Well Control Training & Assessment

Acronyms and Definitions

Please note: This document is still under development. Additions and

modifications may be made as various IADC workgroups complete their tasks.

Page 2 – Acronyms: The acronyms listed match those used in the question
database.

Page 4 – Definitions: The definitions listed relate to specific terminology used

throughout the IADC Well Control Standard, accompanying curricula and the
question database.
 IADC’s Well Control Training & Assessment

The following table lists Acronyms used in the WellCAP curricula and knowledge assessments.
Where there are common alternatives to an acronym, these alternatives have been written in
italics. For the purpose of the curriculum, they mean the same thing.

It is the intention to use only those bold acronyms in the exam question database.

Please note: Terms in italics are alternate acronyms common to the industry.

Acronym Term
API Std. American Petroleum Institute Standard
API RP American Petroleum Institute Recommended Practice
BBL or BBLS Barrel or Barrels
BHA Bottom Hole Assembly
BHP Bottom Hole Pressure
BOP Blow Out Preventer
BOPE Blow Out Preventer Equipment
BPM Barrels per Minute
CLF Choke Line Friction
CO2 Carbon Dioxide
DM Drillers Method
ECD Equivalent Circulating Density
EDS Emergency Disconnect System
EMW Equivalent Mud Weight
FCP Final Circulating Pressure
FIT Formation Integrity Test
FOSV Full Opening Safety Valve
H2S Hydrogen Sulfide
HCR High Closing Ratio
(HCV) (Hydraulically Controlled Valve)
HPHT High Pressure High Temperature
IBOP Inside Blow Out Preventer
ICP Initial Circulating Pressure
KLF Kill Line Friction
KOP Kick Off Point
KWM Kill Weight Mud
LCM Lost Circulation Material
LMRP Lower Marine Riser Package
LOT Leak Off Test
LWD Logging While Drilling
MAASP Maximum Allowable Annular Surface Pressure
(MACP) (Maximum Allowable Casing Pressure)
MAMW Maximum Allowable Mud Weight
MASP Maximum Anticipated Surface Pressure
MD Measured Depth
MGS Mud Gas Separator
MPD Managed Pressure Drilling
MW Mud Weight

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MWD Measurement While Drilling

NAF Non Aqueous Fluid
(OBM) (Oil based Mud)
(SBM) (Synthetic Based Mud)
NRV Non Return Valve
OIM Offshore Installation Manager
OMW Original Mud Weight
PWD Pressure While Drilling
PVT Pit Volume Totalizer
PI Pressure Increment
PPG Pounds Per Gallon
PSI Pounds per Square Inch
ROP Rate of Penetration
ROV Remote Operated Vehicle
RPM Revolutions per Minute (of drillstring)
RWP Rated Working Pressure
SCR Slow Circulating Rate
SCRP Slow Circulating Rate Pressure
SPR Slow Pump Rate
SICP Shut-in Casing Pressure or Shut in Choke Pressure
SIDPP Shut-in Drill Pipe Pressure
SIKLP Shut-in Kill Line Pressure
SPM Strokes per Minute
SPM (subsea
Sub-Plate Mounted
equipment only)
STK or STKs Stroke or Strokes
TVD True Vertical Depth
UBD Underbalanced Drilling
VBR Variable Bore Ram
WOB Weight on Bit
W&W Wait and Weight

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IADC Well Control Glossary of Terms

