Abstract

In this paper we present a Shell developed, chemical EOR technique in which dimethyl ether (DME), a widely-used industrial compound, is utilised as a miscible solvent in conjunction with conventional waterflooding. The technology, laboratory results, PVT workflows and numerical aspects of DME enhanced waterflooding have been reported recently. This paper describes various aspects of upscaling from pattern scale production to field scale while conforming to various development constraints.

In a DME enhanced waterflood, advantage is taken of DME's solubility in water and miscibility with hydrocarbons: water is used as a carrier for DME during injection and upon contact with reservoir fluids, DME preferentially partitions into the hydrocarbon phase thereby swelling and mobilising the oil phase. This is followed by a DME-free water chase to recover the remaining mobile oil and DME. Residual oil saturation after sweep is reduced, significantly below that typically achieved by waterflood alone. Furthermore, the DME can be extracted from the produced wellstream fluids by partly non-standard operations such as stripping, distillation and/or absorption processes, and re-used for injection.

The DME Enhanced Waterflooding (DEW) technique takes advantage of the unique solubility properties of dimethyl ether to improve oil mobility and reduce residual oil saturations. Significant research into the pressure-volume-temperature (PVT) behaviour of DME and DME/crude oil mixtures has been carried out in recent years of which a summary is reported by Groot et al. (2016); in particular the partitioning behaviour of the solvent and mixing rules for the various mass transfer properties affecting mobility. The PVT-driven behaviour and the overall displacement efficiency of the DEW technique have been observed in core flood experiments using both carbonate and clastic core plugs.

Considering the application of the DEW technique to a tertiary field development, the practical realities of solvent flooding become more apparent. In field developments that involve the injection of DME and solvents in general, solvent recycling and reinjection is mostly required. This is a result of the inherently high value of the solvents and is needed to increase the utilization of the solvents manufactured locally or imported. This paper describes the requirements from both subsurface as well as surface point of view to make a successful field solvent EOR development possible.

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