A Glossary for Citizen-Explorers Bravely Entering the Controversy over Hydraulic Fracturing

By Adrianne Kroepsch, Will Rempel, and Patty Limerick


A Note to Glossary Readers

Unconventional oil and gas development is not an easy subject for productive conversation. It demands the use of technical language (if you wonder what that means, turn to the to the entry here on biogenic methane). Much of the action takes place in a space that cannot be penetrated by television cameras, radio microphones, or their human creators and users. The depths of the earth are, for purely physical reasons, out of the public eye (see, for example, deep groundwater). And if those two factors were not enough to frustrate even the most committed and determined of conversationalists, here is another: the public terrain where discussions take place is noisy, confusing, and tense. Separating sources of trustworthy information from those that are not requires skill, patience, and even self-examination (for more, visit confirmation bias). Even the most fundamental terms can lead conversationalists into muddles; in some instances, participants in the unconventional oil and gas debate use the exact same words in very different ways (for a case study, head straight to hydraulic fracturing).

Yet members of the public simply must talk about unconventional oil and gas development. Voters have been making, and will continue to make, decisions about when and where energy extraction should take place. Residents of communities sitting atop hydrocarbons pursued by oil and gas operators are debating, and will continue to debate, decisions and choices made by local, state, and federal regulators and elected officials, as well as by operators themselves. Members of the oil and gas industry are participating in, and will continue to take part in these discussions as they aspire to earn a social license to operate. Dialogue – personal and public – will play an important role in all of these circumstances. Recognizing that, we have tried to identify and map the many pitfalls and logjams that now plague public discussion.

This glossary is our effort to help participants in the debate with the difficult work of communication in such technical, opaque, and unruly terrain. We offer entries that explain the industry jargon needed to understand the subject (see casing for starters), the roles of key actors with less-than-obvious names (COGCC and landman, to name a few), the important words that are often embedded in other terms (start with BTEX, then find benzene, then try volatile organic compounds), and the common turns of phrase that frequently muck up conversation (the entries for anti-industry and industry aim at inviting a more precise and less simply polarized casting of the characters in this drama).

The text that follows here requires three further points of explanation. First, because we are writing from Colorado’s northern Front Range, we have drawn examples from the Denver-Julesburg Basin to provide on-the-ground context in our definitions. These entries carry broad relevance despite our geographic focus. Second, we have worked to make our explanations both informative and enjoyable to read. Please do not interpret our occasional infusions of liveliness as an indication that we take the subject of unconventional oil and gas extraction lightly. We do not. And, third, this is a living document. Please check back for new entries. Better yet, please write with nominations for new entries, as well as your feedback, to adrianne.kroepsch@colorado.edu.

Finally, we would like to thank several reviewers for their feedback on individual glossary entries and the glossary as a whole. Dr. Allfred William (Bill) Eustes of the Colorado School of Mines provided multiple rounds of commentary on the technical petroleum engineering-related items in the glossary. Kathryn Mutz, JD, an oil and gas policy expert at the University of Colorado’s Natural Resources Law Center, and Dr. Jana Milford, an air quality specialist in the Mechanical Engineering department, provided the inspiration for, and insightful feedback on, the “industry” and “anti-industry” entries. Dr. Gabrielle Petron, an atmospheric scientist with the National Oceanic and Atmospheric Administration’s Earth Systems Research Laboratory, provided helpful pointers on the air quality and climate change-related glossary items. Dr. John Adgate, chair of the Department of Environmental and Occupational Health at the Colorado School of Public Health, and Dr. Bernard Goldstein, professor of Environmental and Occupational Health at the University of Pittsburgh, contributed generous comments on the public health-related entries. And the 35 speakers who shared their varied perspectives on hydraulic fracturing in the 2013-2015 run of the Center of the American West’s multi-part FrackingSENSE series contributed important context, commentary, and citations during their time with us, whether they knew it then or not. Of course, any errors in the glossary are solely the authors’ responsibility.

Happy Reading (and Conversing),

Adrianne Kroepsch signature

Adrianne Kroepsch

Will Rempel Signature

Will Rempel

Patty Limerick signature

Patty Limerick


The findings in this article rest on work supported by the National Science Foundation’s Sustainability Research Network – Air Water Gas (SRN-AWG) project; the Center of the American West was affiliated with the project from September 2012 – October 2014. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.


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In geometric terms, an annulus is any space between two concentric or eccentric circles. In general oil and gas terms, an annulus is any space between a well casing and another casing, between casing and tubing, or between casing and the open hole of the wellbore. A well may have several annuli. For example, working from narrowest to widest on an imaginary well with three sections of casing, one would find an annulus between the wellbore and the production casing, an annulus between the production casing and the surface casing, and an annulus between the surface casing and the conductor casing. (For more on these different types of casing, please see the casing entry below.) All of these annuli would be filled with cement to various heights, based on state regulations. In Colorado, for example, the surface casing must be cemented from 50-feet below the deepest drinking water aquifer to the surface of the ground.1 Operators monitor well annuluses to make sure that pressures at the surface are zero, or that pressures do not change significantly inside of them. An unexpected pressure change would suggest a breach or a dysfunction of some kind, and therefore compromised wellbore integrity.2

Like the word “industry,” the word “anti-industry” is a vague and misleading term that obscures a great deal of real-world complexity. For example, the word is often used to describe environmentalists only, when there are both environmental and non-environmental reasons for people to raise questions about, or oppose, oil and gas development. It also assumes that all environmentalists strictly oppose natural gas development, when environmentalists’ views are decidedly more mixed and complex than that. When the term “anti-industry” is used indiscriminately to label environmentalists, community organizations, and citizen coalitions, it improperly portrays those groups as collections of people who stubbornly oppose industrial development of any kind. In reality, the members of those purportedly “anti-industry” groups may have clearly-defined concerns about specific aspects of oil and gas extraction. Broad mischaracterizations make it difficult for those groups to communicate clearly their ideas and policy proposals, which, in turn, can stymie problem-solving and compromise. For each of these reasons, we’re all better off steering clear of the term “anti-industry” and substituting phrasing that more precisely characterizes the person or group in focus. Here are a few tips: First, when searching for the proper term to describe somebody who is critical of the oil and gas industry for one reason or another, ask yourself if you must label that person at all. If you think that a descriptor like “anti-industry” is indeed necessary, ask yourself whether a more accurate term might be available to you. Could you describe this person as a citizen concerned about methane emissions? As a critic of drilling in residential areas? As an advocate for baseline groundwater quality monitoring? It is likely that, without too much trouble, a more specific and considerate descriptor will come to mind. It is also likely that using that more precise term will enhance the clarity of your point and boost the productivity of the conversation you’re having.


