Date of Award
Spring 5-2024
Degree Type
Thesis
Degree Name
Master of Science - Geology
Department
Geology
First Advisor
Dr. Julie Bloxson
Second Advisor
Dr. R. LaRell Nielson
Third Advisor
Dr. Melinda Faulkner
Fourth Advisor
Dr. Robert Friedfeld
Abstract
The Lower Clear Fork from Tex-Mex, S.E. Field on the Central Basin Platform is a typical complex reservoir that displays high heterogeneity in lithological and petrophysical properties. The unit represents a producing reservoir succession of Leonardian platform carbonates deposited in shallow marine water during the Early Permian. The sediment of the Lower Clear Fork is composed of a mixed succession of dolomite interbedded with anhydrite, minor clay minerals, and siliciclastics. The high heterolithic nature of the reservoir makes efficient recovery of hydrocarbons difficult. This situation requires an understanding of the variability in depositional facies in terms of mineralogy, depositional textures and structures, and an assessment of its petrophysical properties. As of December 2023, cumulative production of hydrocarbon from the Tex-Mex, S.E. Field reached about 88,308 barrels of oil equivalent.
The study at Tex-Mex, S.E. Field utilized 338.9 ft (103.3 m) of Lower Clear Fork cored sample, core data, and wireline data from a key well. Key data utilized included core descriptions, wireline logs, routine core analysis data, petrographic thin sections, and whole rock mineralogical data from X-ray Diffraction. These data helped to (1) determine the paleoenvironments under which the Lower Clear Fork sediments were deposited, (2) build a core-calibrated petrophysical mineral model of the Lower Clear Fork from wireline logs and XRD mineralogy, and (3) assess the petrophysical properties of the Lower Clear Fork reservoir.
The integration of core/log analysis, XRD data, routine core data, and petrographic observations revealed seven (7) facies regrouped into four (4) major facies associations each representing the mineralogy, sedimentary textures, pore characteristics, and paleodepositional environment. The Lower Clear Fork, a second-order Leonardian sequence represents facies transitioning from dolomitized inner to ramp crest facies (skeletal/peloidal wackestone to grain-dominated packstone) in the lower part, to dolomitized restricted lagoon and tidal flats/sabkha facies (dolomudstone/anhydrite) in the upper part. The petrophysical characteristics of the Lower Clear Fork reservoir were dominantly controlled by post-depositional processes that altered the primary carbonate mineralogy and pore development. The principal diagenetic processes included reflux dolomitization, gypsum precipitation (later transformed into anhydrite), and dissolution of anhydrite and dolomite cement.
Mineralogical results revealed the dominance of dolomite, anhydrite with minor amounts of clay, and siliciclastics. Calibrated porosity values within the interval vary from 0.5% to 10%, while Klinkenberg permeability was in the range of 10-4 mD to 17.6 mD. The Lower Clear Fork facies showed dominance of high water saturation values, reaching up to 95.4%, and comparatively low oil saturation levels, peaking at a value of 14.4% in the dolopackstone facies. Overall, the Lower Clear Fork reservoir is of low quality, however, the grain-rich dolopackstone facies offered the most favorable reservoir properties when compared with other facies in the interval.
Repository Citation
Nyamasekpor, Seyram, "Depositional Facies and Petrophysical Characterization of the Leonardian Carbonate (Lower Clear Fork), Tex-Mex, S.E. Field, Central Basin Platform, West Texas" (2024). Electronic Theses and Dissertations. 532.
https://scholarworks.sfasu.edu/etds/532
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