As a breakthrough progress in the development of borehole imaging technology, digital panoramic borehole camera technology has been widely employed in actual projects, such as geotechnical engineering, hydropower and mining engineering, and a large number of actual high-accuracy borehole images have been obtained. The borehole images accurately record the geological features, especially for the structural features of discontinuities. However, the identification of these features is usually done by hand with large workload, which is usually affected by many human factors. To solve this problem, this paper takes a practical borehole in drilling engineering as example to show the application of an automatic recognition method for the identification of structural planes in the borehole image logs, which are obtained by our Digital Panoramic Borehole Camera System (DBCS) at Wudongde hydropower station, Yunnan, China. The automatic recognition method uses image gray, gradient values and projection method to distinguish the occurrence region of structural planes. Then, standard sine function matching method is employed to search the structure plane in the region. Lastly, the optimal sine curve is screened out and adopted as the feature curve of structure plane. And the related parameters of feature curve are analyzed and converted into the parameters of structure plane. This method realizes the automatic recognition and parameters extraction of structure planes in borehole image. Results show the structural planes of borehole image logs can be automatically recognized quickly within 2 hours for 100 m depth borehole image, and about 90 % discontinuities can identified continuously without human intervention. The related structural parameters of discontinuities, such as plane central position, orientation, dip angle and fracture width, can be also obtained from the process of automatic recognition. These obtained parameters are reliable and match actual engineering situation within an acceptable error range. It solves the problem of manual operation and human intervention. Compared with traditional methods, the automatic recognition of structural planes had greatly improved the progress of project and saved a lot of time with high working efficiency and easy, convenient way. For example, For 12 boreholes each about 50 meters in depth, the method has a 98 % detection rate for major structural planes for each borehole, with an accuracy rate of 87 % and a deviation less than 4 %, in a total period of about 3 hours. The application of the automatic recognition method provides a successful example for actual engineering project. It promotes the development and application of borehole image signal processing in drilling engineering.

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