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  • Back-off

    the action of securing a section of drill-pipe while another is unscrewed from it.


    unit of pressure. One bar is equal to .987 standard atmospheric pressure, or 14.5 pounds per square inch


    a non-self-propelled vessel used as a base for drilling equipment, to carry cranes, support facilities, accommodation modules, etc., to lay underwater pipelines or to transport crude oil or its products over short distances.

    Barrel (bbl)

    the unit of volume measurement used for petroleum and its products; 1 barrel = 42 US gallons, 35 imperial gallons (approx), or 159 litres (approx): 7.3 barrels = 1 ton (approx): 6.29 barrels = 1 cubic metre.

    BCF (bcf)

    billion cubic feet of natural gas.

    BCM (bcm)

    billion cubic metres.


    barrels of condensate per day (from a gas well)


    below drill floor. Depth reference


    a geological term describing a stratum (layer of sediments or sedimentary rock) of considerable thickness and uniform composition and texture.


    the simplest aromatic compound with a ring of six carbon atoms; one of the most important feedstocks for the chemical industry.


    bottom hole pressure


    see drill bit.


    the subdivision of a nation's exploration and production acreage. Blocks are generally defined in terms of latitude and longitude, at one-degree intervals.

    Block number

    the number assigned to a particular licence block or subdivision thereof in a given national sector of the continental shelf.


    a method of producing a gas/condensate reservoir by letting the reservoir depressure over time without re-injecting any gas. With this method of production some condensate may condense within the reservoir, where its recovery is no longer a practical proposition.


    the situation that occurs when gas, oil or salt water escapes in an uncontrolled manner from a well due either to a release of pressure in the reservoir rock that the various containment systems fail to check or to the failure of the containment systems during production.

    Blowout preventor (BOP)

    a hydraulically operated wellhead device designed to ensure that a blowout cannot occur.

    BOE (Barrel oil equivalent)

    a term frequently used to compare gas with oil and to provide a common measure for different quality gases. It is the number of barrels of stabilised crude oil which contains approximately the same amount of energy as the gas: for example: 5.8 tcf (of lean gas) approximates to 1 billion boe.

    BOPD (bopd)

    in production terms, the number of barrels of oil produced from a well over a 24 hour period, normally an average figure from a longer period of time.


    the wellbore, with or without casing. See open hole.

    Bottomhole assembly (BHA)

    the lower end of the drill string comprising the drill bit, drill collars, heavyweight drill pipe and ancillary equipment.

    Bottomhole money

    Contribution to a joint-venture well, payable only if a specified horizon is reached.

    Bottoms up

    One complete circulation. When a drilling break is seen it may be decided to circulate 'bottoms up' (ie., all sample out of the hole) prior to proceeding.

    Bourdon gauge

    an instrument for measuring the pressure of steam or other gases.

    Brent blend

    a blend of North Sea crudes, used as an international marker for crude oil pricing.

    Bridge plug

    Packer run into the hole on drillpipe or wireline and left in the hole to seal it. Can be used while the B.O.P. is being changed or a seat for cement when abandoning the well. Some types can be retrieved and reused; others are drilled up after use or abandoned in the hole.

    Btu or British Thermal Unit

    the quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit. The value of a natural gas is governed by its 'Btu value'.


    abbreviation of the aromatic hydrocarbons, benzene, toluene and xylene.


    the lowest series of formations laid down during the Triassic Period of geological time; it includes sandstones that sometimes contain hydrocarbon


    a hydrocarbon consisting of four carbon atoms and ten hydrogen atoms. Normally a gas, but easily liquified for transport and storage; used in gasolines and for cooking and heating. See also LPG.


    Barrels of water per day

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