Codell Sandstone

Jorgensen (1968) investigated a case of water quality deterioration in a municipal well at Avon, South Dakota. The city wells pumped the free water table aquifer of the Codell sandstone (Fig. 16.9). Well A had a significantly... 

Dakota sandstone water Codell sandstone water Pumping test well A water % Dakota water in A... 

Formation, Codell Sandstone, and Dakota J Sandstone yield gas at the underlying Wattenberg field. 

Fig. 2. Columnar section for the Wattenberg area of the Denver Basin. The primary source rocks are the shales and limestones of the Dakota Group, Benton Group, and Niobrara Formation. The most important hydrocarbon reservoirs are the Dakota J Sandstone and the Hygiene and Terry sandstones of the Middle Pierre Shale. The Lyons Sandstone, Codell Sandstone of the Benton Group, and limestone of the Niobrara Formation also produce hydrocarbons...

Not only is the shallowest formation (Fox Hills) plagioclase-rich, but it also has the most porosity attributable to plagioclase dissolution. The Codell Sandstone is highly argillaceous with low permeability, which has retarded the dissolution of framework grains. In all sandstones, secondary porosity attributable to dissolution of K-feldspar is limited to trace amounts. The third form of secondary porosity, which is dissolution of calcite cement and replacement, is sparse (maximum of 1.5vol%) and absent in most samples. Trace amounts of secondary porosity also formed by the dissolution of lithic fragments. 

Even using the conservative approach discussed above, the majority of the porosity in sandstones in this portion of the Denver Basin is secondary in origin (Fig. 7). Mean values for the percentage of secondary porosity grouped stratigraphically are Fox Hills, 74% sandstones in the Middle Pierre Shale, 78% Codell, 100% Dakota J, 53% and Lyons, 56%. 

Carbonate cement/replacement in sandstones of the Denver Basin is most commonly ferroan calcite based on staining techniques. Dolomite may occur, but is volumetrically unimportant except in the Fox Hills Formation where dolomite (mean of 6.7vol%) is more common than ferroan calcite (mean of 4.5vol%). Ferroan calcite averages 2.8vol% for sandstones of the Middle Pierre Shale compared with less than 1 vol% for dolomite. Sandstones in the two Codell cores are quite different in terms of the amount of ferroan calcite cement, but average 2.1vol% with no dolomite. The Dakota J Sandstone has only trace amounts of ferroan calcite and dolomite cement. The Lyons Sandstone contains trace amounts of calcite and no dolomite. 

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