Miscible WAG injection has been implemented in a number of oil fields around the world and there are a number of numerical studies investigating the effect of rate, gravity, slug size and heterogeneity on WAG performance. However there are very few laboratory studies of WAG displacement efficiency reported in the literature.

In this paper we report the results from a series of well-characterised WAG displacements through glass bead-packs. The aim of these experiments was

  • to investigate the impact of first contact miscible WAG injection on oil recovery

  • to clarify the physical processes during displacements.

  • to provide benchmark data-sets to validate reservoir simulations.

The use of bead-packs rather than cores enabled us to observe visually, for the first time to our knowledge, the fluid interactions during each WAG experiment.

A series of secondary, miscible WAG displacements were conducted at WAG ratios of 1:1, 4:1 and 1:4. These were performed at a range of flow rates to investigate the influence of capillary number on recovery efficiency. Their behaviour was compared with that obtained from simple miscible injection and waterflooding.

We show that recovery efficiency is a function of rate as well as WAG ratio. We also find that the water-oil and the water-solvent relative permeabilities are not the same for the analogue fluids used. This is despite the fact that the oil and solvent are first contact miscible. If this is true for reservoir fluids then clearly it will affect the prediction of WAG recovery efficiency.

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