[PDF] Chemostratigraphy Of The Late Cretaceous Eagle Ford Group South Texass eBook

Author : Robert Francis Nikirk
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Page : 60 pages
File Size : 18,69 MB
Release : 2014
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Strata of the Eagle Ford Group of South Texas, deposited during the Cenomanian and Turonian of the Late Cretaceous, are largely characterized as mixed siliciclastic and carbonate mudrocks rich in organic carbon. The Eagle Ford Group records deposition within the Maverick Basin, along the Comanche Shelf, at the southern margin of the Western Interior Seaway in present-day South Texas. In recent years, the Eagle Ford has emerged as one of the premiere petroleum plays, as it has been proven to be capable of producing significant volumes of dry gas, wet gas/condensates, and oil. It is believed the Eagle Ford represents deposition during the globally correlative Ocean Anoxic Event #2, characterized by the accumulation and preservation of vast amounts of organic carbon due to the expansion of large deep-water oxygen minimum zones. This study integrates geochemical analyses of six drill cores from Gonzales, Guadalupe, La Salle and Wilson counties of South Texas. These cores were studied to determine bulk geochemistry, redox conditions, and degree of basin restriction and deepwater renewal times in order to provide a detailed assessment of the chemostratigraphy and paleoceanography of the Eagle Ford Group. Each core was scanned at one foot intervals with a handheld X-ray fluorescence (XRF) spectrometer to obtain quantitative measurements of major elements, such as Ca, Al and Si, as well as redox sensitive trace metals, such as V, Zn, Ni and Mo. In addition, some cores were analyzed for total organic carbon (TOC), total inorganic carbon (TIC), and stable isotope ([delta]13C and [delta]18O) signatures of the inorganic, carbonate component. The elevated levels of redox sensitive trace metals of the Lower Eagle Ford, represented here by the Lake Waco and Pepper Shale Formations, reveals deposition during a time of anoxic or euxinic conditions leading to the preservation of large amounts of organic carbon (~5% TOC). The South Bosque Formation, representing the Upper Eagle Ford, displays reduced levels of these trace metals, suggesting a return to a more oxygenated environment prior to the deposition of the overlying, fully oxygenated and heavily bioturbated Austin Chalk. The physical paleoceanography of the Eagle Ford is revealed to be restricted at times and more open at others with lower deep-water renewal times, yet remained mainly within an anoxic or euxinic state. In regard to the inorganic stable isotopic data, the [delta]13C carb values, which other studies have shown to display a positive excursion at the time of OAE2, suggest this event is not preserved within the cores analyzed.

Author : Brett Huffman
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Page : pages
File Size : 18,40 MB
Release : 2013
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The fine-grained organic-rich rocks of the Eagle Ford (Cenomanian-Turonian) were deposited during the Upper Cretaceous in the shallow waters of the Western Interior Seaway. Five drill cores recovered from two counties, four from Travis County, Texas and one from Frio County, Texas, have been scanned from between two foot and half foot intervals with a hand-held energy-dispersive x-ray fluorescence (HH-ED-XRF) spectrometer to acquire major (e.g. Ca, Si, Al) and trace (e.g. Mo, V, Ni) element data for quantitative analysis. Additionally, gamma ray logs have been analyzed for two of the cores. Major element geochemistry indicates the Eagle Ford deposited in South Texas is different from the Eagle Ford deposited in Central Texas. South Texas Eagle Ford is much more Ca (carbonate) rich, with a noticeably lower Al (clay) content. South Texas and Central Texas Eagle Ford both have low Si (quartz) content relative to the Al and Ca content, indicating a negligible siliciclastic contribution during deposition. Trace element analysis reveals the redox conditions of the bottom waters during deposition. Mn -- an element which becomes mobile and may be removed from an open system in reducing conditions -- levels are much higher in the Austin Chalk and Buda with notably lower values in the Eagle Ford in both Central Texas and South Texas. Mo, an element which tends to bind with organic matter or sulfides during reducing conditions, is notably higher in the Eagle Ford of both South Texas and Central Texas. The correlation of decreased Mn levels and increased Mo levels suggests that the Eagle Ford was deposited in reducing conditions in an open system capable of removing mobilized Mn. Geochemical analysis of major and trace elements obtained from ED-XRF may be used in the petroleum industry in concert with XRD, electric logs, and standard core analysis to give a more complete picture of the depositional environment, clay type and volume, geophysical rock properties, and areal extent of a potential unconventional shale reservoir for hydrocarbon extraction. XRF data offers insight about the rocks, leading to improved understanding of the depositional environment and chemical makeup. Applying these technologies to the Eagle Ford helps unlock the potential of this significant hydrocarbon source and reservoir.

