The hydraulic fracturing process, also known as “well stimulation,” is vital to extracting natural gas from the Marcellus Shale and other geological formations in Pennsylvania. Over the course of 60 years, well stimulation has been researched, advanced and used across the United States as a safe and effective method to create tiny cracks in the targeted formation that allow natural gas to flow freely into a wellbore and up to the earth’s surface.

The Well Stimulation Process

Well developers begin the stimulation process once a well has been drilled to a desired vertical and horizontal depth, with a series of steel pipes, called casing strings, cemented in place along the length of the wellbore. The steel and cement isolates the well from the surrounding geology and groundwater zones found above. Groundwater sources are typically located a mile or more above the Marcellus Shale formation. A device known as a perforating gun is first lowered into the well to a designated location in the shale, and a charge is fired down the well from a wire at ground surface to perforate the steel casing, cement and the shale formation. This perforation stage creates small cracks, or fractures, in the rock.

A mixture of water, sand and chemicals is then injected into the wellbore under high pressure. The sand holds open the cracks in the rock to allow the well to produce natural gas. Water and sand make up about 99.5 percent of the fluid injected into the well, and the chemicals used in the process – both small in number and dilute in concentration – can be found in many household items.

Once the first zone of the well has been perforated and stimulated, a rubber plug is placed to isolate that area from the rest of the horizontal wellbore. The perforation and stimulation process then continues multiple times along the length of the formation to make the well as productive as possible. A bit is lowered into the well after the process is completed to drill out the rubber plugs and allow gas to flow to the surface.

Completing the Process

At the completion of the stimulation process, approximately 20-30 percent of the water flows back up the wellbore, where it is collected and stored in tanks or lined impoundments. This “flowback” water is transported to a permitted wastewater treatment facility for treatment and disposal, or treated and conveyed to another well site where it is recycled. Over the productive life of the well, additional “produced” water slowly comes to the surface, where it is collected in on-site storage tanks and transported as needed for treatment.

Protecting Groundwater

Agencies in Pennsylvania enforce stringent regulations to protect groundwater during both the drilling and well stimulation process. Marcellus Shale wells require multiple, redundant layers of steel casing and cement as well as strict quality control procedures to protect groundwater sources.

State oil and gas regulatory agencies, including the Pennsylvania Department of Environmental Protection, have not documented a case of drinking water contamination related to the stimulation of an oil or natural gas well. In April 2009, the Ground Water Protection Council stated that the chances of groundwater contamination due to this process are as low as 1 in 200,000,000.

Regulation of Water Withdrawals

Water use in the well stimulation process is regulated in Pennsylvania either by the state DEP, or the federal Susquehanna or Delaware River Basin Commissions, with approval
required for every withdrawal from streams or rivers. These withdrawals are limited to fraction of a waterway’s normal flow to protect aquatic life, and stream withdrawals can be halted in the event of low flow conditions. Water is either trucked or piped to drilling locations, where it is stored in secure, lined impoundments or tanks for use in the fracture process.

According to an analysis by the Susquehanna River Basin Commission, Marcellus Shale development at its anticipated peak levels of production in the Susquehanna River watershed would require the use of 60 million gallons of water a day. This amount is less than half of what is needed for recreational purposes, such as irrigating golf courses or making snow at ski resorts.

Recycling and New Technologies

The companies developing the Marcellus Shale are also advancing the treatment and recycling of water for use in multiple well stimulation procedures, along with research into using water impaired by acid mine drainage and other “lesser quality” water sources. Recycling efforts allow for a reduction in fresh water use required for each well, while the use of water from historic mining areas removes that water from stream flows, improving the quality of water in those streams in the process.

An equal amount of work is taking place to research the use of additives that are biodegradable and do not bioaccumulate in the environment, including ingredients found in many foods. Guar gum, a thickener used in dairy products, baked goods and ketchup, is used as a friction reducer in the well stimulation process, while citric acid, used in the production of soft drinks and wine, is effective in controlling iron in a wellbore. Pennsylvania’s winters have also led to the discovery of environmentally friendly additives required to prevent water from freezing during cold weather well stimulation, with the increased use of glycerin and potassium formate over material such as methanol, which is found in windshield cleaning solutions. Research continues to enhance recycling capabilities and identify effective biodegradable additives.

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Posted At: Pioga.org