R&D and experimental research of pressure-preserved triggering device for horizontal pressure-preserved coring in coal mines

Gas content is an important evaluation index of safe coal mining, as well as the exploitation and utilization of coalbed methane resources. Pressure-preserved coring is an effective way to improve the measurement accuracy of gas content in coal seams. Aiming at the special operating conditions of horizontal pressure-preserved coring in coal mines and based on the principle and technology of pressure- and gas-preserved coring in coal mines, this study developed a pressure-preserved triggering device and systematically designed the key components of the device, such as the sealing and pressure-preserved unit, the hydraulic drive module, and the salvager-unstuck mechanism between the spearhead and horizontal fisher. The purpose is to improve the recovery rate of pressure-preserved core samples. Furthermore, this study developed the ground test system for the performance of the pressure-preserved triggering device and conducted experimental research on the technological performance of the device using this system. As shown by the results, various function modules of the device operated stably, and the pressure-preserved controller successively turned over in five typical directions of the controller’s valve cover. Meanwhile, the wire rope was successively taken from the coring drill rod, effectively avoiding equipment failures caused by the winding of the wire rope when the corer was lifted from the borehole bottom to the borehole head. After the performance test, the pressure chamber of the corer was tested using an electric pressure test pump. The test results show that under the maximum pressure of 4.1 MPa, the pressure gauge readings remained stable, and the pressure fluids inside the pressure chamber did not leak, further indicating that the device can trigger the sealing and pressure-preserved functions of the corer. Finally, this study carried out an industrial test of the device under practical operating conditions of a coal mine. The results also show that the pressure-preserved triggering device can achieve the sealing and pressure-preserved functions of the corer stably under the actual working conditions of coal seams, with a coal sample recovery rate of up to 90%. The results of this study can promote the development of horizontal pressure coring technology for coal mines and are of great significance for the accurate determination of gas content in the coal seam.