Reservoir pore fluid pressure that is greater than the
Abnormal Pressure hydrostatic pressure of a full column of water or brine with
salinity normally found in the local formation.
Part of the mud storage system that is an active part of the
circulation system. These pits are monitored for downhole
Active Pits losses and gains. The suction pit feeds the mud pumps and
returns from the well go to the return pit. In small systems,
both suction and return can be the same pit.
Abbreviation for American Petroleum Institute, a trade
association sponsored by the oil and gas industry and
API
recognized worldwide for setting industry standards and
recommended practices.
Annular Pressure Loss Pressure loss caused by the flow of fluid up the annulus. (Also
(APL) referred to as annular friction loss.)
A safety system that is designed to automatically shut-in the
wellbore in the event of a ‘disconnect’ of the LMRP. When
Autoshear
the Autoshear is engaged, disconnecting the LMRP closes the
shear rams.
A state of pressure differential between static or circulating
mud pressure on the formation compared to the formation
fluid pressure. Balance occurs when pressure exerted on the
Balance/Underbalance/ formation is equal to the formation fluid pressure.
Overbalance Underbalance occurs when the pressure exerted on the
formation is less than the formation fluid pressure.
Overbalance occurs when the pressure exerted on the
formation is greater than the formation fluid pressure.
Well ballooning is caused by the loss of drilling fluid into the
formation when the equivalent circulating density (ECD)
exerted on the wellbore is nearly equal to the formation
equivalent fracture pressure. When the pumps are turned off,
ECD is lost and the fluid returns to the wellbore from the
Ballooning
formation. The rate of return will vary with the formation and
the returning fluid may be contaminated with formation fluids.
At the surface, this process appears as losses while drilling and
gains during connections or trips. (Also referred to as wellbore
breathing, supercharging, or micro fracturing.)

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A single, dependent component or practice that contributes to

the total system reliability. Well barriers are used to isolate
Barrier (Barrier Element)
flow from the formation and reduce the risk associated with
drilling, production, and intervention activities.
Barrier System (Barrier One or several barrier elements that act in a series to prevent
Envelope) flow from the formation. (Also called a barrier envelope.)
Term used to describe soft sticky clay formations that stick to
Bit Balling the bit (and stabilizers) and impede drilling. The balling effect
can also increase swab and surge pressures.
The sum of all the pressures acting on the wellbore at total
Bottom Hole Pressure (BHP)
depth.
The circulation of the mud column, measured from the bottom
Bottoms-Up of the well to surface. Often referred to when collecting
samples or cleaning the wellbore before drilling ahead.
An uncontrolled exit of formation fluids at the surface or mud
Blowout
line.
A situation that can occur in an atmospheric mud gas separator
(MGS) when the pressure generated inside the separator and
associated vent line exceeds the hydrostatic pressure created
by fluid in the separator u-tube (dip tube). This can result in
Blow through
well fluids in the gaseous state being “blown through” the
MGS to the shale shaker area in a gaseous state. This affects
fluid properties and can be hazardous if the shale shaker area
is enclosed.
Document that aligns and co-ordinates the requirements and
responses of various parties in relation to a specific aspect of a
Bridging document
project. Commonly used to align and co-ordinate the
emergency response procedures for owner and contractors.
The venting of fluids to the surface or to the seabed through
Broaching
channels external to the casing.
An operation to determine Shut-In Drill Pipe Pressure that
Bumping float
cannot be determined until a ‘float’ in the drillstring is opened.
The effect of the mud density on the immersed weight of the
Buoyancy
drillstring.
A device with either a fixed or variable installed in a line to
Choke
restrict and control the flow of fluids and gas.
Circulating friction generated by circulating mud along the
Choke Line Friction
choke line. Same effect applies to the kill line.

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The pressure resulting from the restriction of flow

downstream. It occurs when fluid is forced through a small
opening or orifice (choke). Under dynamic conditions, the
Choke Pressure
choke pressure creates a surface pressure that is imposed on all
points in the circulating system, including the bottom of the
hole. (Also called back pressure.)
Activities that prepare a well for the initial production of oil
and gas; a flow path for hydrocarbons is established between
Completion the reservoir and the surface. Examples of completions include
open hole, cased hole perforated, single string, dual string, and
gravel packed completions or other purposes such as injection.
Any fluid used during completion or workover operations of
sufficient density to control formation pressure. Generally, it
Completion Fluids
is low solids or solids-free fluid to minimize formation
damage.
General term applied to non-aqueous fluids (oil or synthetic)
that exhibit a mud density increase with increasing pressure.
Compressible fluid
The result can be a greater hydrostatic pressure on bottomhole
than expected based on surface mud density measurements.
A term used to describe a number that is inserted into an
equation to convert elements of the equation to a common
Constant
unit. For example, 0.052 allows the different units of ppg and
feet to be used to calculate a pressure in psi.
An operation to close a float collar that has been held open
during the running of casing in the hole. Flow rate and
Converting the Casing Float
pressure are increased to the manufacturer’s recommended
Collar
level for releasing the auto-fill device and allowing the casing
float valve(s) to close.
Formation pieces that break away due to the action of the bit
teeth. Cuttings are screened out of the liquid mud system at the
Cuttings shale shakers and monitored for composition, size, shape,
color, texture, hydrocarbon content, and other properties by
the mud engineer, the mud logger, or other on-site personnel.
An inside blowout preventer that locates into a “dart-sub” at
Dart Valve the bottom of the drillpipe. (Also called a drop-in check
valve.)
A buried anchor or holding device installed in the ground to
which guy wires are attached to steady the derrick, mast,
Deadman
stacks. The “Deadman anchor” is a common term to define the
fixed end of the drilling line.

