In-situ stress is a natural stress existing in rock mass. As an important basic parameter, accurate acquisition of in-situ stress is of great significance to the theoretical research and engineering application of rock mechanics.
In the in-situ stress testing under the deep-borehole environment of high temperature and high pressure, the testing process is complex and the measuring elements are easy to fail, which restricts the development of in-situ stress deep-borehole testing technology. In this paper, an in-situ stress measurement method based on borehole cross-sectional shape analysis is proposed, a borehole crosssectional shape measuring device based on micro-optical imaging measurement is developed, the whole process test auxiliary equipment based on wireline coring drilling tool is designed, formed a complete in-situ stress testing technology. The in-situ stress testing technology has been successfully applied in a deep borehole of 703 m.
The testing results are as follows: (1) At 636 m, the whole process of in-situ stress testing operation, such as "drilling operation of test hole", "equipment installation operation", "stress relief operation", "equipment salvage operation" has been completed, which only takes about 3 hours; (2) Through the calculation of the elastic mechanics based on the cross-sectional shape of the borehole at the testing point, the maximum horizontal principal stress is 23.14 MPa, the minimum horizontal principal stress is 16.59 MPa, and the maximum horizontal principal stress direction is 181.3 °. By comparing with the pumping pressure in the process of hydraulic fracturing and the geological structural phenomena, the results of in-situ stress measurement are consistent. In a word, the in-situ stress measurement technology based on borehole shape analysis is feasible, reliable and operable, and makes in-situ stress test possible to rapidly carry out in the deep borehole with complex environment.
In the field of geological engineering, in-situ stress is the basic data for the design of oil and gas field development schemes, the study of hydraulic fracturing crack propagation law, and the prediction of stratum fracture pressure. Obtaining accurate in-situ stress data is of great significance for oil and gas field exploration and development.