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
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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.

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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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.

An Oil-source Rock Correlation Examining the Potential of the Chattanooga Shale as a Source Rock for Oil Within the Spivey-Grabs-Basil Field, Kingman and Harper Counties, Kansas

An Oil-source Rock Correlation Examining the Potential of the Chattanooga Shale as a Source Rock for Oil Within the Spivey-Grabs-Basil Field, Kingman and Harper Counties, Kansas
Author: Meagan Wall
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Release: 2015
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Oil production in Kansas has a long history with plays being found on all sides of the state. The source of Kansas's hydrocarbons has been traditionally thought to be outside the state due to low thermal maturity and the shallow burial of potential source rocks within Kansas. This research addresses the question regarding the source of the oil in Kansas, at least within a small geographic area of roughly 146mi2. The Spivey-Grabs-Basil Field has been one of the more successful fields within the state of Kansas since the 1960's. This field is compartmentalized and offers a natural laboratory in which to conduct the field's first formal oil-source rock correlation since oils are locked into place. While the main focus of this research relies heavily on pyrolysis and GCMS for biomarker analysis, it also investigates the possibility of using rare earth element (REE) concentrations as a possible fingerprint of organic matter within a source bed. TOC values of the Chattanooga shale samples from the Spivey-Grabs-Basil filed range from 0.75 and 3.95 wt. %, well within productive capacity. Pyrograms show both the potential for additional production, and the likely previous expulsion of hydrocarbons. Biomarker concentration percentages between C2--, C2, and C29 steranes, as well as pentacyclic terpane ratios compared between crude oil from the Spivey-Grabs-Basil and the Chattanooga shale show a definite genetic relationship. REE values of the organic fraction of the Chattanooga inversely correlate with those of the crude oils, suggesting fractionation during oil generation. After comparison of results with the Woodford shale in Oklahoma, the conclusion of this study is that the Chattanooga shale which underlies the Spivey-Grabs-Basil oil field of southern Kansas is the probable source rock which generated the oil now being produced.