Summary
In this paper, we present flow visualization experiments and numerical
simulations that demonstrate the combined effects of viscous and capillary
forces and gravity segregation on crossflow that occurs in two-phase
displacements in layered porous media.
We report results of a series of immiscible flooding experiments in 2D,
two-layered glass bead models. Favorable mobility-ratio imbibition and
unfavorable mobility-ratio drainage experiments were performed. We used
pre-equilibrated immiscible phases from a ternary isooctane/isopropanol/water
system, which allowed control of the interfacial tension (IFT) by varying the
isopropanol concentration. Experiments were performed for a wide range of
capillary and gravity numbers. The experimental results illustrate the
transitions from flow dominated by capillary pressure at high IFT to flow
dominated by gravity and viscous forces at low IFT. The experiments also
illustrate the complex interplay of capillary, gravity, and viscous forces that
controls crossflow. The experimental results confirm that the transition ranges
of scaling groups suggested by Zhou et al. (1994) are appropriate/valid.
We report also results of simulations of the displacement experiments by two
different numerical techniques: finite-difference and streamline methods. The
numerical simulation results agree well with experimental observations when
gravity and viscous forces were most important. For capillary-dominated flows,
the simulation results are in reasonable agreement with experimental
observations.
Introduction
Streamline methods are very efficient numerical techniques for field-scale
reservoir simulation, but they are not without limitations. They treat flow
along each streamline as independent of adjacent streamlines and therefore do
not typically represent crossflow in the simulations. If users of streamline
methods are to interpret simulation results reliably, they will need to assess
whether any of the mechanisms not modeled in the simulations ar.important
enough to limit the accuracy of the simulations appreciably.
Transfer of fluid in the direction transverse to streamlines can result from
diffusion and dispersion, crossflow caused by viscous and capillary forces, and
gravity segregation. The scaling of diffusion and dispersion has been
investigated in a number of previous studies. If the injected gas is miscible
or partially miscible with the oil, diffusion and dispersion mechanisms may
play a significant role in the displacement (Mohanty and Johnson 1993; Fayers
and Lee 1994; Tchelepi 1994; Jiang and Butler 1994; Burger and Mohanty 1997).
In particular, Burger and Mohanty (1997) showed that diffusion through the oil
phase can limit mass transfer from oil residing in low-permeability regions.
Similar arguments can also apply to other mechanisms of crossflow: viscous and
capillary crossflow as well as gravity segregation (Fayers and Lee 1994.Burger
and Mohanty 1997; Zapata and Lake 1981; Zhou et al. 1994).
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
7 June 2004
- Revised manuscript received:
21 October 2005
- Manuscript approved:
18 November 2005
- Version of record:
20 June 2006
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