The Geo People

On this page are explanations of terms and abbreviations used on this website and across the oil & gas industry.


Accelerometer – instrument to measure the acceleration of the Earth's surface caused by acoustic vibrations.

Acoustic impedance – the product of rock density and velocity of sound within the rock, represented by Z.

Acoustic traveltime  the time it takes for a seismic signal to travel from the source through the Earth and back to the receiver.

Aeromagnetic survey  Earth's magnetic field intensity measurements acquired by aircraft in which the magnetometers are towed by a plane or helicopter. Comparisons are made between the actual and theoretical Earth's magnetic field and differences / anomalies are attributed to the changes in rock type or thickness of rocks.

AGC  automatic gain control. This increases the amplitude of an electrical signal, automatically. Used in seismic processing to compensate for amplitude decay through spherical divergence or atttenuation.

Aliasing  caused by inadequately sampling a seismic signal. This can be avoided by filtering out frequencies above the Nyquist frequency, the highest frequency that can be defined accurately by the sample interval.

Amplitude anomaly  a seismic amplitude anomaly that can indicate the presence of hydrocarbons. However, they can also be the result from seismic processing problems, focussing in geometry or velocities or lithology changes.

Autocorrelation  the comparison or correlation of a seismic waveform with itself. It is used to identify multiples or other regularly repeating signals.

AVA  amplitude variation with angle of incidence.

AVAZ  amplitude variation with azimuth.

Average velocity  the depth divided by the traveltime of a seismic wave to that depth. It is usually calculated by assuming a vertical, straight ray paths and parallel geological layers, not actually found in the Earth.

AVO  amplitude variation with offset. Variation in seismic reflection amplitude with change in distance between source and receiver indicating differences in thickness, porosity, density, velocity, lithology and fluid content in rocks above and below the reflector.

AVOAZ  amplitude variation with offset and azimuth.



Backscatter  occurs when no coherent reflected energy can be identified and the energy is scattered in all directions.

Band-pass filter – a filter that passes a range of frequencies and rejects the others.

Base map  a base map shows the position of concession boundaries, wells, seismic survey points, buildings and roads.

Base of weathering  this is the lower boundary of the low-velocity near-surface layer. This is compensated for by applying static corrections to the seismic data.

Base station  a reference location for a survey, whose measured values can be used to normalize other survey points.

Baseline  a line joining two base stations.

Basement  the layer of rock below which oil and gas is not expected to be found. Normally made of older,  igneous or metamorphic rocks.

Basic wavelet  the wavelet produced by a reflection at one interface with a positive reflection coefficient. Used in generating a convolutional model.

BCF  billion cubic feet, units used for large volumes of natural gas.

Beaufort scale  wind strength scale which ranges from 0 to 12, 12 being for hurricane strength winds.

Benchmark  a permanently fixed marker of known position usually made of concrete or steel plate used in surveying.

Bias  the shifting of the baseline of reflections during seismic processing to accentuate the peaks or troughs.

Bin  the area of a three-dimensional survey is divided into bins, usually about 25m long and 25m wide. Traces falling within a bin are stacked (averaged out) to create one output trace for each bin

Bird – an instrument containing a magnetometer and possibly other instruments towed by an aircraft in aeromagnetic surveying or in a marine seismic streamer to provide dynamic information about the streamer position and depth (using a depth sensor).

Bird controller  streamer depth controller. They allow the vessel operator to bring the cable to the surface in shallow water or to dive the cable to avoid shipping traffic.

BLPD  the daily total production in terms of volume of oil and water from a well. A barrel is equivalent to 42 US gallons.

BOSIET  basic offshore safety induction and emergency training  for new entrants to the offshore oil and gas industry

Bouger anomaly  the residual gravitational attraction after accounting for theoretical gravitational attraction, latitude, height above sea level, the Bouger correction and the free-air correction.

Bright spot  a high amplitude anomaly on a seismogram that may indicate the presence of hydrocarbons. They result from large changes in acoustic impedance.

Brute stack  a processed seismogram containing summed CMP traces which have had approximate sound velocities applied, so the normal-moveout correction is a first attempt. For land surveys, static corrections are not normally applied before the brute stack.

Brute stack  a seismogram containing traces from CMPs that have been added together - only very rough sound velocities are applied.

