Horizontal Directional Drilling: Utility and Pipeline Applications

Appendix F: Glossary

A-C

annuls:
In drilling, the annulus refers to the place that surrounds the drill pipe and is enclosed by the borehole wall.
API:
American Petroleum Institute.
ASTM:
American Society for Testing and Materials.
azimuth:
Horizontal direction expressed as an angle measured clockwise from any meridian. In drilling, azimuths are typically measured from magnetic north.
barite:
Natural barium sulfate used for increasing the density of drilling fluids.
barrel reamer:
An enclosed cylindrical soft soil reaming tool with cutting teeth and fluid nozzles arrayed on the end faces. Barrel reamers may be designed with specific buoyancies to aid in borehole enlargement.
bedding plane:
Any of the division planes that separate the individual strata or depositional layers in sedimentary or stratified rock.
bent sub:
A short threaded piece of pipe manufactured with an axial offset or angel. In directional drilling, a bent sub is used to produce a leading edge asymmetry in a nonrotating directional drill string.
bentonite:
Colloidal clay, composed primarily of montmorillonite, that swells when wet. Because of its gel-forming properties, bentonite is a major component of drilling mud.
bentonite extenders:
Group of polymers that can maintain or increase the viscosity of bentonite while flocculating other clay solids in the mud. With bentonite extenders, desired viscosity can often be maintained using only half the amount of bentonite that would otherwise be required.
bottom hole assembly (BHA):
The combination of bit, downhole motor, subs, survey probe, and non magnetic collars assembled...

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