Abstract
Reservoir studies indicated that horizontal wells drilled in seam and intersecting vertical production wells were the optimal design to produce coal seam gas from the Narrabri CSG Project. An aggressive campaign of production pilots was drilled in 2009 and early 2010 to prove the potential of three coal seams in the Project area. The pilot wells included two dual lateral horizontal wells, with each horizontal well intersecting three vertical wells; a tri-lateral horizontal well which intersected four vertical wells; two long and three short single lateral horizontal wells intersecting one vertical well each; and three short, single lateral horizontal wells drilled from a single drilling pad to intersect three vertical wells. The importance to the company of the results required a high degree of certainty in well construction success.
There was very little time for rig start up issues to be addressed before the first horizontal well was drilled and early development of a competent wellsite team was essential. With little precedent and many unknowns, a low risk, fully engineered approach to the well design and drilling operations was adopted.
Connection of the vertical and horizontal wellbores is critical, and intersection techniques have been developed and refined. The Rotating Magnet Ranging System was introduced to Australia for this project, and adoption of this technology has subtle implications for directional drilling equipment and techniques. The wellbore hydraulics design and management while drilling program differed in several respects to conventional horizontal drilling, and performed very well.
The selection of the rig package, down-hole equipment and personnel underpinned the success of the 2009 – 2010 drilling campaign, and is described. The technical standards developed by the operation will interest other coal seam gas operators who face the challenge of economic extraction of coal seam gas, particularly from anisotropically fractured or deeper, lower permeability coals.
