Predicting the Quality of Potentially Biodegraded Oils in Deep Offshore Lower Congo Basin: An Integrated Approach

Alain Morash¹, Jean-Luc Pittion¹, Denis Levache¹, Jean-Michel Gaulier², Eric Mure³, and llidio Silva^4
1 TOTAL, Pau, France
² TOTAL, Paris La Defense Cedes, France
³ Total E & P Angola, Luanda, Angola
⁴ Sonangol DPP, Luanda, Angola

After more than 10 years of successful exploration in deep water, TOTAL has defined an operational way of working in order to optimize the oil quality prognosis. Very early in the exploration process, to predict the nature of hydrocarbon appeared to be a decisive economic challenge. Beyond the classical differentiation between oil and gas, the value of oil in shallow buried horizons was one of the key issues. Apart from the reservoir parameters, this value depends on gravity (discount on oil price) and on viscosity (impact on productivity). Simple plots of gravity versus depth, or better versus burial depth, were useful to suggest trends but appeared to be insufficient very soon.

Industry and Academies launched fundamental research on degradation processes of oils, biological and chemical; numerous parameters were collected and processed using sophisticated statistical methods.

Dynamic history of burial, temperature evolution, nature of source rock, migration, continuous or multipulse trap charging, sealing capacity, have been investigated as major factors impacting the final quality of the oil. Trap geometry, areal extent of water interface, water chemical composition, gas stripping have also been considered. A simple formula or over simplistic modelling does not account for the very large distribution of oil qualities all over the world.

On the other hand, a basin per basin, or better sub-basin per sub-basin careful analysis, helps to reduce the uncertainty.