Abstract

In the $40 million Joint Implementation of Vapor Extraction Program (JIVE), an experiment was performed to investigate CSI behaviour in the Lloydminster region under pressure support from CH4 injection at an offset well. The oil sand pack had high permeability (500 Darcy) and low permeability (3 Darcy) zones that represented regions with and without wormholes. Primary production was followed by two CSI cycles in which the solvent (60% CH4–40% C3H8) was injected at the high permeability end. CH4 offset gas was injected at the low permeability end during CSI production periods. Solvent recovery strategies were evaluated.

The primary production drawdown strategy (designed using numerical simulation) resulted in 10.0% oil recovery.

Production was only obtained after 6 hours due to a delay in gas exsolution and foamy oil drive. During CSI, a delay in oil recovery also occurred as the pressure-supporting offset gas required time to drive foamy oil generated in that region into the high permeability region. Cycle 1 oil recovery was 6.2%.

Cycle 2 had low oil recovery. Post-run gas saturations indicated gravity override occurred. Asphaltene precipitation/deposition occurred as seen from microscopic observation. The asphaltene content was reduced in the produced oil and increased in the post-run oil sand.

A rapid pressure drawdown after a third solvent injection period caused 1.7% oil recovery and foamy oil in the production line (Figure 1c). Additional oil recovery (4.5%) was obtained from offset CH4 injection, heating of the sand pack to ~60 °C, and 22 °C nitrogen offset gas injection.

Numerical simulations of primary production and CSI cycles showed:

  • the best strategy is rapid well depressurization during production

  • high offset gas rate enhances gravity override and reduces oil production

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