Barnett Shale DD
The Barnett Shale gas play in North Texas’s Fort Worth Basin is the largest and youngest in the United States. The area’s source rock has massive organic–matter deposits and has proven to be a prolific hydrocarbon generator. At depths up to 10,000 feet, the Barnett Shale is one of the 10 richest hydrocarbon systems in the world.
Formation Characteristics
The Fort Worth Basin presents an enormous opportunity to tap unconventional natural gas reserves. This large, geologically continuous gas accumulation occupies a structurally low position straddling the basin axis. The accumulation is characterized by moderate depth; gas downdip from water–saturated rocks; low matrix permeability (microdarcy and nanodarcy); and natural fractures. In addition, the shale does not contain any lithologic or structural barrier that separates the updip water and downdip gas
North Texas’s Barnett Shale formation is similar to other black shale formations in the United States, such as those found in the “Devonian” shales of the Appalachian Basin. These shales are rich in organic content and are solid. The Barnet Shale’s thickness ranges from 50 feet to 1,000 feet, forming storage sites for stranded gas throughout the formation. Thus, the Barnett Shale readily lends itself to the drilling technique of fracturing to stimulate production. Fracturing involves the injection of water and sand into a well after it has been drilled, creating pencil-thin cracks in the shale to facilitate gas flow.
Most vertical wells are completed in the southern part of the Barnett Shale with perforations typically spanning 200 feet to 300 feet. Most horizontal wells are completed with a leg of at least 3,000 feet, using slotted liner technology and multi–stage fracture stimulation.
Drilling Activity
Although operators have been drilling in the Barnett Shale since the early 1980s, most companies overlooked the formation until the late 1990s when higher oil prices and advancements in hydraulic fracturing techniques made this unconventional gas play economically viable.
Today, the Barnett Shale is a hotbed of activity and opportunity. About 100 companies are drilling in the area, representing five percent of the North American rig count. More than 3,800 successful wells have been completed to date, with few marginal wells and dry holes. The Barnett Shale’s current aggregate production exceeds 1.2 billion cubic feet of gas per day, and proven gas reserves amount to more than 4 trillion cubic feet.
Operators are currently expanding the gas play beyond the initial core area of Denton, Tarrant and Wise counties. Drilling activity has moved south and west of the original area into what is referred to as the Lower Barnett, encompassing 15 counties in North Texas.
