Multiple Generations of Hydrocarbon Charge in the Mississippian Reservoirs of the STACK Play, Central Oklahoma: Evidence From Structural, Production and Geochemical Data

Abstract

Mississippian Meramec reservoirs in the central Oklahoma STACK play produce hydrocarbons across a wide range of liquids yields. Organic material in these reservoirs is primarily migrated bitumen and is not present in sufficient abundances for the system to be self-sourced. Geochemical comparison of oils from both Devonian and Mississippian reservoirs reveals that oils from the Meramec siltstone were derived from underlying source rock in the Devonian Woodford Shale. These oils show similar isoprenoid and sterane distributions from saturate biomarkers; minor variations in carbon isotope and triaromatic steranes are in alignment with variation of thermal maturity in these oils.

In spite of the genetic link between Woodford source rock and Mississippian oils, Woodford Shale maturity trends fail to provide accurate predictions of Meramec liquids production. We propose that this is because hydrocarbons migrated into the Mississippian system in multiple charging episodes.

We present a multi-step model of hydrocarbon migration for the STACK play in which thick deposits of organic-rich Woodford Shale in western Canadian County (AKA Cana field) provided the most significant hydrocarbon source for the STACK Play. Overpressure associated with petroleum transformation drove waves of progressively lighter hydrocarbons upward and outward from the Cana depocenter into Meramec strata, where they were sealed by the Chester Shale above. Low system permeability in Mississippian reservoirs prevented development of a conventional hydrocarbon column. Rather, early-generated oil displaced formation water, and was in turn displaced by gas condensate and then dry gas. The result of this radial hydrocarbon migration is observable in arcuate GOR contours around the Cana Woodford depocenter.

A second phase of hydrocarbon charge is confirmed by comparison of gas and oil maturities from Meramec wells. This migration episode carried more mature hydrocarbons into the Meramec and was influenced by certain N-S trending faults and other structures. In some areas this secondary charge dramatically altered the fluid mix predicted by regional trends. Using 3-dimensional seismic data, we discern the nature of those structures which appear to have affected hydrocarbon migration, as well as some of those that did not. The impact of only certain geological structures on the latter phase of hydrocarbon migration helps constrain the tectonic history of the eastern Anadarko Basin.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018