Summary
Steam injection is often not a good alternative for oil recovery from
shallow bitumen reservoirs. For instance, the thin caprock creates the danger
of steam breakthrough. For deeper reservoirs, the heat losses from injection
wells may be prohibitive. A technology that may be better suited is oil
recovery aided by low-frequency electrical heating of the reservoir. This
technology, well known for environmental remedial applications, has been field
tried recently, yielding promising results. The process uses electric
conductivity of connate water to propagate an alternating current between
electrodes, inducing the Joule heating of the reservoir. An associated problem
is the appearance of hot spots around the electrodes that may be relieved by
water circulation. However, the water circulation may have a significant effect
on the heating process because the electric conductivity of the circulated
water depends on its salt content.
To find out the influence of salt concentration on process efficiency, we
have studied the process of salt-water recirculation around an electrode using
numerical simulation. The physical properties and operational data for
Athabasca bitumen have been collected from the literature. The model built with
Computer Modelling Group's STARS simulator and tested first with available
analytical solutions has been validated, and the proper choice of the
underlying grid and numerical tuning parameters has been verified. The process
was also simulated at field scale for a common pattern of electrodes and
production wells. The salt penetrated into the reservoir, far beyond the major
water-circulation zone around the electrodes. This process increases the
electric conductivity in a large region between electrodes, which improves the
heating of the reservoir. The single-electrode simulation studies using
different tools yielded similar results for a simple problem. More-complex (and
more-realistic) field-scale simulations show that adding salt enhances the oil
production. In practice, an upper concentration limit may be given by corrosion
problems at the electrodes.
The reservoir simulation of bitumen recovery assisted by low-frequency
heating is a challenging multiphysics problem. The understanding of the
influence of salt concentration on the circulated water provided by this work
is an important key in process-design considerations.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
23 February 2010
- Meeting paper published:
24 April 2010
- Revised manuscript received:
16 July 2010
- Manuscript approved:
16 September 2010
- Published online:
23 March 2011
- Version of record:
15 September 2011
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