Helping You Understand The Eagle Ford Shale In South Texas


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Shale Drilling Terms

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Shale Drilling Terms Explained


There are many unusual slang expressions and technical terms used in hydraulic fracturing, horizontal drilling, well completion and production in shale plays such as the Eagle Ford.  Many of these terms evolved over the long and colorful history of the oil and gas industry and the origin of some of them, such as "possum belly" is unclear.  This is not a complete list of all terms used in shale drilling, by any means. If you see an important shale drilling term that has been left out, please feel free to contact us and so we can add it.

Annulus The area between the casing and the tubing or between the wellbore and the casing, etc. Refers to a space between tubulars and other tubulars or the earth that must be calculated when figuring drilling fluid volume, cement jobs, etc.

bbl  Abbreviation used for barrel of oil, which is equal to 42 US gallons or 159 Liters of liquid.

BOP  The Blowout Preventer is a series of heavy valves and rams which can be engaged to prevent a blowout from occurring. There are typically several different rams and shears utilized in a BOP stack. These can either squeeze off the annulus, or space between the drill pipe and casing, or even shear off the drill pipe itself to close the hole. Drilling companies frequently conduct BOP drills which familiarize the crew with how to quickly close BOP valves to prevent a blowout.

Brady Brown  A type of frac sand (see Proppant) used in Eagle Ford Shale wells. Obtained from mines near the Texas towns of Brady and Voca.

Chalkford  Transition zone play involving both Austin Chalk and Eagle Ford Shale formations.

Curve This is the point in a directional well where it turns from a vertical hole to a horizontal hole. You may hear directional drillers speaking of "building the curve." This is the process of using an mud motor with a specific bend in it to gently create a curve in the wellbore over a distance of several hundred feet. Once the curve has been built, mud motors more suited for horizontal drilling, and made only for applying slight corrections are typically used.

Condensate This refers to high API gravity, low density liquid hydrocarbons that are often produced along with natural gas in Eagle Ford Shale. Condensate is a valuable liquid since refineries use it to mix with heavier grades of crude, such as that from the Alberta tar sands.

Disposal Well  A well that is typically drilled into a porous rock formation which is nonproductive (of oil or gas) and into which oilfield waste water, such as produced saltwater, is disposed using injection pumps. Disposal wells and facilities are regulated by the Texas Railroad Commission and are used throughout the Eagle Ford Shale to dispose of produced water.

Directional Driller  These are highly trained drillers who work alongside the rig's regular drillers to direct the horizontal drilling process. An oil company brings in the directional crew, including the directional driller and MWD (measure while drilling) employees when it is time to deviate the well from vertical and build the "curve" and "lateral" portions of the well. Directional drillers are some of the highest paid service hands in the oilfield, however much is expected of them and the pressure can of the job can be great at times. Directional driller can be abbreviated "DD." If the DD does not build the curve properly or does not keep the well on target, it could cost the company thousands of dollars to correct the problem by drilling another hole.

Downspacing Refers reducing the number of acres required for oil or gas wells so that more wells are drilled in a given space. Downspacing is being researched by several oil and gas companies in the Eagle Ford Shale as a means of boosting the overall oil and gas recovery factor.

Eaglebine Play  Refers to areas where oil companies can produce from both Eagle Ford Shale and Woodbine formation in a single well.

EUR Estimated Ultimate Recovery. Refers to the ultimate oil and gas production of the well over its lifetime. Companies may project EUR across a field to show investors how returns on investment will likely occur over a period of time.

Frac. Refers to the process of hydraulically fracturing a well using water, sand and some chemicals. (Propane is also used to frac wells as part of a new technology invented by GasFrac, a Canadian company.) Frac can be used as a noun (they did a frac or frac job on the well,) and as a verb, (they are going to frac the well next week.)

Flare Gas flares are used to burn off waste gas, typically containing H2S or hydrogen sulfide, so that it does not pose a hazard to humans or animals. Flares used on Eagle Ford Shale wells typically contain a self-igniting system to keep the flame burning. Can be used as a verb, as in "they are flaring gas now."

Flowback  The process where frac fluids, (including water, oil and natural gas,) return to the surface following a hydraulic fracturing operation. Flowback technicians may stay on the wellsite for several days as this process is completed, checking the amount of oil and gas production and adjusting chokes (restrictive valves) in the well that regulate how much gas and fluid flows back. The flowback  process is very critical, since damage can be done to the oil and gas producing formation and the well if it is not done correctly.

GOR Gas To Oil ratio refers to the amount of crude oil produced compared to produced natural gas. High GOR wells produce more gas than oil. In Texas, a gas well is defined as one where the GOR is 100 Mcf/bbl or more.

