Allogenic Controls on Organic Matter Accumulation in the Woodford Shale in Southern Oklahoma

Allogenic Controls on Organic Matter Accumulation in the Woodford Shale in Southern Oklahoma
Author: Brayton Avery Pew
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Total Pages:
Release: 2021
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The Woodford Shale is an organic-rich formation found in southern Oklahoma and Kansas and has been extensively studied due to recent advancements in hydrocarbon recovery in mudrock successions. The controls on organic matter formation and preservation within the Woodford are not entirely clear in southern Oklahoma, but previous work points towards upwelling and anoxic bottom-waters as leading factors for the high organic content. This study was performed on a Woodford Shale outcrop located along Interstate 35 (mile marker 44) in Carter County, Oklahoma and contains the middle and upper Woodford succession. The integration of facies and chemical analyses, including hand-held X-ray fluorescence (HHXRF), inductively-coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD) and total organic carbon (TOC), were performed to construct sedimentologic-chemostratigraphic logs that allowed the establishment of a stratigraphic framework and evaluation of depositional parameters such as detrital input, primary productivity, and degree of oxygenation during the accumulation of the studied succession. The I-35 Woodford Shale outcrop can be divided into three main sequences (1, 2, and 3, from base to top), with sequences 2 and 3 further subdivided into subsequences (A and B), based on changes in chemostratigraphic indices proxies for detrital input, primary productivity, and degree of oxygenation, and accompanied facies associations. Sequence 1 is characterized by distal, pelagic settling sediments with 12-13% TOC deposited under conditions of stable anoxia/euxinia, with low-moderate primary productivity. Sequence 2A is defined by interbedded pelagic and hemipelagic deposits with TOC between 7-11%. It was deposited in more oxic environments because of decreased water depths, resulting in less preservation of organics. The continued accumulation of pelagic and hemipelagic deposits in Sequence 2B is accompanied by increased primary productivity following an increase in nutrient supply from upwelling and continental waters, which resulted in organic contents of about 12%. The hemipelagic deposits of Sequence 3A display the highest TOC in the entire succession (14-20%), as a consequence of productivity boosts due to riverine nutrient input, despite the presence of overall oxic bottom waters with occasional anoxic events. Sequence 3B accumulated in a low to moderately productive environment under strongly anoxic conditions, resulting in the lowest TOC in the entire section (2-8%). The detailed study of the I-35 Woodford Shale outcrop indicates that high organic content (TOC>10%) is found in settings where primary productivity is high, regardless of the bottom-water conditions. Primary productivity was boosted by riverine nutrient input associated with shallowing waters. The results of this study suggest that organic flux is more important than anoxia in the burial of organics in the sediments, with anoxia oftentimes being a consequence of high organic flux.

A Study of the Effects of Organic Matter on Illitization in the Woodford Shale, Oklahoma and Kansas

A Study of the Effects of Organic Matter on Illitization in the Woodford Shale, Oklahoma and Kansas
Author: Kale W. Janssen
Publisher:
Total Pages:
Release: 2017
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The Woodford Shale has received significant research interest as the number of productive wells has increased. The Woodford is productive over a wide range of thermal maturity (based upon vitrinite reflectance), yet most clay mineral studies report primarily illite (Caldwell, 2011 & Whittington, 2009). A previous report contrasts this behavior to other late Paleozoic shales in Oklahoma (Kowal, 2016). The major difference between these units is the amount of organic matter, which is much higher in most Woodford samples. In this study, Woodford shale samples were analyzed for several different characteristics, and combined with organic fraction data from previous work on the same samples (Lambert, 1993). Clay mineralogy was determined using an X-ray diffractometer (XRD) with the goal of finding the amount, and the degree of crystallinity of illite in a suite of samples. X-ray fluorescence (XRF) analysis was conducted to determine the variability of elemental concentrations within the samples. The bulk powder XRD data were combined with the major element concentrations to calculate mineral percentages. These data were compared to thermal maturity based upon vitrinite reflectance and Tmax values to determine the role of burial diagenesis on the clay mineralogy within Woodford Shale. The predominant clay mineral found within the samples was illite, with no recognizable mixed-layer smectite present, suggesting illitization is occurring early in the diagenetic process. A positive correlation between K/Rb ratios and TOC was found, supporting the control of organic matter on potassium in shales. No correlation between amount illite and thermal maturity was found, providing more evidence for the theory that high amounts of organics are driving illitization rather than thermal maturity.

