Oil and Gas Terms Beginning with “N”

Abbreviation for natural gas liquids.

The procedure in seismicprocessing that compensates for the effects of the separation between seismic sources and receivers in the case of a horizontal reflector.

Pertaining to a measurement of the nuclear magnetic properties of formation hydrogen. The basic core and log measurement is the T2 decay, presented as a distribution of T2 amplitudes versus time at each sample depth, typically from 0.3 ms to 3 s. The T2 decay is further processed to give the total pore volume (the total porosity) and pore volumes within different ranges of T2. The most common volumes are the bound fluid and free fluid. A permeability estimate is made using a transform such as the Timur-Coates or SDR permeability transforms. By running the log with different acquisition parameters, direct hydrocarbon typing and enhanced diffusion are possible.

An analytical tool used in forecasting the performance of the various elements comprising the completion and production system. NODAL* analysis is used to optimize the completion design to suit the reservoir deliverability, identify restrictions or limits present in the production system and identify any means of improving production efficiency.*NODAL (production system analysis) is a mark of Schlumberger.

Abbreviation for "National Pollutant Discharge Elimination System." The US Congress passed this Clean Water Act to control discharges of contaminants. Discharges are allowed in to US water only by NPDES permits. Drilling fluids, drill cuttings, produced water, drilling rig deck drainage and blowout preventor fluids are covered specifically. Barite must be monitored for heavy metals to allow mud discharges. Oils are banned from discharge.

The magnetization retained by rocks from previous magnetic fields,abbreviated NRM. NRM is a record of the Earth's magnetic field as it existed at the time that the rock formed, such as when magnetic crystals in igneous rocks solidified (also known as chemical remanent magnetism, CRM) or at the time of deposition of sedimentary rocks (known as depositional remanent magnetism, DRM). During deposition of sediments that become sedimentary rock, magnetized particles can settle with their magnetic pole aligned with that of the Earth at that time.

Conventional marineseismic data acquired using a single vessel to tow one or two seismic source arrays in front of a receiverspread. The resulting angle between the source and receivers, is about 20°.

A fluid that has a constant viscosity at all shear rates at a constant temperature and pressure, and can be described by a one-parameterrheologicalmodel. An equation describing a Newtonian fluid is given below. Water, sugar solutions, glycerin, silicone oils, light-hydrocarbon oils, air and other gases are Newtonian fluids. Most drilling fluids are non-Newtonian.

Crude oil containing asphaltic materials but very little or no paraffin wax. This type of oil is suitable for making gasoline, lubricating oil and asphalt. It is also called asphalt-base crude.

A type of organic compound of carbon and hydrogen that contains one or more saturated cyclic (ring) structures, or contains such structures as a major portion of the molecule. The general formula is CnH2n. Naphthenic compounds are sometimes called naphthenes, cycloparaffins or hydrogenated benzenes. Naphtha is a refined petroleum fraction that contains a high percentage of these types of hydrocarbons. In drilling fluids, particularly oil-base muds, the amounts and types of hydrocarbons in the mud can be an important parameter in the overall performance of the mud.

Clays incorporated into a so-called native-solids mud when drilling shallow formations. Native clays are undesirable in muds that are (or will be) weighted with barite. The viscosity of weighted fluids can rise quickly with added native clays, making it difficult to control and pump the mud. Better mud properties result when the drilled solids level, including the level of native clays, is kept low.

A core taken so as to preserve the in-situ water saturation of the rock. A native-state core is usually drilled with oil-base mud or crude oil from the same reservoir.

A mud in which the suspended solids are dispersed clays, sand, chert and other rock that originated from formations being drilled. A spud mud is commonly a type of native-solids mud. Native muds can be economically diluted with water and passed through banks of desilters and desanders to keep solids down. No expensive weighting materials are being discarded and replaced in such a process. At the depth that higher density is required, native mud is usually totally or partially discarded and new mud is made using commercially prepared mud additives and barite.

A completion system designed to utilize the natural flow capability of the reservoir.