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A device attached to the wellhead or marine riser used to

direct flow away from the rig. A diverter, often used to control
Diverter
shallow flows, closes the vertical flow path and allows the
well to flow through a side outlet and diverter line.
Kill method that involves first circulation out the influx and
Driller’s Method
secondly circulation kill mud around the well.
A significant increase or decrease in the rate of penetration
that is sustained for an agreed number of feet. The “break”
Drilling Break will represent a change in formation downhole that may result
in losses or gains. Commonly used criteria include a 50%
change in rate of penetration sustained over 5 feet.
A liquid or slurry pumped down the drillstring and up the
annulus during the drilling operation. One function is to
provide sufficient differential pressure against exposed
Drilling Fluids
permeable formations. Drilling fluid can be air, gas, water, oil-
based, synthetic mud, or a combination of such. (Also called
mud.)
The difference between the maximum pore pressure and the
minimum effective fracture pressure. It can be determined for
Drilling Window
any point within an open-hole interval. Drilling margin is
usually expressed in terms of equivalent mud weight.
Well control drills carried out by crewmembers to ensure
positive and effective reaction to a well control situation. Pit
drill involves recognizing and reacting to a change in pit level.
Trip drill involves recognizing and reacting to a kick while
tripping. Strip drills allow the crew to practice stripping in or
Drills (Pit, Trip, Strip, out of the hole. Choke drills allow crewmembers to practice
Choke, Abandon, Diverter) choke operations with the well under pressure. Abandon drills
are generally a part of regular rig drill that involves evacuation
to a safe position (especially in the case of H2S) or to the
lifeboat stations (offshore). Diverter drills allow the rig floor
crew to practice diverting procedure and immediate following
actions.
A term that is used in a number of well control techniques that
Dynamic Kill uses circulating friction losses to maintain a back pressure on
the well that overcomes an “underbalanced” condition.
The effective density of the circulating fluid in the wellbore
Equivalent Circulating
resulting from the sum of the hydrostatic pressure imposed by
Density (ECD)
the static fluid column and the circulating friction pressure.

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Emergency Disconnect The operation of unlatching of the riser connector to separate

System (EDS) the riser and LMRP from the BOP stack.
A pressure exerted at a specific depth and expressed as density
Equivalent Mud Weight
of a static column of fluid that would create the same pressure
(EMW)
at that depth.
The calculated pumping pressure to achieve when circulated
Final Circulating Pressure
kill mud reaches the Bit. Used in the Wait and Weight method.
A technique used to establish ‘normal’ circulating conditions
and compare with current conditions to see if the well has any
Fingerprinting stability issues (flowing or losses). For example: measuring
flowback at connections to determine if well is ballooning or
kicking.
An observation performed on a static well to verify stable well
conditions, the integrity of a plug, valve or flow-control device
Flow Check
or to identify possible/suspected loss of hydrostatic
overbalance during well operations.
The application of pressure on the formation by superimposing
Formation Integrity Test
a surface pressure on a fluid column to verify the ability of a
(FIT)
subsurface zone to withstand a certain hydrostatic pressure.
The pressure exerted by fluids in the rock pore spaces.
Knowledge of formation pressure helps determine the
hydrostatic pressure and mud weight required to drill the well.
Formation Fluid Pressure
If the formation pressure is greater than the hydrostatic
(Pore Pressure)
pressure, formation fluids may flow into the well from
permeable formations. (Also called pore pressure, reservoir
pressure, or shut-in bottomhole pressure.)
The pressure exerted on a formation that causes the formation
to fracture and take fluid. The fracture may be permanent or
Fracture Pressure and
may close once pressure is released. The fracture gradient is
Fracture Gradient
the fracture pressure expressed in a gradient form, for example
psi/ft.
Drilling fluid that is contaminated with gas causing a reduction
Gas-Cut Mud
in the effective mud weight.
The upward movement of gas in the drilling fluid. Movement
Gas Migration
occurs due to gas being lighter than the drilling fluid.
Following shut-in on a subsea well, the pipe tool joint is
Hang-Off
suspended on a closed ram.

