Deconvolving Biogeochemical Controls on Source Rock Reservoir Development using a Quantitative Multivariate Approach: A Case Study from the Late Ordovician Utica-Point Pleasant Formation

Abstract

The Middle to Late Ordovician was a dynamic interval, characterized by environmental upheaval and intensified biogeochemical feedback mechanisms as the Earth system transitioned toward a steady state in which the geosphere and biosphere became more intimately linked. The Late Ordovician (and early Silurian) also saw widespread deposition of organic-rich shales, many of which serve as source rocks for some of the world’s prolific petroleum systems or are themselves being exploited as source rock reservoirs (SRRs). Here, we utilize the Katian Utica-Point Pleasant (U-PP) Fm. of the Appalachian basin to explore the record of Late Ordovician biogeochemical feedback mechanisms and the extent to which these feedbacks influence organic matter availability, preservation potential, and ultimately SRR development using a quantitative, integrated approach. Three cores from the western basin margin (present-day eastern Ohio) were logged and a set of samples are being analyzed for Fe-speciation, major and trace elemental composition, TOC, δ13C-org, and biomarker composition. Preliminary results suggest that the U-PP can be characterized by 3-5 distinct facies that represent both tectonic and glacioeustatic controls on sea level, resulting in carbonate platform drowning and development of a clastic-dominated foreland basin. Across the U-PP, Fe-speciation data indicate a broad transition from oxic to ferruginous (anoxic, Fe-replete) conditions while redox-sensitive trace elements sustain near-crustal values, supporting a local control (water depth) on redox and a stable global ocean. Analysis of one sample of the most distal facies returned abundant lipid biomarkers that suggest a dominance of eukaryotic primary producers. This work represents the first SRR-specific study to apply multivariate statistical techniques to inorganic and organic geochemical data within a stratigraphic framework, such that significant correlations between parameters and facies may reveal enigmatic mechanistic relationships between biological, geological and chemical processes. Ultimately, understanding these complex interactions – for example, the role of terrestrialization on organic matter burial through the intermediate processes of weathering, clay formation, Fe-cycling, and microbial community turnover – is crucial to interpret signals preserved in the sedimentary record more accurately and thus improve SRR exploration and production methods today.

AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019