Glossary
Browse the IADC Lexicon alphabetically or by category. Get comprehensive definitions of drilling industry terms.
Sub
Definition(s)
Sub
Short, threaded piece of pipe used to connect parts for the drilling assembly for various reasons, such as crossing over to a different connection, or to save wear and tear on more expensive elements. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsStraight Sub
Definition(s)
Straight Sub
Sub with no outside diameter change. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsStabilizer
Definition(s)
Stabilizer
Member of the drill stem assembly used to centralize or control the direction of the bottom-hole assembly. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsNippling Down
Definition(s)
Nippling Down
The process of removing well-control or pressure-control equipment such as a BOP system. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsND
Definition(s)
ND
Nippling down. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsNAF
Definition(s)
NAF
Non-aqueous fluid. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMudline Suspension Wells
Definition(s)
Mudline Suspension Wells
A well drilled using a mudline suspension system and a surface blowout preventer (BOP). The mudline suspension well may be completed as either a surface well or as a subsea well. Source: API RP 90, Annular Casing Pressure Management for Offshore Wells, Upstream Segment. First Edition, August 2006. Global StandardsMudline Suspension Wells
A well drilled using a mudline suspension system and a surface BOP. The mudline suspension well may be completed as either a surface well or as a subsea well. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMudline Suspension System
Definition(s)
Mudline Suspension System
A casing suspension system that allows a well to be drilled using a surface BOP, surface wellhead and surface drilling equipment. The mudline suspension equipment provides for individual casing hangers to be installed with each casing string that interconnects with each other at a preset point below the mudline. The mudline suspension casing hangers do not provide a pressure barrier. After the well is drilled and cemented, these casing hangers allow for the removal of the casing string between the casing hanger and the surface wellhead. After these strings are removed, a cap can be placed over each casing string, isolating each casing string and the annular space between it and the previously capped casing string inside, at the casing hanger interface. These wells are tied back prior to the well completion in one of two methods: 1. Individually connecting two or more tie back casing production riser strings back to a surface casing head, tubing head/tubing hanger, and christmas tree (mudline surface well). Each string has its own tie-back connector, which provides a structural and pressure-containing connection between the casing strings below the mudline and the tie-back casing production riser string from the seafloor up to the surface. See Figure 13.1.3 in Appendix C. 2. Individually connecting two or more tie-back casing strings back to a subsea tubing head, using individual tie back connectors, followed by the installation of a subsea tubing hanger and subsea tree (mudline conversion well or mudline subsea well). See Figures 13.4.1 through 13.4.9 in Appendix C. Source: API RP 90, Annular Casing Pressure Management for Offshore Wells, Upstream Segment. First Edition, August 2006. Global StandardsMudline Suspension System
Drilling system consisting of a series of housings used to support casing strings at the mudline, installed from a bottom-supported rig using a surface BOP. Source: API SPEC 17D, Design and Operation of Subsea Production Systems—Subsea Wellhead and Tree Equipment, Upstream Segment, Second Edition May 2011 (Errata September 2011). Global StandardsMudline Suspension System
A casing suspension system that allows a well to be drilled using a surface BOP and wellhead. The mudline suspension equipment provides for individual casing hangers to be installed with each casing string that interconnect with each other at a preset point below the mudline. The mudline suspension casing hangers do not provide a pressure barrier. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMudline Packoff or Packer
Definition(s)
Mudline Packoff or Packer
An upper packer run on the production tubing and set in the production casing below the mudline wellhead to isolate the production riser section from the production casing. This configuration is common in hybrid wells. Source: API RP 90, Annular Casing Pressure Management for Offshore Wells, Upstream Segment. First Edition, August 2006. Global StandardsMudline Packoff or Packer
