Abstract
The solvent-based process appears to be an increasingly feasible technology
for the extraction of heavy oil reserves. However, there is a lack of
fundamental understanding of how fracture geometrical characteristics control
the oil recovery efficiency in this type of enhanced oil recovery (EOR)
technique. In this work, a series of experiments were performed whereby the
pure and mixed hydrocarbon solvents (HCS) displaced heavy oil in fractured
five-spot glass micro-models. Successive images of the solvent injection
process were recorded. The oil recovery factor, as a function of injected pore
volume of solvents, was measured using image analysis of the provided pictures.
It has been observed that the oil recovery decreased when the fractures’
spacing, discontinuity, overlap, and distribution increased. In contrast, the
oil recovery increased when the orientation angle, discontinuity-distribution
and the number of fractures increased. Also, it has been found that there is an
optimum solvent composition, which maximizes the oil recovery. Finally, some
pore-level visualization representing the role of asphaltene precipitation
during miscible injection was illustrated using these experiments. This study
demonstrates the applicability of the micro-models for the fundamental studying
of the solvent-based process in fractured five-spot systems, which are used to
investigate the effect of fracture geometrical characteristics and their effect
on oil recovery.
Introduction
Heavy oil and bitumen reserves represent a considerable portion of worldwide
energy resources. It is estimated that these reservoirs contain six trillion
barrels of oil originally in place (OOIP), which is much more than the total
conventional oil reservoirs. Great consumption of light oil reserves and their
resulting dramatic decline encourages more interest in exploitation of highly
viscous oil and bitumen for future energy demands. For optimum conditions, the
primary recovery of these reservoirs would not exceed 10% of the OOIP(1). A
variety of thermal methods, including cyclic steam stimulation, in-situ
combustion and steam assisted gravity drainage are currently being applied for
extraction of these crudes. As far as the reservoir’s oil is heated, the main
fraction of thermal energy is used up in heating the formation itself. For the
reservoirs with a thin pay zone, bottom water zone and/or overlying gas zone,
excessive depths, low thermal conductivity of rock matrix, high water
saturation, etc., the economical applicability of thermal methods is doubtful.
With respect to current available recovery technologies, these reservoirs are
categorized as problematic reservoirs(2,3).
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
21 March 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
9 November 2009
- Manuscript approved:
7 December 2009
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