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A solid, crystalline compound of water and a low-boiling-

point gas (e.g., methane and propane), in which the water
Hydrate combines with the gas molecule to form a solid. They are
formed under reduced temperature and pressure conditions,
can impede fluid flow, and resemble snow or ice.
Pressure exerted by a column of fluid at rest. It increases
Hydrostatic pressure directly with the density and the depth of the fluid and is
expressed in pounds per square inch.
Drill pipe pressure required to circulate initially at the selected
Initial Circulating Pressure kill-rate; numerically equal to kill-rate circulating pressure
(ICP) plus closed-in drill pipe pressure. Minimum pressure needed to
maintain a constant BHP during well kill operations.
A device installed in the drillstring that acts as a check valve
Inside Blowout Preventer allowing drilling fluid to be circulated down the string but
(IBOP) prevents back flow. (Also called an internal blowout
preventer.)
An unplanned and unintended flow of formation fluids from
the reservoir into the wellbore. It occurs when the pressure
Kick
exerted by a column of fluid is less than the pressure exerted
by the formation fluids.
Is the difference between the maximum anticipated pore
Kick Intensity
pressure and current/planned mud weight.
A calculation used during well planning to determine the
maximum kick volume that can be taken into the well and
Kick Tolerance
circulated out without causing formation damage. Dependent
upon depth (usually the casing shoe), and kick intensity.
Drilling fluid with sufficient density to provide hydrostatic
Kill Weight Mud
overbalance and regain primary well control.
The time lapse that occurs between a surface pressure change
Lag Time on one side of a wellbore (u-tube) and the resulting pressure
change on the other side.
Application of incremental surface pressure on a fluid column
to determine the pressure at which the exposed formation
Leak Off Test (LOT) accepts fluid. Pressure is applied to a closed system and used
to determine the fracture strength of an open/exposed
formation.
A well control technique that replaces an influx, located
immediately below the BOP, with drilling fluid. It involves
Lube and Bleed
repeatedly pumping in small quantities of kill mud into the
well bore and then bleeding off excess pressure. It works on

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the principle that the heavier kill mud will sink below the
lighter well bore fluids and so bleeding off the pressure will
remove the latter leaving an increasing quantity of kill mud in
the well bore with successive steps.
An adaptive drilling process used to more precisely control the
Managed Pressure Drilling
annular pressure profile throughout the wellbore.
A calculated value for casing pressure that, if exceeded, may
Maximum Allowable
result in fluid loss to the formation at the casing shoe
Annular Surface Pressure
(formation fracture) or casing burst. (Also called maximum
(MAASP)
allowable casing pressure [MACP].)
Maximum Allowable Mud A calculation to determine the maximum allowable mud
Weight (MAMW) weight based on the leak off test data.
The highest pressure predicted to be encountered at the surface
of the well. In a “worst case” condition, this pressure
Maximum Anticipated
prediction is based upon formation pressure minus a wellbore
Surface Pressure (MASP)
filled with dry gas. It is used to determine casing design and
BOPE working pressure requirements.
Downhole tools that take specific measurements of formation
Measurement While Drilling
properties and relay the data to surface for analysis.
A device to measure the density of the drilling fluid. There are
Mud Balance
two main types: atmospheric and pressurized.
A test on a barrier element in which the hydrostatic pressure is
Negative Test reduced such that the net differential pressure direction is from
the formation into the wellbore.
An emulsion where the continuous phase is a water-
immiscible fluid (i.e., synthetic or mineral oil) and where
Non-Aqueous Fluid (NAF)
water (commonly brine) is the discontinuous, dispersed
internal phase.
Tool or tubular that is used in the well that cannot be sheared
Non-shearable
by the Shear Ram installed in the Blowout Preventer.
A fluid in which the continuous phase is a product obtained
Oil-Based Mud (OBM)
from petroleum distillation (e.g., diesel oil or mineral oil).
The major component to most downhole completion designs
is a packer. The major function of a packer is to provide a
pressure tight seal between the tubing and casing so fluid flow
Packer
will be diverted up the tubing rather than up the tubing-casing
annulus. This protects the casing from pressure and corrosive
fluids.
The ability of fluid to flow from one pore space to another.
Permeability
Unit of measurement is the millidarcy or 0.001 darcy.
Pill(s) A small quantity of a specific fluid that is pumped into the

