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Abstract

Upper Mannville G, U and W pools in the Little Bow field are hosted by separate parallel elongate estuarine sandstone bodies within an incised valley fill Each sandstone body is 3-4 km long, 300-500 m wide, up to 22 m thick, with an average porosity of 22%. Values of horizontal and (vertical) permeability vary widely and average 1324 (125) md in G pool, 2005 (472) md in U pool, and 258 (73) md in W pool.

G pool was discovered in 1972 and placed on primary production. Oil production declined gradually and was accompanied by modestly increasing GOR and WOR. U and W pools were discovered in 1982 and 1983 respectively, and produced by primary methods until initiation of waterflooding in 1985. Response to waterflooding these two pools has been a rise, then decline, in the GOR, followed by rapidly rising WOR, to values much greater than those predicted from reservoir modelling, currently up to 10:1 in wells adjacent to water injectors. Despite the wide variation in permeability values and the different production histories, similar proportions of oil have been produced: 9.2% OOIP in G Pool; 10.5% in U Pool; and 9.3% in W Pool. Production response indicates controls by mesoscale and microscale reservoir heterogeneities.

Mesoscale heterogeneities include permeable sandstone beds several meters thick that are continuous between adjacent wells, and stochastic shale beds up to 80 cm thick. Rapid breakth of water has occurred in producing wells adjacent to injectors due to channeling in thick permeable sandstone beds between

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