BOREHOLE WALL IMAGING
Borehole Televiewer: Optical vs Acoustic Imaging
Learn how optical and acoustic borehole televiewers record continuous wall images to support fracture mapping, rock mass assessment and ground investigation.
DIRECT ANSWER
What Is Borehole Televiewer Logging?
Borehole televiewers generate continuous images of the borehole wall that support interpretation of fractures, bedding, foliation and other geological features.
Optical televiewers photograph the borehole wall, while acoustic televiewers use the amplitude and travel time of reflected acoustic signals to form an oriented image. These are different measurement principles; their suitability depends on fluid clarity, borehole condition, depth and the geological question.
Fractures that intersect the borehole can appear as sinusoids on an unwrapped 360-degree image. Combined with reliable tool orientation and hole trajectory, these features can be interpreted for dip and dip direction.
OUTPUTS
What Engineers Obtain from a Televiewer Survey
Borehole imagery becomes useful when it is tied to location, orientation and independent geological evidence.
Oriented wall images
Depth-tagged, unwrapped images highlighting discontinuities and contacts.
Structure measurements
Interpreted fracture orientation, bedding, joints and zones of damage.
Hole geometry
Acoustic travel times may help assess borehole wall geometry and irregularity.
Images should be delivered with borehole deviation and orientation metadata, interpretation logs, uncertainty flags and representative quality-control examples.
APPLICATIONS
Where Televiewer Logging Is Useful
Use the method to complement—not replace—geological core descriptions and physical observations.
Rock mass characterisation
Identify fracture sets and geological structures for rock excavation and tunnelling.
Groundwater pathways
Compare potential water-bearing discontinuities with fluid and flow logging.
Foundation and underground works
Review discontinuity orientation and borehole condition around foundation or underground infrastructure studies.
METHOD COMPARISON
Optical Televiewer vs Acoustic Televiewer
Tool selection should be based on visibility, fluid conditions and the details needed from the log.
| Consideration | Optical televiewer | Acoustic televiewer |
|---|---|---|
| Measurement | Photographic image of the borehole wall. | Reflected acoustic amplitude and travel-time image. |
| Fluid clarity | Needs adequate visibility; turbidity can limit image quality. | Often remains useful where fluid is cloudy, provided acoustic coupling is suitable. |
| Primary advantage | Direct colour and textural observations. | Discontinuity imaging despite limited optical visibility. |
| Key limitation | Poor visibility or dark surfaces can hide features. | Requires suitable fluid coupling; interpretation is not equivalent to photography. |
SURVEY DELIVERY
Borehole Readiness and Logging Workflow
Poor borehole preparation and missing reference data can undermine an otherwise high-resolution survey.
- Check borehole diameter, deviation, casing intervals, water level and access before mobilising.
- Confirm whether an optical image is likely to be clear and whether acoustic coupling is possible.
- Capture hole orientation, tool heading and depth registration with field QA/QC checks.
- Provide processed unwrapped image logs and separate interpreted structural data.
- Compare interpreted features with core photographs, geological logs and other measurements.
LIMITATIONS
Interpretation Risks to Control
Images identify possible structures; they do not by themselves prove aperture, permeability or structural significance.
- Magnetic interference and strongly deviated holes can affect orientation if corrections are not properly applied.
- Image quality falls in poor optical conditions and in acoustic conditions with inadequate coupling.
- Fractures parallel to the borehole or features that do not intersect it may not be observed.
- Core loss, borehole breakout and tool artefacts can mimic or obscure genuine geology.
- A visually distinctive fracture is not automatically open, conductive, unstable or persistent beyond the hole.
QUALITY CONTROL
QA/QC for Discontinuity Measurements
Link every interpreted structure to a verifiable image feature and a clear survey coordinate system.
- Check depth ties and orientation calibration against borehole deviation information.
- Differentiate manually interpreted features from automatically detected candidates.
- Retain original images so reviewers can revisit uncertain picks.
- State confidence, image quality, tool orientation and blind intervals.
- Resolve ambiguous picks using core, groundwater and other geophysical evidence where available.
FREQUENT QUESTIONS
Televiewer Questions
Answers for engineering teams planning borehole imaging.
Which televiewer works in muddy water?
An acoustic televiewer can often image fractures where an optical televiewer cannot see clearly, provided fluid coupling and the tool setup are suitable.
Can televiewer logging replace core recovery?
No. Borehole images complement core descriptions and can reveal structural orientation, but do not provide all material properties.
Can it measure fractures in a deviated borehole?
Yes, if orientation and borehole trajectory are properly measured and processed; an uncorrected orientation can be misleading.
EVIDENCE
USGS Research and GEOOE Technical Links
USGS publications provide independent descriptions of acoustic and optical image capabilities and limitations.
ENGINEERING DISCUSSION
Plan a Borehole Televiewer Survey
Describe the rock type, borehole condition, water clarity and geological information needed.
GEOOE approaches this topic through engineering-led method selection, monitoring data quality and technology collaboration. For a project-specific discussion, share the asset or site type, the engineering question, available records and the expected deliverable.