SEMM Logging suggests televiewer as the preferred methodology for structural measurements

SEMM logging is a service provider to the mining, geotechnical and oil & gas industries specializing in downhole geophysical logging solutions. Headquartered in France, the company has its main Canadian office in Quebec City with satellite bureaus in the Abitibi, Montreal and British Columbia.

Borehole Imaging Technologies

Image log, borehole imaging, televiewer, how should we call it? Borehole imaging in the mining industry is the process of acquiring an image log with a tool called televiewer (OTV & ATV) Two methodologies exists: optical, ultrasonic and electrical. The development of these technologies was motivated by

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oil and gas exploration decades ago and are routinely used, worldwide. Televiewer tools are being rapidly adopted by the mining and geotechnical industries. The resulting image logs are presented as unwrapped, 360 degrees image of the borehole. Lithologies can be identified, a structural analysis is done, and geotechnical statistics and calculations can also be extracted. Results are delivered in .las format that can easily be imported in your database. Structures are oriented using magnetometric trajectometry with built-in magnetometer and accelerometer. A high precision gyroscopic deviation survey is a great complement and a must in magnetic environments.

Optical: Optical Borehole Imaging (OBI or OTV)

The optical televiewer uses a high-resolution optical camera that takes an oriented, 360 degrees image of the borehole. With 0.20 - 1mm pixels, this high-resolution image with real colors can be of such quality that granulometry, texture, facies will be recognized. The operator of the tool adjusts the following parameters before recording the best image possible: frame rate, exposure, intensity of light, etc.

A preliminary .jpg picture can be exported from the acquisition software directly in the field. Afterwards, processing of the log is done manually. Planar structures such as lithology contacts, bedding, veins, joints, faults and even foliation are handpicked, and their orientation/inclination is automatically plotted on stereonets. A suite of graphs and diagrams display picked structures and in-depth geostatistical analysis of the data can also be performed.

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Ultrasonic: Acoustic Borehole Imaging (ABI or ATV)

In fluid filled holes, the acoustic televiewer sends a high frequency sonic pulse onto the borehole wall. Two parameters of interest are measured: time and amplitude of the reflected wave.

 

Amplitude: The intensity of the signal of the reflected wave is a function of the acoustic impedance of the surface investigated. Competent rock will not weaken the amplitude of the signal of the reflected wave as much as rock that is softer, fractured or rich in discontinuities. The resulting precise and oriented reflectivity image can be displayed with any colour palette that will best represent the local contrasts.

 

Travel time: Travel time of the wave through the fluid allows to calculate the geometry of the borehole, therefore, to detect fracturing.

The acoustic televiewer reveals itself as a very powerful geotechnical tool. A 3d reconstruction or the core is also possible using both amplitude and travel time. Frac spacing and RQD calculations will be performed and further analysis of breakouts and/or ovalisation of the borehole can even lead to determining local stress direction.

Increased confidence of structural data sets compared to traditional core-orientation methods

In situ measurements of structures with televiewer tools is a far superior and highly accurate methodology. Many typical errors of traditional core-orientations methods are avoided. For example: inaccurate initial orientation mark on a core orienter tool due to equipment deficiency or high turnaround of driller helpers, badly drawn orientation line, data loss through closely jointed sections, etc. With borehole imaging, virtually all structures can be picked and much more rapidly than manual measurements on drill core. Borehole imaging supplied data sets are more complete, and the possible under-representation of major structural data sets is avoided. This high confidence methodology represents not only a cost-effective solution for your geotechnical or exploration programs but a permanent, auditable record of orientation measurements.

Please contact us to discuss the possibilities of performing televiewer surveys to unlock the structural complexities of your project. To complement to service, SEMM Logging is a distributor of high-quality North Seeking Gyro tools.