Development and application of a pressure-preserving sampler for long boreholes in coal mines

In underground coal mine long borehole sampling, significant challenges include substantial gas loss, complex borehole conditions, and low coal sample drilling rates. To address these issues, a pressure-preserving sampler is designed, integrating high-pressure water as the driving force, a piston drive, and a ball valve seal. This sampler controls the opening and closing of the ball valve through water pressure changes transmitted via the drill rod, enabling efficient coal sample drilling and pressure-preserving sealing. Experiments using the sampler included three sets of conventional borehole samples and eighteen sets of long borehole samples, with a maximum sampling depth of 297 meters. The sampler ensured coal seam exposure time during sampling was controlled within 5 minutes. Seam gas content measurement results indicated that, within the same working face, the gas content measured by the pressure-preserving sampler was 0.01-1.34 m³/t higher than that from conventional methods. Additionally, the sampling depth of long boreholes showed no significant impact on gas content values, demonstrating the sampler's effective sealing and pressure-preserving performance post-sampling. The pressure-preserving sampler successfully fulfills the objective of measuring coal seam gas content in underground coal mine long borehole sampling.