Abstract
Some heavy oil reservoirs in Canada show atypically high production rates
and high primary oil recoveries under solution-gas drive. Much attention has
been given to the anomalous behaviour observed in such heavy oil reservoirs,
and several models have been suggested to explain these anomalies.
There are two classes of effects responsible for the unusual behaviour of
solution-gas drive in heavy oil reservoirs, including fluid effects and
rock/geomechanical effects. This study focuses exclusively on fluid
effects.
In at least two ways, solution-gas drive in heavy oils differs from that in
light oils. In heavy oils, the concentration of gas in the oil can be
significantly greater than the equilibrium value; the oil could be
significantly supersaturated. Additionally in heavy oils, recovery and gas
mobility show rate dependent behaviour. Both of these effects are taken into
consideration in this study.
In this paper, we develop a dynamic model that captures many important
processes that affect heavy oil recovery. The non-equilibrium early time
behaviour is modelled by introducing a kinetic equation describing the rate of
evolution of solution gas into free gas. The equation is derived based on a
phenomenological analysis which takes into account bubble nucleation and
growth. A second component of this model captures the low gas mobility in heavy
oil reservoirs and its dependency on viscous forces. To account for the effect
of viscous forces on gas mobility, relative permeability functions are
introduced that not only depend on gas saturation but also on local oil phase
velocity and viscosity.
While many of the previous models apply several kinetic equations associated
with a large number of parameters, we have shown that the modifications
suggested in this study enable predicting many of the unusual behaviours
observed in solution-gas drive in heavy oil reservoirs, using only one kinetic
equation with a smaller number of fitting parameters.
© 2009. Society of Petroleum Engineers
View full textPDF
(
1,214 KB
)
History
- Original manuscript received:
23 April 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
24 April 2009
- Manuscript approved:
29 October 2009
View Cart
