Development and application of a mine-used dynamic azimuth gamma instrument while drilling

Gas drainage borehole along coal seams is the most direct and effective gas control method at present. As a common basis for identifying coal bearing formations, natural gamma can tell whether the borehole trajectory is in the target layer according to the formation radioactivity. However, the existing mine-used gamma logging tools can only carry out sliding drilling measurement, which are not applicable to compound drilling or rotary steering drilling, and cannot meet the working condition of continuous gamma dynamic measurement. On the basis of the analysis of the characteristics of the working conditions of MWD and the principle of gamma logging in coal mines, the real-time transmission of multi sector azimuth gamma data at the bottom of the hole is carried out by low-voltage DC carrier two-way communication technology. The 8-sector partition measurement of the single gamma crystal is realized through the structure design of shielding window. On the basis of the different frequency characteristics of the three-axis MEMS acceleration sensor and three-axis MEMS gyroscope, the dynamic measurement method of complementary filtering is adopted, which overcomes the influence of vibration and rotation on tool facing angle measurement in rotary drilling. Ground performance tests and underground industrial tests have verified that the instrument can correctly reflect the variation law of formation radioactivity at the interface of different radioactive formations. The test results show that the instrument can meet the requirements of geosteering measurement in compound rotary directional drilling, and provide technical support for directional drilling along coal seams in coal mines.