 0.2 to 1.8 pore volume. For the DME slug sizes more than two pore volumes, no significant increase of the oil recovery is observed. Our net present value (NPV) calculations show that the highest profit of the DEW operation in the studied chalk reservoirs is achieved by injecting one pore volume of DME solution with a DME concentration of 10 wt%.