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Geophysical Borehole Logging

Bedrock fracture delineation with acoustic and optical televiewers

Borehole geophysics utilizes boreholes or wells to make geophysical measurements. Compared to geophysical measurements made on the ground surface, they have better resolution in the depth dimension.

The application includes but not limited to:

  • Lithology
  • Bedrock fracture characterization
  • Identification of water-bearing zones
  • Delineation of groundwater quality
  • Borehole fluid vertical flow
  • Borehole deviation
  • Borehole diameter
  • Borehole fluid conductivity estimates
  • Well construction inspection
  • Screen section delineation of potable wells
  • Video surveys

Fracture statistics.jpg

Fracture Statistics

The understanding of target characteristics, borehole/well conditions and advantages/limitations of downhole tools is crucial for the successful survey of a particular application. Enviroprobe's experienced geophysicists and geophysical technicians provide varieties of logging tools along with the Matrix logging console and 500m winch from Mount Sopris Instruments. The downhole tools include but not limited to:

2PCA-1000 - 3-arm Caliper

Record borehole diameter. Changes in borehole diameter are related to well construction to fracturing or caving along the borehole wall.

Logging setup.jpg

2PGA-1000 - Gamma-SP-SPR

Gamma - Record the amount of natural gamma radiation emitted by the rocks surrounding the borehole. Clay- and shale-bearing rocks commonly emit relatively high gamma radiation.

SP - Record the electrical resistance from points within the borehole to an electrical ground at land surface. In general, resistance increases with increasing grain size and decreases with increasing borehole diameter, fracture density, and dissolved-solids concentration of the water. SP logs can be used in the determination of lithology and water quality. SP logs are limited to water- or mud-filled open holes.

SPR - Record the electrical resistance from points within the borehole to an electrical ground at land surface. In general, resistance increases with increasing grain size and decreases with increasing borehole diameter, fracture density, and dissolved-solids concentration of the water. SPR logs are useful in determination of lithology, water quality, and locations of fracture zones. SPR logs are limited to water– or mud– filled open holes.

2PFA-1000 - Temp & Fluid Conductivity

Fluid temperature - Record the water temperature in the borehole. Temperature logs are useful for delineating water-bearing zones and identifying vertical flow in the borehole between zones of differing hydraulic head penetrated by wells. Borehole flow between zones is indicated by temperature gradients that are less than the regional geothermal gradient, which is about 1 degree Fahrenheit per 100 feet of depth.

Fluid conductivity - Record electric conductivity/resistivity of water/fluid in the borehole. Changes in fluid resistivity reflect differences in dissolved-solids concentration of water. Fluid conductivity logs are useful for delineating water-bearing zones and identifying vertical flow in boreholes.

2PEA-1000 - 8-16-32-64 Normal Resistivity

Record electrical resistivity of borehole environment and surrounding rocks and water as measured by variably spaced potential electrodes on the logging probe. Typical spacing for potential electrodes are 16 inches for short-normal resistivity and 64 inches for long-normal resistivity. Normal-resistivity logs are affected by bed thickness, borehole diameter, and borehole fluid and can only be collected in water- or mud-filled open holes.

Enviroprobe recently acquired 2nd generation optical and acoustic televiewers from ALT, doubling the logging speed compared to the older ones.

OBI-2G and 2OIA-1000 - Optical Televiewer

Record a magnetically oriented, color optical image of the borehole. The optical image can be viewed and recorded in real time in a control computer. Well construction, lithology and fractures, water level, cascading water from above the water level, and changes in borehole water quality (chemical precipitates, suspended particles, and gas) can be viewed directly with the televiewer.

ABI-2G and 2AIA-1000 - Acoustic Televiewer

Record a magnetically oriented, photographic image of the acoustic reflectivity of the borehole wall. Acoustic televiewer logs indicate the location, strike and dip of fractures and lithologic contacts. Acoustic televiewer logs are limited to water- or mud-filled open holes.

Borehole logging televiewer.jpg

HFP-2293 - Heat Pulse Flow Meter 

Click here for HFP-2293 Specification

Record the direction and rate of vertical flow in the borehole. Borehole-flow rates can be calculated from downhole-velocity measurements and borehole diameter recorded by the caliper log. Flowmeter logs can be collected under non-pumping and/or pumping conditions. The heat-pulse flowmeter can resolve velocities of less than 0.1 ft/min.

Click here for an example of geophysical borehole logs


 
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