Report: APP CMHS Project 1

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3.8.4. Oil and Gas

Gas and oil drilling technology has been trialled in coal seams in the early to mid 1990’s, but generally with little success. It relied on single well holes and multiple seam stimulation. The general lack of success was due to low permeability of coal and seams and loss of completion effectiveness with production time because of clogging of perforations from gel and coal fires in the holes.

The current technology for coalbed methane drilling and drainage combines conventional vertical drilling technology with horizontal directional, multilateral and under-balanced drilling. The vertical well hole provides the carrier string and water sump and pump components. The horizontal hole is drilled using either medium or tight radius drilling to place it into the coal seam. Multiple holes can then be drilled into multiple seams using this method (pinnate or herringbone patterns). This provides 10-20 times productivity improvement, fewer wells and gathering systems, as a result, lower financial and environmental impacts. This drilling technology is further improved with underbalanced drilling, that is where the drilling fluid pressure is less than the pressure of the material being drilled. This improves gas production due to mitigation of formation damage. This technology is then enhanced with hydraulic fracture treatments with water or other fluid with or without proppants such as sand or gel, acidisation and other leachate removal of materials.

As an adjunct to this technology nitrogen is injected into low permeability areas of coal seams to enhance gas flow in coalbed methane operations. This has been used in coalbed methane operations in San Juan Basin of USA, Fenn-Big Valley in Canada; and Hokkaido in Japan.

The other technology of interest derived from the oil industry in particular is the Safety Case style of safety management. This is summarised as a three part approach to the holistic management of a site comprising Facility Description, Formal Safety Assessment, and Safety Management System. In essence, it is a thorough and detailed approach to manage all hazards and processes at a facility.

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