Tue, Sep 13|
FWGS September 2022 Luncheon
Dr. Richard Denne - Dual Carbon Sinks: the Organic- and Coccolith-rich Mudstones of the Eagle Ford of Texas
Time & Location
Sep 13, 2022, 11:30 AM – 1:00 PM CDT
Fort Worth, 777 Main St, Fort Worth, TX 76102, USA
Richard Denne is the founding chairholder of the Hunter Enis Endowed Chair in Petroleum Geology at Texas Christian University and the former Director of the TCU Energy Institute. Richard worked as a geologist in the oil and gas industry for over 25 years, working with integrated teams in the exploration and production of deep-water basins across the globe, including the Gulf of Mexico, West Africa, Brazil, Trinidad, and the North Sea. He has also been heavily involved in unconventional mudstone plays, particularly the Haynesville and Eagle Ford of Texas. Richard worked at Exxon, Applied Biostratigraphix, and Marathon Oil, where he was the corporate Biostratigraphy Subject Matter Expert with oversight of the application and integration of biostratigraphy and chemostratigraphy in unconventional shale, deep-water, and carbonate plays. His specialty is using biostratigraphy and geochemistry to resolve the sequence stratigraphy, paleoenvironment, and paleoceanography of hydrocarbon reservoirs and source-rocks, with expertise in the biostratigraphic application of microfossils such as calcareous nannofossils and foraminifera. His current research is focused on depositional systems that have produced organic-rich rocks, especially those from the Cretaceous of Texas and the Eagle Ford / Woodbine systems. He has also published the results of several studies on the effects of the end- Cretaceous Chicxulub bolide impact on the Gulf of Mexico. Richard is a graduate of the University of Iowa (B.S.) and Louisiana State University (Ph.D).
Box models of the long-term carbon cycle are used to estimate ancient atmospheric CO2and O2 levels and to understand rates of geologic carbon sequestration during perturbations in the carbon cycle. These models are based on carbon volumes calculated using average values of Ccarb and Corg for each rock and basin type at the epoch/series level, so data at much finer time scales using actual measurements will eventually be needed to accurately model periods of major carbon volume changes. Calcareous mudstones with high abundances of organic carbon (TOC) are of particular interest, as they can store carbon as both Ccarb and Corg, which is termed here a dual carbon sink. Coccolithophores are microscopic, marine, planktonic algae with calcareous tests that are the main calcite source for Cretaceous chalks, and also act as a source of organic matter. Coccoliths (coccolithophore plates) are rare in the platform carbonates of the Cretaceous Texas Shelf, and are generally uncommon in the mudstone-dominated sections associated with Lower Cretaceous Oceanic Anoxic Events (OAEs). However, within the Cenomanian-Turonian Eagle Ford Shale, which contains up to 18% TOC after correcting for thermal maturity, coccoliths are the dominant calcite source for mudstones that are 40% to 90% calcite. Analyses of core from the south Texas producing region found that although the mudstones of the organic-rich lower Eagle Ford contained only an average of 8% more carbon than the Coniacian portion of the overlying Austin Chalk (0.31 vs. 0.28 gC/cm3; calcite = 0.3252 gC/cm3), they stored an average of 75% more carbon per 100 k.y. than the Austin Chalk due to their higher rock accumulation rates. The upper Eagle Ford, which in the study area typically has lower abundances of TOC than the lower Eagle Ford, has carbon abundances and carbon accumulation rates similar to the Austin Chalk.
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