Eastburn field/ Vernon County, Missouri, produces heavy, 21° API, crude oil at a depth of 33 m (110 ft) from a thin, 6-9 m (20-30 ft), sandstone stratigraphic trap in the Cherokee Group of middle Pennsylvanian age. Sedimentary structures, grain size trends, geometry of the sandstone, and the nature of associated sediments indicate the fluvio-deltaic origin of the reservoir . Development drilling at very close spacing, 60 m (200 ft) between wells, provided information from which a sedimentologic model of porosity and permeability distribution in the Eastburn field reservoir could be developed early in project life. From this model, strategies were proposed that guided further drilling and completion of wells, extension of the field, and placement of production facilities. Development drilling guided by the fluvial sandstone model resulted in tripling the known volume of the heavy-oil resource, with a minimum number of dry development wells being drilled . The reservoir sandstone is composed mostly of medium to very fine quartz sand, rock fragments, and mica, with abundant interstitial detrital silt and clay. Authigenic kaolinite clay and calcite and siderite cements reduce reservoir quality and contribute to problems in production, such as low injectivity of steam and exhaust gases in the thermal recovery process. Identification of the permeability-reducing minerals aided in design of well-stimulation treatments and contributed to increased productivity . In a few cases, where contouring of the sandstone thickness was doubtful, production performance of individual wells provided additional data to guide the geologic interpretation. This synergistic approach helped to minimize the cost and maximize the efficiency of the field development .