A

Accumulation: The quantity of hydrocarbons (oil and natural gas) found in the reservoir rock in an oil or gas field.

Annulus: The volume between two concentric well casings or between the inner casing and the tubing (see also gas lift).

Artificial Lift: A technique used for increasing the productivity of wells with low reservoir pressure and/or heavy fluids (water, heavy oil) and enabling them to flow to surface either by introducing lighter weight fluid (gas) into the stream deep in the well or by providing a downhole pumping system (electrical or hydraulic submersible pumps - ESPs/HSPs).

B

Bit: A tool used in drilling to break up rock mechanically in order to gradually penetrate the subsoil. The bit digs a circular hole.

Blow-out: Uncontrolled escape of gas and/or oil from a well often when the drill bit enters a zone of unexpectedly high pressure and/or due to failure of one or more of the mechanical barriers isolating the well fluid from the environment.

Butane: The saturated hydrocarbon (alkane) with four carbon atoms in its molecule. The fourth member of the paraffin series. A gas at atmospheric pressure and normal temperature, but easily liquefied by pressure for transportation and subsequent use.

C

Christmas Tree: An assembly of valves at each wellhead to control and shut off the flow to or from the well.

Condensate: A light hydrocarbon liquid derived from produced or separated gas, composed largely of methane, ethane, propane, butane and pentane.

D

Discharge: The outlet of a pump or compressor.

E

EMAS: Eco Management and Audit Scheme.

ESV or ESDV: Emergency shut-down valve.

ESP: Electric submersible pump.

F

Flare: A device to safely dispose of surplus hydrocarbon vapours by burning.

Flowline: Pipework extending from the Christmas Tree to the manifold.

G

Gas lift: Is the injection of gas through the well annulus down to calibrated gas lift valves to lighten the produced fluid column in the tubing. Used to start up well-flow and enhance flowrates.

H

H2S: Hydrogen sulphide - a highly toxic gas which may be present in crude oil and associated gas as a result of bacterial action on the reservoir fluids. It has the odour of rotten eggs at low concentration but cannot be smelt at high concentration.

HP/HT: High pressure, high temperature.

Hydrocarbons: A compound of carbon and hydrogen. Used as a general term to encompass produced (natural) gas, condensates, LPG, crude oils and refined products such as diesel fuel.

I

Inhibitor: Is a substance which is added to petroleum products to prevent or minimise an undesirable change in the product or the condition of the equipment in which it is used. The changes which are often prevented are corrosion, oxidation, solidification or deposition (wax, hydrate, asphaltene).

Injection: Term applied to the technique of introducing gases and liquids under pressure into a system. More specifically, water or gas to maintain oilfield reservoir pressure (see also gas lift ).

J

Jacket: The supporting steel structure of the platform which is installed on the seabed.

Jack-up: A platform with retractable legs which is towed into position and "jacked-down" or lowered onto the seabed where it is secured into its location.

K

Kick: The detected unplanned influx of formation fluid(s) or gas into the wellbore causing an increase in pressure.

L

Lifeboats: A boat designed for the preservation of life at sea. Lifeboats can either be of a free-fall or davit winch design.

LPG: Liquefied petroleum gas is a term usually applied to refined or processed condensate. It is a light hydrocarbon which is normally less gaseous, but which is held in the liquid state by pressure to make storage and transport easier. Commercial liquefied petroleum gas consists mainly of propane or butane.

M

Manifold: A pipework or header system, usually inter-connected by means of valves.

Methane: The hydrocarbon with the lightest molecule. The first member of the paraffin (alkane) series - a gas under normal conditions.

Mud: Mud is a liquid made up of many different chemicals (mainly clay) which can be water or oil based. By circulation in the well during drilling, mud:

• cools the drilling bit,
• removes cuttings from the bottom of the hole,
• prevents the hole behind the bit from caving in,
• prevents the intrusion of water, gas or oil into the hole until it is completed with steel piping,
• prevents oil or other hydrocarbon fluids from flowing back, out of the reservoir.

Multi-Phase Pumps (MPPs): Multi-phase pumps can be used in a variety of applications (on land, a platform or subsea) to boost the pressure of multi-phasic (oil, gas, water) streams usually emanating from one or multiple wells (via a manifold) in order to push them on to the final processing location, without the need to separate the fluids at that point in the system and boost and compress the separated oil and gas streams respectively.

N

NG: Natural Gas Liquid - a general term encompassing condensates and LPG.

P

Pig: A Pipeline Inspection Gauge which is used to internally inspect and clean pipes.

Pipeline: Pipe carrying hydrocarbons - oil/gas.

Pipeline Bundle: An outer carrier pipe which accommodates other pipes inside it, providing protection, insulation and a controlled environment.

Propane: The saturated hydrocarbon (alkane) with three carbon atoms in its molecule. The third member of the paraffin series - a gas under normal conditions.

PUQ: Production/Utilities/Quarters platform.

R

Reservoir: A continuous volume of rock containing voids, pores, or a network of cracks, and in which fluids (hydrocarbons, water, and inert gases) can circulate.

Riser: The section of an export or import pipeline extending from the seabed to the ESV on the platform topsides. For a floating rig it is the section of pipe linking the rig to the wellhead on the seabed, to allow drilling operations.

S

Separator: A vessel or device for separating the components of a multi-phase fluid mixture, eg oil, water and gas.

Slug: A rapid increase in flow and pressure in a pipeline. An unstable flow condition in a flowline.

Spudding: The process of starting to drill a well by making a hole in the seabed using a large diameter bit.

Step-out Well: A well drilled beyond the proven limits of a field to investigate a possible extension to that field; sometimes also called an out step well.

Subsoil: Part of the earth's crust located bellow the surface .

SUSA: Safe Un-Safe Acts Scheme.

T

Temporary Safe Refuge (TSR): The temporary refuge is a specially designated area on board every offshore oil and gas production platform which is designed to ensure that personnel can muster in safety for a period of protection while an incident is being assessed and a decision taken on whether or not to abandon the installation. The temporary refuge is equipped, amongst other things, with command, communication, monitoring, mustering and medical facilities.

Topsides: The facilities and equipment of the platform installation which are located above the water.

Tubing: The innermost pipe within a well connecting the reservoir to the wellhead through which fluids are produced or injected.

W

Well: A hole drilled underground for oil exploration and production. By extension, any apparatus used for this purpose.

Wellhead: The point at which a well terminates at surface, on an offshore platform or on the seabed, normally in a Christmas Tree.