glossary

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Barrels of oil per day	A barrel of oil is a measure of capacity and corresponds to 42 US gallons or around 159 litres and works as a common unit of measurement for the daily volume of crude oil produced by a well or from a field.

Basin	A depression in the crust of the Earth, caused by plate tectonic activity and subsidence, in which sediments accumulate. If rich hydrocarbon source rocks occur in combination with appropriate depth and duration of burial, then a petroleum system can develop within the basin. Most basins contain some amount of shale, thus providing opportunities for shale gas or shale oil exploration and production (see oil production).

Bcf	Abbreviation for billion cubic feet, a unit of measurement for large volumes of natural gas.

Bending stiffness	The resistance to axial bending of a drill collar (expressed in Nm/Rad or ft-lb/degree of deflection). It is equal to the bending moment required to produce a unit deflection of a collar when one end is fixed. This value is supplied to drilling engineers for the comparison of the angle building characteristic of an MWD drill collar to that of a standard API drill collar.

Bit run	The amount of footage made by a bit. It may also mean one trip in the well with the drill string. Typically, the driller will sequentially number all bit runs.

Bitumen	Bitumen is a designation for a hydrocarbon fluid with a gravity of 10° API or lower. It is the fraction of naturally occurring, inflammable organic matter that is extractable from rock using organic solvents. Many petroleum precursors are composed of bitumen, but most are formed from kerogen in the process of petroleum generation. Bitumen includes hydrocarbons such as asphalt and mineral wax.

Blowout	An uncontrolled flow of fluid from a well. See also blowout preventer.

Blowout Preventer (BOP)	A blowout preventer is a large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. By closing this valve (usually operated remotely), the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to open the BOP and retain pressure control of the formation. See also blowout.

Borehole	The wellbore itself, including the open hole or uncased portion of the well.

Bottomhole assembly (BHA)	The portion of the drilling assembly below the drill pipe. The bottomhole assembly (BHA) typically consists of drill collars, stabilizers and drilling tools (i.e. mud motor and MWD) and the bit.

Bottomhole temperature (BHT)	The temperature of the formation at the total depth of the well at the time of the activity being performed on the well (e.g. drilling, producing (see oil production), injecting, logging (see log)). This is not necessarily the true temperature of the formation. The bottomhole temperature (BHT) is given in degree Fahrenheit or degree Celsius.

Brownfield	An oil or gas accumulation that has matured to a production plateau or even progressed to a stage of declining production (see depletion). Operating companies seek to extend the economic producing life of the field using cost-effective, low-risk technologies. Stimulation or refracturing operations (see hydraulic fracturing), completing (see completion) additional zones, and installing artificial lift equipment are a few technologies commonly applied in brownfields before any drilling options are attempted.

Bubble point pressure	Bubble point pressure is that pressure measured at a reservoir temperature below which hydrocarbon gas will exist along with hydrocarbon liquid. At discovery, all petroleum reservoir oils contain some natural gas in solution. Often the oil is saturated with gas when discovered, meaning that the oil is holding all the gas it can at the reservoir temperature and pressure, and that it is at its bubblepoint. Occasionally, the oil will be undersaturated. In this case, as the pressure is lowered, the pressure at which the first gas begins to evolve from the oil is defined as the bubblepoint.

Build angle	The rate of increase in inclination of a wellbore. This is sometimes expressed as Rate-of-Build (ROB) and expressed in degrees/unit length, often degrees/100 ft or similar length. Bottomhole assemblies (BHA) are designed to either build, hold, or drop angle as the well is drilled. Some BHAs, when combined with drilling motors, are designed to turn in a desired direction.