New Drilling Technique - June 2004

In an industry where tradition plays a strong role, innovative drillers Mitchell Drilling have chalked up the 100th example of their revolutionary Dymaxion surface to in-seam (SIS) methane gas drainage hole for gas producer CH4 Limited at their Moranbah Gas Project in Central Queensland.

The Moranbah Gas Project is the first in Australia to rely totally on surface to in-seam drilling and due to the efficiencies of the Dymaxion technology, is currently running well ahead of schedule.

The success of the Mitchell Drilling pioneered drilling method is crucial to the proficient extraction at the gas field and will yield 12Pj of gas per annum to fuel Ergon Energy's Townsville Power Station when production drilling is complete.

"With support from CH4 we have had an excellent opportunity to demonstrate the power, efficiency and reliability of this fairly radical technique we have developed", said Nathan Mitchell, Managing Director of Mitchell Drilling.

"Our 250th hole proves the potential of this 'leap forward' approach and the long term possibilities for the industry to benefit from it", Mr Mitchell said.

The Dymaxion technique uses modified rigs, cutting edge drilling technology and specially trained personnel and allows for significant savings over alternate underground gas drainage drilling methods as well as offering major advantages in drilling Greenfield commercial methane gas production wells.

"From the perspective of the coal industry's needs, our Dymaxion SIS drilling can provide significant savings as unlike traditional gas drainage methods, ours isn't tied to mine production schedules nor does it hinder mining operations in any way", Mr Mitchell said.

Dymaxion SIS drilling can be completed well in advance of mining, utilising longer drainage lead times, resulting in wider spacing between boreholes and thus reducing costs. The valuable data collected through the SIS process can provide information on seam rolls and faults, allowing for greater certainty in mine planning and development.

In Greenfield commercial gas production wells, the area degassed by an SIS hole in a medium depth seam is far greater than conventional vertical wells. These gains can be achieved by controlling the bore trajectory to take advantage of the directional permeability of a particular seam, by drilling multiple seams from the single collar and by drilling multiple inseam holes in a variety of patterns to intersect a single production well.

"We think that Dymaxion SIS drilling will achieve gains for the gas industry that will turn marginal or uneconomical gas deposits into profitable holdings and assist many explorers to continue to grow their businesses", Mr Mitchell said.

Dymaxion SIS Process Overview

Using modified, multipurpose mineral drill rigs and specially designed bottom hole assemblies, the Dymaxion SIS technique involves drilling a 60 to 90 degree hole from the surface and steering it through a medium radius bend to enter the target coal seam horizontally.

The 120mm hole is then steered for up to 1200 metres in the seam towards a previously drilled vertical production well.

Intersection with the vertical well is aided by the use of a homing device lowered down the vertical well to the target seam. To date, Mitchell Drilling have achieved an intersection success rate of 100%.

The vertical well is equipped with a suitable pump to dewater the seam with pumping continuing over the life of the well. Once the hydrostatic head has been lowered sufficiently, gas will flow to the surface.