Date of this Version
Still, J.P., 2013,Oil-Source Rock Correlation in the Late Paleozoic, Denver Basin, Nebraska -The Search for a Negative δ¹³C Anomaly in Pennsylvanian-Permian Cyclothems. MS thesis, University of Nebraska.
Late Paleozoic sedimentation in the Denver basin occurred in two environmentally distinct depocenters. The northern-most Alliance Basin has been interpreted to have a restricted character: anhydrite-bearing mudstones are present in cyclothems comprising wackestone, packstone and mudstone. The source of petroleum produced from these intervals is considered to be organic-rich units within these cyclothems. Oil recovered from late Paleozoic reservoirs has δ13C values that range from -30.8‰ to -28.8‰: values that are lower than those reported previously for prospective source rocks from this interval. Cores from seven wells that penetrate upper Pennsylvanian to lower Permian rocks have been chosen for analysis. The top unit in many of these cyclothems consists of thin (~1 ft) organic-rich marlstone, mudstone or microbial laminites. Geophysical log correlation is used to identify rocks that have not been tested previously as potential sources for the petroleum recovered from Paleozoic reservoirs. Facies relationships indicate that these rocks where deposited in a hypersaline environment. Burial history plots show that these intervals were subjected to subsurface conditions conducive to the release of hydrocarbons. Analysis of kerogen samples reveals δ13C values that are lower than seen in prior work. Two anomalies are noted (Pennsylvanian and Missourian) that contain prospective source rocks with δ13C values approaching -31.0‰. Burial history, TOC values, lithologic relationships and δ13C data all indicate that organic-rich strata deposited during the two negative δ13C anomalies are the sources for some of the Paleozoic oils.
Advisor: Richard M. Kettler