Discussion and prospects of the development on measurement while drilling technology in oil and gas wells

Accurately obtaining the tensile strength of rocks and comprehensively understanding the evolution mechanism of rock tensile failure is one of the key issues in the theoretical research of rock mechanics and the application of rock engineering. Due to the limitations of direct tensile testing, such as difficulty in sample clamping, significant stress concentration at the end, and low success rate, indirect methods are usually used to test the tensile strength of rock materials. The Brazilian disk test, as the most widely used testing technique among indirect methods, has become a research hotspot in the field of rock mechanics since its proposal due to its special mechanical mechanism. However, the accuracy and effectiveness of its results have also been widely questioned and discussed. This article systematically investigated indoor experiments, analytical models, and numerical simulation studies related to the Brazilian disc test, summarized and analyzed the development trend of this method, the different experimental standards formed, and the basic basis and applicability proposed by each standard. Based on experimental data from domestic research, the differences in test results between Brazilian disc and direct tensile test were compared, and the key factors controlling effective cracking of Brazilian disc were analyzed. The influence of external factors (loading conditions, geometric shape) and internal factors (mechanical properties, heterogeneity) on the fracture mechanism and test results of Brazilian disc was clarified. Finally, the effectiveness of Brazilian disk testing for rock tensile strength under actual conditions was discussed from the two stages of initial crack initiation and propagation crack extension. Combined with several innovative rock tensile testing methods in recent years, the development direction of tensile strength testing methods in the field of rock mechanics was pointed out.