Bubble effect  in marine towed airguns, gas bubbles produced by the air guns oscillate producing subsequent pulses/ noise. By using combinations of air guns, destructive interference of bubble pulses reduce the bubble effect.


CDP  common depth point. Where the geological layers do not dip, the CMP on a reflector is the same as for a CDP. However, for dipping beds, smearing occurs and dip move out processing should be applied.

Circle shooting  used to acquire full-azimuth (FAZ) marine towed streamer seismic data where the vessel acquires data in a series of overlapping, continuously linked circles. FAZ data acquisition is used where the geology is complex.

CMP  in multichannel seismic acquisition and for non-dipping geological layers, the common mid point (CMP) is the point on the surface halfway between the source and receiver that is shared by the other source-receiver pairs.

Coherent noise  unwanted seismic energy with consistent phase from trace to trace, as found in multiples and ground roll.

Convolution  in seismic processing convolution is applied to any two functions of time or space to produce a third function such that one of the functions is a filter acting on the other function. Deconvolution is used to counteract the filtering of the seismic energy by the rock sequences of the Earth.

Correlation  comparison of different seismic waveforms in the time domain.

Coupling  the extent to which two entities are attached. In land seismic acquisition a geophone is well-planted if coupled to the Earth's surface.

Cross correlation  comparison of different seismic waveforms to quantify their similarity. A correlation coefficient which varies between zero and one is equal to one if the waveforms are identical.

Crossline  a line perpendicular to the direction in which seismic data were acquired.

CRS  coordinate reference system.


Datum correction  a time value applied to seismic data reflection times compensating for the location of the receiver and source relative to the seismic datum in a land survey.

dB  the decibel is the unit of measurement comparing the relative intensity of acoustic or electrical signal, equal to one-tenth of a bel. The logarithm of the ratio of the sound or signal to a reference provides the decibel measurement. The number of decibels is ten times the logarithm to base 10 of the ratio of two power quantities, or of the ratio of the squares of two field amplitude quantities.

Deconvolution  deconvolution recovers high frequencies, attenuates multiples, equalizes amplitudes by producing a zero-phase wavelet in seismic data processing, often called inverse filtering.

Deep tow  in marine seismic acquisition when the vessel tows a streamer much lower beneath the surface than normal to get closer to features of interest or to reduce noise resulting from sea conditions. Deep tow devices are sometimes also used for side-scan sonar, gravity and magnetic surveys.

Depth controller  an instrument used in towed streamer acquisition to maintain streamers at a certain depth in the water, usually called a 'bird'.

Depth migration  used in seismic processing so that time domain data are moved to their correct positioins in space. This is required in areas of changeable lateral and vertical velocities which distort the time seismogram and requires accurate knowledge of the variability of vertical and horizontal seismic velocities.

Detonator  a small, explosive charge that explodes a larger charge and is set off electronically. Also called caps, they are used in land seismic acquisition to obtain consistent detonation timing.

Diapir  diapirs are made from relatively low-density rock types, such as salt, shale and hot magma and intrude vertically through more dense rocks. They can form anticlines, salt domes and other structures able to trap hydrocarbons (salt and shale diapirs only).

Difference map  a reservoir map is of an area created by two different seismic surveys taken at different times. An isochron map shows the variation in time between two seismic events.

Differential corrections  differential global positioning system (DGPS) is an enhancement to GPS that provides improved location accuracy, from the 15m nominal GPS accuracy to about 10cm in case of the best implementations. DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. These stations broadcast the difference between the measured satellite pseudoranges and actual (internally computed) pseudoranges, and receiver stations may correct their pseudoranges by the same amount. The digital correction signal is typically broadcast locally over ground-based transmitters of shorter range.

Diffraction  produced by the radial scattering of a wave into new wavefronts caused by a fault surface, an unconformity or sudden change in type of rock. Diffractions are represented by hyperbolic events on a seismogram and migration of seismic data uses this diffracted energy position reflections where they should be.

Diffraction stack  also called Kirchhoff migration, using the integral form of the wave equation. It requires a model of constant or smoothly varying velocity and basically, it stacks the data along curves that trace the arrival time of the scattered energy.

DMO  dip moveout is the difference in the traveltimes of a reflected wave, measured by receivers at two different offsets when the reflectors dip.

