Cementing technology by super diameter casing in coal field

In the exploiting process in Coal field, in order to guarantee the safety and improve the underground working environment, large diameter wells are being drilling for gas drainage and air blasting to cool the underground in recent years. However, the drilling rig is small with limited lifting capacity, so the large diameter casing is difficult to trip down in petroleum engineering method during well completion. The large outer and inner annular volumes make cementing slurry easily to channel during injection, resulting in long working time, so it is difficult to ensure the cementing quality. Through losing weight by buoyancy piston, flushing air in pipe column, optimizing slurry system and interpolated-pipe cementing technology, the difficulties were successfully resolved, which were tripping the large diameter casing by small drilling rigs, low squeezing strength of large diameter casing, etc. The on-site field applications on 9 wells showed the results of 100% cementing success rate, and good cementing quality. It provides experiences for the future cementing by super diameter casing.