Facilities for well logging

Well logging involves recording physical characteristics of the well, soil type and water in and around the well, plotted against the depth. Well logging yields detailed information about the lithology (sand, clay, peat, etc.), water quality (fresh, saline and pollutants) and the condition of the well and/or filters.

Physical parameters

Deltares measures various physical parameters in wells (including open wells), depending on the requirement:

• Electrical resistance (LN) and (SN) and spontaneous potential (SP), in order to determine stratum transitions, water quality and the coarseness of sand bodies.
• The well diameter (CAL) provides information about the layout and finishing of the pit.
• Natural gamma radiation (NG), from which the soil type can be determined. Can also be measured in cased wells.
• Temperature (T), also in cased wells.
• Electromagnetic induction (EM). The electrical conductivity of the subsoil (bottom and interstitial water) can be measured using EM induction. These measurements are suitable for testing grout seals in wells, among other things. In cased wells as well.
• Spectral gamma (SG), to determine from which isotopes (potassium, uranium and thorium) the gamma radiation originates. In cased wells as well.
• An environmental probe measures the pH, oxygen percentage, conductivity and temperature of the water in open wells, filters and cased wells.
• The acoustic televiewer measures the diameter of the well and scans the wall in order to detect breaks, cracks and washouts.
• The flowmeter measures the water yield of for example thermal storage and drinking water wells.
• Deviation and magnetism. The slant of a well or filter is measured. Magnetic grout can be used to check whether the grout seals have been applied and whether they are in the correct places.
  

Application of well logging

Logging a well provides information about the well itself, which is used for laying out and finishing the pit (drinking water, thermal storage) and the filters in the well:

• determining the optimal route for setting up filters in porous bodies
• determining and checking the exact depth of grouting and filters
• determining the most suitable zone for observation filters in fresh, brackish and saline water-bearing bodies or polluted zones
• measuring the water production of the different filters
  detecting filter blockages
• investigating the well wall for breaks, cracks and washouts (by means of a well scan) and the intended filter route in thin clay and peat layers can be inspected accurately

Other parameters measured in a well provide information about the groundwater and the geology around the well:

• monitoring the water quality in existing level filters, for example changes in the fresh/saline interface
• we can reconstruct the lithology of the subsoil by interpreting the measurement parameters
  determining the route for laying salt monitor cables
• pH, redox potential, oxygen percentage, conductivity and temperature in open wells and filters. These measurements can be used to determine the water quality and to trace/prevent possible problems with thermal storage installations.
• spectral gamma measurements are often carried out for geological purposes. These measurements can be used to determine how long a particular deposit has been on the surface, for example.