Doodlebugger  slang term for a field seismologist.

Down dip  a position lower down a slope of a dipping surface.

Drill noise vertical seismic profile  a vertical seismic profile (VSP) can use the noise of the drill bit as a source with the receivers laid out along the ground or seabed. In deep water however, the receivers can be deployed vertically. It results in time-depth information being aquired during drilling (sometimes reflection information) helping with time-depth conversions while drilling and deciding the placement of casing and evaluate anomalous pore pressures.

Dropout test  dropout analysis, with automatic test of all dropout combinations to a given maximum number of guns can be performed. Dropout set up can then be statistically analyzed with user-defined threshold for acceptable losses in primary amplitude, primary-to-bubble amplitude ratio, correlation coefficient, and frequency attributes such as average and maximum spectrum difference within a given frequency band.

Dropout  loss of seismic data from a receiver to record a number of shots in a seismic survey.

Dynamic range  difference between the highest and the lowest signal, that can be detected by an instrument without distortion.


Enhanced oil recovery  enhanced oil recovery (EOR) changes the original properties of oil to restore formation pressure and improve oil displacement and fluid flow within the reservoir. Chemical flooding, miscible displacement and thermal recovery are the three methods for EOR.

EPA  Environmental Protection Agency, a branch of the US government.

ERGO  explosive remnants of geophysical operations.

Evaporite  a type of sedimentary rock formed by precipitation from evaporating aqueous fluid e.g. halite, gypsum and anhydrite, which can form as seawater evaporates, and the rocks limestone and dolostone. They have minimal porosity and they tend to deform plastically and so make good cap rocks.


Fan shooting  a seismic refraction method whereby the the geophones are placed in an arc or fan shape around high-velocity features such as salt domes with a central shotpoint. These data are then calibrated with a control seismogram acquired away from the salt dome.

Fast fourier transform  an iterative computer algorithm to rapidly perform the Fourier transform of digitized waveforms

Feather angle  the angle between the actual cable position and the shot-line direction (the boat track) is called the feathering angle. This angle is not always constant, even along the same cable associated with a single shot.

First arrival  the first arrival of energy arriving from the seismic source to the receiver.

FLO  fishing liaison officer.

FLQC  first line QC is employed to verify the navigation computer parameters, data quality and the integrity of the final deliverables (P2 and P1 datasets).

FOET  further offshore emergency training, repeatable every four years after the initial BOSIET.

Fold of data  fold is defined as the number of midpoints which are stacked within a CMP bin.

Footprint  in marine seismic acquisition, this is the area covered by an array of towed streamers.

Four component seismic data  the acquisition of four-component (4C) marine seismic using three orthogonally-oriented geophones and a hydrophone using OBC (nodes or cables). The geophones record shear (S) waves and the hydrophone measures compressional (P) waves.

Four dimensional seismic data  two 3D seismic datasets acquired at different times over the same area to observe changes in the reservoir over a period of time.

Fresnel zone  the part of a reflector from which most of the energy is returned. Arrival times differ by less than half a period from the first break and waves with such arrival times interfere constructively and will appear as a single arrival. Features on the reflector smaller than the Fresnel zone cannot usually be identified using seismic waves.

Full azimuth towed streamer acquisition  single-vessel seismic acquisition whereby a complete range of azimuths is obtained by towing the streamers in a circular path.


Gas show  gas that rises to the surface which can be detected by the mud logger, measuring combustible gases (e.g. methane, ethane, butane).

Geochemical seep surveys  high resolution Multibeam data to detect pockmarks and plumes in the water column and Subbottom data to to detect faults and potential seep areas are acquired before undisturbed sediment samples from water depths up to 5,000m are taken. A wide range of analysis including the basic analyses quantity of free gaseous and liquid hydrocarbons, and the more complex detailed evaluation of hydrocarbons and carbon isotope is performed  and the data presented and interpreted.

Gravity anomaly  the difference between the gravity value measured and the value predicted by a particular Earth model. Usually determined by correcting the known gravity value at a reference station by Bouguer and free-air corrections etc and taking away the final predicted value from the measurement.

Ground roll  coherent noise generated by a land surface wave, usually a low-velocity, low-frequency, high-amplitude Rayleigh wave. Can mask seismic signal, but it's effects can be reduced by selecting the optimum source and geophone arrays and seismic processing parameters.