The frequency of the normal, free oscillation or vibration of an entity or a system, such as the vibration of a tuning fork when struck or the open string of a musical instrument when plucked. A system oscillating at its natural frequency is said to resonate.

The technique of measuring the spectrum, or number and energy, of gamma rays emitted as natural radioactivity by the formation. There are three sources of natural radioactivity in the Earth: 40K, 232Th and 238U, or potassium, thorium and uranium. These radioactive isotopes emit gamma rays that have characteristic energy levels. The quantity and energy of these gamma rays can be measured in a scintillation detector. A log of natural gamma ray spectroscopy is usually presented as a total gamma ray log and the weight fraction of potassium (%), thorium (ppm) and uranium (ppm). The primary standards for the weight fractions are formations with known quantities of the three isotopes. Natural gamma ray spectroscopy logs were introduced in the early 1970s, although they had been studied from the 1950s.

Natural gas produced from shale reservoirs is known as shale gas. The composition of the gas stream is a function of the thermal maturity of the rock. Thermally immature rocks will contain heavier hydrocarbon components, possibly even liquid components. Overmature reservoirs typically contain appreciable quantities of carbon dioxide [CO2].

Components of natural gas that are liquid at surface in field facilities or in gas-processing plants. Natural gas liquids can be classified according to their vapor pressures as low (condensate), intermediate (natural gasoline) and high (liquefied petroleum gas) vapor pressure.Natural gas liquids include propane, butane, pentane, hexane and heptane, but not methane and ethane, since these hydrocarbons need refrigeration to be liquefied. The term is commonly abbreviated as NGL.

A natural gas liquid with a vapor pressure intermediate between condensate and liquefied petroleum gas. This liquid hydrocarbon mixture is recovered at normal pressure and temperature and is much more volatile and unstable than commercial gasoline.

The magnetization retained by rocks from previous magnetic fields,abbreviated NRM. NRM is a record of the Earth's magnetic field as it existed at the time that the rock formed, such as when magnetic crystals in igneous rocks solidified (also known as chemical remanent magnetism, CRM) or at the time of deposition of sedimentary rocks (known as depositional remanent magnetism, DRM). During deposition of sediments that become sedimentary rock, magnetized particles can settle with their magnetic pole aligned with that of the Earth at that time.

A well in which the formation pressure is sufficient to produce oil at a commercial rate without requiring a pump. Most reservoirs are initially at pressures high enough to allow a well to flow naturally.

Materials typically found in certain types of barium or strontium scales that may be deposited in the wellbore or productiontubulars. Any attempt to remove and dispose of NORM materials should be performed according to the legislation and policies associated with such potentially hazardous materials.

Cement that has no additives to modify its setting time or rheological properties.

Describing the environment and conditions of the marine zone between low tide and the edge of the continental shelf, a depth of roughly 200 m [656 ft]. A neritic environment supports marine organisms, also described as neritic, that are capable of surviving in shallow water with moderate exposure to sunlight.

A geophone array. Nests can contain numerous closely spaced geophones.

Any model that incorporates more than one variable that is represented by fractal geometry or a fractal function. These models can become very complex if the variables are interdependent.

The volume of gas produced less gas injected.

The volume of oil produced less oil injected. In hydraulic pumping, the oil injected is known as power oil.

A share of net proceeds from production paid solely from the working interest owners share. It is sometimes granted in lieu of a royalty interest.

A share of production after all burdens, such as royalty and overriding royalty, have been deducted from the working interest. It is the percentage of production that each party actually receives.

A concept for advanced computer calculations developed by Alan Turing to mimic some of the operations of the neurons in a brain. Memory elements (neurons) are conceptually interconnected by multiple paths connected with on-off switches to emulate the synapses of the brain. The original intent was to build a data-processing machine.Modern applications reduce the concept to structured digital software processing models. Repeated processing through a neural network allows the network to learn from the data it processes. The learned process obtained from a set of training data with solutions can then be applied to other data sets for which no solution exists. An oilfield example includes training a network with wireline log and core data and then using the network to interpret further log data in terms of the core data. Neural networks are also being used in seismic processing, geological mapping and petrophysical analysis.

