In this paper Robert B. Jackson formerly of Duke University and now at Stanford, Avner Vengosh, still at Duke University, J. William Carey, from Los Alamos National Laboratory, Richard J. Davies, from Durham University, Thomas H. Darrah, for Ohio State University, Francis O’Sullivan, from MIT and Gabrielle P´etron from the University of Colorado at Boulder reviewed all 166 fracking studies that have been performed and peer reviewed to consolidate all that we know about fracking and identify the areas where more research needs to be performed. This paper is not a primer, but is a complete and thorough review of all the risks and benefits associated with the hydrocarbon extraction method known as fracking.
Fracking is the current method of extracting unconventional oil and natural gas that is locked inside impermeable geological formations. Fracking is enabled by horizontal drilling and hydraulic fracturing (thus the name fracking). Fracking or hydraulic fracturing as it is more properly known involves the pressurized injection of fluids made up of mostly water and chemical additives into a geologic formation. The pressure used exceeds the rock strength and the fluid opens or enlarges fractures in the rock. As the formation is fractured, a “propping agent,” such as sand or ceramic beads, is pumped into the fractures to keep them from closing as the pumping pressure is released. The fracturing fluids (water and chemical additives) are partially recovered and returned to the surface or deep well injected for disposal. Natural gas or oil will flow from pores and fractures in the rock into the wells allowing for enhanced access to the methane or oil reserves.
Over the past decade, the use of hydraulic fracturing for gas extraction has increased and has expanded over a wide diversity of geographic regions and geologic formations throughout the United States and Canada. The annual production of methane (CH4) in the United States had increased 30% from 2005 to about 30,171 billion cubic feet of gas a year. The ability to frack oil and natural gas has profoundly changed the estimates of recoverable oil and gas resources and the energy future of this century. There is now known to be adequate natural gas resources for the foreseeable future. Many countries, including Algeria, Argentina, Australia, Brazil, Canada, China, France, Libya, Mexico, Poland, Russia, South Africa, the United States, and Venezuela, are estimated to possess significant shale oil and gas reserves that are now accessible to man. Fracked oil and gas can result in an economic boom as it generates income. If fracking is done carefully and properly the safely extracted gas can reduce air pollution and even water use compared with other fossil fuels. However, the authors point out that availability of vast quantities of natural gas is likely to slow the adoption of renewable energy sources and, if fracking is done poorly toxic chemicals from fracking fluid could be released into our water supplies and methane could be release to the air.
As fracking has expanded, so has a public and regulatory concern about the possible environmental consequences of fracking and horizontal drilling. Fracking is banned in France and there is a moratorium in New York State based on health and environmental concerns. These concerns include air pollution from the operation of heavy equipment, human health effects for workers and people living near well pads from chemical exposure, noise and dust, induced seismicity from the disposal of fracking fluids, and increased greenhouse gas emissions from poor well head control and continued use of hydrocarbons. However, the biggest health and environmental concerns remains the potential for drinking water contamination from fracturing fluids, natural formation waters, and stray gases.
In the drought plagued west a significant problem is the amount of water needed to hydraulically fracture a well. On average takes 3.8 million gallons of water for each well. Though about half the water will be returned, the recovered water will contain chemical and radiological contaminants. The study found that surprisingly, shale-gas extraction and processing are less water intensive than many other forms of energy extraction. The water intensities for coal, nuclear, and oil extraction are approximately 2 times, 3 times, and 10 times greater than for shale gas, respectively. Corn ethanol production uses substantially more water because of the evapotranspiration of the plants, and 1,000 times more water than shale gas if the plants are irrigated. Conventional natural gas uses less water and renewable forms of energy such as wind and solar that consume almost no water.
Maintaining well integrity and reducing surface spills and improper wastewater disposal have been found to be the way to minimize contamination from the chemicals used in fracking fluid and from naturally occurring contaminants such as salts, metals, and radioactivity found in oil and gas wastewaters that are returned to the surface. Though, there have been few definitive studies of the frequency, consequences, and severity of well integrity failure. Studies done in Ohio and Texas found over a 25-year period on a mix of traditional and shale gas wells found an extremely low level of incidence of groundwater contamination, In Ohio they found 185 cases of groundwater contamination caused primarily by failures of wastewater pits or well integrity out of about 60,000 producing wells, for an incident rate of about 0.1%.The rate for Texas was found to be even lower at about 0.02%, The Texas study included 16,000 horizontal shale-gas wells with none reporting groundwater contamination.
A significant concern is that hydraulic fracturing could open small cracks thousands of feet underground, connecting shallow drinking-water aquifers to deeper layers and providing a pathway for the chemicals used in fracking and naturally occurring geological formational brines to migrate upward. In practice, according to Dr. Jackson and the others this is unlikely because of the depths of most (but not all) shale formations tends to be 3,000-10,000 feet below ground level, and man-made hydro-fractures rarely propagate more than 2,000 feet. According to Dr. Jackson a more plausible scenario would be for man-made fractures to connect to a natural fault or fracture, an abandoned well, or some other underground pathway, allowing fluids to migrate upward).A simpler pathway for groundwater contamination, though, is through poor well construction and integrity. In the first study to test for potential drinking-water contamination associated with unconventional energy extraction, In studies overlying the Marcellus Shale in Pennsylvania that is what they found.
The scientists found that the number of peer-reviewed studies that have examined potential water contamination is surprisingly low. Wastewater from oil and gas exploration is generally classified into flowback and produced waters. Flowback water is the fluids that are return to the surface after the hydraulic fracturing and before oil and gas production begins, primarily during the days when the well is completed. Typically it consists of 10–40% of the injected fracturing fluids and chemicals pumped underground that return to the surface mixed with an increasing proportion of natural brines from the shale formations over time. Produced water is the fluid that flows to the surface during extended oil and gas production. It primarily reflects the chemistry and geology of deep formation waters. These naturally occurring brines are often saline to hypersaline and can contain toxic levels of elements such as barium, arsenic, and radioactive radium.However, more work needs to be done to understand fracking’s impact and gather the data necessary for improved geomechanical models for how hydraulic fracturing affects the wellbore environment and how fluids move through rock formations.
Throughout their study the scientist recommend a series of research questions that should be answered to more fully model and understand fracking. In addition they emphasize the need for greater transparency from companies and regulating agencies in information and the need for baseline studies prior to drilling is critical to even know if water or human health has been impacted. Predrilling data needs to include measurements of groundwater and surface-water quality and quantity as well as air quality, and human health. The scientists pointed out that there have been virtually no comprehensive studies on the impact of fracking on human health while state regulators and law in some instances allow fracking virtually in people’s backyards.The fact that the Pavillion, Wyoming field with no vertical separation could be legally fracked highlights the problem. Fracking needs to be well understood and the risks managed to make sure that is a boon to mankind and only is used in appropriate and low risk locations.