Integration of fluid and rock geochemical parameters to constrain thermal maturity in Paleozoic organic-rich intervals

Integration of source rock pyrolysis geochemical parameters along with fluid/extract analyses is critical for assessment of thermal maturity in Paleozoic source rocks with a complex burial history, erratic vitrinite reflectance measurements (%VRo), vitrinite suppression, and dearth of vitrinite macerals in Paleozoic intervals. The relative abundance and distribution of aromatic markers and biomarkers in ten selected samples from the Devonian-Mississippian New Albany Shale Group (NAS) in the Illinois Basin were investigated by gas chromatography-mass spectrometry (GCMS) and correlated with source rock pyrolysis parameters to assess thermal maturation trends. An initial screening of common maturity indicators from fluid data were compared with rock data derived from computed organic matter transformation due to hydrocarbon generation (transformation ratios). A robust maturity correlation between EN-ethylnaphthalene, DMN-dimethylnapthalene, TEMN-tetramethylnaphthalene, MP-methylphenanthrene, TS/TM-18alpha and 17alpha -trisnorhopane, and C29 beta beta /alpha alpha 20S and 20R sterane ratios and transformation ratio (TR) values indicate the utility in thermal stress differentiation. The EN and DMN maturity indices are useful between 0.58 to approximately 0.80 TR, while the TEMN and MP aromatic marker indicators correlate with pyrolysis data between 0.4 and 0.78 TR. The sterane and trisnorhopane indices span the widest range of source rock pyrolysis maturity indicators, between 0.35-0.8 TR. This fluid/rock correlation will aid in constraining problematic low (high) pyrolysis-generated thermal maturity indicators. This technique may also assist in discrimination of fracture-migration in low porosity and permeability unconventional reservoirs as it differentiates discontinuities in thermal maturation response between source rock pyrolysis and fluid data.