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Abstract Operating decisions for steamfloods can be improved by accounting for fluid migration across pattern boundaries. a new parameter, called Fluid Migration Index (FMI), is based upuon simplified steamflood material balance considerations and can easily be calculated from field injection and production data. This parameter can be used to correct individual pattern performance. The validity of the fluid migration index was further checked with available subsurface information. Reservoir simulation, with a newly-designed internal accounting system that can track fluid movements across pattern boundaries, was used to corroborate the FMI concept and also to calculate true allocation factors of well production from surrounding patterns. Simulation results show improved accuracy in calculating fluid migration and evaluating pattern performance. It is anticipated that using the results of this paper will improve current steamflooding policies and optimize the design of future projects. Introduction In steamfloods with repeated patterns, it is frequently assumed that fluid is confined within the pattern such that there is no fluid migration across pattern boundaries. This assumption is not always valid. Fluid migration was reported in the Kern River and Deerfield steamfloods.1,2 Fluid migration has also long been recognized in the South Belrdige steamflood.3 Significant fluid migration from the structural crest of the Tulare formation to the flank has resulted in discrepancies in pattern oil recovery calculations between allocated production data and open-hole logs from infill wells. Reservoir pressure gradients due to dip, reservoir heterogeneities, and local variation in the injection and production conditions during the steamflood operation are probable causes for fluid migration. If fluid migration across a pattern boundary is not properly accounted for, the commonly used pattern performance indicators, such oil/steam ratio and oil recovery, could be deceiving. Investment and operating decisions that are based on these misleading indicators could be in error. Therefore, there is a need to quantify the fluid migration and develop a methodology to evaluate its impact on steamflood operations. Peake4 estimated the amount of fluid migration form a 16-pattern pilot study based on a simple steamflood material balance. Production data from the offset pilot provided evidence that the magnitude of the oil migration estimate was reasonable. A new parameter, Fluid Migration Index (FMI), is introduced in this paper to quantify fluid migration. The validity of the parameter was checked with available openhole logs from infill wells. Reservoir simulation is coupled with analytical techniques to track fluid movements and characterize producing well performance. The objectives of the simulation study are to help understand the effects of fluid migration across field patterns and develop new procedures that better quantify these effects. |
