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Friday, 23 October 2015

A Short Shale Gas Glossary

Here is a short shale gas glossary for those of you confused by terminology and jargon.

A single underground geological formation, or group of formations, containing water. Those near the surface often contain freshwater that is recharged by rainfall and that can be used as a source of drinking (potable) water. Deep aquifers also exist. The water in deep aquifers is often salty and has been locked away for millions of years. Carbon dioxide injection into deep saline aquifers is one of the proposed ways of carbon capture and storage (CCS).
Antrim shale
A shale deposit located in the northern Michigan basin that is a Devonian age rock formation lying at a relatively shallow depth of 1,000 feet. Gas has been produced from this formation for several decades primarily via vertical, rather than horizontal, wells. The Energy Information Administration (EIA) estimates the technically recoverable Antrim shale resource at 20 trillion cubic feet (Tcf).
Appalachian basin
The geological formations that roughly follow the Appalachian Mountain range and contain potentially exploitable shale gas resources. The U.S. Department of Energy (DOE) associates the Appalachian Basin with the Marcellus Shale, the Devonian Shale and the Utica Shale.
Barnett shale
A newly developed major play within the Fort Worth Basin in Northeast Texas. Wells are in the 6,000-to-8,000 foot depth range and the EIA estimated technically recoverable resource is 43 Tcf.
Baseline survey
A survey carried out prior to any operations to determine the natural background levels of certain substances or conditions (e..g., the presence of carbon dioxide or the intensity of the background noise).
Becquerel (symbol Bq)
The unit of the amount or activity of a radionuclide. Describes the rate which transformations occur. 1 Bq = 1 transformation per second.
Becquerel per cubic metre of air (Bq m–3).
The amount of a radionuclide in each cubic metre of air. Often referred to as the activity concentration.
British Geological Survey – a UK Government agency.
An additive that kills bacteria.
Biogenic gas
Natural gas commonly found in aquifers that is produced by bacteria in the subsurface.
A sudden and uncontrolled escape of fluids from a well up to the surface.
Blowout preventer
High pressure wellhead valves, designed to shut off the uncontrolled flow of hydrocarbons.
The hole or shaft in the earth made by a well drill; also, the uncased drill hole from the surface to the bottom of the well. Also see ‘wellbore’.
Bowland-Hodder shale
Shale occurring in basins across the north of England predominantly in Lancashire and Yorkshire, coast-to-coast.
A secondary enclosure to contain leaks and spills.
Caney shale
Located in Arkoma Basin of Northeastern Oklahoma; has only recently been developed following the success of the Barnett Shale in Texas.
Cap rock
A layer of relatively impermeable rock overlying an oil- or gas-bearing rock.
Carbon footprint
A measurement of the impact of activities on the environment by the amount of greenhouse gases they produce. It is measured in units of carbon dioxide equivalent.
Steel pipe cemented in an oil or gas well to protect both subsurface formations and the wellbore,  to stop formation fluids leaking into and damaging other rocks formations, and to keep the borehole from caving in. Smaller diameter “strings” of casing are cemented inside larger diameter strings as a well is deepened.
Cement bond log
A method of testing the integrity of cement used in the construction of the well, especially whether the cement is adhering effectively to both sides of the annulus between casings or between the outer casing and the rock sides.
Coal bed methane (CBM)
A form of natural gas extracted from coal beds. Along with tight and shale gas, CBM is considered an unconventional natural gas resource. Unlike shale gas CBM gas is often from a shallow source, and although it generally does not require fracking, it can pose a significant danger to surface aquifers.
Conesauga shale
Cambrian Age shale deposits located in north central Alabama currently being evaluated for development.
Consumptive water
The water that is completely used up in a process. For example, drinking.
Conventional natural gas reservoir
A geological formation in which the natural gas is in interconnected pore spaces, much like a kitchen sponge, that allows easier flow to a well.
Department of Energy and Climate Change – responsible for PEDL licenses for onshore and offshore oil and gas exploration and production.
Devonian shale
The general term used to describe the thick sequence of shales in the Appalachian Basin that has been produced for more than a century. Development was greatest in the 1930s-through-1980s, using vertical wells and explosive fracturing. However, any shale deposited during the Devonian geologic period (360 million to 406 million years ago) is considered to be Devonian shale.
Directional drilling
The intentional deviation of a wellbore from the approximately vertical path it would take naturally.
Disposal well
A well, sometimes a depleted oil or gas well, into which waste fluids can be injected for safe disposal.
