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Alternative CBM extraction methods

World Coal,

Dart Energy has proposed alternative drilling practices for extracting CBM in the UK. The proposed method differs from those techniques currently employed in the US and Australia.

The technique has been described in the latest Ricardo-AEA report on unconventional gas in the UK. The report explains that companies “drill a vertical well and a "surface to in-seam well" (SIS well) to produce gas from the coal seams and bring it back to surface in a controlled manner. Firstly, a vertical well is drilled to approximately 100 m below the lowest targeted coal seam, this operation takes around 14 days to complete.

During the process of drilling an SIS well, the rig drills down towards the targeted coal seams and, when the trajectory reaches the coal seam, it drills horizontally within the coal towards the vertical borehole previously drilled approximately 400 m away. The SIS well will intersect the vertical well, and will then continue drilling horizontally along the coal seam for up to 1000 m in the coal. This drilling process can be continued in other target coal seams at different depths branching off from the initial SIS wellbore. These additional wellbores will all intersect the vertical production well. In the US, the vertical production well is situated close to the point where the directional borehole first becomes horizontal. The horizontal borehole intersects the vertical well, or a lateral leading from it, and then continues for lengths up to 1525 m (5000 ft).

The process of drilling a horizontal SIS well is approximately 90 days working a continuous 24 hour drilling programme.

The author of the report, Dr Mark Broomfield, noted that “It would appear that application of this technique would allow the use of several horizontally drilled well pads intersecting a single vertical production well.”

Edited from various sources by Sam Dodson

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