Guided wave  an elastic wave which travels within a geological layer which has a velocity lower than that in the adjacent layers.


H2S  a very poisonous gas which is lethal at high concentrations and odorless. As hydrogen sulfide gas is present in some subsurface formations, awareness, detection and monitoring of H2S is very important.

HAZID  hazard identification (HAZID)  a well organisesd HAZID study will provide good identification of hazards and safeguards at an early stage of an operation.

Heliportable survey  land seismic survey where helicopters are the primary means of transport.

HSEA  HSE advisor.


IMAS and clearance SOPs 

Impedence  the product of velocity times density, also called acoustic impedance (Z). The reflection coefficient of an interface depends on the contrast in acoustic impedance of the two rock layers.

In-line  in marine seismic acquisition, the in-line direction is that in which the receivers are towed.

IOGP P1/11  Geophysical position data exchange format. The OGP P1/11 format replaces the UKOOA P1/90, SEG P1 and other legacy positional exchange formats and is designed for the exchange of position data typically resulting from in-field survey operations such as geophysical (including seismic), hydrographic etc.

ISO  International Organization for Standardization. ISO is a group of national-standards institutes from 157 countries (with one member per country) and managed by offices in Geneva. ISO is derived from the Greek isos, meaning equal.

Isochron map  a contour map that shows the difference in time between two seismic horizons.

IVMS  the IVMS (in-vehicle monitoring system) tracks speed, acceleration, deceleration, kilometers and hours  driven (as a minimum). A data management system (DMS) analyses the information and feeds it back to the driver.


Jackup rig  a combination of a drilling rig and floating barge, with long support legs which are raised or lowered independently of each other.

Journey management system  the control of all aspects of transportation by dedicated senior staff who monitor progress and respond to deviations and emergencies.

Jug  slang term for a geophone.

Lost time incident  an injury to an employee that will ultimately lead to the loss of the work time in the form of delayed work time

Low velocity layer  the near-surface, often unconsolidated layer of low seismic velocity also called the weathering layer. The bottom of this layer often coincides with the water table at which point the seismic velocity increases significantly.


Magnetic field  the superposition of magnetic fields from the main magnetic field, the field from the Earth's crust, the field from external disturbance and the local magnetic interference.

Magnetometer  device used to measure the strength and/or direction of the Earth's magnetic field.

MAZ  multi azimuth survey  the 3D towed streamer data is acquisred a number of times (typically 3 - 6)  in different directions.

Medevac  medical evacuation, often shortened to medevac or medivac, is the timely and efficient movement and en route care provided by medical personnel to injured patients being evacuated from the scene of an accident to receiving medical facilities.

Minimum phase filter  the passband of a minimum phase (Butterworth) filter is more complex and involves two cutoff frequencies where the filter is at approximately half power.

Mis tie  when the predicted and actual values differ in seismic interpretation, or when there is no closure on an interpreted reflector or tie on intersecting lines; or when the interpreted seismic data does not match results from drilling a well. Commonly occurs when data of different phases are interpreted together, or when data with different datum corrections are tied.

MIST  minimum industry safety training  for those who have attended the BOSIET course.

MMO  marine mammal observer.

Mute  the removal of part of selected seismic traces in a stack to minimise air waves, ground roll and other early-arriving noise. Low-frequency traces and long-offset traces are usually muted.


Near surface correction  also called static correction  a bulk time shift of a seismic trace. Static corrections can be the weathering correction, differences in topography and differences in the elevations of sources and receivers.

NMO – normal moveout (NMO) is the result of the separation between receiver and source on the arrival time of a signal from a horizontal reflector. The separation between the source and receivers induces a delay in the arrival time of a reflection from a horizontal surface at depth compared to if they were positioned in the same place (zero offset). The plot of two way travel time versus offset is hyperbolic in shape.

Node survey  the nodes are not connected by cables and typically contain one (1C) sensor or three sensors (three component, 3C) geophones. Benefits of the nodal system over a cable system are to reduce exposure of personnel and vehicles as well as save time, reduced environmental impact, can bury/hide the nodes.


