Australian independent Melbana Energy is having to sidetrack the Zapato-1 wildcat, its latest exploration well on the Block 9 production sharing contract onshore in Cuba, after the drill string became stuck.

After reaching a depth of 1666 metes and logging the open hole, the 11¾-inch liner was successfully run and cemented. Once the hole was cleaned out, drilling continued within the ophiolite overburden section to a depth of 1698 metres at which point the drilling string became stuck.

However, while attempting to retrieve the drill string, free oil was observed on the shakers at the surface, “which is most encouraging”, Melbana said. Zapato-1 is intended to test a target with a best estimate prospective resource of 95 million barrels of oil, with a 23% chance of success, the operator said earlier.

The decision was made to sever the string above the stuck point and recover the remaining drillpipe. Operations have now been started to initiate a sidetrack and continue drilling to the main carbonate target below the ophiolite.

“While the stuck pipe event and the need to sidetrack the well is a little frustrating, these are normal operations that sometimes occur in the course of some drilling programmes and our operations team is well equipped to manage this and commence the sidetrack drill,” Melbana executive chairman Andrew Purcell said.

Encouragement for target interval

“Despite this, what is particularly encouraging is the observation of oil over the shakers while still within the ophiolite overburden section. This provides encouragement for the target interval yet to be encountered.”

The 2344-square kilometre Block 9 PSC is located on the north coast of Cuba, 140 kilometres east of Havana in a proven hydrocarbon system and along trend with the multi-billion-barrel Varadero oil field.

Independent consultants McDaniel & Associates pegged Block 9 as having a best estimate resource of around 15.7 billion barrels of oil in place and a prospective resource of 676 million barrels.

Melbana was awarded a 100% participating interest in the PSC seven years ago and in May 2020 it agreed to transfer a 70% interest to Sonangol, with the Angolan national company funding 85% of two exploration wells there.

The two-well campaign — that comprises the Alameda and Zapato wells — is designed to test four separate targets with a combined 235 million barrels of best estimated prospective resource. The Alameda wildcat encountered oil shows over a significant interval.

Alameda-1 encountered up to 300 metres of net hydrocarbon pay across three independent zones, but early and short tests of the deeper oil intervals could not be performed effectively with the original well design owing to high formation pressures. The joint venture aims to do this testing following completion of Zapato-1.