Benzene is one of the BTEX compounds (benzene, toluene, ethylene, xylene). Like other volatile organic compounds, it is a colorless, flammable liquid that evaporates (or “volatilizes”) quickly when exposed to air. Benzene can be formed through natural processes (by volcanic eruptions and forest fires, for example), but most of our benzene exposure comes from all-too-human activities. Benzene is a component of plastics, detergents, and pesticides. It is also a natural component of crude oil and gasoline (and therefore motor vehicle exhaust), as well as a component of tobacco smoke.3 Because benzene is a known carcinogen, with links to leukemia and cancers of other blood cells, the Environmental Protection Agency (EPA) limits its non-industrial applications, including its concentration in gasoline (reduced to 0.62% by the EPA in 2011).4 Outdoor air may contain low levels of benzene from gas stations, wood smoke, exhaust from motor vehicles, and industrial emissions.5 According to an extensive, but now dated, EPA inventory from 1989, about half of documented benzene exposures in the United States were from smoking; 5% more were from secondhand smoke; 20% were from automobile-related activities such as driving, refueling, and breathing in gasoline fumes in garages; and another 20% were from automobile exhaust and industrial emissions.6 Researchers are currently grappling with the extent of benzene emissions from unconventional oil and gas activities, as well as the related question of whether benzene emissions from oil and gas extraction translate into benzene exposure to humans. In a recent review article of the potential public health hazards from unconventional oil and gas extraction, Adgate et al. call for more research on the frequency and degree of benzene exposures that might be experienced by two key categories of people – energy industry workers and people living near well pads – over both the short- and the long-term.7 The researchers also cite studies that raise concerns about the effects of oil and gas activity on ambient benzene concentrations in the air around Dallas-Fort Worth Area of Texas and in Garfield County, Colorado. Even more recently (2015), researchers at the National Institute for Occupational Safety and Health published a study that showed workers at oil and gas sites being exposed to benzene at levels higher than the allowable standards. Inhalation risks were highest for workers operating in close proximity to, or opening, the hatches of flowback and oil and gas production tanks8.

Biogenic Methane:
Methane is the primary component of what we call “natural gas.” It comes in two varieties – biogenic and thermogenic. Biogenic methane is the least commercially useful of the two types of natural gas. Oil and gas companies do not target it for extraction because it is usually found in small quantities and in the absence of other valuable hydrocarbons, such as oil, ethane, propane, or butane. Unlike its deep and coveted thermogenic counterpart, biogenic methane is produced in the shallow subsurface, which is why it is sometimes naturally found in drinking water aquifers. Biogenic methane is churned out by billions of tiny microbes known as methanogens that are dedicated to decomposing organic matter in oxygen-free environments underground. Methanogens can be found in other places, too, such as the guts of cows, where they help digest grass. Yes, we can thank these miniscule microorganisms for the fact that the average cow “emits” around 250 liters of methane per day.9 The fact that methane comes in two varieties is useful for regulators. For example, if domestic water well owners discover methane in their drinking water in Colorado, the COGCC will use the molecular differences between biogenic and thermogenic methane to determine if the unwelcome gas came from a shallow source or a deep one. If the gas has a biogenic signature, it likely got into the groundwater system naturally, through the activity of shallow methanogens. If the gas has a thermogenic signature, it may have been transported from the depths by oil and gas extraction. However, when lit afire from a kitchen faucet for viewers on YouTube, both types of methane look and act the same. A proper hydrologic investigation and isotopic analysis are essential for figuring out where the gas came from.

Black Swan Event:
As genetic variation would have it, black swans do exist. So do the “black swan events” named after them: unexpected, low-probability, game-changing incidents or phenomena that usually seem foreseeable in hindsight, but do not announce their impending arrival. In the oil and gas context, people use the term to describe the kinds of catastrophic failures that occur when several unlikely things go wrong at the same time during the development of a well. The 2010 explosion of BP’s Deepwater Horizon offshore oil rig is frequently cited as a “black swan” event, for example. Scholar Nassim Nicholas Taleb, a statistician of randomness (not to be confused with a random statistician), coined the term based on the seventeenth century European belief that swans could only be white. A Dutch explorer discovered how wrong that assumption was when he came across a rare black swan in Australia in 1697. The species is now protected there, but the equally rare, high-impact events named after it know no geographic limits or bounds.10

BTEX Compounds:
The term “BTEX” is often tossed about in public meetings and scientific reports without proper introduction. BTEX compounds do not share in the health-promoting virtues of GORE-TEX or Latex. BTEX is the acronym for a group of four Volatile Organic Compounds associated with derivatives of petroleum and oil and natural gas production: benzene, toluene, ethylbenzene, and xylene. Depending on level and length of exposure, BTEX compounds can irritate skin, eyes, and the respiratory system, cause nausea, headaches, and blood disorders, and even lead to cancer. Because of these potential health risks, BTEX compounds are a major focus of local, state, and federal environmental regulations.11


In order to protect groundwater systems from oil and gas extraction and to isolate well production from the surrounding environment, state regulators require operators to install multiple layers of steel pipe (known as “casing”) in the wellbore of an oil and/or gas well during the drilling process. These layers of casing are designed to isolate the hydrocarbon-bearing geologic zone targeted by the operator from the geologic formations above, including aquifers. They are reinforced in this task by multiple layers of cement that hold them in place and further isolate the hydrocarbons and fluids in the wellbore from groundwater systems and other geologic formations. In order of installation, the major layers of casing (known in the industry as “strings” of casing) are the conductor casingsurface casingintermediate casing, and production casing. (For more on each of these types of casing, please see their individual entries listed alphabetically throughout the glossary.) State oil and gas regulators specify the necessary depths of these protective layers and require operators to perform a variety of tests to ensure that a well’s casing and cement components are structurally sound and effectively isolate the wellbore from groundwater systems.12

Cement receives but little admiration from its beneficiaries even though it is a key component of our bridges, bypasses, beltways, and buildings. It gets even less credit for important work performed in spaces that are out of our sight – underground in an oil or gas well, where the proper application of cement is crucial to preventing leaks and isolating aquifers from drilling activities. Several parts of a well’s anatomy require cement. Cement locks in place the sections of steel pipe, known as casing, that go into the wellbore, primarily in the well’s shallower regions. From the outside-in, those sections of pipe are the conductor casingsurface casingintermediate casing(s), and production casing. Cement holds each layer of casing in place at depths set by regulators and geological constraints. For example, in Colorado the cement that envelops the surface casing starts 50 feet below local aquifers and continues back to the surface in order to provide them with extra protection from drilling fluids and gases.13 Cement is pumped into a well to the bottom of the casing and back up towards the surface in the annulus. The technique of applying cement from the bottom-up, known as “circulating” cement, is used to ensure that all of the annulus in the zone of the cement job will be filled in. The exact composition of cement used in each well depends on state regulations and the characteristics of surrounding rock formations.14

Closed-loop Drilling:
This term describes a variety of strategies for dealing with wastewater during drilling and hydraulic fracturing, the best of which eliminate the use of drilling pits and incorporate the recycling of flowback fluids and produced water for reuse on later wells. In order to reuse these fluids, oil and gas operators need special on-site equipment for storing wastewater and treating it to a workable caliber. Closed-loop drilling processes make for a superior alternative to storing wastewater in open reserve pits, first because they keep wastes closely contained and, second, because they reduce operators’ overall water needs.15 Wastewater that cannot be recycled or reused during closed-loop drilling is typically disposed of via deep well injection – a form of wastewater disposal that has its own pros and cons. (For more information, please see the entry on deep well injection.)

Coalbed Methane:
Natural gas (methane) can be found in all sorts of geologic formations, including in deposits of coal. When natural gas is extracted from a coal deposit it is called coalbed methane or “CBM.” Like shale, coal formations are considered to be “unconventional” sources of hydrocarbons, which is to say that extracting methane from a coalbed registers as a form of unconventional oil and gas development. Coalbed methane development accounts for about 8% of natural gas production in the United States.16 It has been an active form of natural gas production since the 1990s. The Powder River Basin of Wyoming and Montana is perhaps the best-known region of coalbed methane development in the United States. Colorado has two major areas of coalbed methane extraction: the Raton Basin and San Juan Basin, both in the southern part of the state. Coalbed methane extraction differs from shale gas development in three important ways. First, coalbed methane production often occurs at shallower depths, typically ranging from hundreds to one or two thousand feet.17 By comparison, Colorado’s Niobrara shale is tapped at depths of 7,000 feet, on average.18 Second, because coal formations are more permeable than shale formations, it is sometimes (though not always) possible to extract coalbed methane without hydraulic fracturing. And third, coalbed methane extraction requires the removal of large volumes of deep groundwater (known as “produced water” after it is withdrawn from the subsurface). Coal formations are typically saturated with groundwater, which helps to trap the methane inside them. That groundwater must be removed in order for methane to flow to the wellbore. In the first several months of production, a coalbed methane well will produce much more water than gas.19 The chemistry of produced water from coalbed methane wells varies. In some regions, it is very saline and must be disposed of carefully. In other regions, it is relatively free of contaminants and can be released into surface streams.

