Shale Gas Drilling 101

This information is re-posted from the ABC Alliance.

The Barnett Shale covers 23 counties with more than 14,000 wells now in North Texas. The earliest wells were drilled ten years ago in Denton and Wise Counties. The first step is to erect a tower that supports the drilling equipment and bring in the crew that drills deep into the earth until natural gas is found. For the Barnett Shale, many wells are between 6,000 and 10,000 feet deep. The work is dangerous. On a rig set up off Brush Creek Road in early 2007, a worker fell from the top of the rig. The 90-foot fall is usually fatal, but the man managed to land on his feet and survive with broken bones.

To drill, a rotating bit attached to a length of hollow drill pipe bores a hole in the ground by chipping and cutting rock. A stream of drilling “mud” – a mixture of clay, chemicals, and water – is continuously pumped through the drill pipe and through holes in the drill bit. The “mud” cools the drill bit, plasters the walls of the hole to prevent cave-ins, carries crushed rock to the surface, and prevents “blowouts” by equalizing pressure inside the hole. Workers lost control of a well at this stage in the Palo Pinto county town of Brad in December 2006 and it blew a 250-yard crater in the earth that burned for several days.

Many wells are dug with a drilling pit nearby, where the crew can store drilling fluids. This practice is not permitted in many states, but it is still allowed in Texas. Some Barnett Shale cities require a closed-loop system, which limits the environmental impact the pits have. For example, spring rains overwhelmed pits in Krum and Sanger in 2006 and 2007, where mud flowed into neighboring properties, including a lot by a church and its playground.

After natural gas is found, the crew pulls the bit and pipe from the well, and lowers a casing in, cementing the casing in place and capping it until the wellhead can be attached. Wells must be lined with concrete in order to keep fluids, with brine water at the bottom, oil – if any – at the next level, natural gas above that, and finally fresh water on top. If a well is not properly lined, it can contaminate fresh water supplies around it. Bentonite is often used in drilling mud, and residents have been reporting this fine, gray-colored clay is showing up in both private and public water wells increasingly in recent months. Former railroad commission candidate Dale Henry, an expert in this process, said scores of wells are not cemented properly.

After the well is drilled, a team comes to inject water mixed with sand and chemicals under high pressure to fracture the rock so the gas is released from the rock. Many wells in the Barnett Shale are dug with new directional techniques, at angles of up to 90 degrees, to recover more natural gas without having to dig another wellhead. Experts in Colorado have identified more than 250 chemicals that can be used in the process, but the industry enjoys broad exemptions from laws that would normally require them to disclose the chemicals, many of which are highly toxic and pose a serious risk to human health and the environment. Energy investors have recently begun insisting that gas exploration and production companies disclose those chemicals so that they, too, can better assess their exposure to risk.

Drillers use anywhere from 1 to 7 million gallons of fresh water for each frack job. In Denton County, much of this fresh water is coming from the Trinity Aquifer, and thus unavailable for any other use. The local groundwater conservation district tallied, from metered sources, at least 1.1 billion gallons were used in 2009. (Most draws from the Trinity are not metered, so this number is likely grossly underestimated). The toxic wastewater must be trucked off and injected into other geologic formations, which caused earthquakes in parts of Tarrant and Johnson Counties recently. Thousands of truckloads are required for each well. Recently, the people of Arkansas determined that trucks caused $119 million in road damage where traffic was heaviest in the Haynesville Shale. No estimate has ever been proffered for damage to Denton County roads. A bridge on Brush Creek collapsed from a drilling truck and was not repaired for two years.

Another crew sets up the “Christmas Tree” – the wellhead system of pipes and valves that use the natural pressure to force the gas into separation and storage tanks. Workers were at this stage of the process when they lost control of the well in Forest Hill. One worker was killed.

Energy companies build pipelines to transport the gas to nearby processing plants. In Texas, the energy companies can form a public utility for their pipeline and use eminent domain. This option is not available to energy companies in most other states. Scores of Denton County residents have relinquished property to pipeline easements, many have multiple, redundant pipelines across their land. Workers recently hit one of those large pipelines in a neighboring county, triggering an explosion and fire that killed one and severely burned several others. It was not immediately clear whether they struck one of those redundant pipelines across an easement already in use.

The gas processing plants remove impurities – water, sulfur, and natural gas liquids – piping it back to consumers. Recent investigations by the Texas Commission on Environmental Quality have consistently found elevated levels of toxic compounds at natural gas plants and compression stations, where blow-downs, relief valves, tanks and other equipment regularly release gas to maintain safe pressure levels. A blow-down at a new plant being built in Connecticut to burn natural gas for electricity caught fire and killed six and injured 26 others.

Crews come in to clean up and maintain the well site, including the wastewater haulers, who come daily to take the produced water for disposal into injection wells. They are not allowed to dump in creeks or dry beds, although such illegal dumping has occurred all over the shale, including high profile incidents in Northlake and Bartonville, since the boom began.

SOURCES: Denton Record-Chronicle Archives, the U.S. Department of Labor, Oil and Gas Extraction,, and the Texas Railroad Commission,