Microseismic technology navigates directional drilling for coal gas
Microseismic technology has been used for the first time to guide underground directional drilling for coal gas production, say scientists at the Australian Commonwealth Scientific Research Organisation. A trial was conducted at a coal field test site in Queensland, Australia.
Team leader Dr Xun Luo says, ‘Seismic signals are generated by [noise from] the drill bit cutting the coal and drilling vibration. These signals propagate the rock mass and can be detected remotely using triaxial geophones, and used to determine the back azimuth of seismic rays from the drill bit for its location’. This information is fed back to a navigational system for geo-guidance.
‘Directional drilling for coal gas production is relatively new,’ explains Luo. A vertical production well in the subsurface is linked to another borehole in the main seam, where the gas is generated and channelled. However, when connecting the two holes, the drill bit often misses the target.
Luo adds, ‘Up until now, steering of the drill bit has been based on information obtained using traditional survey techniques, [which] are time consuming and may include cumulative inaccuracies, and magnetometers [which have] a short survey range (less than 40m) and must be deployed down a target well if the operating bit is deep underground’.
The greater detectable distance of microseismic monitoring in real time enables more effective navigation, such as 1,200m from the test site, offering significant savings in mining and exploration.
A filtering and cancelling algorithm overcomes contamination of seismic data by periodic electrical noise signals.