Oil and Gas Glossary

packer

A downhole, expanding plug-like device which is used to seal off certain parts of tubing, casing, or open hole when cementing, acidizing, or isolating specific zones of a formation for production or testing. Packers can be run on logging cables, tubing, drill pipe, or casing and when in position can be expanded to form a seal to confine fluid flow to the inside bore of the packer.

pay

The part of a formation which produces or is capable of producing oil or gas, or other economic product.

permeability

The ability, or measurement of a rock's ability, to transmit fluids, typically measured in darcies or millidarcies. Formations that transmit fluids readily, such as sandstones, are described as permeable and tend to have many large, well-connected pores. Impermeable formations, such as shales and siltstones, tend to be finer grained or of a mixed grain size, with smaller, fewer, or less interconnected pores. Absolute permeability is the measurement of the permeability conducted when a single fluid, or phase, is present in the rock. Effective permeability is the ability to preferentially flow or transmit a particular fluid through a rock when other immiscible fluids are present in the reservoir (for example, effective permeability of gas in a gas-water reservoir). The relative saturations of the fluids as well as the nature of the reservoir affect the effective permeability. Relative permeability is the ratio of effective permeability of a particular fluid at a particular saturation to absolute permeability of that fluid at total saturation. If a single fluid is present in a rock, its relative permeability is 1.0. Calculation of relative permeability allows for comparison of the different abilities of fluids to flow in the presence of each other, since the presence of more than one fluid generally inhibits flow.

petroliferous

Containing petroleum (of rocks).

plug and abandon

P&A. To place a cement plug into a dry hole or noneconomic well and abandon the well.

plug back

To place cement in or near the bottom of a well or side-track to prevent water production. Plugging back also can be accomplished by a mechanical plug set by wireline, tubing, or drill pipe.

pore

A discrete void within a rock, which can contain air, water, hydrocarbons or other fluids. In a body of rock, the percentage of pore space is the porosity.

pore pressure

Pressure exerted by fluids contained within the pores of rock.

porosity

The percentage of pore volume or void space, or that volume within rock that can contain fluids. Porosity can be a relic of deposition (primary porosity, such as space between grains that were not compacted together completely) or can develop through alteration of the rock (secondary porosity, such as when feldspar grains or fossils are preferentially dissolved from sandstones). Effective porosity is the interconnected pore volume in a rock that contributes to fluid flow in a reservoir. It excludes isolated pores. Total porosity is the total void space in the rock whether or not it contributes to fluid flow. Thus, effective porosity is typically less than total porosity.

pressure gradient

A scale of pressure differences in which there is a uniform variation of pressure from point to point. For example, the pressure gradient of a column of pure water is about 0.433 psi/ft of vertical elevation (9.79 kPa/m).

pressure transient testing and analysis

A pressure transient test is a test during which the flow rate of a well is carefully controlled in order to obtain pressure transient data. Pressure transient analysis is the careful evaluation of pressure variation as a function of time in order to determine qualitatively those parameters which control fluid flow.

primary porosity

Porosity which is present in sediment at the time of deposition or formed during sedimentation. Compare secondary porosity.

primary recovery

The first stage of hydrocarbon production, in which natural reservoir energy, such as gasdrive, waterdrive or gravity drainage, displaces hydrocarbons from the reservoir, into the wellbore and up to surface. Initially, the reservoir pressure is considerably higher than the bottomhole pressure inside the wellbore. This high natural differential pressure drives hydrocarbons toward the well and up to surface. However, as the reservoir pressure declines because of production, so does the differential pressure. To reduce the bottomhole pressure or increase the differential pressure to increase hydrocarbon production, it is necessary to implement an artificial lift system, such as a rod pump, an electrical submersible pump or a gas-lift installation. Production using artificial lift is considered primary recovery.

production

The phase that occurs after successful exploration and development and during which hydrocarbons are drained from an oil or gas field.

production casing

Long string. The last string of casing set in a well prior to production.

production log

A well log run in a production or injection well. Small diameter tools are used so that they can be lowered through tubing. Services and devices include continuous flowmeter, packer flowmeter, gradiomanometer, manometer, densimeter, watercutmeter, thermometer, radioactive-tracer logs, temperature logs, calipers, casing collar locator, fluid sampler, water entry survey, etc.

proximity log

A microresistivity log, similar to the microlaterolog, made from a tool which focuses survey current issuing from a sidewall pad. The electrodes are mounted on a wider pad than that used by the microlaterolog, and survey current is focused deeper into the formation. These design features result in measurements which have less sensitivity to the mud cake. A caliper curve usually is recorded simultaneously.

pulsed neutron log

A term with broad application. Includes all logs made while using neutron bursts or pulses. This term quite often is used in referring to neutron decay time logs such as the Thermal Decay Time Log, Neutron Lifetime Log, and Thermal Multigate Decay Log. A neutron generator, which emits neutrons in controlled cyclic pulses, is the source of radiation. The term also applies to other nuclear logs where cyclic neutron pulses must be used; e.g., some induced spectral gamma-ray logs.

pressure, volume, and temperature (PVT) analysis

An examination of reservoir fluids in a laboratory under various pressures, volumes, and temperatures to determine the characteristics and behaviour of the fluid.