Discussion for application of stereo pair imaging technique in borehole breakout method
HAN Zengqiang，WANG Chuanying，ZOU Xianjian，HU Sheng
(State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China)
Deep borehole wall breakout formation is a rupture phenomenon that has been found in almost all rock types. It is usually assumed that breakouts occur in two diametrically opposed zones along the direction of the minimum horizontal in situ stress which is the theoretical foundation of borehole breakout method. The principle of borehole breakout method is discussed in this paper. A new method of measuring borehole wall breakout shape using stereo pair imaging technique is proposed. Describing the imaging principle of stereo pair imaging is in detail，the image processing algorithm is given and the formula for calculating the distance from one point in borehole wall to the center axis is derived. A stereo pair imaging device based on combined double cone mirrors have been developed. The process of imaging test and data analysis is introduced in this paper. Combined with specific examples，the deep in situ stress is calculated by using the data of borehole wall breakouts. Finally，the possible problems encountered in the borehole breakouts measurement using stereo pair imaging technique are discussed. The conclusions of this paper show that borehole stereo pair imaging technique has broken through the limitation that the conventional borehole camera system can only obtain two dimensional borehole wall images. Using borehole data obtained at any depth，the three-dimensional measurement of 360 degree wall shape is realized including three dimensional shape measurement of borehole wall breakouts. Borehole stereo pair imaging technique provides a new method for in-situ stress measurement of borehole breakouts.
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2018, Vol. 37 
