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Reservoir characterization of the Codell sandstone at Redtail field, Weld County, Colorado
Damon, Nick
Damon, Nick
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2022
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Abstract
The Late Turonian Codell Sandstone of the Carlile Formation is one of the primary reservoirs targeted for hydrocarbon development within the Denver Basin. Although recent improvements in multi-stage hydraulic fracture stimulation and advanced recovery techniques have increased production, the Codell Sandstone remains a difficult exploration target due to its low porosity, permeability, and heterogeneities in its reservoir properties around the Basin. The goal of this study was to use a multiscale approach to examine the mineralogical and depositional properties of the Codell Sandstone and determine their impacts on reservoir quality in the Redtail Field area.
Redtail Field was drilled extensively for oil and gas by Whiting Petroleum. The Razor 25-2514H well is considered the type well for the field. In this well, the Codell Sandstone displays above average porosity (10-25%) when compared to other parts of the Denver Basin. Analytical methods such as petrographic analysis, core description, and scanning electron microscopy were employed to uncover what exactly makes the Codell Sandstone at Redtail Field display superior or inferior reservoir quality than its counterparts in the region.
The Codell Sandstone is comprised of very fine-to fine-grained sandstone and was deposited during a major regressive period at the end of the Greenhorn cycle in the Western Cretaceous Interior Seaway (WKIS). The Codell Sandstone is interpreted to be a shallow marine sediment between the Greenhorn and Niobrara Formations. The Codell Sandstone is bounded unconformably above and below by the Fort Hays Limestone and Carlile Shale, respectively. In Redtail Field, we have delineated the Codell Sandstone into three distinct facies: lower bioturbated silty sandstone facies, planar- to low-angle cross-stratified-sandstone facies, and upper bioturbated sandy siltstone facies. The planar- to low angle cross-stratified facies was identified as the primary reservoir facies due to its superior porosity, permeability, water saturation, and resistivity characteristics. The lower porosity and permeability in the Codell Sandstone and its characteristic low resistivity in well logs is caused by high clay content observed within the reservoir. Reservoirs that are analogs to the Codell are targeted worldwide and knowledge gained from this study could potentially be used as a framework for evaluating reservoir quality in these unconventional, shallow marine sandstones.
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