OBI-40  OPTICAL TELEVIEWER

Borehole Probes

General

The tool generates a continuous oriented 360° image of the borehole wall unwrapped using an optical imaging system. (downhole CCD camera which views a reflection of the borehole wall in a conic mirror). The tool includes a full orientation device consisting of a precision 3 axis magnetometer and 2 accelerometers thus allowing for both accurate borehole deviation data to be obtained during the same logging run, and for accurate and precise orientation of the image.

The optical televiewer is fully downhole digital and can be run on any standard winches (mono, 4 conductors, 7 conductors). It is directly compatible with the ALT acquisition system using acquisition and processing software (ALTlogger and WellCAD). Resolution is user definable (up to 0.5 mm Vertical resolution and 720 pixels Azimuthal resolution)

Applications

The purpose of the optical imaging tool is to provide detailed, oriented, structural information when the acoustic cannot be operated (air or clean water filled boreholes).

• fracture detection and evaluation 
• detection of thin beds and bedding dip 
• lithological characterization 
• casing inspection 
• true-color imaging

Logging conditions 

• Hole diameter           45 mm to 300 mm maximum
• Logging speed         up to 6m/min depending on resolutions
• Logging mode          depth or time sampled

Log parameters 

• 360° RGB optical image 
• Borehole azimuth and dip

Technical specifications 

Tool max OD	40mm
Tool length: approx.	200 mm
Electronic section housing	stainless steel
Pressure rating	maximum 200 bars
Temperature rating:	50°C
Optical subsystem	downhole A/D conversion
Image digitizing	24 bit RGB value
Azimuthal resolution	user definable 90/180/360 or 720 pixels /360°
Vertical resolution	user definable, depth or time sampling rate
Sensor type	CCD    582x500 elements
Orientation	real time orientation of image on North or highside using a 3 axis magnetometer and 2 accelerometers. Accuracy depends on borehole configuration and latitude (inclination accuracy +/- 0.2 degree, azimuth accuracy +/- 5 degree)

Surface acquisition system

• Systems : ALTlogger system, Mount Sopris MGX II Logger with peripheral modem
• Data communications: ALT digital format asynchronous binary transmission fully compatible with ALTLogger and MSLog acquisition.

Processing Software using WellCAD image module

WellCAD for Win32 is designed to work with many types of log data. WellCAD image module is an add on module and allows image log display and processing like:

• unfolded image : zoom, aspect ratio, scrolling, brightness, contrast (RGB), filtering. 
• images logs reorientation and filtering 
• 3D image logs or cores ( step and rotate) 
• Cross section log 
• fracture picking on image log 
• Structure log (projection or tadpole) 
• Polar and Rose logs (stereograms, wulff/schmidts ,…)

Example of data file (logs processed and printed by wellCAD software)


Acoustic vs. Optical Televiewer

A comparison of the acoustic televiewer travel-time and amplitude plots vs. the optical televiewer RGB image. Water level is 4.6 meters. Note the differences in the two logs at 5.1, and 5.3 meters. The optical televiewer shows two discrete fractures at 5.1 meters whereas the acoustic appears to mask the this feature. At 5.3 meters the very high resolution of the acoustic televiewer shows the vertical rectangular feature, but the optical televiewer does not appear to resolve this feature as well.



Ordering Information

Description		Order Number
OBI-40 Optical Televiewer Borehole Probe		420-2000-OBI40