Barnett Shale

Barnett Shale
Country	United States
Region	Bend Arch-Fort Worth Basin, Texas
Offshore/onshore	Onshore
Operators	Devon, Chesapeake, GEV Group, EOG, XTO, Range Resources, EnCana, ConocoPhillips, Quicksilver, Chief Oil and Gas, Denbury
Field history
Discovery	1980s
Start of production	1999
Production
Estimated oil in place	2.1–30×1012 cu ft (59–850×109 m3)
Producing formations	Barnett Shale

The Barnett Shale is a geological formation located in the Bend Arch-Fort Worth Basin. It consists of sedimentary rocks of Mississippian age (354–323 million years ago) in Texas. The formation underlies the city of Fort Worth and underlies 5,000 mi² (13,000 km²) and at least 17 counties.

Some experts have suggested the Barnett Shale may have the largest producible reserves of any onshore natural gas field in the United States. The field is proven to have 2.5×10^¹² cu ft (71 km³) of natural gas, and is widely estimated to contain as much as 30×10^¹² cu ft (850 km³) of natural gas resources. Oil also has been found in lesser quantities, but sufficient (with recent high oil prices) to be commercially viable.

The Barnett Shale is known as a "tight" gas reservoir, indicating that the gas is not easily extracted. The shale is very hard, and it was virtually impossible to produce gas in commercial quantities from this formation until recent improvements were made in hydraulic fracturing technology and horizontal drilling, and there was an upturn in the natural gas price.

Future development of the field will be hampered in part by the fact that major portions of the field are in urban areas, including the rapidly growing Dallas-Fort Worth Metroplex. Some local governments are researching means by which they can drill on existing public land (e.g., parks) without disrupting other activities so they may obtain royalties on any minerals found, whereas others are seeking compensation from drilling companies for damage to roads caused by overweight vehicles (many of the roads are rural and not designed for use by heavy equipment). In addition, drilling and exploration have generated significant controversy because of environmental damage including contamination to the ground water sources.

History

The formation is named after John W. Barnett, who settled in San Saba County during the late 19th century, where he named a local stream the Barnett Stream. In the early 20th century during a geological mapping expedition, scientists noted a thick black organic-rich shale in an outcrop close to the stream. The shale was consequently named the Barnett Shale.

The Barnett shale has acted as a source and sealing cap rock for more conventional oil and gas reservoirs in the area. It was thought that only a few of the thicker sections close to Fort Worth would be able to support economic drilling, until new advances in horizontal drilling were developed in the 1980s. Techniques such as fracturing, or "fracking", wells, used by Mitchell Energy, opened the possibility of more large scale production. Even with new techniques, significant drilling did not begin until gas prices increased in the late 1990s.

Well completion

Barnett Shale gas drilling rig near Alvarado, Texas (2008)

Two key developments in well design and completions have fostered development of the Barnett Shale. These are horizontal, or "slant" drilling, and hydraulic fracturing. In addition, changes to the Clean Water Act made in the 2005 Energy Policy Act exempt natural gas explorers from disclosing what chemicals they use in hydraulic fracturing, allowing those explorers to avoid costly regulatory oversight.

Horizontal drilling

As of 2007, recent advances in the technology of horizontal drilling have opened up the potential of the Barnett Shale as a major source of natural gas. Horizontal drilling has changed the way oil and gas drilling is done by allowing producers access to reservoirs which were otherwise too thin to be economically viable through vertical drilling. Much of the gas in the Barnett Shale is beneath the City of Fort Worth. The new technology has attracted a number of gas-production companies.

In addition to extended reach, horizontal drilling drastically increases production. In "tight" rock (low permeability) like the Barnett Shale, the gas uses fractures to move out of the rock and into the wellbore. The fractures may be natural or induced (see below). A horizontal well exposes more rock (and therefore more fractures) to the wellbore because it is usually designed with the horizontal portion of the well in the productive formation.

In 2005–2007 horizontal drilling in the Barnett Shale extended south into Johnson, Hill, and Bosque counties, with a 100% success rate on completed wells. An experimental vertical well is being drilled in McLennan County (near Waco) to assess the potential for drilling along the Ouachita Fold, a geological barrier which defines the southern limit of the Barnett Shale.

Hydraulic fracturing

Hydraulic fracturing carried out in the Barnett Shale is done by pumping a mixture of water, sand, and various chemical additives (to affect viscosity, flow rates, etc.) into the well bore at a sufficient pressure to create and propagate a fracture in the surrounding rock formation down hole. This is crucial in low permeability rock as it exposes more of the formation to the well bore and greater volumes of gas can be produced by the increased surface area. Without hydraulic fracturing, the wells would not produce at an economically feasible rate.

Scientists at the Jackson School of Geosciences at the University of Texas at Austin, who have worked closely with producing companies to develop the Barnett play, also see potential for conflict in some parts of the Barnett where water use for hydraulic fracturing could begin competing with other uses such as drinking and agriculture.

