Research on three-stage automatic hole packer for gas extraction drilling in underground coal mine

In view of the requirements of hole sealing during gas extraction drilling in underground coal mine for manual packer installation and sealing material injection, as well as the low automation level of hole sealing technology, a three-stage automatic hole packer for gas extraction drilling in underground coal mine was developed, with the appearance similar to the drill pipe. The hole packer could be mechanized into the drilling hole by an automatic drilling machine, and realize the automatic injection of sealing material. Herein, the Mooney-Rivlin hyperelastic constitutive model was used to represent the strain energy function by the finite element analysis method. Thereby, the stress of the rubber seal ring under the dynamic sealing mechanism of the hole packer, and the expansion of the rubber sleeve of different rubber materials under different expansion forces, were obtained, thus providing a reference for the determination of the sliding force value of the dynamic sealing mechanism and the selection of the rubber sleeve material. Using the method of theoretical calculation, the hydraulic calculation was carried out for the flow channel of the three-stage automatic hole packer under working conditions. In this way, the water flow and pressure of the three-stage automatic hole packer were obtained, which provides reference for the determination of automatic hole sealing parameters. Besides, the stress of the liquid storage chamber of the hole packer was checked with the finite element analysis method, and the rationality of the structure design of the core components of the three-stage automatic hole packer was analyzed to ensure the normal operation of the hole packer. In addition, the experimental prototype was made, and the laboratory sealing experiment and the sealing effect comparison experiment were carried out with the three-stage automatic hole packer. The laboratory sealing experiment shows that the dynamic sealing mechanism of the hole packer has good sealing effect, the hole sealing material is automatically injected into the simulated drilling hole, the natural rubber sleeve is automatically expanded to fill the simulated drilling hole and can effectively seal the hole sealing material. Therefore, it is feasible to use the three-stage automatic hole packer. The hole sealing effect comparison experiment shows that the sealing effect of automatic hole packer is similar to that of existing polyurethane pressure injection process, and better than that of the traditional polyurethane winding process. The three-stage automatic hole packer can reduce the labor intensity of coal mine workers, improve the sealing efficiency and standardize the sealing process, thus providing reference for the research on the automatic hole sealing technology and equipment for underground gas extraction drilling in coal mine.