Analysis of conductive heat transfer during in-situ electrical heating of oil sands

• A model is used to estimate rate of makeup water required in electrical heating.
• Typically 5–10 m3/day of water per km of a well is needed to maintain heat flux.
• Use of solvents as working fluids to deliver heat to the formation was examined.
• Makeup rate for a solvent such as hexane is five times the rate of makeup for water.
• Low-porosity and high-thermal conductivity formations require lower makeup water.

Low oil prices have motivated development of lower cost recovery processes for production of heavy oil and bitumen. Electrical heating using heaters has been proposed recently to not only lower costs, but also improve energy efficiency and reduce environmental impact compared to current thermal recovery methods such as steam assisted gravity drainage. Elimination of steam injection from bitumen recovery processes greatly decreases the capital and operating costs of oil sand development projects and also minimizes the environmental footprint of bitumen production. One of the challenges faced during electrical heating of bitumen formations is desiccation of the formation around downhole heaters at high temperatures resulting in reduced heat delivery to the reservoir. This problem can be eased by injection of makeup water or solvent to add a convective heat transfer element to the otherwise mainly conductive heat transfer from the heater to the formation. In this paper a simple analytical model is presented that allows estimation of the rate of makeup water or other fluid required for efficient heat delivery to the bitumen bearing formations. The effects of formation porosity, rock type and fluid saturation on heat transfer are also evaluated.

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