Glossary

Sales gas

raw gas, after processing to remove LPG, condensate and carbon dioxide. Sale gas consists of methane and ethane.

Salt dome

a dome of salt that has broken through overlying formations

Salt dome trap

a trap produced by an impervious salt dome.

Salt pillow

a mass of salt that has risen up under overlying formations, causing them to bulge upwards, but which has not actually broken through

Sampling

the process of obtaining a small quantity of material which is as representative as possible of the total volume.

Sandstone

a type of rock composed primarily of quartz grains. Often forms an excellent reservoir for oil and gas

Saturation

oil or gas saturation is a measure of the proportion of pore space in a reservoir rock that is filled with oil or gas.

SBM (Single Buoy Mooring)

also known as single point mooring (SPM), this consists of a single floating chamber moored near an offshore production platform to serve as a connection to a tanker. It has no storage capacity.

Sealed bid auction

an auction in which the competing parties submit confidential bids by a specified date; sometimes known as a blind auction.

Secondary recovery

recovery of oil or gas from a reservoir by artificially maintaining or enhancing the reservoir pressure by injecting gas, water or other substances into the reservoir.

Sedimentary basin

an area in which thick layers of sedimentary rocks have been laid down over a long period of time.

Sedimentary rocks

rocks laid down by the accumulation of sediments at the bottom of the bottom of a sea, lake, river or swamp over millions of years.

Seismic exploration

an exploration technique involving the use of seismic methods; see seismic survey.

Seismic survey

a technique for determining the detailed structure of the rocks underlying a particular area by passing acoustic shock waves into the strata and detecting and measuring the reflected signals. It is used to locate potential oil or gas bearing structures before drilling.

Semi-submersible rig

a floating drilling platform that is supported by underwater pontoons; generally used for exploration purposes only.

Shale shaker

a vibrating or rotating screen which removes the coarse drill cuttings from the drilling mud prior to its recirculation

Show

an indication of oil or gas from an exploratory well.

Shut-in

the status of a well that has been closed temporarily to become a sealed pressure vessel.

Shuttle tanker

an oil tanker that makes regular round trips between a producing field and an onshore terminal or refinery

Sidetrack drilling

a remedial operation which results in the creation of a new section of well bore for the purpose of detouring around 'junk', redrilling a lost hole or straightening key seats and crooked holes. Also used for geological reasons when there is a desire to reach another part of the reservoir adjacent to the main well bore.

Sidewall cores

cylindrical sections or rock or sediments obtained by shooting hollow cylinders of steel into the wall of the well bore and subsequently recovering them together with their contents.

Skidding the rig

moving the rig from the location of a lost or completed hole preparatory to starting a new hole with little or no dismantling of equipment

Slush pumps

see mud pumps.

Snubbing

the procedure of running pipe or casing into the well while the well is exerting pressure on the surface equipment.

Solution gas

natural gas which is dissolved in the crude oil within the reservoir

Solution gas drive

a primary recovery process in which oil is driven out of a reservoir by the natural pressure exerted by the dissolved gas

Sour crude

crude oil with a high sulphur content.

Sour gas

natural or associated gas with a high sulphur content.

Source rock

the rock in which oil or natural gas originates.

Spar

a floating on-field storage tank into which oil flows from a production platform prior to being transferred to a tanker for shipping ashore.

Specific gravity

the ratio of the density of a substance at a particular temperature to the density of water at 4°C.

Spillage

an accidental release of oil, or another liquid. All spills exceeding 100 kg must be reported.

Spot market

an international market in which oil or oil products are traded for immediate delivery at the current price (the 'spot price').

Spud (spudding in)

to start drilling a new well (or restart), using a large diameter bit.

Spur line

a small-diameter underwater pipeline connecting a production or drilling platform to a terminal platform, on-field storage facility, or main pipeline to the shore

Squeeze

an operation whereby cement is injected under pressure between the casing and the well bore at a particular depth

SS

sub-sea level. Depth reference

Stabbing

inserting the threaded end of a pipe or rod into the coupling at the end of another pipe or rod.

Stabbing board

a retractable platform in the upper part of the derrick on which the derrick man stands in order to align two sections of pipe which are to be joined.

Stand of pipe

a length of drill pipe, tubing or other pipe consisting of one or more sections that is stood, racked or hung in a derrick during drilling operations.

Stand pipe

the rigid pipe that conducts the drilling mud up the derrick into the rotary hose.

Standby boat

a boat (often a converted fishing boat) which maintains permanent station near an offshore structure in order to supply support facilities in an emergency

Steel jacket

the steel lattice structure used to support an offshore steel platform

Step out well

a well drilled beyond the proven limits of a field to investigate a possible extension to that field.

Stinger

the boom used to lower an underwater pipeline onto the seabed from a lay barge.

Strata

successive layers of sediment or sedimentary rock: singular stratum

Stratigraphic trap

a trap formed at the time the sediments containing it were actually laid down and where the hydrocarbons are enclosed as a result of a change from porous to non-porous rock, rather than by subsequent tectonic processes

Stringer

thin, usually discontinuous bed, within a massive lithology, e.g. 'shale with sandstone stringers'

Structural trap

a trap produced by the distortion of once-horizontal strata by some tectonic process(es).

Sub-sea completion

the process of installing a sub-sea, or ocean floor well head

Supply base

an onshore base from which supply boats operate.

Supply boat

a specially designed vessel to ferry supplies, material and equipment to and from offshore structures.

Support vessel

a specially designed vessel that provides a range of safety and support facilities on an offshore field.

Swabbing

inward fluid flow caused by pulling equipment out of a fluid-filled bore hole.

Sweet crude

crude oil with a low sulphur content.

Sweet gas

natural gas with a low sulphur content. Sweet gas reduces sulphur dioxide emissions into the atmosphere.

Swing

the amount by which the rate of gas to be supplied under a contract at any one time may differ from the daily contracted quantity of the buyer's choice.

Swivel

the rotating coupling that connects the rotary hose to the drill string

Syncline

a tectonic structure in which strata are folded so as to form a dip or bowl (i.e. concave on top).

Synthetic gas

methane-rich gas manufactured from oil or coal that has the same basic characteristics and chemical composition as natural gas. After treatment to remove carbon dioxide, it is suitable as low-calorific town gas.