Summary
Approximately one-third of global heavy-oil resources can be found in
fractured reservoirs. In spite of its strategic importance, recovery of heavy
crudes from fractured reservoirs has found few applications because of the
complexity of such reservoirs. In-situ combustion (ISC) is a candidate process
for such reservoirs, especially for those where steam injection is not
feasible. Experimental studies reported in the literature on this topic
mentioned a cone-shaped combustion front, indicating that the process was
governed by diffusion of oxygen into the matrix. The main oil-production
mechanisms were found to be thermal expansion of oil and evaporation of light
components (Schulte and de Vries 1985; Greaves et al. 1991).
In order to confirm these results, we carried out reservoir-simulation
studies presented in Fadaei et al. (2010). We have shown that the front has the
shape of a cone, and we have performed a combustion/extinction analysis
representing the results in a diagram of cumulative production vs. diffusion
coefficient and matrix permeability.
Before obtaining quantitative and qualitative comparisons, we need to
characterize the systems we want to study. Therefore, we also carried out
laboratory experiments using kinetic cells and combustion tubes. The
kinetic-cell studies showed that the presence of carbonates has a significant
effect on combustion kinetics. Our combustion-tube studies confirmed the
previously observed cone-shaped front. Previous studies reported in literature
used heating elements along the combustion tube to regulate the temperature,
which may have caused some undue heating of the core. To avoid that, we chose
to use efficient insulation to minimize heat losses. Combustion advanced faster
in nonconsolidated matrix, in which the permeability was higher than in
consolidated matrix. The results showed that the presence of severe
heterogeneities may prevent the combustion front from propagating. Several runs
were performed for different air-injection rates and pressures and for
different permeability contrasts between the matrix and the fracture.
The next step of our work is the upscaling of ISC in the fractured reservoir
at interwell scale on the basis of knowledge provided by simulation and
experimental studies.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
14 December 2009
- Revised manuscript received:
29 July 2010
- Manuscript approved:
2 August 2010
- Published online:
25 January 2011
- Version of record:
17 June 2011
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