DEFINITIONS AND GLOSSARY OF TERMS Abandon a well (v): to stop drilling or production operations when it becomes unprofitable. A wildcat may be abandoned after poor results from a well test. Cement plugs are placed in the well bore to prevent fluid migration between different zones. Abnormal pressure (n): a formation pressure that deviates from the normal formation fluid hydrostatic pressure. Such pressures may be classified as "subnormal" (lower than normal) or "overpressured" (higher than normal). Accelerometer (n): a surveying instrument that measures components of the Earth's gravitational field. Acidize (v): to apply acids to the walls of oil and gas wells to remove any material that might obstruct flow into the wellbore. Adjustable choke (n): a choke in which a conical needle and seat vary the rate of flow. Air drilling (n): a method of rotary drilling that uses compressed air as the circulating medium. Angle unit (n): the component of a survey instrument used to measure inclination. Annular preventer (n): a large BOP (q.v.) valve that forms a seal in the annular space between the wellbore and the drill pipe. It is usually installed above the ram type preventers in the BOP stack. Annulus (n): the space between the drill string and the wellbore in open hole or cased hole. Anticline (n): a configuration of folded and stratified rock layers in the shape of an arch. Often associated with a trap. API (abbr): American Petroleum Institute. The leading standardizing organization on oilfield drilling and production equipment. 225 226 DIRECTIONAL DRILLING API gravity (n): a measure of the density of liquid petroleum products, expressed in degrees. It can be derived from the following equation: API gravity (degrees) = .141.5. - 131.5 specific gravIty Azimuth (n): used in directional drilling as the direction of the wellbore measured in degrees (0-359) clockwise from True North or Magnetic North. Back otT (v): to disconnect a string of pipe by unscrewing one threaded piece from another. Back pressure (n): the pressure maintained on equipment or systems through which a fluid flows. Back up (v): (1) to hold one section of pipe while another is being screwed into or out of it (as in back up tongs); (2) a piece of equipment held in reserve in case another piece fails. Badger bit (n): a specially designed bit with one large nozzle that can be used as a deflecting tool in soft formations (jet deflection bit). Baffte plate (n): a replaceable metal ring inserted in the BHA (q.v.) to act as a landing collar for a survey tool. Bail (n): a rounded steel bar that supports the swivel and connects it to the hook. May also apply to the steel bars that connect the elevators to the hook (links). Ball up (v): to collect a mass of sticky material (drill cuttings) on compo­ nents of drill string (especially bits and stabilizers). Barge (n): a flat-decked, shallow draft vessel that might accommodate a drilling rig or be used to store equipment materials or for living quarters. Barite (baryte) (n): barium sulphate (BaS04), a mineral used as a weighting material to increase mud weight (specific gravity = 4.2). Barrel (n): a measure of volume for fluids. One barrel (bbl) = 42 US gallons = 0.15899 cubic metres. Bearing (n): (1) a machine part that supports loads and allows other components to turn or slide; (2) used synonymously with azimuth or direction. Bed (n): a geological term to specify one particular layer of rock. Ball nipple (n): the uppermost component of the marine riser attached to the telescopic joint. The top of the nipple is expanded to guide drilling tools into the well. Bentonite (n): a finely powdered clay material (mainly montmorillonite) that swells when mixed with water. Commonly used as a mud additive, and sometimes referred to as "gel". Bent sub (n): a short piece of pipe whose axis is deviated 1-30 off vertical. Used in directional drilling as a deflecting tool. The scribe line on the inside of the bend defines the toolface. BHA (abbr): bottom hole assembly. DEFINITIONS AND GLOSSARY OF TERMS 227 Bit (n): the cutting element at the bottom of the drill string used for boring through the rock. Bit breaker (n): a heavy metal plate that fits into the rotary table and holds the bit while it is being made up or broken out of the drill string. Bit record (n): a report on each bit after it has been pulled out of the hole, containing details of its performance. Bit sub (n): a short length of pipe installed immediately above the bit. Bit walk (n): the tendency for the bit to wander off course by following the direction of rotation (usually to the right). Blind rams (n): an integral part of the BOP (q.v.) stack, designed to close off the wellbore when the drill string is out of the hole. Blocks (n): an assembly of pulleys on a common framework. Blooey line (n): the discharge pipe from a well being drilled with compres­ sed air. It carries the cuttings and reduces fire risk. Blow-out (n): an uncontrolled flow of formation fluids into the atmosphere at surface. BOP (abbr): blow-out preventer. One of several valves installed at the wellhead to control pressure in the event of a kick. A BOP has a full opening bore to allow drilling equipment and tools to pass through. BOP stack (n): a unitized assembly of BOPs consisting of annular preven­ ters and ram type preventers. For land drilling, the BOP stack is installed just below the rig floor; for floating rigs, the stack is positioned on the seabed. Borehole (n): the hole made by the drill bit. Bottom hole assembly (BHA) (n): the part of the drill string that is below the drill pipe. It usually consists of drill collars, stabilizers and various other components. Bottom hole pressure (bhp) (n): the pressure at the bottom of the borehole, or at a point opposite the producing formation. Box (n): the female section of a tool joint. Brake (n): the device operated by the driller to stop the motion of the draw-works. Break-out (v): to unscrew one section of pipe from another. Bridge (n): an obstruction in the borehole usually caused by caving in of an unstable part of the wall. BRT (abbr): below rotary table. Reference point for measuring depth. Buck up (v): to tighten up a threaded connection. Building assembly (n): a BRA (q.v.) specially designed to increase drift angle. Build-up rate (n): the rate at which drift angle is increasing as the wellbore is being deviated from vertical. Usually measured in degrees per 100 ft drilled. Build-up section (n): that part of the wellbore's trajectory where the drift angle is increasing. 228 DIRECTIONAL DRILLING Bumper sub (n): a drilling tool consisting of a short stroke slip joint that allows a more constant WOB when drilling from a floating rig. By-pass (n): a route through which fluid can be pumped around a valve or other control mechanism (e.g. packer). Cable-tool drilling (n): an earlier method of drilling used before the introduction of modern rotary methods. The bit was not rotated but reciprocated by means of a strong wire rope. Caliper log (n): a tool run on wireline that measures the diameter of the wellbore. It may be used for detecting washouts, calculating cement volumes, or detecting internal corrosion of casing. Cap rock (n): an impermeable layer of rock overlying an oil or gas reservoir and preventing the migration of fluids. Cased hole (n): that part of the hole supported by a casing that has been run and cemented in place. Casing (n): large-diameter steel pipe used to line the hole during drilling operations. Its purpose is to prevent the borehole from caving in, and to provide a means of producing the well. Casing head (n): a heavy flanged connection that is installed on top of a casing string. Once it is installed, it provides a housing for the next casing string, which is suspended from it. Also called a spool. Casing hanger (n): a special component made up on top of the casing string to suspend the casing when it is landed in the previous casing housing. Casing shoe (n): a short section of steel filled with concrete and rounded at the bottom. This is installed on the bottom of the casing string to guide the casing past any ledges or irregularities in the borehole. Sometimes called a guide shoe. Casing string (n): the entire length of all the casing joints run into the borehole. Several different sizes of casing string may be required. Cathead (n): a spool-shaped attachment on a winch around which rope is wound. This can be used for hoisting operations on the rig floor. Caving (n): collapse of the walls of the borehole. Also referred to as "sloughing" . Centralizer (n): a device secured around the casing at set intervals to centre the pipe in the hole. Centrifugal pump (n): a pump consisting of impellor, shaft and casing, which discharges fluid by centrifugal force. Often used for mixing mud. Centrifuge (n): an item of solids control equipment that separates out particles of varying density. Cementing (n): the application of a liquid slurry of cement and water to various points inside or outside of the casing. Primary cementing is carried out immediately after the casing is run. Secondary cementing is carried out when remedial work is required. Cement channelling (n): the creation of voids in the cement between the casing and the borehole, thereby reducing the effectiveness of the cement bond.