Drainage drilling for demethanation (methane drilling)

Demethanation of the rock mass by means of drainage holes is currently the most effective line of defence against the methane threat.

The drilling of drainage holes involves:

• drilling holes covering the rock mass relaxation zone of the  mined seam, directed towards the roof and the bottom from ventilation galleries,
• drilling holes from a drainage gallery, i.e., a gallery made in the coal seam, located in the relaxed zone above the mined seam,
• drilling demethanation holes from the faces of galleries drilled within the coal seam.

We drill drainage holes on the basis of a technical demethanation plan along with the drilling technology for a given heading. For drainage drilling, we use rotary drilling rigs, usually electro-hydraulically driven.

The drilling of a drainage hole involves embedding a casing pipe in the rock mass, which undergoes cementation by injecting cement slurry into the space between the pipe wall and the rock mass. The tightness of the pipe is then tested by drilling through the cement plug in the pipe, building an end cap with a pressure gauge, and applying water pressure. Once the casing pipe is leak-proof, a gate valve is built on its flange along with a drilling choke. The gate valve allows the outflowing methane to be cut off, while the choke allows for drilling and drawing methane into the methane pipeline at the same time, so that the methane from the hole is not released into the heading. The drilling of a drainage hole to the depth specified in the plan is done with a drill string ended with a drilling tool, usually a drill bit or a toothed bit. Once the target depth is reached, the drill string is withdrawn from the hole. To maximise the service life of such a hole, we use protection with a casing column ended with a perforated pipe. The column is placed in the hole to the depth specified in the plan. Subsequently, we install an end cap with a spigot, through which it is possible to connect the hole to the methane pipeline via a hose.

We also provide:

• core drilling with full core recovery, with BQ, NQ and HQ diameters to a depth of 1000 meters; we collect coal samples for various types of tests, e.g. (methane content, the calorific value of coal, physicochemical properties, etc.),

• drainage drilling to eliminate underground water reservoirs,

• exploratory drilling to explore a deposit, identify the saturation of rocks with water, identify the geological disturbances existing along the drilled headings, determine the methane hazards and the gas-geodynamic hazards,

• technical drillholes, such as long blasting holes for rock burst prevention, holes for roof bonding and rockfall protection, cased holes for transmitting utilities, i.e.: water, gas, compressed air and others

• directional driling – the drilling of directional boreholes using a downhole motor, with precise determination of its trajectory in the rock mass for the purpose of draining underground water reservoirs, demethanation of coal seams and capturing methane from old goafs,
  
• large-diameter drilling – such as the drilling and casing of ventilation shafts, holes for transporting and discharging the ore, cased holes for transporting methane, ice water for underground air-conditioning systems, cased drainage holes for underground pumping stations. We drill boreholes along with casing up to 1,600 mm in diameter and up to 250 m in length.

For the holes we drill, we can measure their trajectory with inclinometers.