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Analyzing a “Sweet Spot” in the Barnett Shale

Jimmy D. Thomas
Castaneda Consulting LLC

Drilling activity has intensified in the counties west of the Barnett Shale core area and is expected to increase even more in the near future. A detailed study has been conducted using the results of over 20 Barnett Shale vertically drilled gas wells in central Parker County over the last couple of years. Production mapping indicates an area thought to be a “sweet spot” or a limited area with above average gas production in south central Parker County. The basic suite of open hole logs can be used for a general lithologic description of the Barnett Shale, but the logs seem to be limited as to what they can predict about future hydrocarbon production.

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. The largest tectonic feature in south central Parker County is a four-hundred-foot throw fault or fault system that formed during the Atoka. Subsurface mapping with a limited amount of seismic data indicates wrench faulting in the south central part of the county. Fracing into a fault has the potential to result in the energy of the frac going into the fault and/or fracing into a nearby water zone.

Thickening of the Marble Falls formation in this area is thought to be an indication of karst collapse in the underlying Ellenburger. This event may cause micro fractures in the overlying Barnett Shale increasing permeability of the formation. These collapses may also cause an undesired faulting in the area surrounding the collapse. Continued formation evaluations combined with new completion techniques are going to be needed in the step out areas of the Barnett Shale for economic hydrocarbon production.