The point on a string of tubulars at which there are neither tension nor compression forces present. Below the neutral point, there will be compression forces that build toward the bottom of the wellbore. Above the neutral point, tensile forces build to a maximum applied at the hanger or as hook load.

A chemical reaction between an acid and a base to form a salt and water. Neutralization is used in the manufacture of mud products, removal of acidic contaminants from muds and formation of emulsifiers in oil mud. Neutralization is used in the test for alkalinity of mud and mud filtrate.

A fluid prepared to counteract the corrosive effect of acids or acidic treatment fluids. Neutralizing solutions generally are used when the components to be protected cannot be adequately flushed or when there is a risk that residual fluids may cause problems through prolonged exposure. Neutralizing solutions are commonly formulated with soda ash to provide an inexpensive, nondamaging alkaline fluid that does not create excessive disposal difficulties.

A neutron interaction in which the neutron is absorbed by the target nucleus, producing an isotope in an excited state. The activated isotope de-excites instantly through the emission of characteristic gamma rays. Neutron capture, also called thermal capture, usually occurs at low thermal energies at which the neutrons have about the same energy as the surrounding matter, typically below 0.4 eV (0.025 eV at room temperature). Some elements are better thermal absorbers than others. Neutron capture is an important principle behind the pulsed neutron capture log, the elemental capture spectroscopy log, the pulsed neutron spectroscopy log and the thermal neutron porosity measurement.

A device for producing high-energy neutrons by using a charged particle accelerator. Neutron generators are used in various pulsed neutron devices and some neutron porosity measurements. In a typical device, deuterium (2D) and tritium (3T) ions are accelerated towards a target also containing the same isotopes. When 2D and 3T collide, they react to produce a neutron with an energy of about 14.1 MeV. The first neutron generators were built in the late 1950s and soon led to the first pulsed neutron capture log.

Phenomena involving the transfer of energy from neutrons to nuclei. The reaction rate of neutrons with matter depends on the density of neutrons, their velocity, the nuclear density and the particular interaction cross section. There are four principal neutron interactions that affect formation evaluation: elastic neutron scattering, inelastic neutron scattering, fast-neutron reactions and neutron capture.

Normally synonymous with a neutron porosity log. However, the term is sometimes broadened to include an activation log.

Referring to a log of porosity based on the effect of the formation on fast neutrons emitted by a source. Hydrogen has by far the biggest effect in slowing down and capturing neutrons. Since hydrogen is found mainly in the pore fluids, the neutron porosity log responds principally to porosity. However, the matrix and the type of fluid also have an effect. The log is calibrated to read the correct porosity assuming that the pores are filled with fresh water and for a given matrix (limestone, sandstone or dolomite). It is presented in units of porosity (vol/vol or p.u.) for the matrix chosen. Older logs were presented in counts per second or API units. The depth of investigation is several inches, so that the log reads mainly in the flushed zone.The neutron porosity log is strongly affected by clay and gas. Hydrogen occurs in clays and hydrated minerals as well as pore fluids. Gas has a low hydrogen density, so that gas zones have a very low apparent porosity. The measurement is based on either thermal or epithermal neutron detection. Thermal neutrons have about the same energy as the surrounding matter, typically less than 0.4 eV, while epithermal neutrons have higher energy, between about 0.4 and 10 eV. Being a statistical measurement, the precision is greatest at high count rates, which in this case occurs at low porosity.Neutron porosity logs were introduced in the early 1940s. The first tools were known as neutron-gamma tools, since the detector measured the gamma rays emitted on capture. Neutron-neutron tools, using a thermal neutron detector were introduced in about 1950.

