Abstract
An understanding of volumetric sweep and capture efficiency are critical to
optimizing SAGD projects. Capture efficiency refers to how much mobilized and
heated oil is actually produced. Volumetric sweep efficiency can be estimated
reasonably well for SAGD pilots having an abundance of information. A rich data
set may include geological, petrophysical, production, injection, pressure,
temperature observation and 4D seismic data. With this information, excellent
insight into steam chamber development can be assessed. However, determining
volumetric sweep and optimal strategies is a problem where data are
sparse.
This paper summarizes analytical SAGD surveillance methods that estimate
volumetric sweep and presents a work flow that can help optimize SAGD processes
with limited data.
Although the methods each have their assumptions and are not perfect, there
is general agreement. The various techniques are corroborated using public
core, injection/production, temperature observation and 4D seismic for the
Surmont and Christina Lake pilot projects.
Introduction
Evaluating reservoir performance through the surveillance of production data
is an excellent reservoir management tool. For waterflooding, this can be
achieved through a conformance plot(1) that indicates how efficiently net water
throughput affects recovery. Associating a water balance with an oil balance
enhances the understanding of the influx/efflux of fluids and outer boundary
losses out of zones. The plot works well for waterfloods because of the low
compressibility of the fluids. For SAGD, a similar surveillance principle using
abundant data is applied. However, a material balance alone is not definitive
because SAGD is an energy-intensive process where steam is required to reduce
the oil viscosity to a point where it will flow. Therefore, accounting for the
energy within the SAGD process provides a different perspective for multiple
geologies and heterogeneities.
Typical objectives of SAGD surveillance using production and monitoring data
are to determine:
- Original oil in place (OOIP)
- Remaining oil in place (ROIP)
- Mobile ROIP distribution and current condition (saturation, temperature and
pressure)
- Limiting factors in recovery
- Potential improvements to economic oil recovery
- Recovery profile and optimizing recovery factor
- Operating strategies to achieve better volumetric sweep
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
8 July 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
23 November 2009
- Manuscript approved:
5 December 2009
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