Integration of Inorganic/Organic Geochemistry and Geomechanical Stratigraphy to Characterize Permian Shale Plays

Abstract

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. Source rock characters respond to these depositional environmental variations with changes in total organic carbon contents and HI/OI values. Depositional environment dependent biomarker parameters (Pr/Ph, DBT/Phen, etc.) from core extracts also show systematic changes reflecting variations in source rock facies and preservation conditions. Geomechanical properties of these shale formations, such as unconfined compressive strength (UCS) from rebound hammer analysis, also correspond to para‐sequence changes in depositional environments and associated lithological variations. Forward geocellular modeling based on XRF‐defined mineral compositions and burial history, when calibrated with petrophysical properties, allows us to extend well‐ based geomechanical stratigraphy to include all rock volumes from heel to toe. This integrated approach greatly enhances our description of Permian age resource play stratigraphy and petroleum systems, which in turn helps with sweetspot mapping and lateral landing zone definition.

AAPG Datapages/Search and Discovery Article #90349 © 2019 AAPG Hedberg Conference, The Evolution of Petroleum Systems Analysis: Changing of the Guard from Late Mature Experts to Peak Generating Staff, Houston, Texas, March 4-6, 2019