Refers to the closeness of a measurement to the true value.

The product of density and seismic velocity which indicates the ability of a boundary to reflect seismic energy.

A sound wave that is transmitted through material by elastic deformation.

A record of radiation from radionuclides that are produced in the vicinity of a well by irradiation with neutrons; the short half-life radioisotopes usually are identified by energy of their gamma radiation or decay time.

The maximum height of a wave from its average value.

Image created using the measured amplitude of the reflected acoustic pulse propagated by an acoustic televiewer.

The number of protons in a nucleus.

The combined weight of protons, neutrons and electrons in atoms.

An angular measurement that uniquely determines the orientation of a feature on the surface of Earth.

Borehole Magnetic Resonance ? a geophysical method that is used to analyse hydrogeological properties in ground rocks. It involves sending electromagnetic pulses into the ground through a borehole, which excites the hydrogen atoms, as they align with the induced magnetic field. Measuring the response and relaxation time of the hydrogen atoms as they return to their original orbit. BMR provides information on porosity and permeability in ground rocks.

Vertically or near vertically elongated features / cavities in the borehole wall created by the interaction of horizontal stresses on the open hole. Used to determine maximum horizontal stress orientations in the rock mass.

A measure of the ability of a substance to withstand changes in volume when under compression on all sides.

The mass of material per volume, which indicates the density in grams per cubic centimetre of the rock with pore volume filled with fluid.

Counts Per Second. Raw log data is acquired in CPS prior to conversion to calibrated units by the application of calibration equations.

A determination of the log values that correspond to the environmental units, such as porosity or bulk density; calibration isÿusually carried out it pits or by comparison with laboratory analyses of core.

A well logging tool which determines the diameter of a borehole along its depth.

Loging that occurs in a wellbore that has been cased with steel or cement to protect the open hole from fluids, pressures, wellbore stability problems, or a combination of these.

An opening in the borehole wall that extends beyond the nominal borehole diameter.

The normalised area under an induced polarisation (IP) decay curve, between two times, after the transmitted current is stopped in a time domain survey. Usually expressed in millivolt-seconds per volt.

A type of soil that is plastic in nature and has fine particle sizes, that are closely packed together. Clay has limited air spaces and adsorbent properties.

The inelastic scattering of gamma photons by orbital electrons, Compton scattering is related to electron density and is a significant process in density logging.

An aquifer (water-bearing rock) that is overlain by an impermeable rock.

A body of contaminated groundwater flowing from a specific source.

Analyzing physical rock samples in the laboratory to determine key properties.

Locating stratigraphically equivalent rock units in different wells by matching geophysical logs.

Is well logging that provides a continuous record of a formation's bulk density along the length of a borehole.

Similar to Tilt, dip is the angular measurement with reference to the horizontal.

The horizontal direction corresponding to the down dip (borehole or plane) vector orientation with reference to magnetic north, true north or borehole high-side.

A log that provides data on the azimuth and deviation of a borehole from the vertical.

ESG stands for environmental, social, and governance. It is a framework or a set of standards that evaluates how a company performs on sustainability issues.

The unit of measurement of an object's or substance's resistance to being deformed elastically when a stress is applied to it.

The measurable sphere of influence in which electric forced are exerted, and which electric charge acts.

A study conducted in a region to examine the impact of various development projects on the natural environment in a region.

A zone of weakness in the Earth?s crust where failure results in cracks in rock formations.

Substances having a relatively large magnetic susceptibility.

The space in which an effect such as gravity, magnetism or electricity is measurable.

The process of interpreting data obtained from a wireline log for reserve estimation.

Ground penetrating radar ? is a geophysical method that uses pulses (radio and microwaves) to image the subsurface.

A technique that measures natural gamma radiation emitted by rocks to characterise lithology.

Analysing and visualising geophysical data to create subsurface models and make informed decisions about drilling.

The rate of change in temperature with respect to increasing depth in Earth's interior.

A measure to indicate how easily water can pass through rocks.

Magnetisation caused by an applied magnetic field.

Induced polarisation is a geophysical imaging technique used to identify the electrical chargeability of subsurface materials, such as ore.

A method to determine intermediate values from the surrounding known values.ÿ

Data consisting of a discrete value applied to a set depth interval down the hole, defined within “from” and “to” depths.

Log Ascii Standard. A form of ascii file particular to the logging industry. Can be opened in any text file editor.

The distance a nuclear logging probe moves during one time constant.

The general physical characteristics of rocks.

The distance from the borehole collar along the path of the borehole, increasing from zero at the collar to the end of hole.

An abbreviated log title with no spaces in the name. Used to facilitate data import into databases with the need for data preconditioning.

A measure of how much a material will become magnetized in an applied magnetic field.

The variation in minerals occurring rocks.

Logging that occurs in an uncased section of a borehole. All wells are initially open hole wells when they are initially drilled.

A longitudinal seismic wave which is the first type of seismic wave to reach a receiver and is propagated in liquids and solids.

The ability of rocks to allow water to move through them.

A data format consisting of a discrete data value for a given depth down the hole. Also called profile data.

The ratio of transverse contraction (or expansion) strain to longitudinal extension strain in the direction of stretching force. Tensile deformation is considered positive and compressive deformation is considered negative.

A stereo net projection of planar features intersecting the borehole where the poles to the plane are plotted instead of great circles.

The degree of available voids in rocks through which water can pass.

How close measurements are to each other.

Also called sonde or tool, a downhole well-logging instrument package.

Rock Quality Designation is a rough measure of the degree of jointing or fracturing in a rock mass, measured as a percentage of the drill core in lengths of 10 cm or more.

Diagrams used to plot the orientation of joints and dykes.

A transverse seismic elastic wave that is propagated through solids only.

A measure of the ability of a material to resist transverse deformations and is also known as the rigidity.

A zone of localised weakness in the Earth?s crust that accommodates higher strain, resulting in differential movement in the Earth?s crust and mantle. Shear zones occur in regions where higher temperatures prevent faults and fractures from forming.

A type of acoustic log that displays travel time of P-waves versus depth. Sonic logging uses sonic tools to measure the speed of sound in rocks and fluids to determine rock properties.

The structure of layered rocks.

Total dissolved solids are a measure of the combined organic and inorganic contents in a liquid.

The object at which a survey sighting is aimed.

Measurement of the borehole deviation away from vertical with zero degrees being vertical.

Image created using the measured two-way travel time of the reflected acoustic pulse propagated by an acoustic televiewer.

Depth below surface measured vertically and not along the borehole path with increasing value going downwards.

A measure of how clear a water sample is.

An aquifer with its water table open to the atmosphere.

Is the undersaturated portion of the subsurface that lies above the groundwater table.

A general widening of the borehole beyond the nominal drilled size caused by mechanical and fluid effects from the drilling process.

Processing and interpretation software for borehole logs.ÿ

A steel cable used to lower and raise geophysical instruments and tools in a borehole.

A method of collecting geological data by lowering instruments down a borehole to measure various rock properties.

A specialised vehicle equipped with winches for deploying and retrieving wireline logging tools.

is a property of the material that tells us how easily it can stretch and deform and is defined as the ratio of tensile stress (σ) to tensile strain (ε).

Ratio of the atomic number to atomic weight, which affects the relation between the response of gamma-gamma logs and bulkÿdensity logs.