Drilling rig
A structure employing a drill that creates holes or shafts in the ground for purposes of accessing and producing natural gas or oil from subsurface deposits. Those used in the shale gas industry are about 30 m (100 ft.) tall, or the height of an oak tree
Eagle Ford shale
A newly discovered (2009) shale play located in several counties in south Texas. The average gross thickness of the shale is 350 feet and it produces from depths varying from 4,000 to 14,000 feet. Eagle Ford is the most active shale play in the world, with about 250 rigs operating at any single time and the technically recoverable resource is estimated by EIA to be 21 Tcf.
Eastern Gas Shales Project
A program initiated by the U.S. Department of Energy in the late-1970s to evaluate the gas potential of – and to enhance gas production from – the extensive Devonian and Mississippian black shales located in the Appalachian, Illinois and Michigan basins of the eastern United States. The program not only identified and classified shales throughout the three basins, but also focused on developing and implementing new drilling, stimulation and recovery technologies to increase production potential. Between 1978 and 1992, DOE spent about $137 million on the program, which helped develop and demonstrate directional and horizontal drilling technology.
Economic Level of Leakage (ELL)
The Economic Level of Leakage is the level at which the cost to companies and customers of further reducing leakage of water exceeds the cost of producing water from an alternative source.
Energy Information Agency – the US agency responsible for federal energy responsibilities.
Embedded water
The total water required to make and deliver any item.
Enhanced geothermal systems
A geothermal system that uses heat from deep in the ground to generate energy. An enhanced geothermal system is one where the natural connectivity does not permit sufficient flow and additional stimulation (fracking) is required.
Environmental Protection Agency – the US agency responsible for federal environmental protection responsibilities.
Fayetteville shale
Newly developed shale deposit located in the Arkoma Basin of Arkansas, lying at a depth of 1,500-to-6,500 feet. Previously produced from vertical wells but all current wells are horizontal. Technically recoverable resource is estimated by EIA to be 32 Tcf.
The controlled burning of natural gas that can’t be processed for sale or used because of technical or economic reasons. Only enclosed flaring is allowed in the UK, and then only for safety reasons.
Flowback water
The fluid that flows back to surface following a fracturing treatment. It is a mixture of the original fracturing fluid and saline water containing dissolved minerals from the shale formation.
Floyd shale
A shale deposit from the Mississippian geologic age located in the resource-rich Black Warrior Basin of Mississippi and Alabama.
Fossil energy
Energy derived from crude oil, natural gas or coal. Shale gas is a form of fossil energy.
A joint effort by the Ground Water Protection Council (GWPC) and the Interstate Oil and Gas Compact Commission (IOGCC) that is an online registry for companies to publicly disclose the chemicals used in their hydraulic fracturing operations. As of November 2012, more than 30,000 well sites and 200 companies were registered on the site (
Fracturing fluid
The primarily water-based fluid used to fracture shale. It is basically composed of 99 percent water, with the remainder consisting of sand and various chemical additives. Fracturing fluid is pumped into wells at very high pressure to break up and hold open underground rock formations, which in turn releases natural gas.
Fugitive emissions
According to a study by DOE’s Argonne National Laboratory, a primary air quality concern from natural gas production (including shale gas) is leaking and venting throughout the supply chain. These fugitive emissions can potentially result in releases of methane, the primary constituent of natural gas and a potent greenhouse gas (GHG).  In addition, fugitive emissions of natural gas can release volatile organic compounds (VOCs) and hazardous air pollutants (HAPs).
Gas in place
The entire volume of gas contained in a formation regardless of the ability to produce it.
Gcf or Gscf
Thousand million cubic feet of gas.  If it is measured at surface temperatures and pressures Gscf is used. Since gas expands hugely as it comes to the surface and gas is sold by volume, this distinction is extremely important.
Geological formation
A body of earth material with distinctive and characteristic properties and a degree of homogeneity in its physical properties.
Greenhouse gas – type of gas which produce climate change.
Global warming potential
A measure of how much a given mass of a greenhouse gas is estimated to contribute to global warming relative to carbon dioxide.
The supply of usually fresh water found beneath the surface usually in aquifers, which are a body of permeable rock containing water and supplying wells and springs with drinking water.
Gothic shale
A newly exploited shale formation located in the Paradox Basin of Colorado. Only a few wells have been drilled, one testing to 5,700 Mcf (million cubic feet) per day.
Haynesville shale
Along with the Marcellus and Barnett, this is one of the major shale plays. Located in North-western Louisiana, Haynesville is a Jurassic Age formation where vertical wells were drilled as far back as 1905; but it was not considered a major natural gas source until the advent of directional drilling.
A hazard is something (e.g., an object, a property of a substance, a phenomenon or an activity) that can cause adverse effects.