The process of hydraulic fracturing generates significant criticism. Opponents allege that it is inadequately monitored and poses significant threats to water and air quality in surrounding areas, and cite a growing body of scientific evidence.

Economic impact

As of September 2008, gas producers claimed bonuses paid to landowners in the southern counties ranging from $200 to $28,000 per acre ($500–69,000/ha, the latter being paid by Vantage Energy in the fall of 2008) with royalty payments in the 18–25% range. One lease in Johnson County now has 19 wells permitted.

A Fort Worth Star-Telegram article reported over 100,000 new leases were recorded in Tarrant County in 2007. Terms of recent leases have included $15,000 per acre ($37,000/ha) and a 25% royalty for homeowners in Ryan Place, Mistletoe Heights, and Berkley on Fort Worth's south side, and $22,500 per acre and a 25% royalty for a group of homeowners in south Arlington. More recent articles in the Fort Worth Weekly report that many signed lease agreements have not been honored, with lessors alleging that they were paid significantly less than promised or were not paid at all.

Drilling industry advocacy groups claim that by 2015 the Barnett Shale may be responsible for more than 108,000 jobs. Offsets to tax revenues may include cleanup costs for toxic byproducts of gas drilling, such as benzene and naturally occurring radioactive material (NORM). Environmental groups and state regulators have come under increasing pressure to begin forcing cleanups, and one group, the San Juan Citizens Alliance, has sued to force the EPA to tighten regulations. Ed Ireland, of the Barnett Shale Energy Council (an industry advocacy group) has said that he believes regulation will increase under the Obama administration, this is, as of 2012, yet to be seen.

In addition to the drilling work, an expanded gas pipeline network for transporting the gas to market is being sought. The completion of a 42-inch (1,100 mm) natural gas transmission pipeline through Hill County might open up new areas for drilling.

Operators in the Barnett

Operators, such as EOG Resources, Gulftex Operating, Inc, and Devon Energy, stated in public reports in mid-2005 that they estimate that one third to one half of the land in the counties that contain the Barnett Shale, including the most heavily prospected counties like Johnson and Tarrant, will get wells. It would logically follow that the rest of the land will either get pooled in a unit that will have wells, or get nothing at all if the land is in an especially complex area. There have been few dry holes drilled, however, because technology like 3D Seismic allows operators to identify potential hazards before they drill and avoid bad areas. Some of the hazards include faults and karst features (sinkholes). Faults may divert hydraulic fracturing, reducing its effectiveness, and karst features may contain abundant water that limits the production of gas.

Geography of Barnett Shale

The Barnett Shale has been classified into "Core" and "Non-Core" areas of production. To date production has concentrated in the Core area where the shale is thicker and the uncertainty is reduced. This allows for the wells to be drilled at slightly lower gas prices than those in Non-core areas.

Core

• Denton (active)
• Tarrant (active)
• Wise (active)

Non-core

• Bosque (potential)
• Comanche (potential)
• Cooke (active)
• Ellis (potential)
• Erath (active)
• Hamilton (potential)
• Hill (active)

• Hood (active)
• Jack (potential)
• Johnson (active)
• Montague (potential)
• Palo Pinto (active)
• Parker (active)
• Somervell (potential)

Controversy

Several groups in communities in which gas wells have been located have complained of high risk factors for catastrophic accidents, and some allege that accidents have already occurred, including several resulting in fatalities. In addition, some environmental groups and north Texas residents have expressed concern about the effects of drilling on air and water quality in the areas surrounding the drills and transportation pipelines. Texas environmental regulators and the EPA have ordered the Texas Commission on Environmental Quality to begin investigating drilling complaints on-site within 12 hours of reception.

Numerous lawsuits against companies operating in the Barnett Shale allege that companies have reneged on promised lease payments, altered agreements after the fact, or failed to meet their commitments to lessors of land in the shale.

Legacy

The profit potential of the Barnett Shale gas play has spurred companies to search for other sources of shale gas across the United States. Other shale gas prospects in the United States include the Antrim Shale in Michigan, the Fayetteville Shale in Arkansas, the Marcellus Shale in Appalachia, the Woodford Shale in Oklahoma, the Ohio Shale in Kentucky and West Virginia and the Haynesville Shale in Louisiana and East Texas.

See also

• Shale gas in the United States

External links

• Barnett Boom Ignites Hunt for Unconventional Gas Resources Jackson School of Geosciences, January 2007
• Barnett Shale Energy Education Council
• Texas Railroad Commission Online Research Queries
• Texas Railroad Commission: Newark, East (Barnett Shale) Field
• FWCanDo (Fort Worth Citizens Against Neighborhood Drilling Ordinance)
• Hydraulic Fracture

Bibliography

• Scott L. Montgomery, Gas-Shale Play With Multi-Trillion Cubic Foot Potential ; Fact Book</ref>.