Borehole Geophysical Logging

In the same way that surface geophysics makes it possible to “see” beneath the ground surface, boreholeMonitoring a Logging Run geophysical logging makes it possible to see beyond the walls of a boring or well. To perform borehole logging, sensors (or sondes) that measure different physical properties of the formation around the boring are lowered down the hole to record continuous data (or logs). A multi-conductor cable on a motorized winch controls the sonde, and transmits data back up the hole to a computer and graphic display. Often, multiple logs (called a suite) are recorded for a single boring – each measuring a different property – to allow more complete knowledge of subsurface conditions.

Enviroscan’s logging division is Mid-Atlantic Geosciences.  We have used borehole logging to assist clients on projects involving soil and groundwater contamination, groundwater supply, and geotechnical and mining/minerals issues. Common applications are:

  • the location of water-bearing zones (for proper screen placement, or to assist in modeling of recharge or contaminant transport)
  • characterization of groundwater quality and quantity
  • detection and measurement of fractures, joints, or other discontinuities
  • determination of existing well construction details and quality (e.g. grout presence and condition, depth of screened intervals or casing collars, presence of casing cracks or offsets, etc.)
  • characterization of strata with regard to their porosity and permeability, or their water, clay or other mineral content
  • and much more…

Acoustic Televiewer Images of an Open Hole Bedrock BoringGeophysical logs provide “hard” data on lithology and features.  These data are not affected by the subjectivity and human error inherent in even expert visual logging of core samples. In addition, geophysical logging typically samples a larger volume of material around the borehole – providing more representative, in-situ and undisturbed data than a core sample. Monitoring Well Logs

Enviroscan’s logging capabilities include:

  • natural gamma (ng)
  • single-point resistance (SPR)
  • spontaneous potential (SP)
  • short and long normal resistivity
  • electromagnetic induction
  • magnetic susceptibility
  • three-component magnetic field
  • fluid conductivity
  • fluid temperature
  • caliper (borehole diameter)
  • cavity sonar (measurement/imaging of solution cavities, mine voids, etc.)
  • impeller and heat pulse flowmeter
  • seismic velocity (for both P- and S-waves)
  • cement bond logging (CBL)
  • optical and acoustic televiewer
  • digital color video.

In addition, Mid-Atlantic Geosciences performs state-of-the-art acoustic and optical borehole televiewer logging.  These tools allow quantitative and statistical measurement of the depth, thickness, and orientation of features such as fractures and joints. In this case, downhole geophysical measurements can actually be better core samples since the televiewers depict in-situ conditions, are magnetically referenced to true north (eliminating the need for oriented cores), and are not affected by incomplete core recovery (a common problem in fractured rock).

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