Horizontal drilling
The process of drilling the deeper portion of a well horizontally to enable access to more of the target formation. Horizontal drilling can be oriented in a direction that maximizes the number of natural fractures present in the shale, which provide pathways for natural gas to escape once the hydraulic fracturing operation takes place. The more generic term, “directional drilling,” refers to any non-vertical well.
Health and Safety Executive – a UK Government agency.
Hydraulic fracturing
1. The use of water, sand and chemical additives pumped under high pressure to fracture subsurface non-porous rock formations such as shale to improve the flow of natural gas into the well. Hydraulic fracturing is a mature technology that has been used for 60 years and today accounts for 95% of all new wells drilled.
2. A means of increasing the flow of oil or gas from a rock formation by pumping fluid at high pressure into the well, causing fractures to open in the formation and increase its permeability.
The geology of groundwater, especially concerning the physical, biological and chemical properties of its occurrence and movement.
International Energy Agency
Kick-off point
The depth at which a well starts deviating from the vertical when drilling a directional or horizontal well.
The horizontal portion of a horizontally drilled well.
Leak-off test
A test used to determine the pressure required to initiate fracturing of the rock formation.
Thousands of barrels of oil.
Millions of barrels of oil.
Mcf or Mscf
Thousand cubic feet of gas.  If it is measured at surface temperatures and pressures Mscf is used. Since gas expands hugely as it comes to the surface and gas is sold by volume, this distinction is extremely important.
MMcf or MMscf
Million cubic feet of gas.  If it is measured at surface temperatures and pressures MMscf is used. Since gas expands hugely as it comes to the surface and gas is sold by volume, this distinction is extremely important.
Megawatthour – a unit of energy. One may also find kWh, GWh and TWh used for a thousand watthours, a thousand million watthours and a trillion watthours, respectively.
One of a number of different measures of the size or strength of an earthquake using a logarithmic scale (please see text for details).
Marcellus shale
A large play that underlies most of the U.S. Northeast, the Marcellus is a Devonian-age shale that is estimated by the Energy Information Administration to contain at least 410 Tcf of unproved, technically recoverable gas. Most of the play is at the 5,000-to-8,000 foot level below the surface and was long considered too expensive to access until advances in drilling and fracturing technology.
Very small seismic events, normally below -1.5 ML.
New Albany shale
This Devonian to Mississippian age shale deposit is located in the Illinois Basin and has been a producer of natural gas for over 100 years. Most wells are shallow, between 120 and 2,100 feet; new drilling and completion technologies and competitive prices have resulted in energy companies revisiting old leases and drilling new wells. Estimated by EIA to contain 11 Tcf of technically recoverable resources.
Natural gas
A naturally occurring mixture of hydrocarbon and non-hydrocarbon gases beneath the surface, the principal component of which (50 to 90%) is methane.
Naturally occurring radioactive material (NORM)
Radioactive elements and their decay products found in the environment that have been generated from natural processes.
Non-consumptive water
Water that is used in a process but not consumed. For example, swimming pools.
On-site water treatment
A practice employed by many shale gas producers to facilitate reuse of flowback fluids. In this instance, mobile and fixed treatment units are employed using processes such as evaporation, distillation, oxidation, and membrane filtration for recycling and reuse. On-site treatment technologies may be capable of returning 70-80% of the initial water to potable water standards, making it immediately available for reuse.
Office for Unconventional Oil and Gas. A new office of the UK Government within the DECC that was set up in 2014 for the management of onshore shale gas and other unconventional hydrocarbon exploitation.
Petroleum Exploration Development License. Managed by the DECC.
The study of the physical properties of all rocks, whether they contain hydrocarbons or not.
The measure of the ability of a material, such as rock, to allow fluids to pass through it.
Pearsall shale
Located in the Maverick Basin of south-western Texas. Located about 2,500 feet below the Eagle Ford Shale and is approximately 500-600 feet in thickness.
Public Health England – a UK Government agency.
A ratio between the volume of the pore space in reservoir rock and the total volume of the rock. The pore space determines the amount of space available for fluids such as gas or water.
Pressure test
A method of testing well integrity by raising the internal pressure of the well up to maximum expected design parameters.
Produced water
The fluid that returns to the surface during the production phase of a well that contains both fracturing fluid and saline water from the rock formation.
A granular substance that is mixed with and carried by fracturing fluid pumped into a shale gas well. It is often sand, but increasingly hard ceramic spheres that have been manufactured are used, especially at great depths. Its purpose is to keep cracks and fractures that occur during the hydraulic fracturing process open after the initial high fracturing pressures have been removed so trapped natural gas can escape. Otherwise the weight of rocks above the fractures would soon close them again.
Proved reserves
The volume of resources that can be demonstrated to be economically and legally producible using current best technology.
Radon action level

The recommended limit for the activity concentration of radon in UK homes. Its value, expressed as the annual average radon gas concentration in the home, is 200 Bq m–3.
