A potential extension of the Barnett Shale oil play: a subsurface play analysis of the Mississippian (Osagean-Meramecian) strata in Shackelford County, Texas

Abstract

Repeatable, unconventional Barnett Shale completions have been constrained to the gas-rich, eastern portion of the play in Fort Worth Basin due to the presence of fracture barriers protecting the play from unwanted water production from the underlying Ellenburger Group. This project conducts a subsurface study on the Mississippian-aged strata (Chappel Limestone through the Barnett Shale) within the oil-rich, western extent of the Barnett Shale play in Shackelford County, Texas. The subsurface study results identify two distinct depositional mechanisms of facies formation within the Chester Limestone that overlap to give play potential for oil-rich Barnett Shale completions west of the Viola pinchout in the Bend Arch-Fort Worth Basin area. The upper portion of the Chester Limestone contains a higher porosity cherty zone that shows reservoir potential. The basal portion of the Chester Limestone is referred to as the Mississippian Shale , and it shows potential to act as a fracture barrier that could prevent downward fracture growth into the Ellenburger in areas with widespread deposition and significance difference in rock mechanics (ductile) from the upper cherty zone (brittle). Subsurface correlations were done utilizing over 100 wells that contained gamma-ray (GR) and bulk density (RHOB) within the 64 mi2 AOI (area of interest). Rock mechanics were tested utilizing the Equotip Bambino micro-rebound hammer and by observing the difference in RHOB of the play units. The main conclusions of this study include: (1) the identification of the Mississippian Shale as a potential fracture barrier for the Barnett Shale play to potentially extend the play in to the oil window; (2) sweet spot maps that identify areas with the most geologic potential to prevent downward growth of stimulation fractures into the Ellenburger in areas related to the growth of the Chappel reefs; (3) the identification of