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Comet Ridge: Mahalo Block – Mira field operational update

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Oilfield Technology,

Comet Ridge Limited has provided an update on the field work presently occurring in and around the Mira production pilot, in the northern central part of the Mahalo Block, approximately 240 km west of Gladstone in central Queensland.

The Joint Venture has approved the Mira 6 horizontal well, which will be drilled immediately after the Humboldt South 1 vertical corehole and will be positioned to intersect the Mira 2 well, running down through the centre of the Mira pilot scheme (see Figure 1). The objective of this horizontal well is to produce alongside the Mira vertical wells to accelerate water and gas production from the Mira field and to assess the optimal production well design for the first phase of development at Mira.

The previously drilled Mahalo 7 horizontal well made a significant performance difference at the Mahalo field, 13km to the northwest, and the proposed Mira 6 horizontal well has been designed to achieve similar positive outcomes.

Comet Ridge commenced the current workover programme at Mira on 2 August 2017. Mira 5 is the first of three wells in the Mira Pilot programme, to have been successfully under-reamed across the Castor and Pollux coal seams. A new pump has also been installed to equip the well for production. The workover rig was released from Mira 5 on Monday 7 August and has now commenced under-reaming operations on Mira 4 (refer Figure 1).

Under-reaming is a production enhancement process commonly used in coal seam gas production operations in Queensland. Coal plugged by drilling fines, is removed from around the wellbore area, providing an easier pathway for gas and water to reach the well. In its simplest form, under-reaming occurs when a drilling tool is run into the well, down inside the 7 inch diameter production casing and out the bottom of that casing to the coals.

The under-reaming tool is placed opposite the required coal interval and then rotated at high speed. Collapsible blades on the underreaming tool expand out to approx. 48 in. in diameter and the tool is then moved down slowly to cut the coal and expand the hole out to a much larger size.

Water, pumped down the inside of the drillpipe, returns to the surface outside of the drillpipe (and inside the casing) and carries the coal material up and out of the well.

Once this process has been completed, production tubing and a downhole pump are run back into the well to equip it for production.

During Mira 5 operations, approximately 15 cubic metres of coal material was recovered from the well in the tanks at surface, indicating the hole size has been expanded significantly and the operations were successful. Figure 2 (above) shows a schematic of the wellbore after under-reaming.

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