Radon affected areas
Parts of the country with a 1% probability or more of present or future homes being above the Action Level.
The clean up or restoring a well site to its pre-existing condition after drilling operations cease. Reclamation activities, which are governed by state, federal and local laws and regulations in the USA, can include soil replacement, compacting and re-seeding of natural vegetation. In the UK it is the body which grants planning permission who dictates what reclamation is required and checks that it is carried out fully. UK reclamation is always reversion to the sites initial pre-developed state.
A subsurface body of rock that acts as a store for hydrocarbons.
A risk is the likelihood that a hazard will actually cause its adverse effects, together with a measure of the effect.
A payment received by a lessor or property owner from an oil, gas or minerals-producing company, based on the production of a well or other extraction process and market prices.
Scale inhibitor
A chemical treatment used to control or prevent deposits building up in the well.
Sudden geological phenomena that release energy in the form of vibrations that travel through the earth as compression (primary) or shear (secondary) waves.
Seismic reflection surveys
A technique that uses reflected seismic waves to map the structure of rock layers in two- or three-dimensions.
A fine-grained sedimentary rock composed mostly of consolidated clay or mud. Some large shale gas formations were formed more than 300 million years ago during the Devonian period of Earth’s history, where conditions were particularly favourable for the preservation of organic material within the sediment. Methane that remained locked in the shale layers is the source of today’s shale gas.
Shale gas
Natural gas produced from shale formations. Shale gas is widely distributed around the world and is currently being produced in 16 states of the USA.
Shale gas play
A set of discovered, undiscovered or possible natural gas accumulations that exhibit similar geological characteristics. Shale plays are located within basins, which are large-scale geologic depressions, often hundreds of miles across, which also may contain other oil and natural gas resources.
Surface water
Water that is open to the atmosphere, such as rivers, lakes, ponds, reservoirs, streams, impoundments, seas and estuaries.
A chemical that lowers the surface tension or interfacial tension between fluids or between a fluid and a solid.
Sweet spot
Regions in oil and gas reservoirs with high concentrations of carbon which are most amenable to production.
Tcf or Tscf
Trillion cubic feet of gas.  If it is measured at surface temperatures and pressures Tscf is used. Since gas expands hugely as it comes to the surface and gas is sold by volume, this distinction is extremely important.
Technically recoverable resource
The volume of gas within a formation considered to be recoverable with existing technology.
Thermogenic methane
Methane produced by the alteration of organic matter under high temperatures and pressures over long time periods.
Tight gas
Natural gas found in low-permeability sandstones and carbonate reservoirs. The rock layers that hold the gas are very dense, preventing easy flow.
An instrument used to detect microdeformations in surrounding rock.
A chemical additive that can be used to identify the presence of the fracturing fluid by subsequent monitoring.
Traffic light system
An early warning monitoring system with thresholds to indicate when hydraulic fracturing operations should proceed with caution or halt.
Unconventional gas
Gas found in a reservoir of low permeability.
Unconventional natural gas reservoir
Coal bed methane, shale or tight gas, where the natural gas does not flow naturally to the well, but instead requires some form of extensive stimulation to generate economic flow rates.
Underground injection well
A steel and concrete-encased shaft into which hazardous waste is deposited by force and under pressure that is not allowed in the UK or the rest of Europe. The US Environmental Protection Agency’s (EPA’s) Underground Injection Control Program (UIC) is responsible for regulating the construction, operation, permitting and closure of injection wells that place fluids underground for storage or disposal. Nevertheless this process is associated with the sharp rise in anomalous earthquakes in mid-USA.
Utica shale
An Ordovician age natural gas-containing rock formation located below the Marcellus Shale. The formation (also called the Utica-Point Pleasant in some areas) extends from eastern Ohio through much of Pennsylvania to western New York. It is currently being actively developed in eastern Ohio.
Volatile organic compounds – those organic liquids which evaporate easily.
The Water Exploitation Index (WEI)
A way of measuring how much water we use compared to that available. It is the comparison between how much fresh water we extract from surface sources and aquifers and the long term rainfall available for use. Usually it is considered that a region is under ‘water stress’ if the Water Exploitation Index is above 20%.
Watt (W)
The watt is a unit of power describing how fast something can convert energy. It is usually found in megawatts (MW), which is a million watts, or gigawatts (GW) which is a thousand million watts, or terrawatts (TW) which is a trillion watts.
The hole created by drilling operations, also known as the ‘borehole’.
Well integrity
The ability of the well to prevent hydrocarbons or operational fluids leaking into the surrounding environment.
Well pad
The surface infrastructure of the drilling operations.
World Health Organisation

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