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Horizontal drilling for oil and gas

Developing reservoirs in the Cooper and Eromanga basins.

The first horizontal well drilled in South Australia was Meranji 14 DW1 in 1993 targeting oil in the Eromanga Basin. Since then 42 horizontal wells have been drilled in the Cooper and Eromanga basins. Most recently the technique is being used to develop the following oil and gas reservoirs:

  • Beach Energy’s Stunsail 6 oil development well in Petroleum Production Licence (PPL) 260 is the first horizontal well to test Birkhead Formation oil reservoirs on the western flank. A 585 m lateral section was drilled and encountered 203 m of net oil pay – the well will be completed and oil production is anticipated later this year.
  • Beach Energy Stunsail 7 drilled a 528 m lateral section in the McKinlay Member primary target and encountered 509 m of net oil pay. The well has been completed as a future McKinlay Member producer.
  • Senex Energy drilled Growler 15 this year, its second western flank horizontal Birkhead Formation oil development well in PPL 242. Growler 15 drilled a 1,037 m lateral section where it encountered 578 m of net oil pay. The well has been completed as a future Birkhead Formation producer.
  • Senex Energy drilled Silver Star 1 DW1 gas exploration well in Petroleum Exploration Licence (PEL) 638 in 2017 targeting basin-centred gas in the Patchawarra Trough. The well reached a total depth of 4,969 m including the horizontal lateral of 1,180 m in the Patchawarra Formation and is currently suspended.
  • Strike Energy is drilling Jaws 1 horizontal well targeting Cooper Basin coals at their Southern Cooper Basin Gas Project in PEL 96. The well is planned to intersect a recently drilled vertical well with the aim of proving commercial gas flow rates.

Background

Figure 1 Schematic diagram showing the downhole trajectory for vertical, deviated and horizontal wells.
Figure 1 Schematic diagram showing the downhole trajectory for vertical, deviated and horizontal wells.

Horizontal drilling involves deliberately deviating the well trajectory from the vertical to intersect a reservoir target and drill a significant length with a near-horizontal path. Reasons for horizontal drilling include:

  • Avoiding a surface location that is operationally difficult or environmentally sensitive.
  • Reducing surface impacts by drilling several wells in different directions from the one surface location (pad drilling).
  • Enhancing oil and gas recovery – a horizontal well accesses a greater length of the reservoir, and offers significant production improvement (sweep efficiency) over a vertical or deviated well (Fig. 1).

Horizontal drilling has occurred in three distinct phases in the Cooper and Eromanga basins. From 1993 to 2004 the Santos Joint Venture used the technique mainly to drill Eromanga Basin (Namur and Hutton sandstone) oil targets in large fields such as Moomba and Big Lake as well as Cooper Basin gas targets in the Pondrinie Field. In 2012 it was applied by Beach to test unconventional deep shale targets in the Nappamerri Trough and in 2014 by the Santos JV on the flanks of Moomba Field. The latest phase has seen 17 horizontal wells drilled in the last three years including 7 Eromanga oil wells in the Merrimelia and McKinlay fields and 3 Cooper gas wells drilled by Santos in addition to the drilling detailed above.

– Alan Sansome and Elinor Alexander

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