OBC  ocean bottom cable (OBC) receiver cables are laid out on the sea bed and the source is towed just under the sea surface either parallel or othoganal to the the axis of the receiver cables. The receivers contain hydrophones (for P-waves) and three  component geophones (for S-waves). OBC surveys are used in water depths from 50m to about 500m.

OBN  ocean bottom node survey. Receivers are coupled to the sea bed and not connected by cables. The receivers typically contain hydrophones and three component geophones (four components or 4C).

OSHA  Occupational Safety & Health Act (USA). Laws to protect the safety and health of workers and give them the right to know what materials they are handling. For example safe handling of mud chemicals and monitoring for H2S in air around the rig and testing the mud for sulfides are an important part of rig safety.


P wave  a compressional elastic wave in which the particles oscillate in the direction of wave propagation.

PAM  passive acoustic monitoring.

Patch  a large set of seismic receivers whose output is sent to one common data channel to record a seismic trace.

PCN  primary control network.

Permafrost  subsoil that is permanently frozen in arctic regions.

PPE  personal protective equipment. PPE should be used when all other measures are inadequate to control exposure. It protects only the wearer, while being worn.

PRA  project risk assessment  a live document which is reviewed on a monthly basis as set by HSE calendar.

Primary reflection  seismic events where the energy has been reflected once as opposed to multiples where the energy has been reflected more than once.

PSO  protected species observer.


Q wave  a type of surface wave whereby the particles oscillate both horizontally and perpendicularly to the direction of wave propagation.

Quick look  part of a 3D seismic survey (low fold or simplified processing) to be seen quickly after the seismic acquisition.


Radial array  where the sources or receivers radiate out from a central point, usually a borehole.

Residual oil  oil that remains when fluids are flowed through the rock as in primary and secondary recovery and invasion.

ROV  remotely operated vehicle.

Run in  the distance necessary to bring the fold from its minimum to its nominal value in the shooting direction.

RWP  remedial work plan.


S wave  shear wave  an elastic wave which oscillates perpendicular to wave propogation direction  can only travel through solids

Sabkha  an environment which is devoid of vegetation made of coastal sediments in arid or semiarid conditions above the high tide mark.

Scouting  to inspect an area prior to a survey or to monitor activity.

Seep  a slow leakage of fluid  water, oil or gas at the Earth's surface

Semblance  the coherence of seismic data from multiple channels that is equal to the energy of a stacked trace divided by the energy of all the traces in the stack.

Semisubmersible  a floating vessel that is supported by large pontoons submerged below the sea surface. The operating decks are elevated above the pontoons by large steel columns,  minimizing loading from waves and wind.

Sequence stratigraphy  the interpretation of sedimentary basin deposits in combination with eustasy, sedimentation and subsidence to correlate strata and predict stratigraphy.

Side scan sonar  generates a pulse (with frequencies from 30 to 120kHz) that is reflected from the seafloor to produce an image of the seafloor and shallow sediments.

Sideswipe  when a feature (such as an anticline of fault) out of the plane of a 2D seismic section is apparent. The process of migration in a 3D survey would eliminate this.

SIMOPS  performing two or more of the following operations simultaneously: construction, anchoring, derrick barge operations, heavy lifts, diving operations, shared road networks, mobilisation and demobilisation of equipment, seismic or geotechnical operations, aircraft landing/takeoff, emergency/spill response.

SIMOPS  simultaneous operations

Site survey  a high resolution 2D seismic survey that takes place to ensure safe drilling/installation of a rig. It usually includes an echo-sounder survey, side scan sonar and seafloor coring.

Slant stack  whereby traces are stacked by shifting traces in time in proportion to their offset  useful where reflectors dip.

Smile  an upward concave event in seismic data usually caused by poor data migration or migration of noise.

Soft start procedure  power of the seismic gun arrays is built up slowly from a low energy start-up (e.g. starting with the smallest airgun in the array and gradually adding in others) over at least 20 minutes to give adequate time for marine mammals to leave the area.

Source pattern  the arrangement of seismic sources, with each individual source being activated at a certain time.

Stacking velocity  the distance-time relationship determined from NMO measurements from CDP gathers. Used to correct the arrival times of events in the traces for their varying offsets prior to summing, or stacking, the traces to improve the signal-to-noise ratio of the data.

