Glossary

Take-or-pay

a contractual clause obliging a gas buyer to pay the seller for a contracted amount of gas in a fixed period, whether or not he takes physical delivery of it.

Tanker

a ship or vehicle used to transport oil, refined products or liquefied gas.

Tar sands

mixture of sand, water and heavy hydrocarbons; a potential alternative source of hydrocarbons

TD

total depth, or planned final depth.

Tectonic process

a process whereby rocks or strata are deformed by natural forces within the Earth's crust.

Terminal

an onshore installation designed to receive oil and/or gas from a pipeline or from tankers; it is not a refinery.

Terminal platform

an offshore platform from which oil or gas is pumped ashore through a pipeline.

Tertiary era

the era of geological time which began approx 60 million years ago and ended approx one million years ago

Tertiary recovery

recovery of oil or gas from a reservoir over and above that which can be obtained by primary and secondary recovery; it generally involves using sophisticated techniques such as heating the reservoir to reduce the viscosity of the oil.

Therm

100,000 British Thermal Units; a unit used to measure quantities of gas.

Throughput

a term used to describe the total amount of raw materials that are processed by a plant, such as an oil refinery, in a given period

Tight hole

a well in which the information obtained is restricted and passed only to those who may be authorised to receive information. Often occurs if nearby acreage is unlicensed and the company wants to maintain a competitive advantage

Tongs

hydraulically operated grabs used to hold sections of pipe during screwing or unscrewing; sometimes known as pipe tongs.

Toolpusher

the supervisor in charge of the drilling rig and associated equipment.

Town gas

gas piped to consumers from a gas plant. It can comprise manufactured gas, as well as natural gas for enrichment.

Transmission

the transport of large quantities of gas at high pressures, often through national or regional transmission systems. From the latter, gas is transferred into local distribution centre, for supply to customers, at lower pressures.

Transmission pipeline

a network of pipelines distributing natural gas from an onshore station, via compressor stations, to storage centres or distribution points

Trap

a geological structure in which hydrocarbons build up to form an oil or gas field.

Travelling block

the moving pulley system used in conjunction with the (fixed) crown block for raising and lowering the drill string, casing, etc.

Triassic period

the period of geological time which began approx 230 million years ago and ended roughly 180 million years ago

Turbine drilling

drilling in which the drill string remains stationary, the bit being rotated by a down-hole multi-stage turbine powered by the drilling mud

Turbodrill

the down-hole drilling mechanism used in turbine drilling.

Twist-off

catastrophic failure at the joint of drillpipe and collar, usually caused by the application of excessive torque from the rotary table