Oil and Gas Terms Beginning with “O” — Page 3

A small sensor in a production logging tool that distinguishes the type of fluid in its vicinity as it is moved up and down a production well. The optical probe is sensitive to the optical index of the fluid in front of… Read more →

A type of organic fluid, such as acetic or formic acid, used in oil and gas well-stimulation treatments. The use of inhibited HCl at elevated temperatures is limited to relatively short exposure times because of the… Read more →

A type of damage in which heavy hydrocarbons precipitate when temperature or pressure is reduced. These deposits are commonly located in the tubing, gravel pack and perforations, or inside the formation. The injection… Read more →

Pertaining to a material that associates with organic and oily surfaces and liquids and rejects aqueous systems. An example of organophilic behavior in drilling fluids is the organophilic coating applied to clays and… Read more →

Clay minerals whose surfaces have been coated with a chemical to make them oil-dispersible. Bentonite and hectorite (plate-like clays) and attapulgite and sepiolite (rod-shaped clays) are treated with oil-wetting agents… Read more →

A lignite that has been coated with a chemical that renders it dispersible in oil. The treatment is usually accomplished with a type of quaternary amine compound. Read more →

An instrument that records the flow rate of gas through a pipeline. The flow rate is calculated from the pressure differential created by the fluid passing through an orifice of a particular size and other parameters… Read more →

A type of valve, typically found on small-diameter pipework, that incorporates an orifice or flow-restriction device to control fluid flow. Read more →

A major episode of plate tectonic activity in which lithospheric plates collide and produce mountain belts, in some cases including the formation of subduction zones and igneous activity. Thrust faults and folds are… Read more →

The movement of water from one aqueous system to another through a semipermeable membrane. Osmotic movement is driven by activity differences between the two systems and can be considered as a vapor-phase transfer. An… Read more →

The pressure that must be applied to the low-salinity side of an osmotic system to prevent water movement into the high-salinity side by osmosis. Conversely, it is the suction pressure that a high-salinity system exerts… Read more →

A body of rock exposed at the surface of the Earth. Construction of highways and other man-made facilities and resultant removal of soil and rock has created spectacular outcrops in some regions. Read more →

Outside or outer diameter. Casing and tubing are commonly described in terms of inside diameter (ID) and outside diameter. Read more →

The maximum distortion permitted on the cross-sectional profile of a coiled tubing string. The mechanical performance of oval tubing deteriorates as the degree of ovality increases. The most critical effect is the… Read more →

The amount of pressure (or force per unit area) in the wellbore that exceeds the pressure of fluids in the formation. This excess pressure is needed to prevent reservoir fluids (oil, gas, water) from entering the… Read more →

(noun) The total thickness of rock and sediment overlying a formation of interest, from the surface (or mudline in offshore environments) to the top of that formation. Overburden stress, generated by the cumulative… Read more →

A specially prepared fluid used to displace matrix acid treatments away from the wellbore at the conclusion of a stimulation treatment. The overflush is typically formulated from a weak acid solution or brine to… Read more →

Pertaining to a hydrocarbon source rock that has generated as much hydrocarbon as possible and is becoming thermally altered. Read more →

What Is Overpressure? Overpressure (also called abnormal pressure or geopressure) is a subsurface pore fluid pressure that exceeds the hydrostatic pressure expected for the depth of burial — the pressure a continuous… Read more →

What Is an Overriding Royalty Interest? An overriding royalty interest (ORRI) is a non-cost-bearing fractional interest in oil and gas production carved out of the working interest, entitling the holder to a percentage… Read more →

Ownership in a percentage of production or production revenues, free of the cost of production, created by the lessee, company and/or working interest owner and paid by the lessee, company and/or working interest owner… Read more →

A downhole tool used in fishing operations to engage on the outside surface of a tube or tool. A grapple, or similar slip mechanism, on the overshot grips the fish, allowing application of tensile force and jarring… Read more →

A thrust fault having a relatively large lateral displacement. Read more →

A condition in downhole pumping operations that occurs when the stroke length at the subsurface sucker-rod pump is longer than the surface stroke length (polished rod). This phenomenon is caused by the elongation of the… Read more →

A model for converting relative elemental yields from a pulsed neutron spectroscopy log to absolute weight concentrations using the assumption that the sum of all oxides in the rockmatrix is 1. The model is based on the… Read more →

A phenomenon exploited for the purpose of detecting and quantifying the flow of water in or around a borehole based on oxygen activation. Oxygen (16O) can be activated by high-energy neutrons to produce an isotope of… Read more →

A chemical agent used in some brines and completion fluids to reduce corrosion resulting from, or exacerbated by, dissolved oxygen. Oxygen scavengers capture the dissolved oxygen in a harmless chemical reaction that… Read more →