Televiewer Overview
Televiewers produce oriented images downhole, allowing measurement of both planar and linear structural features in situ. Orientation is accurate and consistent, and Televiewer can be used in any hole, including core, non-core, historic holes, wells, utility lines, etc.
Data can be visualized as 3D “virtual core” or as 2D “unwrapped core,” and structures can be measured very quickly on a computer. Data is catalogued automatically, ready to import into 3D modelling programs. Common features analyzed include veins, contacts, bedding/foliation, fractures/joints, faults, fold limbs and hinges.
Optical televiewer image log beside the acoustic televiewer amplitude image log. Planar features such as veins, lithology contacts, and fractures appear as sinusoidal waves that that indicate the true orientation and thickness of structural features. Linear structure interpretation from the optical televiewer.
Linear structure interpretation from the optical televiewer.Image curtesy of: ALT, https://www.alt.lu/
Acoustic Televiewer:
Images acoustic reflectivity
Ideal for fracture/texture imaging
Can distinguish open/filled fractures
Also measures hole shape & diameter
Can be used to measure stress – alternative to overcoring, and evaluate rockburst potential
Can image through PVC & thick mud
Requires fluid in the hole
Orientated images based on the amplitude and travel time of the acoustic pulse. The energy is absorbed in fractures, voids, and softer matrices and can be visible in the travel time.
Unwrapped acoustic amplitude image and 3D acoustic log, showing a lithology contact between two texturally different rock types and several small joint/fractures.
Optical/UV Televiewer:
Images color(RGB)
Ideal for lithology and vein logging
Works in dry or wet conditions
NEW: UV imaging available – Identify fluorescent minerals or fluids (e.g. hydrocarbon)
Optical televiewer images showing a lithological contact and several small joint/fractures (same as shown in acoustic televiewer examples above)
Optical televiewer image showing high-angled vein crosscut by tight joint/fracture
Optical and UV televiewer images of fluorescence in the mineralization zone. Images courtesy of ALT: https://www.alt.lu/
Frequently Asked Question: DGI routinely works with drillers to condition the hole for Optical Televiewer
Answer: DGI routinely works with drillers to optimize hole conditions for Optical Televiewer surveying, through choice of drilling fluids, additives, hole conditioning, and bit placement.
Televiewer Interpretation:
OTV and ATV provide complementary information.
Structural measurements can be made very quickly
Interpretation is visually apparent on logplot, easy to QA/QC and edit.
Work can be done remotely.
Additional parameters can be auto-calculated including RQD, Fracture Frequency, Caliper, and stereonets.
Interpreted Acoustic and Optical Televiewer data, with selected features represented as sinusoids and orientation tadpoles. Features are color-coded by type. To the right is additional data derived from the features including fracture frequency, RQD, and caliper (max/min/avg). Lithology is shown to the right and can be client-provided or interpreted by DGI.
Video Inspection
Downhole video camera (down-facing and side-facing) commonly used for:
Well and utility line inspection (screens, casings, liners, etc)
Locating equipment, cables, etc lost downhole
Observing fluid inflow/outflow
Image courtesy of TND Drilling
new curtesy of DGI
Examples of side hole view and downhole view from a video camera pulled along a wireline. These are used but not limited to paste lines and casing inspections.
3D Laser & Sonar
3D Laser & Sonar produce scans of natural or man-made cavities underground or underwater. Laser is used in dry environments, while sonar is used in submerged environments. These drillhole-deployed technologies are commonly used to map spaces that cannot be accessed safely with other methods.
Above: Void imaged via 3D Laser Scanner. The imaged volume is geolocated in 3D, for import and integration into 3D models.
Borehole Radar
Image/locate variations in electromagnetic properties off-hole, such as fluid-filled cavities or faults, boreholes, geologic layering, mine workings, etc.
Above: Radiogram with borehole trace on upper horizontal axis, after which reef structures are imaged intersecting the hole.