SpeakingOilGas

stratigraphy – a description of the rock formations in sequence from top to bottom in a sedimentary basin.

streamer – the string of cable with hydrophones attached which is towed behind a vessel during an offshore seismic survey.

structure – in oil industry terms it refers to a feature within the earth’s crust with the potential to trap migrating hydrocarbons.

submersible – a form of floating drill rig which can be ballasted down to sit on the sea floor or lake floor during marine drilling mode. The term can also refer to a remote-controlled or a manned submarine used in inspection and maintenance offshore.

subsea completion – a production wellhead which is placed on the sea bed instead of on a platform at the surface.

suspended – a well is suspended when it is likely to be re-entered at a later date, either to continue drilling or to run a test of a reservoir that was not possible or convenient during the original drilling. The well is suspended by setting cement plugs that can be drilled out when re-entry takes place.

sweet crude – crude oil that is free of sulphur compounds.

tension leg platform – a type of floating offshore production facility that is tethered to the sea bed with steel cables and uses its buoyancy to keep the cables tight (in tension).

term contracts – when shipments of a particular crude oil or condensate are contracted and sold to one buyer or group of buyers for a specific period of time (often 5–10 years) at a negotiated price which is set at a differential to the floating price of a bench mark crude.

thin stringers – a term referring to oil and gas reservoirs that measure a few metres or less in thickness.

three dimensional seismic survey (3D) – a survey with seismic lines set out in close grid pattern to gain better resolution of detail in an area.

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tight – a term indicating that a formation has little permeability.

time map – a plan of mapped horizons from the seismic sections where the contours connecting equal values in times of waves reaching the geophones are plotted on the grid map for the survey. To convert this to a geological map, velocity measurements are used to change time to depth values.

toolpusher – the chief driller in charge of operations on the rig floor.

top drive – a drilling system where a motor is attached to the top of the drill string in the rig derrick to impart a rotary action directly, rather than use a kelly and rotary table.

trap – a formation in the earth’s subsurface which prevents the onward migration of hydrocarbons.

travelling block – a large pulley with sheaves at the top end that allow the drilling line to pass through and a hook at the bottom end which is attached to the drill pipe. Raising or lowering the drilling line will move the travelling block and the attached drill pipe up or down within the derrick.

tri-cone bit – see rolling cutter bit.

tubing – see liner.

turbo drill – a drill bit which is rotated via a multi-stage turbine mounted at the bottom of the drill pipe. Power to rotate is supplied by the drilling fluid being pumped down hole from the surface.

underbalanced drilling – where the weight of the drilling mud in the well is less than the formation pressure of the rock layers penetrated. This allows formation fluids to rise up the well to the surface where the flow is continuously monitored to detect hydrocarbons.

unitisation agreement – where owners of petroleum reserves pool their individual interests in return for an interest in the overall unit which is then operated by a single company on behalf of the group.

GLOSSARY

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up-dip – a term referring to any point in a reservoir that is higher up in the structure or trap.

vibroseis – a form of survey where the seismic waves are created by mechanically vibrating a steel pad or plate on the earth’s surface.

wet gas – natural gas that contains significant amounts of associated liquid hydrocarbons such as condensate, propane and butane. In terms of quantity, gas is sometimes declared ‘wet’ when 10 or more barrels of liquid hydrocarbons can be separated from 1 million cubic feet of gas.

wet tree – a subsea wellhead where the equipment is exposed to the sea.

whipstock – a wedge-shaped piece of equipment placed in the bottom of a well which forces the bit and the drill pipe to deviate from their original direction when drilling is resumed.

wildcat – the first well drilled in a new area. It can also mean the first well in a new structure or prospect.

wireline logging – an operation to obtain information about the rock formations in the well by lowering a suite of logging tools down the hole on a cable called a wireline.

wireline test – a test for hydrocarbons in a formation by lowering a chamber downhole on the end of a wire and allowing reservoir fluids to flow into it.

working interest – where a company pays a percentage of a survey, drilling or development program and receives a proportional part of the resultant benefits.

workover – the re-entry into a completed well for modification or repair and maintenance work.

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Printed June 2006