Developing natural gas from the Marcellus and Utica shale formations is a process regulated by both state and federal agencies responsible for the protection of the environment and our water resources. In fact, about 35 individual permits, depending on a well’s specific location, are required to drill a natural gas well in Pennsylvania. The industry is committed to planning, drilling and operating its wells in compliance with the regulations that govern natural gas development, and operators typically go beyond what is required by these agencies.
Protecting the environment begins with constructing roads and grading the drill pad location, through the use of controls to prevent soil erosion and sedimentation. Roads are often improved prior to starting the drilling process to accommodate additional truck traffic, with culverts placed along road berms to reduce sedimentation. Filter socks and erosion control blankets are installed and maintained at the pad throughout the drilling process to prevent stormwater runoff, Finally, a high-density plastic liner is placed under the entire drill pad, and then covered with gravel to fully contain any potential spills during drilling and completion.
The drilling process involves driving several increasingly smaller diameter steel pipes, called casing strings, into the wellbore, with the injection of cement into the pipe and up the sides of the wellbore at the completion of each casing string. This isolates the wellbore from the earth with two durable materials – steel and cement –and protects groundwater aquifers. Each successive steel casing string is cemented into place as the well is drilled, extending to the end of the horizontal portion of the wellbore that will produce natural gas. The casing and cementing process is tested as the well is drilled and devices called centralizers keep the pipe and cement centered in the middle of the wellbore. These steel and cement liners ensure the integrity of the well, and remain in place throughout the well’s years of production.
Material called drilling mud, which is also used to drill drinking water wells, is used to lubricate the drill bit and to aid in bringing rock cuttings to surface. The cuttings are then processed through a shaker and allowed to settle, with the rock fragments stored at the drilling location for transportation to a permitted landfill. Drilling mud is processed in an on-site treatment facility and recycled for continued use in the drilling process.
Environmental protection during hydraulic fracturing turns to the careful use of water and the additives required to fracture the shale formation, along with the proper management and recycling of flowback water that returns to the surface. Water allocation permits are required to withdraw water from streams for hydraulic fracturing; the state Department of Environmental Protection and federal interstate river basin commissions monitor withdrawals to ensure the protection of waterways. Permits must also be obtained to purchase water from municipal water suppliers. Water is stored in tanks or in lined, secure impoundments at the drilling location, and water pumps and pipelines are used to greatly reduce truck traffic at well sites.
Approximately 3 to 5 million gallons of water is used to fracture a horizontal well. Of this, about 20-30 percent of the water, flowback, is returned to the surface shortly after drilling. Recent advances in technology to treat and recycle flowback water for multiple fracturing operations are significantly reducing consumptive water use and the need for off-site treatment. Many drilling companies have been successful in recycling 100 percent of flowback water.
Additives used in the fracturing process are transported and managed at the drilling location according to state and federal regulations. There are commonly five additives used in the hydraulic fracturing process, and those materials can be found in products in the home. These include a surfactant (or soap) to reduce the friction of the water, a biocide (similar to an anti-bacterial hand cleaner) to keep the wellbore free of bacteria, a scale inhibitor (comparable to a household product used to keep wastewater pipes free of scale) to prevent the buildup of scale, and a lubricant (similar to vegetable oil) to make the water heavier and reduce friction.
Hydraulic fracturing has not been identified as the source of groundwater contamination, as the fracture process takes place at depths between 5,000-8,000 feet below ground surface. Most groundwater aquifers are found between 100-200 feet below the surface, typically more than a mile above the shale being fractured.
After the drilling and hydraulic fracturing processes are completed, the drilling pad is restored, as agreed to by the property owner. A completed and secure producing well only requires a relatively small surface footprint, and includes the well head, water storage tanks and a small amount of production equipment.
Producing wells are monitored throughout the life of the well by a well tender. Some water slowly returns to the surface over time, which is stored and pumped into trucks for treatment at permitted facilities.
When a well is no longer capable of production, concrete is pumped down the wellbore to seal it from the earth, and production equipment is removed from site. The entire pad is then re-vegetated and fully restored.