An upper packer run on the production tubing and set in the production casing below the mudline wellhead to isolate the production riser section from the production casing. These mechanical barrier devices are commonly installed in hybrid wells. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMudline
Definition(s)
Mudline
Mudline as referenced in subsea operations refers to the seafloor. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMLSH
Definition(s)
MLSH
Mud line suspension hanger. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMechanical Barrier
Definition(s)
Mechanical Barrier
A subset of physical barriers that features mechanical equipment; not set cement or a hydrostatic fluid column. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMechanical barrier
Subset of physical barriers that features engineered, manufactured equipment. NOTE Does not include set cement or a hydrostatic fluid column. EXAMPLES Permanent or retrievable bridge plugs, downhole packers, wellhead hanger seals, and liner hanger seals. Source: API RP 96, Deepwater Well Design and Construction, First Edition, March 2013. Global StandardsMeasurement While Drilling (MWD)
Definition(s)
Measurement While Drilling (MWD)
The measurement of physical properties while drilling, such as pressure, temperature and borehole trajectory, by tools installed in the BHA. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMD
Definition(s)
MD
Millidarcy. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsMD
Measured depth. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global Standards Source: NORSOK D-010, Well integrity in drilling and well operations, Rev. 3, August 2004. Global StandardsMaximum Allowable Wellhead Operating Pressure (MAWOP)
Definition(s)
Maximum Allowable Wellhead Operating Pressure (MAWOP)
The maximum allowable operating pressure for a particular annulus, measured at the wellhead relative to ambient pressure. It applies to SCP, thermal casing pressure and operator-imposed casing pressure. Source: API RP 90, Annular Casing Pressure Management for Offshore Wells, Upstream Segment. First Edition, August 2006. Global StandardsMaximum Allowable Wellhead Operating Pressure (MAWOP)
The maximum allowable operating pressure for a particular annulus, measured at the wellhead relative to ambient pressure. It applies to SCP, thermal casing pressure, pressure from a well control event and operator imposed casing pressure. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsLoss of Well Control (LWC)
Definition(s)
Loss of Well Control (LWC)
A loss of well control incident is an uncontrolled flow of subterranean formation fluids such as gas, oil, water, etc. and/or well fluids into the environment or into a separate underground formation, in which case it is called an underground blowout. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsLoss of Well Control
Loss of well control, as mentioned, means the failure of one or more well barriers [for instance reduction in drilling fluid head leading to influx from the wellbore is failure of well barrier (drilling fluid); this would require closure of the well with the help of BOP to bring the well back under control]. Source: Guidance Notes on Petroleum and Natural Gas (Safety in Offshore Operations) Rules, 2008, Oil Industry Safety Directorate (India), 2012. Regulatory GuidanceLoss of Well Control
Loss of well control as mentioned in the first subsection, means the failure of one or more well barriers. Source: Guidelines Regarding the Activities Regulations, Norway, updated December 2012. Regulatory GuidanceLoss of Well Control
Loss of well control is any incident that results in: • An uncontrolled release of formation or other well fluids • An uncontrolled flow between two or more exposed formations (this includes uncontrolled flow resulting from failures of either surface or subsurface equipment or procedures) or • A flow of formation or other well fluids through a diverter. Note: IRF (www.irfoffshoresafety.com/country/performance/scope.aspx). Source: Incident Reporting and Investigation Guidelines, The Canada-Nova Scotia Offshore Petroleum Board and Canada-Newfoundland and Labrador Offshore Petroleum Board, Canada, November 30, 2012. Regulatory GuidanceLogging While Drilling (LWD)
Definition(s)
Logging While Drilling (LWD)
The measurement of formation properties during the drilling of the borehole by logging tools installed in the BHA. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsLiner Top Packer
Definition(s)
Liner Top Packer (LTP)
A mechanical barrier device typically with flexible, elastomeric sealing elements that can be run into a wellbore with a smaller initial outside diameter that then expands externally to seal the annulus between the liner and the previously installed casing string. Liner top packers are also called liner packers. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsLiner Hanger