Controls on Organic Carbon Accumulation in the Late Devonian New Albany Shale, West-central Kentucky, Illinois Basin

Controls on Organic Carbon Accumulation in the Late Devonian New Albany Shale, West-central Kentucky, Illinois Basin
Author: Seare G. Ocubalidet
Publisher:
Total Pages: 154
Release: 2013
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The Late Devonian-Early Mississippian-age New Albany Shale is both a source rock and reservoir rock for hydrocarbons in the Illinois Basin. Previously suggested models for organic carbon enrichment consider productivity, anoxia, and the interdependent roles of sedimentation, primary production, and microbial metabolism. This study attempts to reconstruct paleoenvironmental conditions during deposition and re-evaluates these models using geochemical data from multiple cores across the eastern edge of the Illinois Basin in west-central Kentucky. Geochemical methods utilizing redox-sensitive major elements (C, S, Fe, P, K, Ti, and Si), trace elements (V and Mo), and ratios (Ni/Co, V/Cr, and V/(V+Ni) are used. Analysis of paleo-redox indicators suggests variable bottom-water conditions during accumulation of the New Albany Shale members including: anoxic to possibly euxinic conditions for the Clegg Creek Member, anoxic to periodically dysoxic conditions for the Camp Run, and dysoxic to oxic (normal marine) for the Morgan Trail and Blocher Members. Variability in redox proxy results suggests that multiple parameters should be utilized in such studies rather than relying on a single proxy. High C/P ratios observed in these members may be controlled by regeneration of P, enhanced productivity, and sequestration of organic carbon (the productivity-anoxia feedback (PAF) mechanism) under anoxic conditions. The lack of correlation between organic carbon content and clastic-influx proxies suggests that organic matter (OM) accumulation was not controlled by sedimentation rate or increased nutrient supply associated with increased sediment influx.

Controls on Organic Carbon Accumulation in the Devonian-Mississippian Black Shales of Central Kentucky, Appalachian Basin

Controls on Organic Carbon Accumulation in the Devonian-Mississippian Black Shales of Central Kentucky, Appalachian Basin
Author: Jack Edward Sanders (Jr)
Publisher:
Total Pages: 118
Release: 2015
Genre: Appalachian Basin
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The environment of deposition of the Ohio Shale of the Appalachian Basin has been studied extensively using various geochemical proxies for each of its members. The accumulation of organic matter (OM) and its preservation in the Late Devonian-Early Mississippian black shales of central Kentucky have been studied extensively, especially the possible correlations between trace metal contents and water-column oxygenation. Previous work has centered on geochemical, petrographic, and isotopic analysis of samples collected throughout the central Appalachian Basin. Mechanisms for OM preservation include high productivity, enhanced preservation due to dysoxic or anoxic bottom waters, and a feedback loop due to high productivity that creates enhanced preservation through the periodic cycling and scavenging of essential nutrients. Usually, a combination of these factors results in the accumulation of enough OM to produce these black shales. This research shows the relationships between trace metal data and the environment of deposition of several cores taken along the eastern side of the Cincinnati Arch in the central Appalachian Basin. Whereas the indices do not all agree in every instance across the breadth of the study area, analyzed together a predominant environment of deposition has been inferred for the shales. The Sunbury Shale and upper part of the Cleveland Member of the Ohio Shale were deposited under euxinic conditions, the lower part of the Cleveland Member was likely euxinic in the northern study region and anoxic throughout the central and southern study areas, whereas the Huron Member of the Ohio Shale was deposited under a range of conditions, from oxic, to dysoxic, to anoxic.