In 2007, the Barnett Shale in the Fort Worth basin of Texas produced 1.1 trillion cubic feet (Tcf) gas and ranked second in U.S gas production. Despite its importance, variations of reservoir properties and their effects on well performances have not been assessed. Therefore, we evaluated production statistics for the 5 Barnett production regions, and to assess controls on Barnett Shale production rates and fluid composition, we related production to completion method, reservoir interval completed, reservoir properties and geologic setting.
In all five production regions, horizontal wells produce approximately twice as much oil and gas as do vertical wells. First Year gas production of horizontal wells (P50) ranges from 30 to 350 MMcf. First Year oil production from horizontal wells ranges from 0 to 8,000 bbl. There are positive relations between the reservoir units perforated and production rates and volume, but there are no obvious monotonic relations between perforation interval thickness and Peak Monthly or First Year oil or gas production. After filtering the wells by the number of fracture and acid treatments, we did not observe any relationships between production and perforated interval thickness.
On the basis of petrophysical characteristics from 800 well logs, we divided the Barnett Shale into 4 reservoir units that are significant to engineering decisions and reservoir performance. The most productive wells are perforated in Reservoir Units 2, 3 and 4, inclusive. Reservoir Unit 1 is a shaly interval that has a hot gamma ray response and is rarely perforated. Reservoir Unit 2 is laminated, siliceous mudstone and marly carbonate zone. Reservoir Unit 3, the most commonly perforated Barnett reservoir unit, is composed of multiple, stacked, thin, upward coarsening sequences of brittle carbonate and siliceous units interbedded with ductile shales. Reservoir Unit 4, the upper Barnett Shale, is composed dominantly of shale interbedded with upward coarsening, laterally persistent carbonate and siliceous units, similar to Reservoir Unit 3.
This research should provide operators with a better understanding of Barnett Shale geologic and reservoir properties and assist with optimizing development strategies and gas recovery. The results may be applicable to other developing shale gas plays.