Gyro: Can be either a wireline (lowered down into the wellbore) or MWD based (instrument placed near the drill bit when well is being drilled) device that uses an electronic gyro-compass to determine the angle of the well. Gyro tools can provide the angle of the wellbore and direction. This information ensures that the well is going in the right direction, stays on target, and does not collide with other wells. Gyro surveys are also required by the Texas Railroad Commission on each vertical or horizontal oil and gas well.

Hotshot   Hotshot services or Hot Shot drivers deliver important items to the rig in a timely manner.  Oil companies use Hotshot drivers to deliver items such as directional drilling equipment, critical parts and other items when they are needed ASAP.  Hotshot trucks typically consist of a 1 ton pickup, a long trailer and gin pole setup for offloading items such as pipe.

IP Rate The Initial Production rate of a well refers to the amount of oil and natural gas initially produced as the well is flowed back (see flowback.) While IP rates can be indicative of how productive the well can be, high IP rates may not translate to sustained long term production or high EUR.

Joint  A length of drill pipe or casing.

Kill   If a well is experiencing a kick, or the early stages of a blowout, the company may need to "kill the well" This may involve pumping heavier drilling mud down the hole or other measures to achieve a balanced mud situation again.

Landman  A land leasing agent who typically works for an oil and gas company. Landmen research county records and locate mineral rights owners, which they may then offer and oil and gas lease to on behalf of an exploration company.

Lease Bonus The amount typically paid to a landowner (per acre) for the right to lease land for oil and gas exploration for a specific period of time (often 2 to 3 years.) This is separate from royalty, which is a percentage of revenue from production that may be paid to a landowner if a productive well is made.

Logging  Well logging refers to using either wireline based instruments, which are lowered down the hole, or MWD - LDW (Measure - Logging While Drilling) equipment to analyze the rock formation being drilled through. Logging tools record properties of rock, such as gamma ray output from the formation, resistivity, conductivity and other factors to create a paper or digital "log" of the well, showing what kind of formation the wellbore penetrated. LWD or logging while drilling is used in the Eagle Ford Shale to help people well on track and in the shale zone instead of above or below it. LWD technology is essential for the horizontal drilling process since it gives the directional driller real-time information that he can use to keep the well  inside the pay zone.

LWD Logging While Drilling equipment (see logging above) refers to equipment placed in the drilling assembly, near the mud motor and bit, to analyze the rock formation being drilled. LWD equipment can tell the directional driller what type of rock (such as sandstone or shale) they are drilling in, so that the well can stay in the desired payzone.

Man Camp   These are typically portable housing, RVs and travel trailers set up in a camp style arrangement for oilfield workers to live in. A shortage of housing in Eagle Ford Shale has led some oil and gas and construction companies to house their workers and temporary “man camps.”

MBOE  The M when used as a prefix for abbreviations such as  “Barrels Of Oil Equivalent” refers to thousands, not millions of some people think. One barrel of oil is generally accepted to contain the same amount of energy content as 6,000 cubic feet of natural gas. The abbreviation MBOE is used by some oil companies and their investor reports to make it seem like wells are producing more oil than they really are, when in fact MBOE refers to a combination of oil, natural gas and natural gas liquids or NGL's.

MMBOE Two letter M's, from Roman numerals,  refer to one million. In this case "MMBOE"  refers to one million barrels of oil equivalent.

Mcf    This abbreviation typically refers to 1000 cubic feet of natural gas. Again, because of the M, some people confuse this with 1,000,000 ft.³. One million cubic feet would be abbreviated as MMCF. You could add "/d"  to either of these abbreviations to indicate how much natural gas was being produced per day.

MWD  Measure While Drilling equipment uses "real time" sensing equipment that is placed near the drill bit in the drilling assembly. It monitors the angle and azimuth (compass direction) that the well is being drilled in. MWD technicians can take periodic surveys (usually when a connection is made) to give the directional driller information on how the well is being directed.

NGL  An abbreviation for Natural Gas Liquids.  These include components of natural gas such as ethane,  propane, butane and ethane which can be liquefied at low temperature and which are typically more valuable than methane when sold to refineries.

Pearsall Shale  A  Cretaceous age geologic formation which lies approximately 2,000' below the  Eagle Ford Shale in South Texas.  The Pearsall shale is currently being explored by several companies, including EOG Resources and Chesapeake,  who are drilling exploratory wells to determine if the formation holds similar potential to the Eagle Ford Shale in terms of producing oil and gas.

