Abstract
VAPEX (vapour extraction) is an oil recovery process, in which heavy oil or
bitumen is mobilized by injection of a low molecular weight hydrocarbon solvent
and is drained by gravity to a horizontal production well. It has attracted
considerable attention because of its potential applicability to problematic
reservoirs and the potential for in-situ upgrading of heavy oil during the
process.
Oil drainage rate under VAPEX is controlled by the viscosity of solvent
diluted oil and can be affected substantially by de-asphalting. In-situ
de-asphalting can be advantageous because it reduces the oil viscosity and
leads to production of upgraded oil. However, the precipitated asphaltenes can
also plug the pores of the formation and cause severe damage to the
permeability.
The objective of the current work was to determine whether the beneficial
effects of asphaltene precipitation would outweigh any formation damage. The
effects of in-situ precipitation and deposition of asphaltenes on the rate of
oil drainage and the quality of the produced oil under different operating
conditions were experimentally evaluated. The experiments were conducted in a
physical model, packed with 140 – 200 mesh sand, and propane was used as the
solvent. The quality of the produced oil samples was evaluated through the SARA
technique and viscosity measurements.
The experimental results show that the oil produced at higher injection
pressures was substantially upgraded, but the viscosity reduction by asphaltene
precipitation did not lead to higher production rates. The effect of viscosity
reduction was negated by the accompanying damage to formation permeability. The
huff and puff injection of toluene into the production well, to remove damage
from the near well zone, was tried but proved to be ineffective. It led to
production of oil with higher asphaltene content with no improvement in the
rate of oil production compared to the lower pressure operation without
asphaltene precipitation. However, co-injection of toluene with propane was
successful in increasing the rate of production and the extent of upgrading
obtained was encouraging.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
25 March 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
5 January 2010
- Manuscript approved:
10 January 2010
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