Understanding Shale Gas Development

The complex process used to extract oil and gas trapped in shale rock formations includes many different stages that take place over a period of years. To see a detailed pictorial representation of shale gas development, see EHP’s handout: Illustrated Stages of Shale Gas Development.​

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• Initial exploration 
  Energy companies search for underground reservoirs of oil or natural gas using mapping, geological clues, seismic testing, and other methods.  

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• Leasing and permitting 
  After an energy company determines that a locality has enough resources to explore, leases are purchased from mineral rights owners (where applicable), and permits are requested and issued by the state.  

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• Well pad development 
  Access roads are constructed and the well site is developed. Next comes the well pad, a large structural platform surrounding the drilling operations that is typically between three and 10 acres. The well pad holds the drilling rig, storage tanks, and other machinery and equipment. The energy company uses the drilling rig to drill the well(s). A typical Marcellus well is drilled 5,000 to 9,000 feet vertically. Horizontally, Marcellus wells vary in length, with some going upwards of 15,000 feet. Several wells may be drilled on one well pad, with some well pads hosting 20+ wells. Note that companies are looking to supersize with larger pads containing numerous wells and longer laterals. Drilling produces waste in the way of drill cuttings and sludge, which may be disposed of in local landfills.  

• Preparation for hydraulic fracturing 
  After the well has been drilled, the drilling rig is removed and the well is ready for hydraulic fracturing. This process requires convoys of trucks to transport vast quantities of water, chemicals, and sand to the well pad. These will be mixed together, creating fracking fluid. This fracking fluid is then injected into the wellbore at high pressure to expand fractures in the shale, forcing sand into the fractures to hold them open. With these fractures open, gas can migrate to the wellbore and then to the surface, where it is collected. 
   

• Production 
  When a well first goes into production, gas and wastewater return to the surface. The gas—and possibly natural gas liquids—is captured. The wastewater is held in pits, tanks, or pools, at the well site until it is treated, recycled, or disposed of in an underground injection well. The wastewater is a mixture of flowback and produced water. Flowback water contains the fracking fluid mentioned above. Produced water is water previously trapped in underground formations that is released with gas and/or oil. Produced water can contain naturally occurring (but still dangerous) materials that are present in the shale layer, including radioactive compounds, toxic organic and inorganic chemicals, and heavy metals such as arsenic. It also contains a significant amount of salt that was trapped in the shale, which is why it is often referred to as "brine."  
  
  Work activity near well sites generally slows at this point once the well is in production, though some wells are re-fracked periodically in an attempt to boost gas production from a site. If a well pad has multiple wells, activity on the well pad may continue. A well, which may be productive from 10-50 years, will continue to generate produced water for the life of the well. 
   

• Transportation and Processing  
  After the gas is accessed, it is processed and transported to end-users. The movement of gas from producing regions to end-users requires an extensive and elaborate transportation system. In many instances, gas has to travel a great distance to reach the point of use, requiring miles of pipelines, pig launchers, compressor stations, and trains. 
  
  The gas may have to be processed to purify the gas by removing common contaminants or to have the natural gas liquids—such as propane, butane, and ethane—separated into their individual products. 
   

• Storage 
  Underground storage facilities, created by converting previously used underground sites such as depleted oil and gas fields, water aquifers, and old salt caverns, are used to store gas to maintain a supply year-round.  
   

• Waste Disposal 
  Throughout the hydraulic fracturing process, several forms of solid, semi-solid, and liquid waste are produced. Class II injection wells are used to dispose of liquid waste brought to the surface from gas production. This liquid waste—mostly brine—contains compounds that can be carried by water, such as naturally occurring radioactive materials (NORMs), hydrocarbons, heavy metals, and other toxic substances.  
  
  Solid waste, including rocks, dirt, and drill cuttings (ground-up rock brought to the surface after drilling), along with semi-solid waste known as "sludge," is disposed of in municipal landfills, which are usually owned by private companies. This waste contains NORMs and other toxic compounds that were present in the rock and used during well development. Due to exemptions in The Resource Conservation and Recovery Act (RCRA), oil and gas waste is not considered toxic or subject to federal cradle-to-grave tracking. Toxic leachate from landfills that accept shale drilling waste is a growing problem. 
   

• Site remediation 
  Remediation involves plugging the well(s) and restoring the site when a well is done producing gas, or if an exploratory well does not produce adequate resources. The process of site restoration involves filling the well with cement, removing waste and equipment, and capping the well. Energy companies may also attempt to restore the original landscape as much as possible with plantings and other landscaping.