One surface borehole with multi-usage gas drainage key technology for abandoned well and its application

Gas drainage from mining area could be realized through the reconstruction and reuse of abandoned surface gas wells in the coal mine area , which has multiple economic and environmental benefits such as ensuring the safe production of mining, the effective utilization of gas resources, and reducing the pressure of gas escape on the environment. In view of this purpose, the idea of “one surface borehole with multi-usage” gas drainage technology for abandoned wells was proposed based on the characteristics of the surface borehole and the abandoned wells in the mining area. By analyzing the conditions of the mining technology, overburden structure and abandoned wells in the test working face, the optimization and identification of abandoned wells, the surface borehole reconstruction technology, the installation of protective devices, the layout of gas drainage system and the gas drainage control technology were studied and put forward, with innovation in the determination method of the length of perforation and fracturing interval for the reconstruction of abandoned wells. Besides, a safety protection method based on the dynamic adjustment of oil casing annulus, double protection of combined casing and grading optimization of screen pipe was invented, thereby forming the "one borehole multi-usage" surface borehole gas drainage technology for abandoned wells. Specifically, the test on reconstruction and reuse of three abandoned wells (YC-50, YC-52 and YC-54) was completed in Yuecheng Coal Mine of Jincheng Mining Area. The cumulative gas drainage volume of surface wells was 2.578 8 million m³, 1.725 0 million m³, and 1.296 0 million m³ respectively. After Well YC-50 was put into production upon reconstruction, the maximum gas volume fraction at the upper corner of the working face within the gas drainage range of the surface well decreased from 0.77% to 0.4%, with a decrease of 48.05%. Besides, the gas volume fraction at the upper corner of the coal working face decreased by 52.38% after Well YC-52 was put into production upon reconstruction. Thus, the safe production of the mining face was ensured effectively, and the goal on “one surface borehole with multi-uasge” of abandoned wells was realized, with good economic and social benefits. The research results provide a reference for the reconstruction and utilization of abandoned wells in other regions. It is suggested that the “one surface borehole with multi-usage” scheme should be considered in the design stage of borehole gas drainage borehole predding wells in the future. Moreover, relevant technology research and development should be carried out to improve the quality of design wells and the problem of continuous reuse, so as to reduce the costs and enhance the efficiency.