Summary
The oil industry has inherited a mixed history of success and failure of
application of air injection as an enhanced-oil-recovery method. Close scrutiny
of these projects shows that in order to conduct a successful
in-situ-combustion-oil-recovery project, sustained propagation of the
combustion front within the reservoirs is necessary. Sufficient air must be
supplied to maintain the propagating combustion front in the desired
bond-scission (carbon-oxide-forming) mode, otherwise unfavourable oxygen
addition [i.e., low-temperature-oxidation (LTO) reactions] will consume oxygen
and immobilize oil. When this happens, the combustion process is deemed to be
exhausted.
Quantification of the minimum air flux required for sustaining
combustion-zone propagation is needed to properly match the capacity of the
air-injection facility to the volume of the reservoir that is to be swept by
the thermal zone. Undersizing the air-injection capacity causes the
in-situ-combustion process to become inefficient at a point when only a small
portion of the reservoir has been "burned."
One-dimensional combustion tubes (CTs) are conventionally used to obtain
important combustion parameters required for designing an air-injection
project. Because of the high heat capacity of laboratory equipment designed for
elevated-temperature and -pressure operation, oxygen addition or LTO reactions
are promoted by the heat transfer through the core-holder walls when the
laboratory tests are performed at low air-injection rates. Therefore, when
operated at elevated pressures, the CTs are unable to operate at the low air
fluxes required to establish the minimum possible air-injection flux while
maintaining the combustion reactions in an effective mode.
To address this issue, a state-of-the-art combustion cell was conceived and
used as a way of addressing the previously mentioned constraints associated
with high-pressure 1D CTs. A conical combustion-cell design was built because
it enables continuous air-flux reductions without having to adjust the
air-injection rate. The heater control strategy was also modified in order to
address the lag-lead operation often used for 1D CTs. To date, the unit has
operated at air fluxes down to 3 std m3/m2•h.
The experimental work described in this paper provides insight into the
limitations in laboratory investigations of in-situ combustion and the expected
behaviour of field applications of the in-situ-combustion process.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
15 March 2011
- Meeting paper published:
8 May 2011
- Revised manuscript received:
24 June 2011
- Manuscript approved:
29 June 2011
- Version of record:
1 November 2011
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