Lower Cretaceous upper Mannville G, U, and W pools in 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, and up to 22 m thick. G pool was discovered in 1972 and placed on primary production; oil production declined gradually and was accompanied by modestly increasing gas-to-oil ratios (GOR) and water-to-oil ratios (WOR). U and W pools were discovered in 1982 and 1983, respectively, and were 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, which is currently up to 10:1 in wells adjacent to water injectors. Production re ponse indicates control 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, which are not yet correlatable between wells. Rapid breakthrough of water occurred in producing wells adjacent to injectors due to channeling in thick permeable sandstone beds between shale beds.

Microscale heterogeneities are principally mineralogically segregated laminae of cross-stratified sandstones. Permeability values from cores indicate variations of one order of magnitude among laminae. It appears that water passes preferentially through low-permeability sandstone laminae due to the higher mobility of water compared to oil.