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:
Bedrock fracture characterization
Identification of water-bearing zones
Delineation of groundwater quality
Borehole fluid vertical flow
Borehole fluid conductivity estimates
Well construction inspection
Screen section delineation of potable wells
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.
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.
HFP-2293 - Heat Pulse Flow Meter
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.