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Angola – Onshore Cabinda South Block

HISTORY
  • The block is in the Lower Congo Basin, a prolific petroleum province.
  • Due to the Angolan civil war, the block had not been explored from the early 1970s until ROC started its activity on the ground in 2005.
  • In 2000 ROC agreed to acquire a 45% interest and operatorship in the block and in 2001 received Government approval for the acquisition. In 2002 the civil war ended.
  • In 2003 ROC acquired a further 15% in the block.
  • In 2004 the PSA was activated.
  • In 2005 ROC-operated 2D and 3D seismic surveys marked the effective return of onshore oil exploration activity in Angola after a hiatus of more than 30 years.
  • Some oil and gas discoveries and shows were recorded from within the block, despite the pre-1972 wells being drilled on gravity data, surface mapping and old seismic data.
  • In April 2009 ROC executed a farmout agreement with Pluspetrol Angola Corporation for the farmout of a 45% interest (56.25% paying interest) in the Block.  Pluspetrol took over as operator of the Block from 1 September 2009.  ROC retains a 15% interest (18.75% paying interest) and will be free-carried through the full 2009 work programme.

REGIONAL ACTIVITY

  • The Lower Congo Basin is a prolific oil producer with a total production in excess of 1.3 million BOPD, approximately one-third of which is produced in the Chevron-operated Block O immediately offshore from the Cabinda South Block.
  • For several decades, offshore oil production platforms have pumped oil to shore-based facilities in Cabinda.
  • No part of ROC's block is more than 50km from Chevron’s onshore oil processing facility at Malongo.
GEOLOGY

The block lies in the Lower Congo Basin, which is one of the salt basins that formed along the Atlantic margin following Early Cretaceous continental breakup.  Reservoirs were deposited in two major phases:  pre- and post-salt deposition.

Pre-Salt Plays

  • The primary reservoirs are the Lucula Sandstone of Jurassic to Early Cretaceous age, sealed by shales of the Bucomazi Formation, and the Aptian-aged Chela Sandstone sealed by the Loeme Salt
  • The Lucula is equivalent to the main reservoir in the M'Boundi Field in the Congo (Brazzaville).
  • The Chela forms the gas reservoir that was encountered by the 123-5 well drilled by Gulf Oil (Cabinda) in 1968.
  • Traps - terrace and onlap/pinchout traps.

Post-Salt Plays

  • The main reservoir is the Vermelha Sandstone.
  • The trap is formed where the sandstones occur in rotated fault blocks, sealed by marine shales.
  • This play accounts for a major portion of the production in the offshore area.
  • Secondary reservoirs include the Iabe Sandstone and Pinda Limestones, both of which produce offshore, and sandstones in the Lago and Mesa Formations.

PERMIT SIZE
  • 1,073km2
JV PARTICIPANTS AND INTERESTS
Beneficial Interest Contributing Interest
Pluspetrol Angola Corporation (Operator) 45.0% 56.25%
Lacula Oil Company Limited (owned by ROC) 15.0% 18.75%
Force Petroleum de Angola, S.A. 20.0% 25.00%
Sonangol P&P 20.0% ---

 

 
ACTIVITY STATUS

In 2005 to 2007 ROC acquired a total of 722km 2D seismic data and 618km2 3D seismic data (573km2 coverage), in three separate surveys. A high resolution aeromagnetic survey was acquired in March 2006, covering the entire Cabinda South Block.

A seven-well exploration drilling programme was completed from June 2007 to September 2008, utilising two rigs - the Simmons Rig 80 and the 100% ROC-owned Explorer rig.

The first well, Massambala-1, discovered a shallow, heavy oil accumulation.  As a result of 3D seismic reprocessing and laboratory analyses, the Joint Venture appraised the discovery with two wells in September-October 2008.  The first appraisal well, MAW-1, confirmed a 9.5m gross heavy oil column and oil-water contact as expected.  The second appraisal well, MAW-4, encountered the primary target deep to prediction and below the oil-water contact as determined from Massambala-1 and MAW-1.

The second and third wells in the programme, Cevada-1 and Soja-1, had good hydrocarbon shows but neither is judged to be commercial and both wells were plugged and abandoned.

The fourth well, Milho-1, was the first well in the current programme to specifically target a pre-salt structure.  The well encountered a classic pre-salt sequence characterised by a thick world-class source rock, with significant oil and gas shows.  This sequence overlies a thick sand interval with good reservoir quality.  While non-commercial, the well provides a very important data point.

The fifth well, Coco-1, produced 26oAPI oil and associated gas to surface during open hole drill stem testing of two separate intervals in the pre-salt sequence.   The well was suspended as an oil discovery with the intention that it will be re-entered and tested.

The sixth well, Sesamo-1, confirmed the existence of the pre-salt target reservoir sands, but there were no hydrocarbon shows.

The final well in the exploration programme, Arroz-1 was plugged and abandoned after final wireline logging indicated only minor hydrocarbon shows.

Preparations are in progress for the testing of the Coco discovery and the drilling of the Castanha-1 exploration well in 4Q 2009.