Exploration in Block 14, Offshore Angola: Geologic Insights from a Decade of Experience

Goff, Douglas¹, Nelson Pacavira², Joy Roth¹, Robert Minck¹, Guy Delorme³, Mark Moon¹, Guido Paparoni¹, Mark I. Smithard⁴ (1) ChevronTexaco Overseas Petroleum, Bellaire, TX (2) Cabinda Gulf Oil Co. Ltd, Luanda, Angola (3) ChevronTexaco, Lagos, Nigeria (4) Chevron Texaco, Houston, TX

The Block 14 exploration permit was awarded in 1995 to the contractor group consist­ing of CABGOC (the operator, a ChevronTexaco company), Sonangol P&P, ENI, GALP, and Total. Over 1 billion bbls of recoverable oil have been discovered in 15 reservoirs. Block 14 successes can be attributed to the hundreds of people that have been involved with explo­ration and field development efforts over the last 10 years.

The initial discovery at Kuito in 1997 was followed by a large 3-D seismic survey that confirmed the presence of Miocene turbidite channel sandstones draped over several large structures. In 1998 discoveries were made at Landana, Benguela and Belize fields. Increased understanding of AVO anomalies lead to Lower Miocene discoveries at Tomboco, Lobito, Tombua and Negage fields. Seismic definition of Lower Miocene sands was improved using proprietary pre-stack inversion “pseudo-gamma ray” volumes. This technique was used at Landana field, identifying previously unrecognized oil bearing sandstones.

Over the past decade, the risk elements that affect Block 14 have been well studied. Three major condensed section seal intervals are present in the Miocene, along with sever­al other more localized seals and are a key control in hydrocarbon accumulations. The largest pre-drill uncertainties are hydrocarbon column and Reservoir Net to Gross due to the lowstand deposition of the reservoir sands. Velocity model error and trap seal are the great­est contributors to this uncertainty. Source and migration have been studied and are consid­ered low risk, but may be more complicated then first believed.