Definition(s)
Liner Hanger
A device used to attach or hang a liner from the internal wall of a previously set casing string. Conventional liner hangers are “hung” (connected to the last casing) by setting slips that grip against the inner wall of the previously set casing string. Expandable liner hangers are hung by external expansion of the hanger against the inner wall of the previously set casing string. Source: API STD 65 – Part 2, Isolating Potential Flow Zones During Well Construction, Upstream Segment, Second Edition, December 2010. Global StandardsQuality Programme
Definition(s)
Quality Programme
Established documented system for ensuring quality. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global Standards Source: API SPEC 17J, Specification for Unbonded Flexible Pipe, Third Edition, July 2008. Global StandardsQuality Programme
A documented set of activities, resources and events serving to implement the quality system of an organisation. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 4, Steel Unit Structures, June 2013, Lloyd’s Register, Global StandardsPitch
Definition(s)
Pitch
Axial distance between successive threads. NOTE In a single start thread, pitch is equivalent to lead. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsPitch
Nominal distance between two adjacent threads roots or crests. Source: API RP 17G, Recommended Practice for Completion/Workover Risers, Second Edition, July 2006 (Reaffirmed April 2011). Global StandardsPipe Body
Definition(s)
Pipe Body
Seamless steel pipe excluding upset and upset-affected areas. See Figure 1. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsPipe Body
Seamless pipe excluding upset and upset-affected areas. See Figure B.1. Source: API SPEC 5DP, Specification for Drill Pipe, First Edition, August 2009. Global StandardsPin Base
Definition(s)
Pin Base
Non-threaded area at the large end of the pin connection adjacent to the shoulder. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsPi Tape
Definition(s)
Pi Tape
Flexible steel tape that, when wrapped around the circumference of a cylinder, indicates the average outside diameter. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsMill Slot
Definition(s)
Mill Slot
Flat machined area on the outside diameter of a tool joint where grade, weight code and optional serial number information is stamped. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsMeasure
Definition(s)
Measure
Determining of dimensional value and recording of it on a worksheet. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsMeasure
Variable to which a value is assigned as the result of measurement. [SOURCE: ISO/IEC 15939:2007]- Note 1 to entry: The term “measures” is used to refer collectively to base measures, derived measures, and indicators.
Measure
Measures includes both plant and equipment (ie hardware) and also management systems (ie software). Source: Prevention of Fire and Explosion, and Emergency Response on Offshore Installations, Offshore Installations (Prevention of Fire and Explosion, and Emergency Response) Regulations 1995, Approved Code of Practice and guidance (UK HSE L65), Second Edition, 1997. Regulatory GuidanceMeasure
Measures has the same meaning as in paragraph 35. In the context of this regulation measures for control purposes include plant, equipment and workplace procedures. Examples are listed in the box below: ESD systems, ballast control system, vents and drains, emergency response procedures, ie sending key personnel to determine the appropriate actions, automatic isolation valves, blowdown and flare systems, portable fire-fighting equipment. Source: Prevention of Fire and Explosion, and Emergency Response on Offshore Installations, Offshore Installations (Prevention of Fire and Explosion, and Emergency Response) Regulations 1995, Approved Code of Practice and guidance (UK HSE L65), Second Edition, 1997. Regulatory GuidanceLead
Definition(s)
Lead
Distance parallel to the thread axis from a point on a thread turn and the nearest corresponding point on the next turn, i.e. the axial displacement of a point following the helix one turn around the thread axis. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsJar
Definition(s)
Jar
Mechanical or hydraulic device used in the drill stem to deliver an impact load to another component of the drill stem, especially when that component is stuck. Source: API RP 7G-2, Recommended Practice for Inspection and Classification of Used Drill Stem Elements, First Edition, August 2009. Global StandardsJar
A tool used to deliver an axial impact load to the downhole string.
Source:API SPECIFICATION 19TT, Specification for Downhole Well Test Tools and Related Equipment, First Edition, October 2016. Global Standards