Multi-phase Well Testing to Calibrate Relative Permeability Measurements for Reservoir Simulation

Abstract

Special core analysis (SCAL) is the standard method for estimating relative permeabilities. These, however, must be upscaled for reservoir simulation and the upscaling process creates uncertainties that are propagated to field performance forecasts. This paper describes a six-stage well testing procedure to calibrate relative permeabilities for reservoir simulation and to reduce uncertainties in relative permeability end points and curvature. The well test includes: (1) single phase oil production; (2) buildup; (3) single phase water injection; (4) falloff; (5) two-phase oil and water production; and (6) a final buildup. The final buildup is initiated at minimum well productivity. Transient pressure analyses of the first buildup (2) and the falloff (4) provide the single phase mobility for each fluid at respective saturation end points. These yield an estimate for endpoint water relative permeability. Analysis of the second buildup yields an estimate of the minimum mobility. Uncertainty in oil and water relative permeability curvature is reduced using all three mobility estimates, while uncertainty in end point saturations can be reduced, for example, by comparing resistivity logs before and after water injection. The procedure is demonstrated by simulating a newly drilled well in a homogeneous oil reservoir. Relative permeability is shown to significantly impact water breakthrough and oil production in an oil field developed by water flood. Sensitivities to reservoir heterogeneity, water cut during the flow back period, numerical dispersion, and capillary pressure have also been explored. Information provided by the proposed test and interpretation procedure allows improved field development decisions early in field life.