Field Glossary

Top element of a BOP stack; a rubber sealing element that closes around pipe of nearly any size or on open hole.

Bottom Hole Assembly. Everything below the drill collars — bit, stabilizers, MWD tools, motors.

BOP rams that seal a fully open hole (no pipe present) using flat steel faces.

Blowout Preventer. High-pressure valve system on the wellhead that seals the well in an emergency.

Basic Offshore Safety Induction & Emergency Training. Mandatory for offshore work, includes HUET.

Piping that allows controlled circulation of fluid out of the well while the BOP is closed.

The operating oil company's on-site representative with final authority on well decisions.

Works the monkey board high in the derrick, guiding pipe stands and managing mud systems.

Specialist who steers the bit along a planned trajectory using MWD tools and downhole motors.

Measure of how sharply a wellbore curves, in degrees per 100 ft. Excessive DLS increases torque/drag.

The winch system on the rig that raises and lowers the drill string via the traveling block.

Heavy thick-walled pipe in the BHA that provides weight on bit (WOB).

Equivalent Circulating Density. Effective mud weight while pumping, including annular friction losses — always higher than static mud weight.

The pressure at which a formation cracks and drilling fluid is lost into the rock. Upper limit of the mud weight window.

Hydrogen sulfide — a toxic, flammable gas found in sour formations. Extremely dangerous even in small concentrations.

Helicopter Underwater Escape Training. Core component of BOSIET for offshore workers.

Heavy Weight Drill Pipe. Thicker-walled transition pipe between drill pipe and drill collars.

Initial Circulating Pressure. The standpipe pressure held at the start of a kill circulation.

International Well Control Forum — issues globally recognized well control certifications, Levels 2-4.

The square or hexagonal pipe historically used to transmit rotation from the rotary table to the drill string; largely replaced by top drives on modern rigs.

An influx of formation fluid into the wellbore, caused by formation pressure exceeding hydrostatic pressure.

The mud weight required to exactly balance formation pressure after a kick — the target weight for well control operations.

The calculation worksheet used during well control to document kick data and the pump schedule for killing the well.

Leak-Off Test. Pumps fluid into the well after each casing shoe to determine fracture gradient.

Logging While Drilling. Real-time formation evaluation data (resistivity, density, gamma ray) transmitted during drilling.

The derrick platform, typically 90-100 ft up, where the derrickman works during tripping operations.

Analyzes drill cuttings and gas shows in real time to identify formation changes and hydrocarbon indications.

Measurement While Drilling. Downhole tools transmitting directional data to surface via mud pulse telemetry.

Offshore Installation Manager. Overall command authority for an offshore installation and its personnel.

The margin by which hydrostatic pressure exceeds pore pressure. Typical safe range: 200-500 psi.

Polycrystalline Diamond Compact bit — synthetic diamond cutters in a shearing action, the dominant bit type today.

BOP rams that close around a specific pipe diameter, sealing the annulus while pipe remains in the hole.

Pull Out Of Hole / Run In Hole — tripping the drill string to surface or back into the wellbore.

The pressure of fluids within reservoir rock pores. Normal gradient roughly 0.433-0.465 psi/ft.

Rig floor crew member who makes up and breaks out pipe connections. Also called a floorhand.

Entry-level general labor position — cleaning, painting, moving equipment. No prior experience required.

Rate of Penetration. How fast the bit is drilling, in ft/hr. A sudden increase is called a drilling break.

Emergency BOP rams that cut through drill pipe and seal the well simultaneously.

Shut-In Casing Pressure. Recorded on the casing side after shutting in on a kick.

Shut-In Drill Pipe Pressure. Directly reflects excess formation pressure above hydrostatic after shut-in.

Overall supervisor of the drilling contractor's rig operations, managing all crews, tools, and equipment.

Motor system that rotates the drill string, allowing continuous rotation while adding stands — replaced the kelly on most modern rigs.

Gas entering the wellbore when pulling the string out of hole due to the swab effect. Monitored by the mud logger.

Weight on Bit. The portion of drill collar weight applied to the bit to create cutting force.