Author : Timothy J. Kearns
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Page : pages
File Size : 49,25 MB
Release : 2011
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The Late Cretaceous Eagle Ford Formation contains the Cenomanian-Turonian Boundary (CTB). It crops out along the Red River and extends southward through the Dallas-Fort Worth Area of Texas, Waco, Austin and west towards Del Rio and Big Bend. The outcrops were not sampled. Sampling was conducted on cores located at the Bureau of Economic Geology (BEG). The cores were collected from Zavala, La Salle, Frio, Gonzalez, De Witt, and Bee Counties. The Austin Chalk Formation is located above the Eagle Ford Formation and the Buda Formation is located below it. Deposition of the Eagle Ford Formation occurred in the southern portion of Western Interior Seaway (WIS) of North America during a period of high temperature due to greenhouse warming stemming from enhanced volcanism and associated CO2 input. Increased CO2 input ultimately resulted in enhanced continental solubility or weathering and enhanced primary productivity, which resulted in stagnant, oxygen, depleted waters. The effect of the former was to possibly cause the second (OAE-2) of six global ocean anoxic events that occurred during the Cretaceous Period. A combination of enhanced carbonate precipitation from primary productivity and enhanced preservation caused by ocean anoxia led to the deposition of highly carbonaceous organic-rich mudrock. All the samples were measured using a Bruker XRF handheld device. Select samples were measured for %TIC, %TOC, %N, %S, ð13C and ð15N. The data revealed that sampled population included not only the upper and lower portion of the Eagle Ford Formation, but the overlaying Austin Chalk and underlying Buda Formations. This was primarily determined by the Molybdenum concentration. Molybdenum concentration less than or equal to 5 ppm indicate the presence of oxic to suboxic water column conditions. Molybdenum concentration that is greater than or equal to 5 ppm, but less than 20 ppm indicates anoxic water column conditions. Molybdenum concentration that is equal to or greater than 20 ppm indicates euxinic water column conditions. The Eagle Ford Formation was deposited mostly under anoxic to euxinic conditions. The overlying Austin Chalk Formation and underlying Buda Formation were both deposited under dominantly oxic to suboxic conditions. Analyses of the results indicate upwelling was prevalent during much of the deposition of each core. Upwelling is indicated by the enrichment of Phosphorus and depletion of Manganese. Increased continental weathering and upwelling were the likely primary controlling influences that caused anoxic-euxinc water column conditions. Such conditions facilitated enhanced organic matter preservation during the deposition of the Eagle Ford Formation.

Author : Josie Danielle Brunick
Publisher :
Page : 298 pages
File Size : 28,47 MB
Release : 2017
Category : Geology, Stratigraphic
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The mixed siliciclastic/carbonate late Cretaceous Eagle Ford Formation is commonly divided into the lower Eagle Ford and the upper Eagle Ford. The lower Eagle Ford is arguably the most obvious organic rich interval highlighted with wireline log data; however, the upper Eagle Ford may have just as much potential for hydrocarbon production success as the lower Eagle Ford has had. A better understanding of the upper Eagle Ford will allow a more thorough and educated assessment into its full potential as an unconventional reservoir, and allow its sweet spots for oil or gas to be found and exploited. This study is based on the description and interpretation of four cores of the upper Eagle Ford located within Karnes and Gonzales counties, Texas, thin sections, and key XRF data in an effort to better understand its sediment sources and depositional regime. Seven lithofacies were identified in the upper Eagle Ford are as follows: 1) Bioturbated Wackestone/Packstone; 2) Deformed Wackestone/Packstone; 3) Wavy Laminated Wackestone/Packstone; 4) Massive Mudstone/Wackestone; 5) Coarsely to Finely Laminated Wackestone/Packstone; 6) Massive packstone/grainstone; 7) Volcanic Ash. The highest Total Organic Carbon (TOC) percent relative to each core always occurred within the base of the upper Eagle Ford. In fact, the highest TOC percentage recorded was 4.5% within the base of the upper Eagle Ford in the most distally located core. Thorium to Uranium ratios of the upper Eagle Ford were on average less than 1 indicating that the upper Eagle Ford contains very little terrigenous sourced material. Nickel, copper, vanadium, molybdenum, and uranium concentrations were also analyzed and correlated to relative organic matter influx and Paleoredox levels within the upper Eagle Ford in each core.

Author : Zain Abdi
Publisher :
Page : 49 pages
File Size : 11,47 MB
Release : 2014
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A single drill core from La Salle, TX was analyzed for its chemical composition and percent concentration of both major and trace elements in order to understand depositional environments and local tectonic activity of the Balcones Fault Zone. The drill core contained the entirety of the Austin Chalk and the upper portion of the Upper Eagle Ford Shale. Samples were taken from 47 boxes at 3 inch intervals which accumulated in a total of 1,680 samples. Each sample was analyzed using a handheld x-ray fluorescence instrument which provided quantitative analysis of the following elements: Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, P, S, Si, Ti, and V. Furthermore, x-ray diffraction analysis was conducted at every 7 feet of the Austin Chalk and every 4 feet of the Upper Eagle Ford Shale. Calcium values ranged from 5% to 40% with the former values arising from the Upper Eagle Ford Shale and the latter values coming from the Austin Chalk. Sulfur percent composition ranged from 0%-20% and had similar trends as Magnesium which had values from 0.04% to 4.8%. The Austin Chalk contained great values of pyrite, illite, quartz, calcite, and dolomite. Trace element concentrations suggest that the depositional environment had periods of anoxic or euxinic events. Mineralogical and major elemental geochemistry suggests a carbonate rich Austin Chalk and calcareous Eagle Ford Shale.