Assessment of oil recovery methods for reservoirs in the Flemish Pass Basin

LaFitte, Chad (2021) Assessment of oil recovery methods for reservoirs in the Flemish Pass Basin. Masters thesis, Memorial University of Newfoundland.

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Abstract

In recent years, the Flemish Pass Basin has been gaining momentum as an area of potential high-volume resources on the frontier of remote, deep-water offshore oil exploration. This simulation study utilizes three sector models representing regional, discovered reservoirs, and two tuned fluid models representing oil sampled from wells in the Flemish Pass Basin. This study evaluates three secondary oil recovery methods, water flooding, gas flooding, and water-alternating-gas (WAG) flooding. These methods are simulated using ECLIPSE reservoir simulator [1] within the sector models from three different quality reservoirs, and the two different quality fluid models. This is accomplished through a sensitivity analysis of the representative Flemish Pass fluid and reservoir models, using both five and twenty year forecast simulation cases. The evaluation results capture an inherent uncertainty given the varied reservoir and fluid qualities while the depletion plan is controlled by recovery method. Dynamic modelling results in a range of possible recovery factors from eighteen simulation cases which quantifies the relative benefit of each oil recovery method. Comprehensive results indicate that implementing WAG as a secondary recovery method can yield a 4% to 10% increase in recovery factor over water flood or gas flood. WAG is usually considered a late-life enhanced oil recovery (EOR) method or tertiary recovery method. Using WAG for secondary recovery is much less common. Implementing WAG in the light oil reservoir yields a ~10% increase in recovery factor over both water flood and gas flood. Using WAG in the medium oil cases yields a 4% to 9% increase in recovery factor over water flood, and a 2% to 16% increase in recovery factor over gas flood. The most benefit from WAG is observed in the ultra-high-quality reservoir. The medium oil responds best to the gas injection phase of the WAG cycle so it may be useful to optimize the cycle such that gas is injected for a longer duration relative to the water injection cycle. Additionally, secondary WAG may extend the production plateau up to 80% depending on the reservoir quality, fluid characteristics, and production constraints. In terms of using WAG as a tertiary recovery method, tertiary WAG is observed to be most beneficial in low to medium quality reservoirs. Tertiary WAG extends the duration of production and results in a consistent ~4% increase in recovery factor over water flooding. Study results go on to quantify the differences in water and gas breakthrough as a factor of pore volume injected (PVI). The conclusions will further provide indication of which reservoirs are best suited for each recovery method.

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