The Colorado Oil and Gas Conservation Commission was established in 1951 to regulate oil and gas extraction in Colorado. The agency’s name is so long that Coloradoans often choose to relay it in acronym form rather than spelling it out word-for-word (COGCC, or sometimes just OGCC). The term “conservation” in the agency’s title reflects the priorities of the era in which it was founded. Before environmentalism went mainstream in the 1960s and 1970s, the word “conservation” had less to do with leaving resources alone and more to do with using them efficiently and with some consideration of the future. In the oil and gas context of the 1950s, “conservation” meant maximizing the retrieval of hydrocarbons by curbing wasteful, laissez faire extraction activities that only partially drained geologic formations and left oil and gas in the ground. COGCC was initially charged with regulating drilling so that operators would extract hydrocarbons as efficiently and thoroughly as possible.20 Today, however, the term “conservation” is as likely to be used in the context of leaving fossil fuels in the ground. The COGCC’s mission has evolved over the years as well, expanding to include the responsible stewardship of the environment and public health in addition to the agency’s traditional charge of “fostering the responsible development of Colorado’s oil and gas resources.”21 Under this expanded mandate, COGCC is essentially tasked with striking a balance between both definitions of the term “conservation” at the same time. A major point of transition in the recent history of the COGCC occurred in 2007 and 2008, when Governor Bill Ritter, with the support of the state legislature, changed the agency’s structure and pushed forward new regulations to better protect the environment and communities neighboring oil and gas development.22 As part of the overhaul, the COGCC’s board grew to nine members (from seven) and expanded its scope of expertise. In addition to having members with oil and gas industry affiliations, the COGCC board is now required to include a local government official, an owner of both land and mineral rights, someone engaged in agriculture, an expert on soil conservation or reclamation, and the directors of the Departments of Natural Resources and Public Health and Environment.23 In 2008, after more than 80 hours of hearings in response to citizen concerns about the rapid increase and expansion of oil and gas extraction in Colorado, the revamped COGCC took Ritter’s reform efforts further still by making extensive changes to its rules. The new regulations updated protections of landowners’ rights, water quality, air quality, wildlife, and public health.24 The COGCC has continued to update its regulations under Governor John Hickenlooper. In the past few years, the agency has made major changes to its groundwater monitoring, well setback, air quality, and spill regulations.

Conductor Casing:
If oil and gas wells were symphonies, the “conductor” casing would do just what you might imagine: show up first, set a course for all the instruments to follow, and generally prevent implosions (musical or otherwise). In the orchestra of oil and gas well bore construction, the “conductor” casing is the shortest and shallowest of the steel casing segments or “strings” (note: we did not make up the latter term, “strings,” to bolster our musical analogy). The conductor casing sets the foundation for well construction, prevents the drilled well hole from caving in, and guides drilling fluids out of the well hole and into tanks on the well pad.25

Confirmation Bias:
In the world of habits of mind, confirmation bias is one of the more durable and difficult to detect. That’s probably because the act of challenging confirmation bias can rattle people to their emotional and intellectual cores. Confirmation bias is the universally popular custom by which human beings embrace information and interpretations that affirm pre-existing beliefs and conviction. Confirmation bias thrives in circumstances of controversy, misinformation, and uncertainty – all of which describe the state of debate surrounding unconventional oil and gas extraction. The exercise of breaking free of this habit of mind may be difficult, and it may be bewildering, but it can also be refreshing and exhilarating. The mental gymnastics can be accomplished in four steps. First, pause for a moment and identify what you already believe about a subject. Second, seek out a situation where you will hear or read ideas that will not match your pre-existing convictions. Third, temporarily remove your confirmation-bias filter (no reason to panic—it can be replaced in a second), and to the best of your ability, take in and contemplate what you hear or read, particularly if it challenges your original assumptions. For the fourth step, you have a wide range of choices. You can reject and abandon your initial beliefs. You can deepen, refine, or modify your starting assumptions. Or you can reaffirm and re-embrace your initial beliefs, after you have determined that they have shown sufficient strength in evidence and reason.

Consumptive and Non-Consumptive Water Use:
Terms of water law are increasingly central to conversations about the water demands of hydraulic fracturing. Two of the legal terms in frequent circulation – “consumptive” and “non-consumptive” – describe the major categories of water use out in the world and in the water courts. Non-consumptive water uses are those that do not remove water from the surface water system (fish hatcheries, for example) or those that remove water from its source only temporarily (like an off-channel hydroelectric plant).26 Consumptive water uses, on the other hand, are those that largely use up the water in question. Consumptive water uses return much less water to the source than originally removed, often because of evaporation. Agricultural water use can be 20-85% consumptive, depending on the crop type, soil type, and irrigation methods, whereas municipal use ranges from 5% consumptive during the winter to 50% consumptive during lawn watering season.27 Hydraulic fracturing is generally a consumptive use of water because the bulk of the water that goes into it is sequestered in the subsurface – either in the fractured geologic formation or in a deep, off-site wastewater disposal well (see entry on deep well injection). Hydraulic fracturing’s consumptive nature makes it a controversial use of water in areas with strained water supplies. Closed-loop drilling has the potential to reduce the water demands of hydraulic fracturing by recycling and reusing produced water and flowback fluid in more than one hydraulic fracturing job, but it is still gaining traction among oil and gas operators. High Sierra Water, a wastewater treatment company that also owns nearly half of the 25 wastewater injection wells in the Wattenberg Field of the Denver Julesburg Basin, recycled less than 5% of the wastewater hauled to its facilities in 2013.28 The company is optimistic that this percentage will increase. Several operators in the Denver Julesburg Basin have publicly mentioned plans to increase wastewater recycling and reuse in the near future.29

Conventional Oil and Gas:
Conventional sources of oil and gas are those hydrocarbon-bearing geologic formations that allow for relatively easy extraction of their hydrocarbon contents because they are made up of permeable sandstone or limestone. Until recently, most oil and gas wells were drilled into conventional geologic formations. Many of those formations held hydrocarbons that accumulated by slowly rising from deeper geologic formations until they reached an impermeable geologic formation known as a “caprock.” The most promising oil and gas reservoirs in the most permeable geologic formations have already been tapped, however, leaving oil and gas operators to look to “unconventional” geologic formations, such as shales, and new means of extraction, such as hydraulic fracturing. (For more, please see the entry on unconventional oil and gas.) In the Denver Julesburg Basin, the “Muddy J” and D sandstones are considered “conventional” sources of oil and gas, while the Niobrara shale/limestone is called an “unconventional” source.30


Deep Groundwater:
Groundwater occurs at different depths. “Shallow” groundwater systems are those that humans can easily tap for drinking and irrigation water. Also known as “aquifers,” these shallow, drinking water-yielding groundwater systems are typically found at depths of tens to hundreds of feet. By comparison, “deep” groundwater occurs thousands of feet beneath the ground surface, at depths far below typical water supply withdrawals and in geologic formations that are largely disconnected from groundwater recharge and the water cycle.31 Deep groundwater is increasingly on people’s radars because it is often found alongside hydrocarbons in deep, unconventional oil and gas deposits. (In this context it is often referred to as “formation water.” When deep groundwater is actively removed from the subsurface in the process of oil and gas extraction, it is called “produced water.”) With a few exceptions, deep groundwater is usually not the kind of groundwater a person would want to drink. The water found in the tiny pore spaces of unconventional oil and gas formations often dates to those formations’ deposition, going back millions of years to the ancient seas that left shales and sandstones behind them. It is usually highly saline (which is why it is often referred to as “brine”) and may carry minerals and compounds of a toxic nature that have dissolved from neighboring rocks over the millennia.

