Oil and Gas Terms Beginning with “O” — Page 2

An oil pool is a discrete subsurface accumulation of oil in a porous and permeable reservoir rock, trapped by a structural or stratigraphic closure and sealed against upward migration by an impermeable caprock, with the… Read more →

Oil sand (also called tar sand or bituminous sand) is a naturally occurring mixture of sand or sandstone grains, clay minerals, water, and a dense, viscous form of petroleum called bitumen — typically containing 10 to… Read more →

Oil swelling refers to the increase in volume that crude oil undergoes when it absorbs dissolved gas under reservoir pressure conditions — the physical phenomenon quantified by the oil formation volume factor (Bo),… Read more →

An oil well is a borehole drilled and completed for the primary purpose of producing crude oil as its principal commercial product. While the defining product is liquid hydrocarbon, oil wells almost never produce oil… Read more →

Oil-base mud (OBM) is an invert-emulsion drilling fluid system in which the continuous (external) phase is oil and the dispersed (internal) phase is brine, providing the operational chemistry needed for water-sensitive… Read more →

An oil-in-water emulsion (O/W emulsion) is a mixture in which tiny droplets of oil are dispersed throughout a continuous water phase. Water is the dominant liquid, and oil exists as microscopic spherical droplets… Read more →

What Is an Oil-Mud Emulsifier? An oil-mud emulsifier is a surface-active chemical added to oil-based and synthetic-base drilling fluids to create and maintain a stable water-in-oil (invert) emulsion by reducing… Read more →

Oil-prone in petroleum geochemistry describes a source rock or organic matter type that preferentially generates liquid hydrocarbons (crude oil and condensate) upon thermal maturation, as distinguished from gas-prone… Read more →

What Is Oil-Water Contact? Oil-water contact (OWC) (also called the oil-water interface or hydrocarbon-water contact) is the subsurface boundary surface that separates the oil-bearing zone of a reservoir from the… Read more →

The surface of contact between a water layer and an oil layer. Read more →

Oil-wet describes a rock surface condition in which crude oil adheres preferentially to the pore walls of the formation rock rather than water, the opposite of the more common water-wet state; wettability, the tendency… Read more →

The oil/brine ratio (OBR) is a fundamental compositional parameter for oil-base mud (OBM) systems that expresses the relative volumes of oil and brine in the mud's liquid phase, calculated as the ratio of the volume… Read more →

The oil/water ratio (OWR) is the volumetric or mass ratio of oil to water in a fluid mixture, used in petroleum engineering in two distinct but related contexts: in drilling engineering, OWR describes the composition of… Read more →

An oilfield battery is a specialized electrochemical power source designed to provide reliable electrical energy to downhole or surface tools used in oil and gas exploration, drilling, and production operations under… Read more →

Olefinic hydrocarbons (olefins, also called alkenes) are a class of hydrocarbons characterized by the presence of one or more carbon-carbon double bonds (C=C) in their molecular structure, giving them higher chemical… Read more →

A low-molecular-weight polymer typically with two to five monomer units. Read more →

(noun) A single seismic trace recording the amplitude of reflected seismic energy as a function of two-way travel time at one surface location, providing a vertical profile of acoustic impedance contrasts in the… Read more →

One-way time is the seismic travel time for acoustic energy to pass once between the surface of the Earth and a receiver at a known depth in a borehole, measured directly during a check-shot survey or a vertical seismic… Read more →

Onlap is a stratal termination pattern in seismic stratigraphy and sequence stratigraphy in which progressively younger strata terminate (pinch out) against an older surface in an updip direction toward the basin margin… Read more →

What Is Open Hole? Open hole refers to the portion of a wellbore that has been drilled through a formation but has not been lined with cemented steel casing, leaving the borehole wall in direct contact with drilling… Read more →

What Is Open-Flow Potential? The open-flow potential (OFP) is the maximum theoretical flow rate a well could sustain if the wellbore flowing pressure were reduced to zero (atmospheric) — representing the absolute upper… Read more →

What Is an Openhole Completion? Openhole completion (also called an open-hole completion or barefoot completion in its simplest form) is a well completion technique in which the production interval is left uncased and… Read more →

An openhole gravel pack (OHGP) is a sand control completion method in which a gravel-filled annulus is created between the borehole wall and a wire-wrapped or pre-packed screen in the uncased, exposed formation… Read more →

An openhole packer is a mechanical sealing device that is set directly against the exposed formation face (the open borehole wall) rather than inside a casing or liner string, creating a pressure seal between the… Read more →

An openhole test is a well test conducted in an uncased wellbore interval, in which a formation or sequence of formations is tested for fluid presence, pore pressure, permeability, and productivity before the production… Read more →

An opening bomb (also called a core bomb or core-opening device) is a pressurized steel cylinder used in petroleum core analysis to safely transfer and open sidewall core samples or conventional core plugs under… Read more →

What Is an Operating Agreement? Operating agreement (also called a joint operating agreement, or JOA) is a contract among co-owners of oil and gas working interests in a jointly developed property that designates one… Read more →

The operating gas lift valve (OGLV) is the deepest and most critically positioned valve in a continuous gas lift completion — the valve that remains open during normal production operations and through which lift gas is… Read more →

What Is Operating Interest? Operating interest (also called working interest) is the fractional share of ownership in an oil and gas lease that entitles its holder to explore for, develop, and produce oil and gas from… Read more →

An operator is the party that holds the right to drill or produce a well and bears day-to-day responsibility for conducting operations, whether that party owns the working interest outright or is contractually appointed… Read more →