Gas control technology of sleeve milling and fishing for directional drilling in broken soft coal seam

Abstract

Aiming at the technical problem of abnormal gas outflow caused by collapsed holes in the process of directional drilling and sleeve milling in broken-soft coal seams, a gas prevention technology was proposed for directional drilling and sleeve-milling salvage in broken-soft coal seams. On the basis of the existing casing milling salvage technology, the gas drainage pipeline system in the casing milling salvaging drilling tool is optimized, and a large amount of gas accumulated in the salvaging drilling tool during the casing milling salvage process is drained and relieved. The salvage orifice airtight gas pumping system and the sleeve milling salvage rod anti-gas device can realize negative pressure extraction, airtight slag discharge and sealing rod addition in the whole process of sleeve milling salvage. The technology was used to successfully deal with a directional drilling stuck accident of crushed soft coal seam with hole depth of 362 m. In the treatment of the accident, the gas gathered in the fishing drill was extracted and pressure relieved through the gas extraction pipeline system in the fishing drill, and the gas gushing out of the hole and the end of the fishing drill pipe was realized through the closed gas extraction system in the hole and the anti-gas device in the rod. There was no over-limit gas accident in the whole salvage process.

Keywords

• directional drilling
• gas gushing
• stuck drill accident
• sleeve milling and fishing
• broken soft coal seam