The Massambala-1CH2 sidetrack hole has reached a prognosed total depth of 491m and wireline and coring programs have been completed. The sidetrack hole was drilled to evaluate a shallow oil zone intersected by Massambala-1, Roc’s first exploration well in Angola.

On August 27, Massambala-1CH2 was suspended for possible re-entry in order to determine the commercial merit of the discovery. Laboratory analyses have been initiated with regard to the fluid and core samples obtained from the sidetrack well and results are expected during the next few weeks, according to Roc.

But a preliminary interpretation of currently available data indicates that the oil is mobile, not residual and is similar in appearance to heavy crudes being refined in other parts of the world, the company said.

The main zone of interest is a 16m gross oil column with about 15m of net oil-saturated sand with good to excellent reservoir qualities and an associated wireline log anomaly.

“At the depth of the shallow oil accumulation, approximately 400 metres, the Massambala feature is currently mapped on 3D seismic data as a gentle four-way dip structure with a vertical relief in the order of 16m at the well, which is located a few metres below the structure’s high point,” Roc said.

“As currently mapped, the area of structural closure is approximately 26 square kilometres and based on an apparent oil-water contact identified in the well, it would seem that the shallow Massambala structure is filled to spill.

“It is far too early to comment specifically on potential recoverable reserves at Massambala but volumetric calculations, based on the most recent 3D seismic mapping and available well data, suggest the in-place oil resource potential could be in the order of 170 million barrels.”

But not all of this oil would be recoverable, Roc said.

“Subject to specific field details, heavy oil recovery techniques can recover a minimum of 10% of the oil in-place, often about 20% and sometimes considerably more,” the company said.

Chief executive John Doran said Roc’s primary exploration target in its Cabinda, Angola acreage would continue to be the more mobile and lighter crudes typical of the region, but the oil discovery at Massambala was still potentially important.

“In Massambala’s case, the thought that it might be possible to produce 20% or more of the in-place oil using standard heavy oil industry production techniques, provides plenty of reason for Roc and its co-venturers to take a very close look at the discovery,” he said.

Doran pointed out that Massambala-1 was not only Roc’s first well in Angola and its first well in onshore Africa, but also the company’s fifth exploration success out of nine exploration wells drilled in three different countries during the last 16 months.

Participating Interests in the Cabinda South Block are: Roc (Operator) 60%, Force Petroleum 20% and Sonangol 20%.