Deep Well Injection:
As it turns out, getting one thing from the subsurface (hydrocarbons) often depends upon putting another thing (wastewater) underground somewhere else. In Colorado, most flowback fluid and produced water find their final resting place in one of the 885 EPA-regulated, Class II deep injection wells in the state. These disposal wells are drilled to great depths with the goal of putting drilling wastewater out of sight, out of mind, and out of the hydrologic cycle.32 An increase in small earthquakes in some areas of deep well wastewater disposal has meant that deep well injection isn’t completely “out of mind,” however. The injection of wastewater into deep geologic formations has the potential to activate typically inactive faults. The U.S. Geological Survey is currently studying recent earthquakes in Arkansas, Colorado, Oklahoma, and Ohio to determine if they were triggered by the disposal of oil and gas wastewater.33 Researchers from the University of Colorado are investigating a recent 3.4 magnitude earthquake in the Wattenberg Field near Greeley, Colorado for similar reasons.34 There are more than 25 deep injection wells in the Wattenberg Field of the Denver Julesburg Basin, where most flowback fluid is currently disposed of in the subsurface because of the difficulty of treating the high-viscosity fracturing fluids necessary in Northern Colorado.35 (By contrast, about half of oil- and gas-related wastewater is recycled in Western Colorado.36)

Drilling Mud:
“Mad Men” have glamorous jobs on popular TV shows. “Mud Men,” on the other hand, get the less glamorous task of determining the optimal composition and application of drilling muds that perform several essential functions during the drilling process. Drilling muds lubricate the drill bit while it’s working, bring rock fragments to the surface, and keep hydrostatic pressure in the wellbore to prevent blowouts. Drilling mud is also known as drilling fluid, and its handlers are more appropriately known as drilling fluids engineers.37 The workers who are focused on what the drilling mud brings to the surface, on the other hand, are known as “mud loggers.” They inspect the rock fragments that circulate up from the drill bit in order to create a log of the different rock formations being drilled through and to track the presence of hydrocarbons in those formations. Mud loggers usually work for a mud logging service company, which is subcontracted by the well operator.


Fate and Transport:
Scientists of chemical “fate and transport” study the ways that substances travel (or don’t travel) through the environment. Sometimes the substances they study move vast distances. Other times they don’t move at all. Still other times, they shift and change form because of reactions with oxygen, water, rocks, dirt, or other chemicals. Current fate and transport studies focused on oil and gas development aim to ascertain how hydraulic fracturing fluid chemicals behave underground – namely, whether they remain toxic, if they have a propensity to travel, or whether they break down into less concerning compounds and do not move.38

Flowback Fluid:
Flowback fluid could not have a more appropriate name. It is literally the portion of fluid that flows back to the surface after hydraulic fracturing is complete. After hydraulic fracturing ceases, natural internal pressures in the geologic formation will push a mixture of fluids back to the surface.39 Flowback fluid is mostly made up of hydraulic fracturing fluid, though it may contain some deep groundwater from the targeted geologic formation. The volume of fracturing fluid that makes this full-circle journey can range from as little as 5% to more than 70% of the original fracture fluid volume, depending primarily on the geology at hand – especially the composition of the target geologic formation and whether it is already saturated with deep groundwater.40,41 Most shales were originally deposited in marine environments, and, as a result, are already saturated with ancient, briny, non-drinkable water and have little room for more fluids. If a geologic layer is not saturated with water however, it will act like a dry sponge and trap fracturing fluid in its pores. By way of comparison, the very dry Haynesville Shale in Arkansas, Texas, and Louisiana traps 95% of the fracturing fluids it receives, while the rather wet Marcellus Shale in Pennsylvania and New York holds onto about 50% of the fracturing fluid injected into it.42 After some fraction of flowback fluid has returned to the surface, the balance of fluids emerging from the well shifts over to the deep groundwater that had saturated the formation prior to hydraulic fracturing. When this deep groundwater (also known as “formation water”) is actively removed from the subsurface in the process of oil and gas extraction, it is called “produced water.”

FracFocus is not the sort of registry you would visit to find somebody a wedding gift. But it is the sort of registry you would visit if you knew that the bride and groom wanted to track the chemicals being used in hydraulic fracturing fluids in their neighborhood, county, or state. Launched in April 2011 by the Groundwater Protection Council and the Interstate Oil and Gas Compact Commission, FracFocus is a voluntary effort by the oil and gas industry to increase disclosure of hydraulic fracturing fluid chemicals and address public concerns about those chemicals. In the years since its launch, several states, including Colorado, have begun to require some disclosure of hydraulic fracturing fluid composition and are relying on FracFocus to serve as the vehicle for those reporting mandates. While the registry does provide the means for more openness on fracturing fluid chemistry, critics point to several shortcomings, such as its delivery of data in individual PDFs that must be aggregated by hand, weak searching functions, and problems with the timing, consistency, and state verification of entries. FracFocus has responded with several updates, but it continues to draw complaints from those who expect more from a registry that has become an official means of regulatory disclosure.43 Also, because public trust in the oil and gas industry is lacking, some users of FracFocus are not confident that operators are fully and properly disclosing their activities on the registry. These users want to see mandatory reporting and closer regulatory oversight.

Public forums, convened by the Center of the American West, that aim to increase the productivity and elevate the character of public dialog about unconventional oil and gas development in Colorado and the American West at large. At FrackingSENSE events, the emphasis is on increasing the signal-to-noise ratio of public discourse through listening, evidence-based discussion, thoughtful questioning, respectful disagreement, and an atmosphere of civility.

Fractures, Faults, and Joints:
The unconventional oil and gas boom has sent many writers of news articles, blog posts, and, yes, glossaries, back to undergraduate geology textbooks in search of the proper vocabulary terms to describe the cracks and voids that occur underground. That’s because fractures, faults, and joints have the potential to serve both as reservoirs for hydrocarbons and as conduits for gasses and hydraulic fracturing fluid to migrate in the subsurface. “Fracture” is a generic term that geologists use to describe cracks found in rocks, which can be categorized into two different types: joints and faults. Joints are generally the smaller of the two. They form when a brittle geologic formation is stretched enough to break, often in parallel patterns, and usually because uplift or erosion has allowed the rock to expand. Faults are larger fractures in geologic formations, along which there has been significant displacement, either because the geologic formation is being pulled apart, pushed together, or is sliding one direction or another.44 Researchers are currently investigating the potential for such natural pathways to influence the movement of oil, gas, and possibly hydraulic fracturing fluids.45 Vertical fractures are a particular concern of researchers and the public, since one might imagine that the most direct natural pathway for hydrocarbons or fracturing fluids to move into an aquifer would be a vertical fracture extending upward from a deep oil and gas zone. But fractures are complicated – arrayed vertically and horizontally in three dimensions, often filled in by mineral deposits, challenging to map and understand, and subject to subsurface pressures that are not always predictable (or vertical, for that matter). Abandoned oil and gas wells from decades past – even centuries past – can also serve as their own form of man-made “vertical fractures,” further complicating the potential subsurface pathways through which fluids and gasses may move.



