Abstract
High-pressure air injection (HPAI) is an enhanced oil recovery (EOR) process
in which compressed air is injected into a deep, light-oil reservoir, with the
expectation that the oxygen in the injected air will react with a fraction of
the reservoir oil at an elevated temperature to produce carbon dioxide.
Over the years, HPAI has been considered a simple flue-gas flood, giving
little credit to the thermal drive as a production mechanism. The truth is
that, although early production during a HPAI process is mainly due to
re-pressurization and gasflood effects, once a pore volume of air has been
injected the combustion front becomes the main driving mechanism.
This paper presents laboratory and field evidence of the presence of a
thermal front during HPAI operations, and of its beneficial impact on oil
production. Production and injection data from the Buffalo Field, which
comprises the oldest HPAI projects currently in operation, were gathered and
analyzed for this purpose. These HPAI projects definitely do not behave as
simple immiscible gasfloods.
This study shows that a HPAI project has the potential to yield higher
recoveries than a simple immiscible gasflood. Furthermore, it gives
recommendations about how to operate the process to take advantage of its full
capabilities.
Introduction
High-Pressure Air Injection (HPAI) is an emerging technology for the
enhanced oil recovery (EOR) of light oils that has proven to be a valuable
process, especially in deep, thin, low-permeability reservoirs(1–7).
A number of successful high-pressure air injection projects in light oil
reservoirs have been documented in the literature(8–10). Most of these projects
have been operating for many years, attesting to their technical and economic
success.
The improvement in recovery of light oil by HPAI involves a combination of
complex processes, each contributing to the overall recovery. These processes
include flue gas sweeping, field re-pressurization, oil swelling, viscosity
reduction, stripping of the lighter components of the oil, and thermal effects.
Early production during the HPAI process is related to re-pressurization and
gasflood effects; hence, the influence of the thermal zone is secondary during
the early life of an injector. The oil displaced directly by the thermal front
will depend on the effectiveness of the generated flue gas on oil displacement
from outside the thermal region.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
27 March 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
15 December 2009
- Manuscript approved:
28 December 2009
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