Heavy Oil Challenges for Development of Gabela Field, Deepwater Block 14 Angola

Kathleen Mabe¹, Rosaria Ambriz², and Masroor Chaudhri^3
1Chevron, Houston, TX
²Sonangol, Houston, TX
³Chevron Energy Technology Company, Houston, TX

The Gabela-1 well marked the 9th oil discovery since the start of the Angola Block 14 deepwater exploration concession operated by Chevron, through its subsidiary Cabinda Gulf Oil Company, with partners Sonangol P&P, Total, ENI, and Galp. The discovery is significant for its size and for being trapped stratigraphically. The main accumulation is late Miocene (CN9), was deposited proximally within a submarine canyon, and appears to be the block's first occurrence of a pure stratigraphic trap.
The canyon's high energy environment caused multiple occurrences of erosion and deposition, yielding complex channel geometries and potentially enhancing connectivity. However, with episodic slumping, debris flows, and the possibility of less sediment sorting, the likelihood for compartmentalization is increased. Direct hydrocarbon indicators from the strong fluid effect suggest the presence of additional fluid contacts within the field. Geochemical analysis, used to compare oils, also suggests reservoir separation between the wells and between zones within the section.
Chevron is addressing these uncertainties by simulating a faulted reservoir model, capturing the complexity of the stratigraphic and structural framework to evaluate recoveries from water injection. The project team is also linking future data acquisition with uncertainty management plans to reduce risk and ensure capital stewardship. In 2006, appraisal drilling delineated the resource base and defined an additional reservoir compartment. Conceptual reservoir basis of design includes long horizontal completions produced with large electric submersible pumps in a subsea environment. Facilities requirements and economics associated with a polymer flood are also being evaluated as well as the use of multi-laterals.
Chevron has utilized many of the lessons learned from other Block 14 producing fields along with company experience in heavy oil deepwater developments.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece