borehole filming with optv - geosigma
TRANSCRIPT
The OPTV filming technique Borehole filming is performed with the OPTV camera probe in the borehole. The camera films the borehole walls at a 360-degree angle. The film is then converted to a high definition image on which information on length and orientation data is stored.
The borehole image can be used for several purposes:
• To provide rock quality data for road, railway and tunneling projects
• To obtain rock quality data for borehole anchoring of large constructions such as bridges, large buildings and windmills
• To inspect the quality of concrete constructions such as dams etc. along boreholes drilled in them.
Prerequisites for borehole filming
Borehole filming can be performed:
• In waterfilled and dry boreholes with casing
• In cored boreholes with a diameter of 56-500 mm
• In geotechnical boreholes with a diameter of 100-500 mm due to lower drilling accuracy
• In boreholes flushed clean after drilling.
• In gently dipping boreholes by using a steering rig.
Borehole filming with OPTV Borehole filming with OPTV (Optical Televiewer) can be done in core and geotechnical boreholes to obtain detailed geological information
The OPTV operates in cored boreholes with a diameter of 56-500 mm.
Steering rig for gently dipping holes
For borehole filming in gently dipping boreholes, an entry rig is required, because the OPTV does not fall on its own weight. Geosigma has designed an entry rig that pushes the OPTV down the borehole at a steady speed and prevents the film from becoming cloudy and pixilated.
The OPTV camera probe
Geosigma uses a Hi-OPTV borehole camera probe. The camera of the probe consists of a wide-angle lens and a CMOS sensor with resolution of 1280x1024 pixels. The probe orients itself by means of an accurate 3-axis magnetometer and accelerometer.
The probe is 1630 mm long and 52 mm in diameter. Peripherals include a winch with a 150 or 500 m long cable, measuring wheels and generators.
Information from borehole filming
• Position, orientation, opening (aperture) of rock fractures
• Position, orientation and thickness of crushed zones (these are difficult to be assessed from core mapping as materials are often washed away during drilling)
• Position, orientation and thickness of rock type boundaries and rock structures
• Concrete casting can be inspected to look for cavities.
Filming with entry rig.
Core mapping in Boremap or WellCAD
Boremap images and cores can be length correlated in by means of a software (Boremap or WellCAD) enabling mapping and digital storage of all rock fractures, structures, zones and rock type characteristics.
Other than geometrical features also the mineral infillings, mineral coating, joint alteration, joint roughness, thickness of layers, color, grain size, structures, textures, piece length and type structures can be identified.
When mapping only based on borehole images most of the properties can also be documented.
The mapping results can be plotted in WellCAD. This visual presentation of the data gives a good understanding of the geology of the borehole and facilitates an overall estimation on how the geology will affect a construction project.
Example from WellCAD.
Example from Boremap.
Examples of OPTV-borehole images
Contacts Sofia Winell [email protected] 010 - 482 88 87
Eva Samuelsson [email protected] 010 - 482 88 37