As of yesterday morning, the Roc-owned Explorer rig had directionally drilled the onshore well, the first to be drilled in the African nation in more than 30 years, to 2192 metres.

While Massambala-1 failed to find hydrocarbons in its primary pre-drill target, the well had “good oil shows” over a 39m interval at a depth of 394-433m.

Of particular interest to Roc were anomalous log responses, which it said indicated a moveable hydrocarbon, over a 20m gross interval in the zone of good oil shows.

Other minor log anomalies are above and below this zone, but do not coincide with oil shows.

Roc said the 20m interval showed good to excellent potential reservoir quality, with 18m (90%) net sand with an average porosity of about 27%.

But wireline sampling did not recover any oil from this zone of interest which, when combined with pressure gradient measurements, suggested the zone was a heavy oil accumulation or, possibly, a residual oil column.

Roc chief executive Dr John Doran said the company was preparing to plug the well back and sidetrack to core the shallow zone of interest.

“Because we are at the beginning of a big drilling campaign, it is essential that we try to nail the exact nature of the shallow oil zone at Massambala-1 as soon as possible because if it proves to be producible, the upside potential is well worth chasing,” he said.

Sidetracking the well is expected to be completed in two weeks, after which the rig will move to drill the second well, Cevada-1, in the eastern part of the Cabinda South block.

The Simmons 80 Rig arrived in Cabinda in late July and is expected to start drilling Soja-1 before the end of August.

Interests in Cabinda South are: Roc (operator – 60%), Force Petroleum (20%) and Sonangol P&P SA (20%).