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Geologic reservoir characterization of the Codell sandstone in NE Silo field, Laramie County, Wyoming
Keator, Matthew
Keator, Matthew
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2023
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2024-12-24
Abstract
The Turonian-aged Codell Sandstone member of the Carlile Shale Formation is a hydrocarbon bearing shaley sandstone that has been interpreted as a regressive, shelf sand deposit that has been reworked by storm waves in the Cretaceous Western Interior Seaway. The Codell Sandstone behaves as a low resistivity pay zone suppressed by the presence of clays and pyrite. Production out of the Codell Sandstone began in northeastern Colorado out of Wattenberg Field in the early 1980’s and has expanded north into southeast Wyoming. The Codell Sandstone is an unconventional tight sand reservoir that has been targeted in Silo Field approximately 20 miles northeast of Cheyenne, Wyoming within Laramie County and is the focus of this study. Structure maps indicate that the Codell Sandstone is approximately 7500 – 9000 feet TVD in the field, whereas isopach maps indicate a thickness of approximately 25 – 35 feet. The Codell Sandstone is 32 feet thick from a core taken from the Helis Cain 16-63-2-11-1CH well and was the targeted formation.
Geochemical analysis of produced oils from the Codell Sandstone and extracted hydrocarbons from the Niobrara C Marl and Greenhorn Limestone indicates a marine shale source from the Graneros Shale, Greenhorn Limestone, or Pierre Shale (Sharon Springs equivalent) formations. Core analysis from the Cain 16-63-2-11-1CH well indicated average permeability to air values of 0.019 millidarcies and average porosities of 12 – 13%. XRD analysis from core indicated clay percent by weight through the Codell interval in the Cain 16-63-2-11-1CH well to be between 16 – 20%. Porosity vs. permeability cross plots indicate a nano pore structure. A Modified Lorenz Plot was constructed along with cumulative storage capacity and cumulative flow capacity vs. depth plots. The Modified Lorenz Plot reveals seven distinct flow units. Flow units one and seven being “poor” while also showing no oil staining in the core under UV light. Flow units two through seven were considered “good” flow units and showed oil staining in the core. A cumulative storage capacity vs. depth plot showed consistent porosity through the section. Cumulative flow capacity vs. depth plot showed variable permeability that was affecting the quality of the flow units. Trace fossils include Teichichnus, Planolites, and Skolithos, indicating a mostly Cuziana ichnofacies. The Cruziana ichnofacies is consistent with a sublittoral zone of deposition between the fair-weather wave base and storm wave base.
Core descriptions of two other cores within Silo Field, the Cirque Berry Unit 13-9 and Cirque Child #30-9 showed a similar thickness of Codell, similar trace fossil ichnofacies, and similar sedimentary structures. The Berry Unit core in northwestern Silo Field is capped by the Sage Breaks Shale Formation, similarly to the Cain 16-63-2-11-1CH core. The Sage Breaks Shale is absent in the Child #30-9 core in southwestern Silo Field. Twenty petrographic thin sections were prepared every two feet through the Sage Breaks Shale and Codell Sandstone section of the Cain 16-63-2-11-1CH core. While thin sections can be difficult to aid with facies separations in the Codell Sandstone, as composition is similar throughout, thin section and core descriptions helped to delineate six distinct facies within this section, three in the Sage Breaks and three within the Codell Sandstone based on varying sand/clay percentages, trace fossil assemblages, and sedimentary structures.
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