Date of Award
Master of Science - Geology
R. LaRell Nielson
Mike T. Read
The Desmoinesian (Middle Pennsylvanian) Capps Limestone Member of the Mineral Wells Formation is a carbonate reservoir located in North Central Texas. It consists of interbedded limestone, sandstone, and shale units. Much of the Capps Limestone exists in the subsurface of Brown, Coleman, Runnels, Coke, Nolan, and Taylor counties, however, the Capps Limestone outcrops on the surface in Brown, Eastland, and Palo Pinto counties.
The cored interval from Runnels County was deposited in a marginal marine environment during the Middle Pennsylvanian Period. Although the Capps Limestone was first described in the 1890s, there is still much to be discovered about its depositional environment and sequence stratigraphy. Here, an analysis of the stratigraphy and depositional environment of the Capps Limestone was undertaken in the North Norton Oil Field in Runnels County, Texas. Data were collected from four cores using thin sections, lithological descriptions, porosity and permeability measurements, wireline log analysis, and X-Ray Fluorescence (XRF). The collected data will provide a more precise idea about the depositional environment, sequence stratigraphy, and petroleum potential of the Capps Limestone. A greater knowledge of the Capps Limestone could provide better insight about the region’s geologic history, particularly other Pennsylvanian units, which developed under similar circumstances. This information will contribute to the
geologic knowledge of the region as a whole and possibly influence future exploration and production prospects.
In Runnels County, the Capps Limestone is approximately 59 to 77 feet (15.5 m – 22.6 m) thick and contains interbedded limestone, mixed carbonate-siliciclastic rocks, sandstone, and shale units. The limestone units range from fossil-bearing mudstones to packstones, composed primarily of phylloid algae and crinoid stems. Non-limestone lithologies include mixed carbonate-siliciclastic rocks that are made up of a mixture of sand grains and fossil remains within a carbonate mud matrix and a thickly bedded quartz arenite to quartz wacke sandstone.
Throughout the Capps Limestone, several shale units are interbedded within the limestone and sandstone units. Shale units present range in thickness from two inches (five centimeters) to three feet (one meter). The Capps Limestone in the North Norton Oil Field in Runnels County appears to have been deposited on a shallow-shelf environment as is indicated by the laminated mudstones and fossiliferous limestones. The sandstone and mixed carbonate-siliciclastic units represent an influx of sand from fluvial-deltaic systems that were possibly active nearby. Shale units may represent deeper areas on the shallow-shelf, a lagoonal environment, an interdistributary bay, or the occurrence of prodelta muds. The deposition of the Capps Limestone occurred as a part of a transgressive systems tract during the Pennsylvanian Period.
Thompson, William, "Stratigraphic Analysis of the Capps Limestone in the North Norton Oil Field in Runnels County, Texas" (2021). Electronic Theses and Dissertations. 425.
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