A record of elemental concentrations derived from the characteristic energy levels of gamma rays emitted by a nucleus that has been activated by neutron bombardment. In the context of productionlogging, the term normally refers to the activation of silicon and aluminum to determine the quality of a gravel pack. Silicon and aluminum are activated by a neutron source to produce isotopes that decay with a half-life of 2.3 minutes emitting a 1.78 MeV gamma ray. These gamma rays are counted in a detector placed below the source, with a high count indicating a high quantity of silicon in a sand pack, or aluminum in a bauxite pack. The log is run slowly so that oxygen and other activated elements have decayed before the detector crosses the activated interval.The carbon-oxygen log, elemental-capture spectroscopy log, pulsed-neutron spectroscopy log, aluminum-activation log and the oxygen-activation log are also examples of neutron-activation logs.

A completion component fabricated as a short section of heavy wall tubular with a machined internal surface that provides a seal area and a locking profile. Landing nipples are included in most completions at predetermined intervals to enable the installation of flow-control devices, such as plugs and chokes. Three basic types of landing nipple are commonly used: no-go nipples, selective-landing nipples and ported or safety-valve nipples.

The process of disassembling well-control or pressure-control equipment on the wellhead. Depending on the configuration of the wellhead and casing strings, it may be necessary to nipple-down and nipple-up the blowout preventer (BOP) system as each casing string is run.

The process of assembling well-control or pressure-control equipment on the wellhead.

A multiphase fluid incorporating a liquid base and gaseous nitrogen. Nitrified fluids are frequently used in stimulation treatments to enhance the performance of the treatment fluid and improve the cleanup process following the treatment.

A column of high-pressure nitrogen typically applied to a tubing string in preparation for drillstem testing or perforating operations in which the reservoir formation is to be opened to the tubing string. The nitrogen cushion allows a precise pressure differential to be applied before opening flow from the reservoir. Once flow begins, the nitrogen cushion pressure can be easily and safely bled down to flow formation fluids under a high degree of control.

A process whereby nitrogen gas is injected into an oil reservoir to increase the oil recovery factor. Below the minimum miscibility pressure (MMP), this is an immiscible process in which recovery is increased by oil swelling, viscosity reduction and limited crude-oil vaporization. Above the MMP, nitrogen injection is a miscible vaporizing drive. Miscibility of nitrogen can be achieved only with light oils that are at high pressures; therefore, the miscible method is suitable only in deep reservoirs.

(noun) A well activation technique in which nitrogen gas is injected into the tubing or annulus to lighten the hydrostatic column and reduce bottomhole pressure, enabling reservoir fluids to flow to the surface. Nitrogen kickoff is commonly used to unload kill fluid or completion fluid after workover operations.

The use of nitrogen gas circulated into the production conduit to displace liquids and reduce the hydrostatic pressure created by the fluid column. Nitrogen lifting is a common technique used to initiate production on a well following workover or overbalanced completion. A coiled tubing string is generally used to apply the treatment, which involves running to depth while pumping high-pressure nitrogen gas. Once the kill-fluid column is unloaded and the well is capable of natural flow, the coiled tubing string is removed and the well is prepared for production.

The injection of nitrogen into the fluid column within the production conduit to initiate fluid flow from the wellbore and production from the reservoir. Nitrogen lifting through a coiled tubing string is a common technique used in well kickoff.

A high-pressure pump or compressor unit capable of delivering high-purity nitrogen gas for use in oil or gas wells. Two basic types of unit are commonly available: a nitrogen converter unit that pumps liquid nitrogen at high pressure through a heat exchanger or converter to deliver high-pressure gas at ambient temperature, and a nitrogen generator unit that compresses and separates air to provide a supply of high-pressure nitrogen gas.

A nipple that incorporates a reduced diameter internal profile that provides a positive indication of seating by preventing the tool or device to be set from passing through the nipple. In many completions, a no-go landing nipple is preferred for the deepest nipple location, providing a no-go barrier to protect against a tool string being run or dropped below the tubing string.

Anything other than desired signal. Noise includes disturbances in seismic data caused by any unwanted seismic energy, such as shot generation ground roll, surface waves, multiples, effects of weather and human activity, or random occurrences in the Earth. Noise can be minimized by using source and receiver arrays, generating minimal noise during acquisition and by filtering and stacking data during processing.

