A Novel Enhanced Oil Recovery Technique: Experimental Results and Modelling Workflow of the DME Enhanced Waterflood Technology

Abstract

Abstract Dimethyl Ether Enhanced Waterflood (DEW) is a novel and promising solvent-based EOR technology developed by Shell. Dimethyl Ether (DME) is a widely-used industrial chemical which is applied as a water soluble solvent for EOR applications to enhance a conventional waterflood. Once the DME-brine solution is injected into the reservoir and comes in contact with the oil, the DME molecules partition into the oil phase which leads to oil swelling and mobilization of residual oil. Moreover the partitioning of the DME into the oil phase decreases the oil viscosity and improves its mobility. The combination of these effects results in both a significantly higher ultimate oil recovery compared to the conventional waterflood as well as accelerated oil production at lower energy footprint compared to thermal technologies. As the solvent is water soluble, it can be very effectively back-recovered from the reservoir by re-dissolving the trapped DME in the DME-free chase water slug. The solvent is recovered from the produced oil and water streams at surface and re-used. The main objectives of this paper are to present the first experimental results, explain the physical mechanisms of this novel concept and demonstrate the extra oil recovery. Additionally, modeling workflows used to interpret the experiments and predict the benefits of field EOR application are illustrated. To gain an insight into physical mechanisms behind the DEW, develop modeling workflows and de-risk the technology, an extensive experimental program was set up to investigate both the fluid-fluid and rock-fluid interactions. Phase behavior of DME/brine and DME/crude mixtures has been carried out, with a focus on the partitioning of the solvent between brine and crude. Mixing rules for properties affecting the phase mobilities have been determined. In parallel, a number of coreflood experiments were conducted on both carbonate and clastic cores of varying permeability to investigate the dynamic DME/crude behavior and DME/rock interaction. PVT experiments were used to build phase equilibrium models. Based on these PVT models, the coreflood experimental data was matched and interpreted using numerical simulation. Coreflood experiments confirmed the phase behavior-driven character of the DEW technology. A good match between the experimental and simulated oil recovery was obtained in most cases. This shows that PVT models, generated using measured basic data, are in a good agreement with the dynamic coreflood experiments.