Basin-Centered Tight Gas Sands and Thrust
Jimmy D. Thomas, MBA
The Fort Worth Basin formed during Early and Middle Pennsylvanian due to the oblique collision of the Afro-South American and North American plates. This tectonic activity not only affected deposition at that time but also affected the underlying formations. Depositional environments changed from shelf carbonates to shallow marine to deep marine then back to shallow marine during basin development. Eustatic cycles combined with tectonic activity have complicated mapping efforts and led to many misunderstandings about the basin. Much of the basin center is unexplored and has potential for enormous gas reserves. Reservoir mapping of just the basin-centered tight gas sediments indicate natural gas reserve potential in the tens of TCF. Is this another giant reservoir that can be "gas farmed" much like the Barnett Shale?
A four-hundred-foot throw thrust fault extends through southern Parker County with open hole logs indicating repeat sections in the Barnett Shale, Atoka and Strawn formations. Due to the cyclicity of sediments during this time, most of these repeat sections can be mapped as separate deposits. It is also believed that due to the oblique collision of the plates, lateral fault movement and faults of different orientations complicate the understanding of tectonics during this time. This tectonic activity has the potential to have created additional "sweet spots" in the Barnett Shale similar to the Newark East gas field. Faulting and fracturing may have created potential permeability enhancement and hydrocarbon traps in the Ellenburger and Marble Falls making these formations exploration and development targets. Due to the lack of drilling, very little is known about these formations in most of the basin. The Fort Worth Basin is a new exploration frontier for combining the advances in geology and engineering technologies.
AAPG Southwest Section 2003 Convention