Green Completions:
“Completion” is shorthand for the final steps involved in preparing an oil or gas well for production. Those final steps may include hydraulic fracturing. A green completion (also known as a “reduced emission completion”) is one that captures gases (mostly methane and VOCs) that might otherwise escape to the atmosphere when flowback fluids reach the surface and are stored in a pit or a tank. Green completion equipment may include a trailer-mounted set of pipes and vessels that collect flowback fluids and separate out the liquid hydrocarbons and gases that accompany them46. The captured hydrocarbons can then be added to the operator’s sales line. Green completion technologies are more costly than the alternative (flaring or simply letting gases escape), which is why they are also less common. Flaring reduces emissions of methane and VOCs by combusting (burning) them, which produces carbon dioxide instead. The Environmental Protection Agency began requiring the use of green completion technologies on the fracturing and re-fracturing of most natural gas wells in January of 2015.47 The EPA will make exceptions for wells for which green completions are technically infeasible, including exploration wells located far from pipelines and low-pressure wells (mainly those extracting coalbed methane). Flaring will be required to reduce emissions from those wells.48

It is possible that hydrogeologists everywhere are rejoicing at the current rush of public attention to hydraulic fracturing, if only because it has put a spotlight on groundwater, a critically important but typically under-recognized and misunderstood water resource. Groundwater is a major source of drinking water and irrigation water in Colorado. Groundwater does not occur in the form of underground lakes or rivers. Rather, groundwater sits in the tiny, interlinked pores of geologic formations, as well as in natural joints and fractures. Scientists use the term “aquifer” to define sources of groundwater that are clean enough, plentiful enough, and mobile enough to be used by people.49 Not all groundwater deposits are aquifers. For example, many oil- and gas-bearing shale formations contain deep groundwater that dates to those geologic formations’ deposition by ancient seas. The water they hold is so deep and salty that it is not a candidate for drinking water, which means that those geologic layers are not considered to be aquifers. Geologists categorize aquifers by the rock formations that house them. “Unconfined” aquifers are usually made of highly permeable gravels and sands, and are found close to the surface in current or former river valleys (these aquifers are also known as “alluvial aquifers”). “Confined” aquifers typically occur in deeper bedrock formations and are capped by an impermeable rock layer above them. Many aquifers share a mix of both characteristics and are known as “semi-confined.” Because unconfined aquifers are replenished by rivers and surface runoff, they are more susceptible to contamination from aboveground events such as leaks or spills.50 The types and depths of aquifers vary by region, primarily because of geologic differences.



Home Rule:
Despite its “king of the castle” sound, the term “Home Rule” applies not to individual domestic units, but to communities on the whole. Municipalities with Home Rule governance are permitted, under the Constitution of the state of Colorado, to establish their own local laws and ordinances. Non-Home Rule, or “Statutory” cities, on the other hand, operate with state statute as their sole source of local law.51 Colorado is currently home to 96 Home Rule municipalities and 171 Statutory municipalities.52 In order for the local ordinances established by Home Rule communities to be legitimate, they must not directly conflict with state or federal laws – a matter which is of central importance in current legal disputes between Front Range communities that have passed oil and gas drilling bans or moratoriums and the oil and gas industry and COGCC. The question at the heart of these legal disputes is whether state oil and gas laws preempt local ordinances on oil and gas development.

Horizontal Drilling:
If you have a hard time imagining how a drill bit, burrowing away many thousands of feet underground, makes a gradual 90-degree turn and then proceeds horizontally for a mile or more, you are not alone. It takes significant engineering prowess to drill a well that is as long (or longer) laterally as it is deep vertically. Horizontal drilling is a relatively recent drilling technique used in oil and gas production. It is sometimes also referred to as “directional drilling” – a less specific term, which basically describes any non-vertical drilling technique. Horizontal wells begin as vertical wells, until the driller reaches a “kickoff point” and bends the wellbore horizontally into the target formation. Though the concept dates back to patents in the 1890s, the technology took on new dimensions of meaning more recently, when it was paired with hydraulic fracturing.53 A long horizontal wellbore exposes more of the target geologic formation for hydraulic fracturing, which breaks up low-permeability rocks and releases hydrocarbons from them. Horizontal drilling also has the advantage of reducing the impacts of drilling above ground because it makes it possible for an operator to tap hydrocarbons across a wider area and in several directions from one drilling site. The current maximum distance for a horizontal well in the Denver Julesburg Basin on Colorado’s Front Range is approximately two miles.54

Hydraulic Fracturing:
The shorter, slang version of this oil and gas term – “fracking” – made Merriam-Webster’s list of new dictionary words in 2014, joining the likes of “hashtag,” “crowdfunding,” “turducken,” and more than 150 other novel items of terminology.55 (For more on these 2014 companion terms we recommend that you put down this glossary and consult the nearest member of the Millennial Generation.) Hydraulic fracturing is an oil and gas extraction technique used to stimulate the flow of hydrocarbons from impermeable geologic formations. It is often conducted along with horizontal drilling. The process – which involves injecting fluid into the subsurface at high pressures – enlarges existing fractures in the target geologic formation and/or creates new ones. Extending several hundred feet away from the wellbore, those fractures serve as conduits for oil and gas to flow from pore spaces within the rock to the well itself.56 (For more details, please see the entries on permeability and unconventional oil and gas.) The fluid used in hydraulic fracturing is made up of water and chemical additives, and carries sand or silica that prop open fractures once they have been created. (For more on hydraulic fracturing fluid, please see the entry below.) A service company with expertise in hydraulic fracturing, such as Halliburton or Schlumberger (pronounced “Shlum-bur-zhay”), conducts the process on the well pad. Members of the oil and gas industry are more apt to call hydraulic fracturing well “stimulation.” When industry members do use the term as shorthand for hydraulic fracturing, they prefer to spell it without the “k” (“fracing”). In public debates about unconventional oil and gas extraction, the terms “hydraulic fracturing” and “fracking” are used in multiple, and sometimes conflicting, ways. The confusion this causes has the potential to derail conversations and stall communication. Some people use “hydraulic fracturing” and “fracking” to mean the particular and specific technique used to fracture oil-and-gas-bearing formations far below the surface. Others use the terms to mean the whole process of constructing and operating a well, plus maintaining and operating surface facilities like compressors, storage ponds, and pipelines. This disconnection in meaning can cause participants in the same conversation to talk past each other. Clear use of terms is key to making conversations on hydraulic fracturing (or “fracking”) productive and meaningful.57

Hydraulic Fracturing Fluid:
Hydraulic fracturing fluids are used for the purpose of fracturing impermeable geologic formations to release the oil and gas they hold. The exact composition of fracturing fluid depends primarily on the characteristics of the rock being fractured, but it almost always includes two primary components: water and a proppant (usually sand or silica), which is used to “prop” fractures open after they are formed. The remaining 2% (by volume) of fracturing fluids are a combination of chemical additives, some of which would be hazardous if they were to come in direct contact with humans. These chemical additives perform specific duties in the wellbore. Some reduce friction, which allows for a higher rate of fluid injection. Others increase or maintain the fluid’s viscosity so that it can carry proppants. Still others are used for well maintenance, injected with the goal of keeping the wellbore strong and clear of any impediments to oil and gas flow. Biocides prevent bacteria that could corrode metal well casing or produce dangerous gasses like hydrogen sulfide from breeding in the warm well environment, fed by guar gum and other organic compounds in fracturing fluid. Oxygen scavengers also prevent corrosion of the well casing. Acids break down drilling muds or other solids in the wellbore. And scale inhibitors remove minerals like calcium, which can build up in the wellbore much as they do in household plumbing.58 After fracturing fluid has been injected into a well at high pressures, some of it remains in the ground and some of it returns to the surface as flowback fluid.

