Abstract
The Solvent Aided Process (SAP), described previously by the authors, is an
improvement to SAGD that promises to enhance the economics of bitumen/heavy oil
recovery projects and reduce water usage.
In SAP, a small amount of hydrocarbon solvent (such as a low molecular weight
alkane) is introduced as an additive to the injected steam during SAGD. The
viscosity of the oil is reduced due to solvent dilution in addition to heating.
SAP holds the promise of significantly improving the energy efficiency of SAGD,
thus, reducing the heat requirement. Encana's field trials of SAP, discussed
elsewhere, have shown the practical upside of this process. This paper
discusses two conceptual optimizations of SAP.
SAP reduces the effective steam-oil ratio (SOR) of SAGD. However, this comes at
a cost as a part of the injected solvent is retained in the reservoir and lost
in terms of economics. The smaller this cost is, the better are the economics
of SAP. In this paper, the merits and drawbacks of using two alternate
substances, SO2 and olefinated light alkanes, as solvents are
discussed.
Bottom-up SAP is a special geometrical configuration of SAP, discussed before.
In this variant of the SAP process, bitumen recovery progresses from the bottom
to the top of the reservoir, and employs injector and producer wells that are
spaced horizontally apart rather than being in the same vertical plane. For
large horizontal spacing between the injector and producer in a well pair,
rates are low. On the other hand, for small spacing, the capital associated
with the project is high. This paper explores the optimal horizontal spacing
between the wells in a bottom-up SAP well pair.
Introduction
Steam-Assisted Gravity Drainage (SAGD) relies primarily on heat supplied to the
reservoir by steam to reduce the viscosity of the oil(1). In
SAP(2-5), solvent dilution is also taken advantage of to aid in this
viscosity reduction. The result is an enhanced rate of oil production and
recovery leading to superior economics with lower energy intensity and a
reduction in water usage. To further improve the economics and energy
efficiency of the process, in this paper, two optimizations of SAP are
discussed; namely, employment of inexpensive solvents and optimal configuration
of bottom-up SAP.
SAP economics depend on the extent of the residual solvent in the
reservoir(3) such that, the higher the inventory and cost of the
unrecovered solvent, the less advantageous it is to carry out SAP. In
principle, any of the commercially-available light alkanes (e.g. propane,
butane or natural gas condensate) can be employed for SAP. However, these
liquids tend to be expensive due to their multiple uses in the industry and
their price generally varies in sync with light sweet crude. This fact
naturally offers an opportunity to further improve the economics of SAP by
looking for other solvents, and the discussion below describes two such
alternative, inexpensive solvents.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
2 April 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
21 July 2008
- Manuscript approved:
1 December 2008
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