Oil and gas glossary

A scale of how light or heavy a crude oil or condensate is. It rises as the liquid gets lighter.

Water-bearing rock in pressure communication with the hydrocarbon column.

Pressure in the well at a stated depth, almost always opposite the reservoir or at a downhole gauge.

The pressure, at reservoir temperature, at which the first free gas comes out of an oil as the oil is depressured.

The pressure difference between the non-wetting and the wetting fluid across their interface in the pores.

Formation water that was already in the pores when the trap filled.

A forecast of future rate from the way past rate has fallen with time or with cumulative production.

The distance from a well to the no-flow boundary of the volume it drains.

Methods aimed at oil that primary depletion and a plain waterflood would leave behind.

The total volume a well, reservoir, or field is expected to produce over its life, including what has already been produced.

The fraction of the pore volume that one fluid occupies.

Extra resistance to flow in the rock or the completion within a short distance of the wellbore.

Reservoir volume occupied by a fluid divided by the volume that same fluid occupies at surface conditions.

The depth where a gas cap sits on the oil column.

Produced gas rate divided by produced oil rate, both at surface conditions.

The relationship between bottomhole flowing pressure and the rate a well can deliver.

Injection rate divided by how far the injection bottomhole pressure sits above reservoir pressure.

The water saturation that further displacement by oil or gas will not reduce, at the capillary pressures that matter.

An inventory that makes produced volumes, injected volumes, and the pressure change consistent with fluid expansion and aquifer influx.

The mobility of the displacing fluid divided by the mobility of the fluid being pushed.

How readily a rock lets fluid pass through it for a given viscosity and pressure gradient.

The fraction of a rock's bulk volume that is pore space rather than solid grain.

Reading permeability, skin, and reservoir limits from the way pressure changes with time after a rate change.

The liquid rate a well delivers for each unit of pressure drawdown.

Laboratory measurement of how a reservoir fluid changes volume, phase, and viscosity with pressure and temperature.

The fraction of the oil or gas initially in place that is produced, or expected to be produced.

The effective permeability to one fluid divided by a reference permeability, usually the absolute permeability.

Oil and gas expected to be produced commercially from a stated date forward, under stated prices, costs, and a development plan.

A body of subsurface rock porous and permeable enough to store hydrocarbons and to give them up to a well.

The oil saturation left after a displacement, once oil no longer flows as a connected phase.

A dimensionless number from a well test that describes extra pressure drop at the sandface compared with an undamaged open hole in the same rock.

The gas, measured at standard surface conditions, dissolved in one stock-tank barrel of oil at a stated reservoir pressure and temperature.

The pressure in the drainage volume when the well is shut in and the transients have died out, or the average pressure used for that volume.

The volume of oil in the reservoir before production, counted as stock-tank barrels rather than reservoir barrels.

How strongly a fluid resists flow.

The depth where the oil column gives way to water.

Injection of water to hold reservoir pressure up and to push oil toward producers.

Which fluid preferentially coats the grain surface: water, oil, or neither cleanly.