When people grow tired of saying “oil and gas,” or distinguishing between them, they often turn to the word “hydrocarbons,” which covers both fuels. Hydrocarbons are organic compounds of hydrogen and carbon that also happen to produce a lot of energy when burned. Methane (natural gas) is a simple hydrocarbon (CH4). Petroleum is a mix of several hydrocarbons. The BTEX compounds are hydrocarbons, too. In fact, all fossil fuels are made up of hydrocarbons of different shapes and sizes.


When one thinks of the word “impact,” a few different things come to mind: meteors smashing into the earth or the lasting influence of a good teacher or mentor, for example. Indeed, the word “impact” can describe forces of good or bad, which is why it is strange that, in environmental debates, the term has come to primarily refer to negative effects. It is possible that the National Environmental Policy Act of 1969 steered the word toward the unfavorable. The law mandated the writing of Environmental Impact Statements, after all. Somehow, we began to use “impact” as a synonym for environmental harm. What matters now is that the term “impact” is everywhere, and that it should, as much as possible, be accompanied by a clear definition of what it means and whether its user is employing it to describe a benefit, an injury, or a combination of both.

The oil and gas industry is not a monolith, though terms like “the oil and gas industry” make it sound that way. The associations that represent the oil and gas industry before state and federal policymakers might wish that “the industry” hung together like El Capitan or the Rock of Gibraltar. Their jobs would be a lot easier if it did. In reality, “the industry” is an agglomeration of different entities with varying personalities and goals – big operators and small operators, privately held companies and publicly held companies, local wildcatters and multinationals. By the Colorado Oil and Gas Association’s count, there are 275 oil and gas operators at work in Colorado now. In fact, when one looks beyond the overly-simplistic term of “the industry,” things get very complicated very quickly. Onlookers to Colorado’s recent rulemaking on air quality got a glimpse at that complexity when various members of the industry disagreed about whether the state’s proposed emissions rules were too burdensome. Some of their disunity stemmed from the cost of compliance, estimated to range from $45-160 million per year across “the industry.” (The state calculated the smaller figure; the Colorado Oil and Gas Association calculated the larger.) Three of Colorado’s large operators (Anadarko, Encana, Noble), one smaller operator (Synergy Resources), and the state’s biggest midstream oil and gas company (DCP Midstream), aligned in public support of the state’s proposed rules. Other oil and gas operators chose not to join them in their approval.59 We cannot say for sure whether that schism reflects variation in environmental commitments among operators, or differences in operators’ ability to accept new compliance costs, or both, or neither, or something else entirely. But it is clear from this example that the term “the industry” falls short of describing the full range of operators, service companies, and members of the midstream (oil and gas gathering and processing) sector at play in any given area of oil and gas extraction, as well as the full-fledged individuality of the many different human beings that work for those companies.

Intermediate Casing:
Of the concentric layers of steel pipes used to case oil and gas wells, intermediate casing is installed between the surface casing and production casing strings. Intermediate casing provides additional protection to the wellbore. It is not always used. Operators install intermediate casing if geology and/or state regulations require it.60



One does not have to be a man in order to be a landman, though the gender reference within this historic term suggests otherwise. One does not have to be Matt Damon either, though the movie Promised Land made Damon the best-known fictional landman in America, if not the world. Landmen negotiate leasing agreements between oil and gas operators and the holders of land and mineral rights, and often do the background research involved in making those agreements. Typical tasks include investigating mineral rights ownership, contacting mineral rights owners, and negotiating the terms of mineral leases and surface use agreements. Landmen are usually private contractors hired by oil and gas operators, though sometimes they may work for an energy company in-house.61


Also known as CH4, methane is the primary chemical component of natural gas. Methane ranks second to carbon dioxide as the most prevalent greenhouse gas in the atmosphere. Both methane and carbon dioxide occur naturally but are presently accumulating in the atmosphere at accelerated rates due to human activities.62 When natural gas is combusted as a source of electricity, it burns cleaner than coal, emitting half as much carbon dioxide and less nitrogen oxide and sulfur dioxide.63 Unfortunately, these emissions benefits can be hampered by leaky gas infrastructure along the supply chain from oil and gas extraction to processing and distribution. Methane is a more potent greenhouse gas than carbon dioxide per unit of mass. In terms of Global Warming Potential (GWP), the two most important features of a greenhouse gas are (1) how well it absorbs energy and (2) how long it stays in the atmosphere. Scientists calculate Global Warming Potential over several standard time intervals – typically 20, 50, and 100 years – so that they can make comparisons between the heat trapping impacts of different greenhouse gases. Over a 100-year period, the Global Warming Potential of methane is 34 times that of the equivalent mass of carbon dioxide. Over a 20-year period, the Global Warming Potential of methane is 86 times that of the equivalent mass of carbon dioxide.64 Methane’s longevity in the atmosphere is shorter than that of carbon dioxide, which explains methane’s higher Global Warming Potential over shorter time scales. Carbon dioxide persists for thousands of years, while methane lasts about ten years.65 Concern about methane’s Global Warming Potential has made methane emissions a major focus of natural gas-related research and regulations. Paired with concerns about methane emissions into the atmosphere are worries about the potential for methane leakage from oil and gas wells into groundwater systems. (For more information on methane in groundwater, see the entries on the two types of methane, biogenic methane and thermogenic methane.)


The operator is the company that is legally in charge of (and liable for) an oil or gas well. The operator is the entity that interacts with the COGCC and agrees to the conditions of a permit to drill, and that bears the responsibility to oversee operations on the well pad and verify that those operations are up to the standards set by the state.66 The operator financially backs well pad operations, holds the well lease, and contracts well pad jobs to companies that specialize in particular tasks, such as service companies that manage tasks like horizontal drilling and hydraulic fracturing, and water haulers that bring water to the well pad.67 Only a few of the bigger operators can be named by members of the general public in Colorado – Anadarko, BP, Encana, and Noble Energy, for example – but there are many more. According to the Colorado Oil and Gas Association’s tally, there are roughly 275 operators currently active in the state, ranging from the very big to the very little. (For more on the range of operators, please see the entry for “industry.”)

Ozone (three oxygen atoms) is a good gas when it is found up high in the stratosphere, where it shields the Earth surface from the sun’s ultraviolet rays. Ozone is a bad gas at ground level, however, where it contributes to smog and can cause respiratory problems. Chemical reactions between volatile organic compounds (VOCs) and nitrogen oxides (NOx) form ground-level ozone, which is why these air pollutants are also often called “ozone precursors.” Oil and gas extractive processes can produce both VOCs and nitrogen oxides and therefore contribute to the formation of ground-level ozone.68


The term “permeability” reflects the relative ease with which fluids or gases may travel or flow between the pore spaces in a rock. Pore spaces are the tiny voids of airspace inside a rock. Pore spaces vary in size in different types of geologic formations. Rocks with higher permeability better allow fluids and gasses to flow through their pore spaces, while rocks with lower permeability trap fluids or gasses.69 Before the unconventional oil and gas boom began, most oil and gas was extracted from conventional source rocks with high permeabilities that easily released hydrocarbons. Unconventional sources of oil and gas, such as shale, have low permabilities and require hydraulic fracturing to encourage the flow of fluids and gasses.