A record of the sound measured at different positions in the borehole. Since fluid turbulence generates sound, high noise amplitudes indicate locations of greater turbulence such as leaks, channels and perforations. Noise logging is used primarily for channel detection, but has also been used to measure flow rates, identify open perforations, detect sandproduction and locate gas-liquid interfaces. The log may be either a continuous record against depth or a series of stationary readings. The log may indicate the total signal over all frequencies, the signal at a single frequency, or consist of a set of logs for different frequency ranges. Different frequency ranges can be tied to different sources of noise or different flow regimes.Although first introduced around 1955, the technique was not used commercially until after laboratory studies in the early 1970s.

A classification of filter used in the cleaning and treatment of brines and solids-free fluids. Nominal filters trap or remove most particles of equal or larger size than the given filter specification.

Fluid flow that deviates from Darcy's law, which assumes laminar flow in the formation. Non-Darcy flow is typically observed in high-rate gas wells when the flow converging to the wellbore reaches flow velocities exceeding the Reynolds number for laminar or Darcy flow, and results in turbulent flow. Since most of the turbulent flow takes place near the wellbore in producing formations, the effect of non-Darcy flow is a rate-dependent skin effect.

A fluid whose viscosity is not constant at all shear rates and does not behave like a Newtonian fluid. Most successful drilling fluids are non-Newtonian. Within that group are several general types and rheological mathematical models to describe them. Pseudoplastic is a general type of shear-thinning, non-Newtonian behavior that is desirable for drilling fluids. Bingham plastic and power-law models describe a psuedoplastic behavior using only two measurements (two parameters). The Herschel-Bulkley model is a three-parameter rheological model.

A mud that does not conduct electricity sufficiently well to allow spontaneous potential (SP) logging or resistivity logging. Oil- and synthetic-base muds are nonconductive drilling fluids. Water muds are not in this category.

A geological surface that separates younger overlying sedimentarystrata from eroded igneous or metamorphic rocks and represents a large gap in the geologic record.

Contaminants such as hydrogen sulfide [H2S], carbon dioxide [CO2], nitrogen [N2], and water, which are commonly associated with oil and gas production.

A gas described by an equation of state of the form pV = znRT, where z is the gas deviation factor dependent on pressure, temperature and gas composition.

A percentage share of production, or the value derived from production, which is free of the costs of drilling and producing, created by the lessor or royalty owner and borne by the lessor or royalty owner out of the lessor royalty. This royalty is paid to nonparticipating interest holders who do not share or participate in bonus or rentals, or a right to explore, or a right to execute oil and gas leases.

Ownership in a share of production, paid to an owner who does not share in the right to explore or develop a lease, or receive bonus or rental payments. It is free of the cost of production, and is deducted from the royalty interest.

Referring to a type of conventional electrical log in which the current emitting electrode (A) and the measure electrode (M) are placed close together on the sonde, and the current return electrode (B) and the measure reference electrode (N) far away. The response is determined mainly by the distance between A and M. The larger AM, the deeper the measurement, but the poorer the bed boundary response. Although many distances have been used, the most common are 16 in. [40 cm], known as the short normal, and 64 in. [162 cm], known as the long normal.

A type of fault in which the hanging wall moves down relative to the footwall, and the fault surface dips steeply, commonly from 50o to 90o. Groups of normal faults can produce horst and graben topography, or a series of relatively high- and low-standing fault blocks, as seen in areas where the crust is rifting or being pulled apart by plate tectonic activity. A growth fault is a type of normal fault that forms during sedimentation and typically has thicker strata on the downthrown hanging wall than the footwall.

The case in which a wavefront is parallel to an interface and its raypath is perpendicular, or normal, to the interface as the wave impinges upon the interface.

A type of acoustic energy that propagates in one direction while being confined in the other two directions, in this case by the borehole wall. Normal modes are propagated as reflections off the borehole wall, and exist only in hard rock. They are highly dispersive, starting with the formationshear velocity at a certain cutoff frequency and decreasing at high frequencies to the borehole fluid velocity. Below the cutoff frequency, they do not exist. Normal mode #0 is often considered to be the tube wave and starts at zero frequency. Normal mode #1 is called the pseudoRayleigh, and starts at around 5 kHz. The other normal modes start at increasingly higher frequencies.

