Directional drilling refers to turning the well to follow the path of the shale layer
The Marcellus is just one shale layer from which drillers are attempting to extract oil and natural gas.
The fracturing of the shale in this part of the drilling process is where the term “fracking” originated
A lot of water (~5 million gallons) is required to hydraulically fracture the wells
Components that return to the surface may be stored in lined pits or closed containers (preferably)
The depth that wells may be drilled varies significantly from region to region
The graphic above created by ProPublica visually explains the process of hydraulic fracturing.
Process In Summary:
After a company determines that a locality has enough resources to explore, leases are purchased from mineral rights owners (where applicable), permits are issued by the state, and the well pad and access roads are constructed. Unconventional O&G drilling then proceeds in two major phases: directional drilling and well stimulation.
- The process begins by drilling to the bottom of a fresh water aquifer
- The drill is then retracted and pulls the loose rocks and sediment to the surface to be discarded (i.e., drilling muds).
- Surface casing (steel piping) is inserted into the bore hole to protect freshwater aquifers by creating a physical barrier between the aquifer and drilling materials. This casing also serves as a foundation for the blowout preventer – a safety device that connects the rig to the wellbore. Cement is then pumped through the casing and out through the opening at the bottom of the casing. The cement is forced up between the casing and the hole, sealing off the wellbore from the fresh water.
- Drilling continues vertically, creating a well approximately 6,000 feet (~1,828 m) deep. The depth of the well will vary by region and formation. In the Marcellus Shale the well is then drilled horizontally an average of 10,000 more feet (~3,048 meters).
- When the target length is achieved, “production casing” is inserted throughout the length of the wellbore.
- The drilling process is now complete and well stimulation can begin.
- A perforating gun is sent into the horizontal portion of the well, where an electrical current originating from the surface sets off a charge that shoots small holes through the casing and cement.
- In the case of hydraulic fracturing, large volumes of fresh water (~6 million gallons1), fracking fluid/chemicals, and sand are then pumped into the well to fracture the shale formation and release the hydrocarbons stored tightly within the rock. In some formations, such as the Monterey Shale in California, acidizing is the preferred stimulation technique. Ohio wells use between 9,600-15,600 gallons of HCl; WV, 5,100-7,700 gallons. Millions of gallons of freshwater, 4,300+ tons of sand or proppant, and thousands of gallons of frac(k) fluid are then pumped into the ground at extremely high pressures in order to fracture the shale and release natural gas and/or oil2.
- Natural gas and oil can then flow up the well to the surface, along with “flowback fluid” – consisting of varying proportions of the injected fluids, and other liquids from the shale layer such as salt-saturated water, drilling muds, or brine.
- These fluids are pumped into a waiting pool (impoundment) or in closed storage tanks where the liquid waste will be either recycled and used at another site or disposed of according to regulatory standards specific to the state in which they are disposed.
- Disposal usually involves the injection of waste into Class II Disposal wells, processing at wastewater treatment facilities, or solidification and surface disposal at licensed waste landfill facilities.
More Information about the Process
Further information about the process of oil and gas extraction as we know it today, as well as the agency’s environmental and health research, can be found on the EPA website.
Where is drilling occurring?
It is difficult to ascertain where unconventional oil and gas extraction is occurring unless one explores oil and gas extraction data state-by-state (and even then it’s not always completely clear). In an attempt to visualize where all of the active (and for the most part, unconventional) wells are in the United States, in 2016 FracTracker analyzed data from 2014-15 to identify active oil and gas wells. We approximate that there are 1.2 million facilities currently operating in the United States. Click the map for more information:
- Water usage by the shale gas industry is increasing 237-317 and 342-522 thousand gallons per quarter per well in Ohio and West Virginia, respectively. Currently, unconventional wells in these two states are using 7.7 and 8.1 million gallons per well.
- According to FracTracker analysis of 505 Ohio Utica wells average production to date has been primarily natural gas to the tune of 157 million kWh Vs 29 kWh from oil.