Glossary

Glossary

Annular Space

The space between two concentric objects, such as between the wellbore and casing or between casing and tubing, where fluid can flow.

Aquifer

Rock or sediment in a formation, group of formations, or part of a formation that is saturated and sufficiently permeable to transmit economic quantities of water to wells and springs.
Applied Hydrogeology. Third edition. C.W.Fetter

Conductivity

[Unit = µS/cm]

The electrical conductivity of a water is the conductance of a water column between two metallic electrodes of 1 cm² surface and separated of 1cm. The conductivity unit is micro-siemens per centimeter (µS/cm). The conductivity is an expression of the total mineralization of the water. The conductivity value depends on the temperature and is generally given for a temperature of 25°C. For a water of a conductivity Ct at a temperature t in Celsius degrees, the conductivity C25°C at the temperature 25°C is:

C25°C =Ct/1+0, 02(t-25)

Core

Cylinder of rock, with a diameter of several centimeters. Every independent part must be identified. One core sample can contain several cuttings that can be put in different boxes. (For an example, see for the Poitiers site)

Drawdown

[Unit: meter]

A lowering of the water table of an unconfined aquifer or the potentiometric surface of a confined aquifer caused by pumping of ground water from wells.
Applied Hydrogeology. Third edition. C.W.Fetter

Permeability

The ability or measurement of a rock’s ability, to transmit fluids. The symbol most commonly used for permeability is k, which is measured in units of darcies or millidarcies. (http://www.glossary.oilfield.slb.com/en/Terms/p/permeability.aspx)

When a construction will be characterized, the permeability indicated will described the horizontal flow in the porous media.

Piezometric level

[Unit: meter]

Water level measured in a piezometer.

Resistivity

[Unit: ohm.cm]

The resistivity is inverse of the conductivity; the unit is ohm.cm (W.cm)

Well Screen

A tubular device with either slots, holes, gauze or continuous-wire wrap; used at the end of a well casing to complete a well. The water enters the well through the well screen.

Well logging

Measurements of the vertical distribution of a parameter within a borehole. Logging has a very wide range of applications:

  • hydraulic (velocity, etc.)
  • physico-chemical (temperature, conductivity, oxygenation, etc.)
  • electrical (spontaneous polarisation, electrical image, etc.)
  • radioactivity (gamma-ray, neutron, etc.)
  • acoustic (wave speed, acoustic imaging, etc.)
  • technical (diameter, inclination, cementing, video, etc.)

Measurements are taken using probes lowered into the borehole. Diameter of the hole produced by the drilling machine and the casing installed. The choice of diameter depends on the objective set for the work to be carried out and the geological risks involved in drilling. The initial drilling diameter must allow a casing to be installed to maintain the levels drilled in the event of damage (landslide, etc.) so that drilling can continue at a smaller diameter. As an indication, the usual diameters used for works not exceeding a few hundred metres are :

Drilling diameter / Casing diameter

  • 17″3/8 441 mm
  • 12″1/8 308 mm
  • 8″1/2 216 mm
  • 6″ 152 mm
  • 3″7/8 96 mm
  • 13″3/8 340 mm
  • 9″5/8 244 mm
  • 6″5/8 168 mm
  • 4″1/2 144 mm

Well and core diameters are given in mm.

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