The procedure in seismic processing that compensates for the effects of the separation between seismic sources and receivers in the case of a horizontal reflector.

The pore pressure of rocks that is considered normal in areas in which the change in pressure per unit of depth is equivalent to hydrostatic pressure. The normal hydrostatic pressure gradient for freshwater is 0.433 pounds per square inch per foot (psi/ft), or 9.792 kilopascals per meter (kPa/m), and 0.465 psi/ft for water with 100,000 ppm total dissolved solids (a typical Gulf Coast water), or 10.516 kPa/m.

A function of time and offset that can be used in seismic processing to compensate for the effects of normal moveout, or the delay in reflectionarrival times when geophones and shotpoints are offset from each other.

A unit of concentration for solutions of reagent chemicals used in testing mud chemistry. Normality provides a simple relationship between the volume in cm3 of reagent added during a titration and the chemical equivalents of a material with which the reagent reacts. A one-normal (1N) solution contains the equivalent weight in grams dissolved in one liter of solution.

A device for measuring the density of fluids in a completed well, using a radioactive source of gamma rays and a detector. In most instruments, a 137Cs (cesium) or 241Am (americium) source is used to induce Compton scattering, as in the openholedensity measurement, except that the device is unfocused. The count rate at the detector then depends primarily on the density of the fluids in the well. In some devices, the fluids pass through an open space in the body of the tool within which the measurement is made. The results then reflect the density of the fluids passing through the tool. In other devices, the source and detector are isolated so that the gamma rays pass outside the tool. The results then reflect some average density of all the fluids within the well. In smaller casings, some formationsignal may contaminate the measurement.Compared with a gradiomanometer, the nuclear fluid densimeter is a less direct measurement of density, and has a statistical uncertainty and less resolution. On the other hand, it is not affected by well deviation, friction or kinetic effects.

Pertaining to a measurement of the nuclear magnetic properties of formation hydrogen. The basic core and log measurement is the T2 decay, presented as a distribution of T2 amplitudes versus time at each sample depth, typically from 0.3 ms to 3 s. The T2 decay is further processed to give the total pore volume (the total porosity) and pore volumes within different ranges of T2. The most common volumes are the bound fluid and free fluid. A permeability estimate is made using a transform such as the Timur-Coates or SDR permeability transforms. By running the log with different acquisition parameters, direct hydrocarbon typing and enhanced diffusion are possible.

A measurement of the nuclear magnetic resonance (NMR) properties of hydrogen in the formation. There are two phases to the measurement: polarization and acquisition. First, the hydrogen atoms are aligned in the direction of a static magnetic field (B0). This polarization takes a characteristic time T1. Second, the hydrogen atoms are tipped by a short burst from an oscillating magnetic field that is designed so that they precess in resonance in a plane perpendicular to B0. The frequency of oscillation is the Larmor frequency. The precession of the hydrogen atoms induces a signal in the antenna. The decay of this signal with time is caused by transverse relaxation and is measured by the CPMG pulse sequence. The decay is the sum of different decay times, called T2. The T2distribution is the basic output of a NMR measurement.The NMR measurement made by both a laboratory instrument and a logging tool follow the same principles very closely. An important feature of the NMR measurement is the time needed to acquire it. In the laboratory, time presents no difficulty. In a log, there is a trade-off between the time needed for polarization and acquisition, logging speed and frequency of sampling. The longer the polarization and acquisition, the more complete the measurement. However, the longer times require either lower logging speed or less frequent samples.

Mathematical methods that require iterative processing of data rather than applying deterministic equations. Some relationships can be solved only by numerical methods, including most integration problems, some differentials and some statistical processes.

A rendering of a model of a reservoir or field in entirely numerical formats. Numerical models, once built, may be used to perform many mathematical operations, including calculations of available reserves and simulations of the behavior of the reservoir.

The mathematical simulation of a numerical model of a reservoir's petrophysical characteristics to analyze and predict fluid behavior in the reservoir over time.