Organic Geochemistry and Crude Oil Source Rock Correlation of Devonian–Mississippian Petroleum Systems in Northern Oklahoma

Abstract

The Mississippian limestone in northern Oklahoma and southern Kansas is a major oil play within the southern Midcontinent region. Mississippian carbonate reservoirs are known for their heterogeneity with respect to reservoir quality and produced fluids. Oil and gas from the Mississippian reservoirs are chemically heterogeneous, and cannot be explained solely by a single Woodford Shale source-rock model. New molecular geochemical data from east and west of the Nemaha uplift in north-central Oklahoma provides a new insight into the source of hydrocarbons in the Mississippian play, and attempts to provide a plausible scenario of the hydrocarbon charge history. Organic-rich zones within the Mississippian carbonate section were sampled and screened for total organic carbon (TOC), organic petrography, Rock-Eval pyrolysis and geochemical markers. Additionally, twelve oil samples were analyzed from Mississippian and Woodford producing wells. Rock extracts and oil samples were analyzed using gaschromatography and gas-chromatography mass-spectrometry techniques for quantitative analysis of diamondoids, saturate and aromatic biomarkers. Results indicate that the Mississippian source-rock has good generation potential (average 2% TOC) and reached the early oil window (average vitrinite reflectance of 0.74% Ro). Extracted bitumen from Mississippian rocks and related oils show unique biomarker signatures; these include the presence of extended tricyclic terpane, high gammacerane index, and high C23 tricyclic terpane relative to hopane, high input of C27 relative to C28 and C29 in regular and rearranged steranes, together with high C27 monoaromatic steroids relative to their C28 and C29 homologues. Moreover, on the basis of diamondoid compound class, the Mississippian samples showed abundance of 4,8-and 4,9-dimethyl dimantanes relative to the 3,4-isomer. The extent of cracking as measured by diamondoids reveals a dramatic change in diamondoid concentration across the Nemaha uplift. A high concentration of diamondoids was observed west of the Nemaha uplift, thus indicating episodic hydrocarbon charge of uncracked oil followed by cracked oil migrating out of the Anadarko Basin, which supports a long-distance migration model. In contrast, the Mississippian samples from east of the Nemaha uplift are depleted in diamondoids, suggesting limited migration and localized hydrocarbon generation under lower thermal stress.

RETRACTED ARTICLE: Light hydrocarbon geochemistry: insight into oils/condensates families and inferred source rocks of the Woodford–Mississippian tight oil play in North-Central Oklahoma, USA

“…This suggests that Group-3 oils were migrated likely from source rocks in deep Anadarko Basin as the source rock was not that mature. From a petroleum systems perspective, such hydrocarbon charge trend coincides with previous studies that postulated that oils in the southern part of Oklahoma are a result of long-distance migration from the depocenter of the Anadarko Basin, whereas oils east of the Nemaha Uplift are a result of localized hydrocarbon charge with no contribution from deep Anadarko (Al Atwah et al 2017;Wang and Philp 2019). Moreover, this explains the inconsistent signature between the isoheptane ratio and buck crude oil parameters of Group-1 and Group-3 oils, whereas the former suggests highly mature fluids, whereas the latter indicates black oils.…”

“…4), whereas Group-3 presumably is a mix of the two end members or from a third source. Within the Anadarko Basin, a number of source rocks have been studied ranging in age from Cambrian to Pennsylvanian (Al Atwah et al 2017;Wang and Philp 1997). Observations from light hydrocarbon source parameters are discussed in the biomarker section below.…”

“…Particularly, Group-1 condensates are located at the eastern edge of the Anadarko Basin, where the Woodford Shale has been reported within the late oil thermal maturity stage (Cardott 1989(Cardott , 2012. "Old" Woodford-sourced oils (Group-3) showed the highest heptane ratios; however, they are located at a shallower depth where thermal maturity is not sufficient for oil generation (lower than 0.6 VRo %), and hence, these fluids may have resulted from long-distance migration from the Anadarko depocenter where source rocks are buried at higher maturity levels (Al Atwah et al 2017). One exception within Group-3 oils is sample ST Mary, which exhibits the feature of a light oil from its bulk characteristics (Table 1) while plotting within normal oils in Fig.…”

“…The Woodford Shale is an organic-rich source of hydrocarbon that charged Woodford-Mississippian tight reservoirs, together with Mississippian mudrocks such as Caney Shale (Al Atwah et al 2015, 2017. Typically, identifying petroleum source rock could be achieved by using a collection of geochemical tools such as molecular and isotopic fingerprints, which include biomarkers together with stable carbon isotopes of saturate and aromatic hydrocarbon fractions (Al Atwah et al 2017;Wang and Philp 1997). Currently, light hydrocarbon markers remain underutilized in crude oil recovered from Woodford-Mississippian tight reservoirs.…”

Petroleum generation kinetics of unconventional Mississippian mudrocks in central Oklahoma, United States

“…Petroleum source rocks in the Anadarko Basin range from Ordovician to Pennsylvanian in age, with the primary source of hydrocarbons being contained within the Devonian-Mississippian rocks (Wang and Philp, 1997;Al Atwah et al, 2019). The Woodford Shale is comprised of organic-rich radioactive shales that are regionally present across Oklahoma (Kirkland et al, 1992;Miceli Romero and Philp, 2012;Rivera et al, 2015;Curiale and Curtis, 2016).…”