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well to perform a specific function, for example, a “stuck-pipe

releasing” pill.
A small hole drilled into the formation before opening it up to
Pilot Hole a larger diameter. Often used when drilling top-hole
formations where there is a risk of shallow gas.

Used to define the relationship between the weight of the drill

string and the force required to strip the string into the well.
Pipe light is when the force required to lower the string is
Pipe Light/Pipe Heavy greater than the weight of the string. In this case the string has
to be ‘snubbed’ into the well. Pipe heavy is when the weight of
the string is greater than the upward force acting on the string.
In this case the string can be ‘stripped’ into the well.
A series of devices that continuously monitor the level of the
drilling mud in the mud tanks. It displays fluid volume and
Pit Volume Totalizer (PVT)
gains and losses contained in a selected combination of fluid
tanks or pits to the Driller.
The spaces within a rock. The ratio of the volume of empty
Porosity space to the volume of solid rock in a formation, indicating
how much fluid a rock can hold.
A test on a barrier element in which the pressure is increased
Positive Test such that the net differential pressure direction is from the
wellbore to the formation.
The pressure gradient of a given fluid is the hydrostatic
Pressure Gradient
pressure per vertical foot of that fluid.
Drilling fluid hydrostatic pressure is sufficient to control the
Primary Well Control
formation fluid pressure.
The speed at which the drill bit can break the rock under it and
Rate of Penetration (ROP) thus deepen the wellbore. This speed is usually reported in
units of feet per hour or meters per hour.
An unmanned submersible vehicle controlled from surface. In
Remote Operated Vehicle deepwater operations, remotely operated vehicles are used to
(ROV) inspect subsea structures and equipment, and to control or
manipulate valves.
A subsurface body of rock having sufficient porosity and
permeability to store and permit extraction of fluids.
Sedimentary rocks are the most common reservoir rocks
Reservoir
because they have more porosity than most igneous and
metamorphic rocks and form under temperature conditions at
which hydrocarbons can be preserved.
Gas in the drilling fluid that is above the subsea BOP and is
Riser Gas
therefore free to migrate upward and expand without any

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control from the well control equipment.

Systematic application of management policies, procedures
and practices to the activities of communicating, consulting,
Risk Management
establishing the context, and identifying, analyzing,
evaluating, treating, monitoring and reviewing risk.
The solid part of the rock; together with the pore spaces
Rock Matrix
(porosity) make up the total volume of the rock.
A pressure, in excess of the minimum pressure, that is applied
to the wellbore to create an overbalance during an operation;
Safety Margin
thus reducing the risk of an underbalance situation and
potential kick.
A clastic sedimentary rock whose grains are predominantly
sand-sized. The term is commonly used to imply consolidated
sand or a rock made of predominantly quartz sand, although
Sandstone
sandstones often contain feldspar, rock fragments, mica and
numerous additional mineral grains held together with silica or
another type of cement.
The use of well control equipment to prevent a further influx
Secondary Well Control
following failure of primary well control.
Casing float equipment that allows the casing to fill when
running in the hole. This can reduce surge pressure on the
Self-Fill (Auto-Fill) Float
formation. In case of float failure regular checks should be
made to ensure casing is kept full.
A fine-grained, fissile, detrital sedimentary rock formed by
consolidation of clay- and silt-sized particles into thin,
Shale
relatively impermeable layers. It is the most abundant
sedimentary rock.
Surface pressure measured at the Choke Manifold that
Shut in Casing Pressure represents the underbalance pressure in the annulus between
the mud hydrostatic pressure and the formation fluid pressure.
Surface pressure measured at the Standpipe Manifold that
Shut In Drill Pipe Pressure represents the underbalance pressure in the drillstring between
the mud hydrostatic pressure and the formation fluid pressure.
Slow Circulation Rate (SCR) Pressure required to overcome friction at a slow pump rate.
Volume of mud pill that is denser than the mud in the drillpipe
and wellbore annulus. A slug is used to displace mud out of
the upper part of the drillpipe before pulling pipe out of the
Slug
hole and is mixed in the pill pit by adding additional weighting
material (barite) to a few barrels of mud from the surface pits.
The pill is pumped into the top of the drillstring to u-tube mud

