This study presents an integrated inorganic/organic geochemistry and geomechanical stratigraphic methods to characterize Permian organic rich mudstones in the Midland Basin, to understand controls on organic carbon richness, such as primary productivity, depositional environments, sediment supply, and bottom water preservation conditions, and its implications on petroleum generation/charge and on shale oil development.

A high frequency sampling of core samples from a thick sequence (∼1000 ft) of argillaceous mudstones, organic-rich mudstones, siliceous mudstones, and carbonate mudstones in the Midland basin were characterized for elemental concentrations and source rock geochemistry, and for high resolution gas chromatography and biomarkers on extracts. The small maturity differences from the top to the bottom of this 1000 ft section and limited migration of hydrocarbons into the rock pore space due to low permeability and high capillary entry pressure allows us to interpret the extract geochemistry fingerprints to compositions of the source rock kerogen and its in-situ generated bitumen.

Geologic, petrophysical, and elemental analysis have divided the section into many depositional packages (chemozones) with distinct signatures. This has suggested cycles of para-sequences with varied sediment (clastic vs carbonate) supply, a likely shift in detrital sediment source and organic matter input, and also changes in bottom water oxygen conditions during the deposition of these organic rich mudstone units. Specifically variations in elemental parameters indicative of detrital sources suggest a significant shift of sediment source area/provenance, probably associated with the transition of late Permian glacial/interglacial climate. A corresponding change in organic matter input is also observed across the glacial/interglacial transition zone. Source rock characters respond to these depositional environmental variations with changes in total organic carbon contents and hydrogen/oxygen index values. Depositional environment dependent biomarker parameters (Pristane/Phytane, Dibenzothiophene/Phenanthrene, etc.) from core extracts also show systematic changes reflecting variations in source rock facies and preservation conditions. Primary productivity, as proxied by Ni concentration in sediment, is the best parameter to explain organic matter enrichment in these sediments, combined with a possible increase in sedimentary anoxia. This integrated approach greatly enhances our understanding of these Permian age resource play petroleum systems, which in turn helps with sweetspot mapping and lateral landing zone definition.