Modeling
Variable-Saturation Multi-Relative Permeability Layered Systems in
Transition-Zone Environments
Byrnes, Alan1, Saibal Bhattacharya2 (1)
Fundamental to reservoir modeling is the
assignment of petrophysical properties to geomodel cells. Imbibition
oil-water relative permeability (kr) measurements
performed on Pennsylvanian-age oomoldic limestones and Mississippian-age moldic-porosity
mudstone to grainstone lime-dolomites show residual
oil saturation after waterflood, Sorw,
increases with increasing initial oil saturation, Soi
due to increasing oil trapping in fine pores, consistent with the Land-defined
trapping characteristic. The trapping characteristic is lithofacies- and porosity-specific.
As Soi decreases with depth in the transition zone,
proper modeling of kr requires a family of kr curves that reflect changes in kr
with changing Soi.
Simulations in a vertically
finely-layered model utilizing a family of kr curves
exhibit higher oil and water recoveries than predicted from models utilizing kr curves with a constant Soi and
Sorw. In the transition zone, proximity to the
oil-water contact leads to lower Sorw(Soi) and higher Sw causing both higher oil and water recoveries.
Transition-zone systems further
illustrate a larger issue with upscaling. Simulation
studies demonstrate that systems comprising layers of different kr cannot be rigorously upscaled
using static kr properties because kr is a function of how the saturation was achieved.
Results indicate that relative permeability is not a state function, as it is
widely applied in simulation, but is dependent on the saturation distribution
which upscaled systems may not fully represent.
Simulation study results demonstrate that fluid recovery from transition-zone
dominated reservoirs is critically influenced by Soi,
Sorw, and kr models and kr upscaling methodology. Proper
modeling provides significant improvement of IOR and EOR implementation.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California