Some oil and gas well sites include open pits for the storage of waste fluids, such as flowback fluid and produced water. Because these wastes can be hazardous to humans, wildlife, and the environment, regulators often require that pits be temporary, and that they be lined with plastic, monitored, and fenced. The risks of fluid leaks and gas emissions from pits are leading some operators to turn to less risky, but more expensive, waste management options, such as closed-loop drilling and containment tanks.70 The Colorado Oil and Gas Conservation Commission (COGCC) regulates oil and gas-related pits in Colorado. Pits are still allowed in the state, but the agency limits their use or insists on extra precautions near environmentally sensitive areas, water resources, and residences.71, 72

Pore Spaces:
All rocks contain tiny voids and airspaces known as pores. The ratio of the volume of void space in a rock to the rock’s total volume is known as its “porosity.” Porosity is often confused with permeability, but the two geologic characteristics are not the same. Porosity is the measure of how many open pore spaces exist within a rock. Porosity is high in most sandstones, for example, which are able to absorb water, gas, and oil as a result. The porosity of a geologic formation is a good indicator of whether it is likely to contain hydrocarbons.73 The permeability of a geologic formation, on the other hand, reflects the ability for water, oil, or gasses to move between pore spaces. The two geologic concepts are key to the current unconventional oil and gas boom, which has taken off because hydraulic fracturing has made it possible to link pore spaces filled with oil and gas in otherwise impermeable geologic formations, allowing the hydrocarbons previously trapped inside them to flow into a well and to the surface.

Produced Water:
It stretches the imagination to realize that, when energy companies extract hydrocarbons from the ground, they also retrieve the stuff of ancient rivers, seas, and glaciers. It is also weird to think that, after their long subsurface isolation, those fossil-aged waters are introduced into a hydrologic scheme managed by humans. When the ancient brines of the deep subsurface are “produced” by oil and gas wells they are called “produced water.” These deep fossil waters (also referred to as “deep groundwater” or “formation water”) are usually high in salts, particularly if they were associated with an ancient marine environment. They can also contain metals (barium, manganese, strontium, and iron, in particular) and organic substances (such as benzene, one of the BTEX compounds). Because of its variable and potentially toxic chemistry, produced water must be either be carefully discarded or carefully treated for reuse (see Deep Well Injection and Closed-Loop Drilling). Coalbed methane development, in particular, is known for its high volumes of produced water, drawn from saturated coal formations. In some places, such as the coalbed methane fields of Wyoming’s Powder River Basin, produced water is of high enough quality to release into surface water systems. Produced water treatment and recycling are an active area of research and development in the oil and gas industry (for more, see deep well injection and closed-loop drilling).74

Production Casing:
The final string of steel pipe well casing is known as the production casing because it extends into the geologic formation that “produces” oil and/or gas and is therefore the string that the “production” comes through. From the top of the well to the bottom, the production casing protects the geologic strata surrounding the wellbore in the places where the wellbore is not already covered by intermediate and surface casing, and provides the well itself with structure. In wells that are hydraulically fractured, the production casing is perforated in the production zone so that fracturing fluid can flow into the target geologic formation.75


Service Companies:
“Service company” is a generic term for the sub-contractors that provide particular services at well pads. Working like a general contractor building a house, the well operator may subcontract with a number of service companies for specific jobs, such as surveying, seismic testing, equipment transportation, water hauling, and drilling techniques such as horizontal drilling and hydraulic fracturing, among others.76 A typical well pad may have a dozen service companies working on it at a time. The operator is legally in charge of, and is the primary entity liable for, the work performed by service companies at the well site.

Social License to Operate:
The social license to operate is not a 2” x 3” plastic card that an oil and gas company can receive by passing a test. To earn a social license to operate, an oil and gas company must earn (and keep) the trust of the community in which it hopes to do business. Oil and gas companies have not always been aware that they should earn a social license in order to conduct their operations (technically speaking, they can, have, and sometimes still do operate without one). The importance of corporate responsibility and the gravity of public approval are now becoming more apparent to members of the oil and gas industry. Gaining public trust requires, among other things, a commitment to the highest possible environmental and social standards during and after the energy extraction process. Industry leaders have recently endeavored to define these high standards. A set of “Golden Rules” published by the International Energy Agency in 2012 emphasizes careful selection of drilling sites, full transparency, and thorough measuring and monitoring of environmental impacts, among other criteria.77 The industry’s unwillingness to fully disclose the chemicals in hydraulic fracturing fluids is often cited as its most costly blunder in the social license realm. The author of a recent Wyoming Law Review article on the social license to operate, Evan J. House, put it this way: “By withholding critical information from the public, especially during the early days of the shale gas boom, industry bred years of public mistrust. Consequently, industry’s social license to operate is now under threat.”78 House sketches a path forward for industry in the same article, writing that industry should take additional steps to “increase operational transparency; address the social anxieties caused by impacts to communities; develop cooperative working relationships with affected communities; and commit to using more environmentally and socially responsible business practices.”79

Split Estate:
Property rights reach new heights (or depths) in complexity and peculiarity when it comes to oil and gas extraction in the American West. That’s because some landowners are living on nearly century-old homesteading claims that divide the ownership of the earth’s surface and subsurface between different owners, effectively “splitting the estate.” This property-partitioning dates back to a handful of different homesteading laws passed at the turn of the twentieth century, but especially the 1916 Stock-Raising and Homestead Act (SHRA), which provided settlers with 640 acres of land for ranching and livestock raising. When it was enacted, the law gave homesteaders surface rights for only a filing fee, but it retained ownership of any subsurface minerals for the federal government in order to raise revenue for federal coffers and prevent private entities from monopolizing the nation’s coal, oil, and gas reserves.80 According to the Bureau of Land Management, which manages the federal mineral estate, the United States government owns 700 million acres of subsurface mineral rights; 58 million of those acres have a non-federal surface owner and are therefore “split estate” lands.81 Some of the 640-acre parcels originally homesteaded under the 1916 SHRA have since been sold off and subdivided into residential areas. Few homebuyers are historically alert enough to investigate whether they are purchasing lots that sit atop reserved mineral rights.82 Splitting surface and mineral rights between two different owners creates two competing legal interests. This reality can generate significant disagreement between landowners and oil and gas developers in Western states. In Colorado, subsurface and surface property rights are considered to have equal legal stature. The details of how the two property rights are supposed to coexist in an equivalent manner are contentious and complicated, however. In 1996, the Colorado Supreme Court ruled that split estate landowners must give oil and gas operators surface access that is “reasonable and necessary” for the extraction of the hydrocarbons under the property. The mineral owner, in turn, must “reasonably accommodate” the landowner’s current surface uses, according to the court.83 The Colorado state legislature passed a law in 2007 that aimed to clarify what “reasonable accommodation” means.84 The oil and gas operator is charged with “minimizing the intrusion upon and damage to the surface of the land” through modes of operation that are “technologically sound, economically practicable, and reasonably available.” The specific conditions of “reasonable accommodation” are negotiated between the operator and the landowner on a case-by-case basis in a legal Surface Use Agreement.

