A New Hydraulic Fracturing Instrument to Measure In Situ Stress and Its Application in Chahasu Coal Mine

• Published in: Geotechnical testing journal 2022-09, Vol.45 (5), p.901-914
• Main Authors: Xu, Qiang, Yao, Qiangling, Shan, Changhao, Zheng, Chuangkai
• Format: Article
• Language: English
• ISSN: 0149-6115; 1945-7545
• DOI: 10.1520/GTJ20210207

Accurate measurements of the in situ stress of the mining area in coal mines are crucial for roadway layouts, support designs, and for coal mining technology selections. Based on the principle of hydraulic fracturing, this study proposes a newly developed instrument, named the instrument for single-loop pneumatic pressurization in situ stress measurements (RBHST-50) and presents its measurement procedures. This instrument boasts four advantages for in situ stress measurements in coal mines: (1) As a safe dynamic in underground coal mines, compressed air provides the driving force of the fracturing fluid; (2) the instrument, which is small and lightweight, can be transported easily from one test point to another; (3) the process of plugging and fracturing is controlled by a simple-loop control system, which avoids the problem of borehole blocking; and (4) the adoption of the integrated impression packer saves the time of conversion between the borehole wall fracturing program and the fracturing impression program, eliminating the error of in situ stress orientation caused by fracture closure. Field investigation was performed in Chahasu Coal Mine in China. The investigation results show that the in situ stress field of Chahasu Coal Mine is dominated by tectonic horizontal stress fields and mainly influenced by the West-North-West tectonic compressive stress, which agrees well with the evaluation results of regression formula. In summary, the proposed RBHST-50 instrument can measure the magnitude and orientation of in situ stress in the coal mine rapidly and accurately while achieving good water plugging capabilities.