Complexities of Canyon Deposition and Methodology to Mitigate Uncertainties: Gabela Field Angola Block 14

Joy M. Roth¹, Kathy Mabe², George Burg³, Robert A. Bartusiak¹, John R. Baillie¹, and William Foley^1
1 ChevronTexaco, Bellaire, TX
² ChevronTexaco
³ Burg GeoConsulting, TX

Canyons are frequently thought of as areas of bypass, but at the Gabela discovery - Angola Block 14 - reservoir exists within a submarine canyon. The CN9 middle Miocene reservoir at Gabela-1 is within the AA canyon, a deeply entrenched paleo-Congo canyon running 50 km across Block 14 and beyond. The canyon's high energy environment caused multiple occurrences of erosion and deposition yielding complex channel geometries which could enhance potential connectivity. However, with episodic slumping, debris flows, and the possibility of less sediment sorting, the likelihood for compartmentalization is increased. Faulting is also present with indications of both open and sealing faults. Evidence of compartmentalization is supported by the presence of two PVT oils ranging from 15-18° API. This type of deposition may perhaps make reservoirs in canyons more prone to stratigraphic trapping as seen at Gabela.

In addition to connectivity, there is uncertainty about reservoir quality. The depositional environments of the other Block 14 discoveries are lower on the slope, so they may not be appropriate sources for analogous petrophysical and reservoir performance data. We are addressing some of these uncertainties by building a faulted reservoir model, capturing the complexity of the stratigraphic and structural framework, to evaluate recoveries from water injection. We are also linking future data acquisition with uncertainty management plans to reduce risk and ensure capital stewardship.