Light Hydrocarbons Geochemistry: Insights Into Analyzing the Mississippian Petroleum Systems in Northern Oklahoma

Abstract

The Mississippian limestone is a prolific hydrocarbon play in the northern region of Oklahoma, and southern part of Kansas. The Mississippian reservoirs feature variations in produced fluids chemistry usually explained by different possible source rocks. Such chemical variations are regularly obtained from bulk, molecular and isotopical characteristics. However, light hydrocarbon markers remain underutilized in the Mississippian limestone play. Oil-oil correlation together with hydrocarbon migration and maturity assessment can be further refined by using the light hydrocarbon markers. In this study we present a new geochemical investigation of gasoline range hydrocarbons produced from Mississippian carbonate intervals over the Anadarko shelf, central Oklahoma and the Cherokee platform. A set of 25 oil samples from 9 different counties was examined using high performance gas-chromatography and mass-spectrometry techniques to analyze for C5-C8 hydrocarbons, saturate and aromatic biomarkers. In terms of oils source, results of biomarkers together with C7 star diagram suggest different oil families over the Anadarko shelf, central Oklahoma and Cherokee platform. Mississippian oils from the Anadarko shelf exhibit enrichment in regular and rearranged C29 steranes. Furthermore, these oils are high in 3,3 dimethylpentane (3,3-DMP) and 2,2-dimethylpentane (2,2-DMP) relative to the rest of C7 isomers. In contrast, oils from central Oklahoma and the Cherokee platform showed enrichment in regular C27 steranes, high 3-ethylpentane and 2,3-dimethylpentane (2,3-DMP) relative to the C7 isomers. Geochemical variations could be attributed to different source rocks contribution and/or co-sourcing. Across the Anadarko shelf, Mississippian reservoirs are mostly charged from the Woodford Shale. Whereas oils from central Oklahoma and Cherokee platform (in addition to the Woodford Shale) are possibly sourced from both Caney Shale and Kinderhookian shaly limestones. Moreover, variations in cyclic relative to normal alkanes were observed relative to oils location. Oils from the Anadarko shelf and the Cherokee platform are high in cyclic hexane and methylcyclohexane relative to n-C6 and n-C7. Conversely, oils from central Oklahoma are enriched in n-alkanes relative to cyclic isomers. These differences could be a result of migration distance and/or source rock maturity.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016