Advanced borehole imaging system

Significance 

Tectonic movements and various geological transformations result in discontinuities in the rock mass whose distributions determine the structural characteristics of the rock. The stability of geotechnical structures depends on these characteristics. Conventional manual excavation and drilling techniques have been used for structural detection of continuities in deep rock mass due to their simplicity and reliability. Unfortunately, its use is limited especially for weak rock mass as it produces inaccurate characteristics of the discontinuities.

Presently, the use of borehole imaging technology for detecting structural planes in borehole walls has increased thanks to the advancement in technology. It overcomes the limitations of the traditional conventional methods. Generally, it is based on the optical principles enabling observation of the interior of boreholes. It is developed through four stages that can be categorized as an analog model for the first two stages (borehole photography and borehole camera) and digital model for the last two stages (panoramic borehole photography and panoramic borehole camera). The first two stages allow for qualitative observation, description, and analysis while the last stages allow for precision and complete analysis of the same. The digital model has overcome some of the challenges posed by the analog model.

Despite the significant improvement of borehole imaging, both the analog and digital modes still experience problems that affect the image quality and the accuracy of the analysis. This includes the assumption that the borehole wall is a cylindrical surface with a constant diameter and cross-sectional area. Consequently, the difficulty in achieving true three-dimensional imaging due to planar imaging problem is a great challenge. To this note, researchers have been looking for alternatives to overcome the challenges in the hope of achieving a true three-dimensioning borehole imaging.

Chinese Academy of Sciences researchers: Professor Chuanying Wang, Associate Professor Zengqiang Han, Assistant Professor Xianjian Zou and Dr. Yiteng Wang in collaboration with Associate Professor Sheng Zhong from Sichuan University developed a panoramic stereopair imaging system for boreholes. The technique utilizes the biconical mirror imaging technology. They analyzed biconical mirror imaging principle and derived the stereopair imaging formulas. Their main objective was to develop an imaging system and processing platform to overcome the initial problems to realize a true three-dimensioning imaging for borehole walls. Their work is published in International Journal of Rock Mechanics and Mining Sciences.

The authors observed the accuracy and correctness of the developed borehole panoramic stereopair imaging technique from the experiments conducted in the indoor boreholes. For instance, it enabled accurate identification of fine structures in the walls of the boreholes through reconstruction of difference images from the obtained stereopair images.

According to the authors, the study presents a new borehole imaging technology owing to its originality, practicality and high level of innovation. Furthermore, the system successfully overcomes the challenges of past borehole imaging technologies and in particular by allowing accurate measurement and description of hole-wall shapes. Therefore, the borehole panoramic imaging system will advance exploration and testing of boreholes during drilling operations.

Fig. 1. Borehole panoramic stereopair imaging system by using a biconical mirror - Advanced Engineering
Fig. 1. Borehole panoramic stereopair imaging system by using a biconical mirror. Credit International Journal of Rock Mechanics and Mining Sciences
Fig. 2. The imaging principle of biconical mirror imaging - Advanced Engineering
Fig. 2. The imaging principle of biconical mirror imaging. Credit International Journal of Rock Mechanics and Mining Sciences
Fig. 3. The profile map of panoramic stereopair imaging device - Advanced Engineering
Fig. 3. The profile map of panoramic stereopair imaging device. Credit International Journal of Rock Mechanics and Mining Sciences
Fig. 4. The diagram of stereopair imaging processing process - Advanced Engineering
Fig. 4. The diagram of stereopair imaging processing process. Credit International Journal of Rock Mechanics and Mining Sciences
Figs. 5. The panoramic stereopair imaging of indoor borehole from a casting cement block - Advanced Engineering
Figs. 5. The panoramic stereopair imaging of indoor borehole from a casting cement block. Credit International Journal of Rock Mechanics and Mining Sciences
Figs. 6. Some differences of tiny structures in rock mass obtained by stereopair images - Advanced Engineering
Figs. 6. Some differences of tiny structures in rock mass obtained by stereopair images. Credit International Journal of Rock Mechanics and Mining Sciences
Figs. 7. The diameter variation of section borehole wall at different depths, (a) H = 62 mm, (b) H = 167 mm, (c) H = 187 mm, (d) H = 363 mm - Advanced Engineering
Figs. 7. The diameter variation of section borehole wall at different depths, (a) H = 62 mm, (b) H = 167 mm, (c) H = 187 mm, (d) H = 363 mm. Credit International Journal of Rock Mechanics and Mining Sciences

About the author

Chuanying Wang, professor and PhD supervisor at Institute of Rock and Soil Mechanics (IRSM), Chinese Academy of Sciences (CAS), Wuhan, China. In 1999, he received his PhD degree in Institute of Rock and Soil Mechanics (IRSM). In 2001, he visited at Carleton University as senior visiting scholar and was invited to give lectures and cooperation study at Carleton University in 2007 and 2008.

He is the academic leader of digital image exploring technique, and has accomplished several funds supported by the National Science Foundation (NSF) and Chinese Academy of Sciences (CAS).

His research areas include borehole camera technology, high-precision imaging measurement technique, rock mass structure surveying technology and in-situ rock stress measurement. He has published one academic monograph, applied for about 20 patents and published more than 80 articles in refereed journals.

About the author

Zengqiang Han, associate professor at Institute of Rock and Soil Mechanics (IRSM), Chinese Academy of Sciences (CAS), Wuhan, China. In 2013, he received his PhD degree in University of Chinese Academy of Sciences.

He has accomplished several funds supported by the National Science Foundation (NSF) and Chinese Academy of Sciences (CAS).

His current research interests include advanced rock mass structure surveying technology, borehole optical imaging technology and in-situ rock stress measurement. He has authored or coauthored more than 30 journal papers in refereed journals.

About the author

Xianjian Zou, assistant professor at Institute of Rock and Soil Mechanics (IRSM), Chinese Academy of Sciences (CAS), Wuhan, China. In 2016, he received his PhD degree in Wuhan University.

His research interests include borehole camera technique, ultrasonic imaging detection and related image signal processing. He has published more than 10 SCI/EI journal papers as first author or corresponding author and more than 20 articles in refereed journals.

Reference

Wang, C., Wang, Y., Zou, X., Han, Z., & Zhong, S. (2018). Study of a borehole panoramic stereopair imaging system. International Journal of Rock Mechanics and Mining Sciences104, 174-181.

Go To International Journal of Rock Mechanics and Mining Sciences

Check Also

Polypropylene geotextiles in marine environments: How long will they last?