Surface Casing:
The second layer of steel pipe in a well, inserted after the conductor casing, is known as the surface casing. Its primary role is to seal off the wellbore from shallow groundwater systems and geologic zones (those nearest the ground surface, as the name suggests) in order to keep drilling, fracturing, and production fluids and gasses from migrating outside the wellbore. The surface casing also performs the opposite task: oil and gas operators do not benefit from getting shallow groundwater or biogenic gasses inside the well system, so the surface casing serves as a barrier to exit and entry alike. Regulators require operators to set surface casing to depths below drinking water aquifers and fill the annulus with cement from that depth back up to surface.85


Thermogenic Methane:
Methane is the primary component of what we call “natural gas.” As explained in the entry for biogenic methane above, thermogenic methane is the more commercially useful of the two different varieties of natural gas that occur in the subsurface. That’s because thermogenic methane is more likely to be found in commercial quantities, and because it is more likely to be associated with other profitable hydrocarbons, such as oil, ethane, propane, and butane. High subsurface temperatures and pressures turn organic matter into thermogenic methane over long periods of time at depths of 1-2 miles underground. Because of its deep subterranean origins and its commercial allure, thermogenic methane has been assigned an important additional role in some instances of oil or gas extraction: that of “smoking gun” in cases of well leakage and/or groundwater contamination. If regulators find thermogenic methane in an unexpected location, such as a shallow aquifer, they have some reason to believe that methane has escaped the confines of an oil or gas well. This “smoking gun” role is complicated by the intricacies of groundwater systems, however. Some aquifers with thermogenic methane in them may have contained that methane since long before extractive activities entered the picture – likely because it accumulated there via natural geologic pathways – which is one reason why pre-drilling baseline groundwater data is so important to understanding groundwater contamination. Regulators can investigate the molecular composition of methane to determine whether it is biogenic or thermogenic in nature.86

When it is used in a public policy context, the term transparency refers to openness and communication. Transparency has direct ties to governmental and corporate accountability. It can increase opportunities for public engagement and collaboration, or it can reduce the need for them.87 Transparency measures are increasingly common features of public policy, particularly as the digital era has made it easier to accumulate, sort, and display vast quantities of information. When it comes to the transparency of unconventional oil and gas extraction, significant public attention has been devoted to industry disclosure of the chemical compounds in hydraulic fracturing fluid. Colorado established rules in 2011 that require oil and gas operators to publicly disclose all the ingredients of fracturing fluids and their maximum concentrations on the FracFocus registry, with the exception of “trade secret” chemicals. Operators may report the identities and concentrations specific “trade secret” chemicals confidentially to the COGCC, under penalty of perjury, but the chemical families of those chemicals must be disclosed publicly.88, 89 The Environmental Protection Agency is also exploring its own set of federal disclosure rules at the time of this writing.90 Expectations of transparency have been growing in the financial sector as well. Institutional investors and organizations promoting corporate accountability have recently been pressing oil and gas companies for greater disclosure of their risk management processes.91 (For more on transparency in the oil and gas business, please visit the related entries on the FracFocus registry, the social license to operate, and trust.)

Merriam Webster defines trust as the “belief that someone or something is reliable, good, honest, and effective.” At present, companies, communities, neighbors, and regulators engaged in the unconventional oil and gas debate seem more likely to see each other as registering short of “reliable, good, honest, and effective.” In the oil and gas context, as in any area of human life, trust is easier to lose than it is to gain. Trust is also easily jeopardized by secrecy, which characterized much of the oil and gas industry’s early response to hydraulic fracturing fluid chemical disclosure and initially set some industry members on a path leading speedily away from public confidence.92 Trust is a key component of the concept of the social license to operate, a sense of public approval that oil and gas operators endeavor to earn in the communities in which they hope to do business.



Unconventional Oil and Gas:
Oil and gas companies used to avoid “unconventional” reservoirs of oil and gas, such as shales and tight sandstones, because their low permeabilities locked hydrocarbons away. But in recent years, advances in drilling technologies – namely horizontal drilling and hydraulic fracturing – have made previously unconventional natural gas deposits the standard fare of oil and gas ventures.93 In the Denver Julesburg Basin today, the major “unconventional” geologic formation of interest is the shale-like Niobrara Formation (which, technically, is more of a limestone), as well as “tight” sandstones, which occur in some parts of the “Muddy J” and the Codell geologic formations.94 Coalbed methane is another unconventional natural gas source of note (for more information on “CBM” wells, see the coalbed methane entry).


Volatile Organic Compounds:
Volatile organic compounds (VOCs) are categorized as such because of their penchant for evaporating (volatilizing into a gas from liquid form). In chemistry, a “volatile” compound is one that is likely to be at least partially in a gaseous state at normal indoor and outdoor temperatures. VOCs are released by the burning of fuels such as wood, coal, and gasoline. They are also emitted in oil and gas fields – through leaky infrastructure or inadequately controlled drilling and completion activities. Some VOCs, such as the BTEX compounds described in this glossary (benzene, toluene, ethylene, xylene), are hazardous air pollutants that, if present in sufficient concentrations, have the ability to cause a range of negative health consequences for people in close and consistent proximity, from skin and eye irritation to cancer. Additionally, in the presence of sunlight VOCs can react with nitrogen oxides (another common emission of natural gas production, and also of power plants) to form ground-level ozone, which also has negative environmental and health effects.95


Water Hauler:
By definition, hydraulic fracturing requires water, which means somebody has to get 2-5 million gallons of it to a well pad, on average, to supply the process. If operators do not have pipelines in place to convey water from source to well pad, they must rely on water hauling trucks. The water hauler may also transport produced water away from the well pad and to a deep well injection disposal site. Because moving water to and from the well site requires numerous round trips, water hauling contributes significantly to oil- and gas-related truck traffic.96 In an effort to reduce truck traffic and save on water delivery costs, some oil and gas operators in Colorado are now laying temporary networks of pipes and pumps to transport water to well pads from rivers and irrigation ditches.97

The “wellbore” of an oil and/or gas well is the actual hole that an operator or service company drills (or “bores”) into the subsurface for the purpose of hydrocarbon extraction. It may also be referred to as the “drill hole” or the “borehole.” Wellbores are lined with steel casing and cement in order to protect the surrounding geologic strata, including groundwater systems, from leaks of drilling and hydraulic fracturing fluidsproduced water, or methane and other gasses. (For more information, see the entry on wellbore integrity.) A wellbore may be vertical or horizontal, depending on whether an operator is conducting horizontal drilling.

Wellbore Integrity:
While this term sounds like it describes the moral virtue of an oil or gas well, it more directly reflects the technical skills and professional commitment of the well’s engineers and technicians. A wellbore that properly contains all oil, gas, and produced water – preventing any and all leaks by virtue of strong casingcement, and other barriers such as production equipment and wellheads – is considered to have high integrity. Indicators of a failed wellbore (one that may have correspondingly low integrity) include unexpected changes in pressure in specific parts of the wellbore, such as the well annulus. Because leaks of oil, gas, produced water, or fracturing fluid can lead to environmental contamination, wellbore integrity is both regulated and monitored.98 The operator monitors wellbore integrity during and after the construction of the well, and reports its findings to COGCC. For example, COGCC requires operators to verify the quality of cement jobs by sending instruments down the wellbore that document the presence or absence of cement along its length (a.k.a., “cement bond logging”). COGCC also has rules that require operators to monitor and report well pressure during well integrity tests and hydraulic fracturing and to take “corrective actions” if well pressure change unexpectedly.99 Rapid changes in well pressure may indicate a failure of wellbore integrity.

The “head” of the well is the portion of the well’s anatomy that shows above ground. It is made up of pipes and valves that cap the wellbore and serve as a site for the gauges used to monitor well pressure. Wellheads are built to withstand high underground pressures in order to prevent well blowouts.100

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