Summary
Phase transformation affects multiphase flow in geothermal and
gas/condensate reservoirs owing to the same substance occurring in different
phases. These effects change the phase behavior and the flow characteristics.
The goals of this research were to compare the flow behavior and relative
permeability differences between two-phase flow with and without
phase-transformation effects in smooth-walled and rough-walled fractures.
During this research, an experimental apparatus was built to capture the
unstable nature of the two-phase flow in fractures and to display the flow
structures in real time. Two-phase-flow experiments with phase-transformation
effects (steam/water flow) and without phase-transformation effects
(nitrogen/water flow) were conducted. The porous-medium approach was used to
calculate two-phase relative permeabilities. From the results in this study,
steam/water relative permeabilities are different from nitrogen/water relative
permeabilities. The enhanced steam-phase relative permeability is caused by the
effects of phase transformation. This shows consistency with some earlier
studies in porous media. The nitrogen/water relative permeability is described
most appropriately by using the viscous coupling model. However, steam/water
flow in the rough-walled fracture, which is coupled with strong
phase-transformation effects, seems to be represented better by Brooks-Corey
relative permeability functions for fractured media (lambda right arrow
infinity). The results from this study suggest that relative permeabilities
accounting for phase-transformation effects must be used in simulations of
geothermal and solution-gas reservoirs to represent two-phase interactions
adequately.
Introduction
Two-phase flow has long been of interest in earth-fluid and energy
production, such as in petroleum reservoir and geothermal-reservoir
engineering. Simulations of these reservoirs need knowledge of relative
permeability functions, which have been studied theoretically and
experimentally in porous media for two-phase, two-component systems (i.e., oil
and water). However, the relative permeability properties of (1) fractured
media and (2) flow with phase-transformation effects are of great importance
but are poorly understood. Fractured reservoirs are not only the major
reservoirs in geothermal fields, but they also represent more than 20% of the
world's oil reserves (Saidi 1983). The phase-transformation effects are a
characteristic of two-phase flows in geothermal reservoirs (steam/water flow)
and gas/condensate reservoirs (gas/oil flow). In spite of considerable
theoretical and experimental efforts during the last 2 decades for both of
these issues, there are still no general models or approaches to describe
relative permeability in fractures, either with or without phase-transformation
effects.
There have been several studies conducted experimentally and theoretically
for the steam/water relative permeability. These studies have been performed in
consolidated or unconsolidated porous media. The results of these studies fell
generally into two contradictory populations. Several studies suggested that in
porous media, the steam/water relative permeability functions behave similarly
to the nitrogen/water (or air/water) relative permeability functions (Sanchez
and Schechter 1990; Piquemal 1994). However, another set of studies suggested
that steam/water relative permeability functions behave differently from
nitrogen/water in porous media (Arihara 1976; Counsil 1979; Verma 1986; Satik
1998; Mahiya 1999; O'Connor 2001). Most these studies showed that the
steam-phase relative permeability is enhanced in comparison with nitrogen-phase
relative permeability. To the best of our knowledge, no steam/water relative
permeability results in fractured media have been reported yet because of the
difficulties of the steam/water experiments and poor knowledge of fracture
modeling for multiphase flows.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
7 June 2004
- Meeting paper published:
26 September 2004
- Revised manuscript received:
9 March 2007
- Manuscript approved:
10 April 2007
- Version of record:
20 October 2007
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