Extraction mode and engineering demonstration of pressure relief three-dimensional of multi-coal seams in Pingdingshan mining area

There are many coal seams and gas-bearing strata in Pingdingshan mining area, and the amount of underground gas control project is large and difficult. In order to establish a new model of gas drainage in Pingdingshan and achieve the purpose of mining one layer and extracting multiple layers, the main gas-bearing layers and gas content of coal measures were accurately identified by combining gas logging and gas content testing. The coal measures gas resources in the mining area and goaf of five pairs of mines in the east are evaluated by the volume method. Based on the theory of “O-ring” and the concept of “prevent-allow-resist”, the positions of wells and the positions of layers, and wellbore structures of the mining wells and of goaf wells were optimized respectively. A multi-coal seam pressure-relieving three-dimensional extraction model of the active mining and goaf area constructed and an engineering demonstration was carried out. The results show that: ① There are three main gas bearing sections within 200 m of the roof of coal seam Ⅱ1, including the fourth coal group, the third coal group, and the sandstone and mudstone interbedded section within 60 m of the roof of coal seam Ⅱ1.The resources of mining area and goaf area in the eastern part of Pingdingshan mining area are 26.36 × 108 m3 and 20.00 × 108 m3 respectively. ② The optimal wells position are 0.17-0.28 times the length of the coal mining face and close to the return airway strip area. The spacing between mining wells is generally 80-100 m. A stable drilling technology system for mining vertical wells with “large diameter, avoiding areas of strong rock deformation, P110 ladder type casing” and a stable production technology system for mining L-shaped horizontal wells with “downward horizontal trajectory+ increasing casing strength” was established, which can ensure the smoothness of gas production channels. The goaf well is generally arranged in an area 30-50 m away from the return airway, and the drilling position is generally within the range of 40-60 m from the roof of the Ⅱ1 coal seam; The sieve tube is arranged from the top plate of the fourth coal section to the bottom of the fracture zone. ③ A long-term stable and efficient extraction technology system for ground wells in goaf areas was established, and a pressure-relieving three-dimensional extraction mode of “ground extraction vertical well/directional well-ground extraction L-shaped horizontal well-goaf well” and realizing multi-gas source three-dimensional extraction has been formed. Up to April 30th, 2024, the cumulative extraction volume reached 52.588 million m3, and the total utilization reached 37.354 million m3, taking the lead in realizing the industrial development of coal measures gas in Henan Province, and playing a significant role in demonstrating and leading.