Stonely wave  a large-amplitude interface, or surface, wave produced by a sonic tool in a borehole. Can aid estimation of the locations of fractures and permeability in a formation. Can be a major source of noise in vertical seismic profiles.

STOP – safety training observation program.


Tail mute  a mute in time and/or offset which eliminates slow surface waves such as ground roll.

Time migration  time migration is applied to seismic data in areas where lateral velocities do not change much, but where there are complex structures. It effectively moves dipping events to their true locations in time. Afterwards, the data is converted to depth using accurate sound velocities so that the data can be tied in with well logs.

Time slice  a horizontal display 3D seismic data at a certain travel time, as opposed to a horizon slice that shows the horizon of a reflector.

Toolbox meeting  a toolbox meeting is an informal group discussion that focuses on a particular safety issue. They are also intended to facilitate health and safety discussions on site.

Towed streamer  towed streamers are employed in deep water seismic surveys. The receivers are towed behind the seismic vessel in a single (2D) or multiple (3D) array.

True amplitude recovery  compensation for attenuation, spherical divergence by adjusting the amplitude of the data so that the reflection amplitudes relate directly to the change in rock properties.

TS dip  temperature salinity dip, a device used to determine the velocity of sound in sea water by measuring the temperature, salinity, and depth and using an equation to relate this to velocity.

TWT  the time taken for a seismic wave to travel from source to reflector and back to a receiver at the Earth's surface.

TZ  the transition zone (TZ) environment is the dynamic and complex environment between land and deeper water. The environment encompasses land, fresh and salt water marsh, swamp, near shoreline, surf and tidal zones, lagoons, coral reef environments and deeper water up to about 100m in depth.


Undershooting  acquisition of seismic data beneath areas that are difficult to access on the surface, such as rivers, drilling rigs, production platforms, environmentally sensitive areas or around salt domes, where the sources and receivers are placed on opposite sides of the feature.

Updip  located up the slope of a dipping surface.

Uphole drilling  seismic 'upholes' are shallow drill holes (20–50m in depth) placed at regular intervals (1–2km) along exploration seismic lines. 'Uphole shooting' allows estimation of the thickness and seismic velocity of the weathered zone as well as the sub-weathering velocity. These data are then used in computing time corrections to a nominal seismic datum, which is a fundamental step in computer processing of seismic field data. Uphole shooting involves successive detonation of a series of charges at varying depths inside the drill hole and recording of the 'uphole time' with a surface geophone placed near the uphole.

UXO  unexploded ordnance.


Velocity analysis  calculating seismic sound velocity to better process seismic data.

Vertical seismic profile  borehole seismic measurements used to correlate with surface seismic data, for high resolution images and for looking ahead of the drill bit; also called a VSP.

Vibrator  commonly used for acquisition of land seismic data as opposed to dynamite as a source. Mounted on large trucks.

VSAT  short for very small aperture terminal, an earthbound station used in satellite communications of data, voice and video signals, excluding broadcast television.

VSP  VSP (vertical seismic profile) is a technique of seismic measurements used for correlation with surface seismic data. The defining characteristic of a VSP (of which there are many types) is that either the energy source, or the detectors (or sometimes both) are in a borehole.


WRIST communications  written, radio, internet, spoken and telephone communications.

WAZ  wide azimuth survey  for each shotpoint, a wide array of receivers are used creating a wide range of source-receiver azimuths. This methodology is used on land and marine (seabed) surveys. Wide azimuth towed streamers (WATS) use multiple source vessels and multiple receiver vessels and the distance between them is increased in successive passes over the same subsurface area.

Wellhead  the surface termination of a wellbore.

Wireline  any aspect of logging using an electrical cable to lower tools into a borehole and transmit data.


Yellow fever certificate  there is a vaccination for yellow fever. Some countries require proof of vaccination (a certificate) against yellow fever before they let you enter the country. You should have a yellow fever vaccination at least 10 days before your travel. This will allow enough time for your body to develop protection against the yellow fever infection. 


Zero offset data  seismic data acquired with no horizontal distance between the source and receiver.

Zero phase filter  the passband of a zero-phase (Ormsby) filter is usually defined by up to four corner frequencies.

Talk to us
We're not called the Geo People for nothing. Get in touch and you can talk to a qualified person about all your consultancy needs.