Summary
The solvent-aided process (SAP) is a solvent-based enhancement of
steam-assisted gravity drainage (SAGD) in which small amounts of solvent, such
as light alkanes or natural-gas liquids, are added to the injected steam to
enhance reservoir performance and associated project economics. Expectedly, the
economics with SAP are sensitive to the solvent recovered from the reservoir,
making its measurement in a field test an important factor.
When a single-component solvent such as butane, which is not generally
present in the produced heavy oil or bitumen, is used in SAP, estimation of the
recovered solvent can be achieved uniquely. But when the solvent also has
heavier components, some of which overlap with the lighter components of the
produced oil, the measurement is not straightforward. The problem is compounded
by the fact that the interaction with the reservoir changes the composition of
the produced solvent and makes it time variant on account of different resident
times associated with different components. The issue is further complicated by
the fact that produced oil also undergoes an in-situ solvent deasphalting
process (SDA), which is also time and space variant in the reservoir. If there
were no in-situ SDA, one potential method to measure the amount of produced
solvent would be to measure the total asphaltene content as an oil "marker" in
the produced blend. Use of a tracer with injected solvent, as well as
regression-based analyses for solvent fraction (using compositional analyses of
solvent, bitumen, and the blend) of the produced blend, is error prone for
these same reasons.
Because of the issues in these approaches, a new method is desirable for a
more-robust and unique assessment of the solvent amount in the produced fluids.
This paper elaborates on the current challenges and proposes a couple of
workable methods, including use of maltenes/metals content as oil markers as
well as the use of boiling-point curves of the produced blend compared with the
boiling point of the base oil.
Such techniques of estimating the recovered solvent can facilitate a
more-objective assessment of SAP field tests and enable economic evaluation of
SAP application to a commercial scale.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
1 March 2011
- Meeting paper published:
20 October 2010
- Revised manuscript received:
7 June 2011
- Manuscript approved:
12 January 2012
- Published online:
22 August 2012
- Version of record:
5 September 2012
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