Possum Belly. On a drilling rig, an open tank where drilling fluid and cuttings return to after coming up from downhole. From the possum belly the fluid enters the shale shakers, which remove the cuttings so the fluid can be re-circulated again.

Proppant Typically fine to medium grained quartz sand or a synthetic material. This is pumped into Eagle Ford Shale wells during the hydraulic fracturing or fracing process. Proppant stays in the formation to hold tiny cracks and channels open and allows oil and gas to flow out around the material. Frac sand is hauled to the Eagle Ford Shale from as far away as Minnesota, where it is mined from stratas of sand which have the ideal properties required for use in oil and gas wells, namely resistance to crushing at extreme pressure and a spherical shape. The two main types of frac sand used in the Eagle Ford Shale are Brady Brown (from the hill country of Texas) and Ottawa White, from states such as Minnesota.

PPE  Personal Protective Equipment refers to protective clothing, eye-wear, shoes, gloves and other items worn by workers in the oil field to protect them from injury. The typical PPE which is required of all employees on a modern drilling rig consist of ANSI approved safety glasses, steel toe boots, flame retardant clothing, ear plugs and a hard hat.

Pumper  An oilfield gauger who checks on producing wells and maintains production equipment. Gaugers or pumpers prepare oil for sale by removing sediment and water (BS&W,) keep pumpjacks, compressors and other equipment running and file production reports on the amount of oil and natural gas produced by each well they are responsible for. Contract pumpers are self employed and do contract gauging work for oil and gas companies, while other pumpers work as direct employees of oil companies.

Rat Hole - Rathole  This term can refer to a couple of things. It can mean a storage place for the Kelly which has been made in the rig floor using heavy piece of steel pipe or casing. It can also mean an extra length of hole drilled at the end of the well to allow logging tools to be able to fully analyze all of the wellbore and for other reasons related to well completion.

Royalty - Royalties  Does not refer to new "shaleionaires" but rather the percentage of proceeds from the sale of oil and gas from a well that the mineral rights owner receives. Royalty percentages in some South Texas oil leases are as high as 27%.

Seismic Survey  This refers to a geophysical survey in which vibrations are produced on the surface using specialized equipment and explosive charges. Those vibrations are then recorded using geo-phones which are placed over a large area of ground and connected by seismic cables. The recordings from these vibrations are then analyzed by geoscientists who use them to create a 3-D model of underground rock formations and pockets of oil and gas.  Most seismic surveys done nowadays utilized three-dimensional or 3-D technology which gives petroleum geologists a better picture of underground oil and gas reservoirs.

Sand King  These  consist of hoppers, conveyor belts and other equipment that handle frac sand that is brought to the well location by truck. Frac sand is used as a "proppant"  in hydraulic fracturing. It helps keep the tiny fractures which are created by high-pressure water open, so that oil and gas can seep out.

Source Rock  Sedimentary rock, such as shale, which has a high TOC (Total Organic Conent) is believed to be the "mother rock" or source of hydrocarbons found in most of the world's major oilfields. The Eagle Ford Shale is believed to be the "source rock" for much of the oil found in South and Eastern Texas.

TVD  Refers to True Vertical Depth, or the actual depth of any part of the wellbore.  (TVD is usually measured from the rig's RKB or rotary kelly bushing elevation.)

Wet Gas  Natural gas that contains high amounts of valuable hydrocarbons such as ethane and propane. (See NGL.)

Wildcat Well  A well listed as "exploratory" with the Texas Railroad Commission, not drilled in part of a known oilfield. Wildcat wells typically refer to wells that are drilled with the purpose of evaluating a specific zone or several zones, and not part of infill drilling between existing wells in a field.

Worm  A new oilfield employee with little or no experience under their belt.

WTI West Texas Intermediate is a grade of crude oil, along with LLS (Light Louisiana Sweet) and Brent Crude. Eagle Ford Shale oil typically trades at a price somewhere between WTI and LLS. WTI prices do not necessarily reflect the quality of crude oil, but rather reflect the "landlocked" nature of oil which is produced in areas such as the Permian Basin, far from coastal shipping and refining areas.

Volatile Oil Window  Area of the Eagle Ford Shale, (located updip from deeper dry gas zone) between dry gas zone and heavy or "black oil" window of the play which is productive of "volatile oil." Light oil and condensate, which typically has an API gravity of 45-60 Degrees, is considered to be "volatile oil."

Zipper Frac Also called "Simul-Frac". Adjacent wells are fraced either simultaneously or alternating, in sequence. By applying pressure on the formation in an adjacent well while the other is fraced, more impact is seen from the frac job on the desired rock.

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If you have any terms you would like to add to the shale drilling terms dictionary, please contact us.


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