CH-5 is a vertical "pathfinder" appraisal well located about 1 km southeast of the CH-1 discovery well. The primary purpose of CH-5 was to determine the nature and extent of the reservoir in the East Ridge portion of the Cliff Head structure which had not previously been drilled. The well encountered the top of the main reservoir target sand 56 meters low to prediction and coincident with the field's oil-water contact. The discrepancy between the prognosed and actual depth at top reservoir target level is currently interpreted to be mainly due to unexpected seismic velocity variations in the overlying sequence in that part of the field. The reservoir quality of the target sand sequence drilled by CH-5 is the best yet encountered in the Cliff Head area.
The results of CH-5 indicate that the depth configuration of the field at top reservoir level needs to be refined in the light of additional subsurface data points and with particular reference to the seismic velocity variations. This work is currently underway. Until the work has been completed, during March 2005, it is not possible to make any definitive statement about the impact which the CH-5 well has had on field reserves. Directionally, however, it would seem that proved and probable recoverable oil reserves at Cliff Head may be reduced by a few to several millions of barrels of oil ("MMBO") from the previously quoted range of 18 to 21 MMBO. It is possible that the addition of the new velocity variation information to the field database will cause other parts of the structure, which are currently mapped as being below the oil-water contact, to be remapped as being above that contact. Whether or not this will prove to be the case will not been known until after the drilling of CH-6 which should be complete in early March 2005. A Final Investment Decision will also wait upon the results of CH-6.
Commenting on the results from CH-5, Dr John Doran, ROC's Chief Executive Officer, stated that:
"Fifty-six meters is a big seismic bust, particularly at relatively shallow depth. Seismic velocity variations of this magnitude can work against you - as they have plainly done at the CH-5 location - or, they can work for you, as could happen in other parts of the structure. However, whether or not that will happen elsewhere within the Cliff Head field is pure speculation at this stage.
The fact that the target reservoir sands in CH-5 represent the best quality sands seen in the field area offers a degree of ironic comfort."
The WA-286-P Joint Venture comprises of Roc Oil as operator with 37.5%; AWE with ;27.5%; Wandoo Petroleum with 24%; Voyager Energy with 6% and CIECO E&P with 5%.
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