Petrophysical Properties of the Woodford Formation in the Ardmore Basin in Oklahoma, U.S.

A prolific source rock in Oklahoma, the Woodford Shale has sourced petroleum reservoirs for millions of years and produced oil and gas since 1939. Not until the shale boom of the early 2000's was the full potential of the Woodford Shale, as a reservoir, realized. The focus of this research is to characterize three (the main ones) of the four petro-physically distinct zones within the Ardmore Woodford Shale in order to investigate the ideal zone for hydrocarbon extraction. The Woodford Shale is composed of tight, organic-rich, interbedded shale and chert beds deposited along a marine slope. Due to its tight nature, petro-physical characteristics such as porosity, permeability and fluid flow behavior are hypothesized to be related to pore-throat distribution on the nano-meter scale. A total of seven samples from two wells, cover three of the four zones within the Woodford Shale. Pore framework and fluid flow were investigated using mercury injection capillary pressure (MICP), contact angle (wettability), and spontaneous imbibition tests. Pyrolysis tests were conducted to analyze thermal maturity and TOC, while X-ray diffraction (XRD) tests provided the samples mineral composition. The samples exhibit mineral compositions of mostly quartz and clays with high wettability and pore connectivity when interacting with a hydrophobic fluid of n-decane. Porosity and permeability values ranged from 0.5 to 3.1% and 4.4x10-7 to 1.5x10 -5 mD respectively, with the majority of pore throats existing within the 5-50 nm range (likely organic matter hosted and/or intraparticle pores). The MICP-derived porosity and permeability results are compared to these obtained from well logs, and a lack of industry standards for measuring tight shale characteristics from core samples makes consistent and repeatable results challenging. An integrated analysis of MICP, imbibition, wettability, geochemistry, well logs, and production data suggests that zone two within the Woodford Shale is the desirable target for hydrocarbon production.