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downward, out of the pipe, thus keeping the upper stands of

pipe empty during trips.
Equipment located on surface that cleans solids from the
Solids Control Equipment drilling fluid, for example: shale shakers, mud cleaners,
desilters, and centrifuges.
The property of a solid, liquid, or gaseous substance called
solute to dissolve in a solid, liquid, or gaseous solvent to form
Solubility a homogeneous solution of the solute in the solvent; for
example, formation gas into oil-based drilling fluid.
A program that provides all operator and contractor/service
personnel, directly or indirectly involved with the operation,
Stop Work Authority the responsibility and authority to cease work until a review of
the activity can be concluded, and it has been found safe to
resume such activity.
Start-up refers to the process of bringing the pumps up to
speed at the start of a kill operation in order to maintain
Start-Up/Shut-Down
correct bottomhole pressure. Shut-down is the reverse—
shutting down the pump.
Used to describe any pressure that is exerted at the top of a
Surface Pressure
column of fluid.
The temporary reduction in the bottomhole pressure that
results from the upward movement of pipe in the hole. The
movement of the drill string or casing through the wellbore is
similar to the movement of a loosely fit piston through a
Swab Pressure
vertical cylinder. A pressure reduction or suction pressure
occurs below as the piston or the pipe is moved upward in the
cylinder or wellbore and a pressure increase occurs below as
they move downward.
Wellbore pressure is temporarily increased as pipe is run into
Surge Pressure
the well.

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Fluid pressure trapped in the well or the piping system.

Trapped Pressure and
Trapped gas occurs when gas is trapped under pressure on the
Trapped Gas
downstream side of the well control equipment.
Additional weight added to the drilling fluid that compensates
Trip Margin for predicted ‘swabbing’ pressure when tripping out of the
hole.
A form that documents pipe ‘tripped’ from the well against
fluid pumped into the well to replace pipe displacement
Trip Sheet
volume; used to detect swabbing. Is also used when tripping in
the hole to detect surging.
A metal tank with a small capacity about 20-40 bbls with 1-bbl
Trip Tank divisions inside used to monitor the well during trips and flow
checks.
A procedure used to drill oil and gas wells where the pressure
in the wellbore is kept lower than the fluid pressure in the
Underbalanced Drilling
formation being drilled. As the well is being drilled, formation
fluid flows into the wellbore and up to the surface.
A way to describe the well where the drill string volume and
U-Tube annulus volume represent the two arms of the u-tube. The
pressures and/or mud levels in each arm balance each other.
Kill method where kill mud is circulated around the well at the
Wait and Weight Method
same time as the influx is removed.
Refer to the inside diameter of the wellbore wall, the rock face
Wellbore
that bounds the drilled hole.
The equipment installed at the surface of the wellbore. The
wellhead incorporates a means of supporting the production
Wellhead
tubing and installing the Christmas tree and surface flow-
control facilities.
Process of performing major maintenance or remedial
treatments on a producing oil or gas well. In many cases,
Workover workover implies the removal and replacement of the
production tubing string after the well has been killed and a
workover rig has been placed on location.

Rev. 0 14 March 2015