Comet Ridge Limited provide a technical update on under-reaming programme at Mahalo block Mira field
Thursday, Oct 05, 2017
Comet Ridge Limited (ASX:COI) is pleased to provide a technical update on the very successful under-reaming programme that has recently been completed at the Mira production pilot. Mira is located in the northern central part of the Mahalo Block, approximately 240km west of Gladstone in central Queensland.

The Mira 3, 4 and 5 wells were under-reamed during August to remove up to 48 inches (diameter) of coal from the immediate near-wellbore region.

When the well is initially drilled, the coal around the wellbore can be damaged by natural fractures being invaded with drilling and completion fluids which contain solid particles. If the fractures are partially plugged, then the flow path for water and gas into the wellbore is restricted and the well’s production performance suffers.

Under-reaming is a means of removing the damaged coal and providing a clear pathway for water and gas to flow to the wellbore through clean fractures.

Pressure build-up (PBU) surveys are commonly utilised in the industry to measure and quantify the magnitude of the blockage or damage in the coal immediately around the well. In a PBU survey, the well is flowed for a period of time, and then flow is stopped for a short period (“shut-in”). The pressure increase in the wellbore is measured and then analysed and a value of wellbore “skin” is determined for the individual well from its pressure response.

A high skin value means significant damage around the well, whilst a low skin value means little damage. The theoretical optimum is to achieve a skin of zero which means no damage at all. However, this is rarely achieved and a very low skin value is usually the best practical outcome.

Over the past week, PBU surveys were completed for all three under-reamed wells at Mira to quantify how successful the under-reaming was in removing damage near the well.

Comet Ridge Managing Director, Tor McCaul, said he was exceptionally pleased with the PBU survey results and that the under-reaming programme has been a great success. The Mahalo 7 well demonstrated that horizontal wells can be very effective in producing gas in this block, and now the productivity potential of the vertical wells has been significantly enhanced.

The longer-term implications of the very low skin values are that water and gas rates from these wells should increase significantly and be much higher than demonstrated in the past with increases in pumping speed. The gradual increases in pumping speeds at the Mira 3, 4 and 5 wells are continuing with the wells having now moved up from 40 rpm to over 70 rpm with corresponding increases in water rates. Mr McCaul said that over the past six days, Mira 5 has delivered measurable, continuous and steadily increasing gas rates.

Comet Ridge is in the final stages of preparation for drilling the Mira 6 horizontal well, which will be positioned to intersect the Mira 2 vertical well running down through the centre of the Mira pilot scheme. 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 well is expected to spud during October and a further update on Mira 6 will be provided at this time.

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