Terminology Series   K

Working within the Oil and Gas space will introduce you to a host of industry-specific vocabulary and new terminology.

This piece focuses on the letter "K", and some words associated with the upstream sector.

Kaolinite: A clay mineral that forms through the weathering of feldspar and mica group minerals. Unlike some clay minerals, kaolinite is not prone to shrinking or swelling with changes in water content.

Karst: A type of topography formed in areas of widespread carbonate rocks through decomposition. Typical features of karst topography include sink holes, caves and pock-marked surfaces.

Kelly: A long square or hexagonal steel bar hollowed out in the middle to make way for a fluid path. The Kelly is used to transmit rotary motion from the Rotary Table or the Kelly Bushing to the Drillstring, whilst allowing the Drillstring to be lowered or raised during rotation. The Kelly goes through the Kelly Bushing, which is driven by the Rotary Table, and turns the entire Drillstring because it’s screwed into the top of the Drillstring itself.

Kelly Bushing: Sometimes known as “Drive Bushing”, this is a tool that serves to connect the Rotary Table to the Kelly. The Kelly Bushing tool’s inside profile matches the Kelly’s outside profile, so that the Kelly can move up and down inside the tool. The rotary motion from the Rotary Table is transmitted to the Bushing through large steel pins, and then to the Kelly itself through the flat surfaces between the Kelly and the Kelly Bushing.

KB: Depth measurements are commonly referenced by “KB”, such as 5,000 ft KB, meaning 5000 feet below the Kelly Bushing.

Drillstring: the combination of the drillpipe, the bottomhole assembly and any other tools used to make the drill bit turn at the bottom of the wellbore.

Rotary table: A drill floor with spinning sections that are used to transmit power and rotary motion through the Kelly Bushing to the Drillstring.

Key-seat: A small-diameter channel worn into the side of a larger diameter wellbore. Often this results from a sharp change in direction of the wellbore, or if a hard formation ledge is left between softer formations that then enlarge over time. The diameter of the channel is generally similar to the diameter of the drill pipe, which causes problems for the larger diameters of drilling tools such as tool joints, drill collars and bits, as they unable to pass through the channel and may become stuck in the key-seat. Preventive measures include ensuring that any turns in the wellbore are gradual and smooth. The solution to key-seating is to enlarge the worn channel so that the larger tools will fit through it.

Kill line: A high-pressure pipe connecting the mud pump and the well, through which drilling fluid can be pumped into the well to control a threatened blowout. During well control operations, kill fluid is pumped through the drillstring and annular fluid is taken out of the well through the choke line, which controls the fluid pressure. If the drillpipe is inaccessible, it may be necessary to pump heavy drilling fluid into the top of the well, wait for gravity to force the fluid to fall, and then remove fluid from the annulus, via both the kill line and choke line. The kill line also provides a measure of redundancy for the operation. In floating offshore operations, the choke and kill lines exit the subsea BOP stack and run along the outside of the riser to the surface.

BOP stack: is one of two or more units which control well pressure, and contain the wellhead and blowout preventers.

Choke: used to control fluid flow rate or downstream system pressure. Chokes have varying configurations -adjustable chokes enable the fluid flow and pressure parameters to be changed to suit process or production requirements.

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