Sand Injections in Deep Offshore Angola: Impact of a Good Characterization
DB17 - GSR, Total EP Angola, Roissy cdg cedex, France
The Zaire turbidite fan is mud rich and single source (Reading and Richards classification). It was initiated during the Oligocene and is still active today. The Angola Oligocene paleo-context is located in the upper middle fan, with geometries such as channel-levees, avulsions, isolated meandering channels, sheets and lobes (channel termination). The contrasted mechanical properties between mud and sand deposits are a key point for understanding injection genesis and distribution. The geometry of deep-water sandstone bodies seems in some cases strongly affected by injection and remobilization. Some years ago, numerous small-scale injections were described on core samples from block 17. Different typologies such as dykes (secant to stratification plane), sills (parallel to the stratification plane), injection breccia and fluidization features were identified. Unfortunately, conventional wireline logs were unable to clearly discriminate these features. Today, thanks to the improvement of borehole dipmeters and imaging (especially in oil base mud) a good discrimination and characterization of the injections can be obtained, particularly when a borehole image to core calibration is available from an offset well. As a result, recent studies revealed that injections were often underestimated in deep offshore Angola. The high resolution 3D seismic also played a great part in a better understanding of these phenomena. Using North Sea analogues, some seismic lines have been cautiously interpreted in terms of injections. The impact of these injections on Block 17 has been generally considered as minor on reservoir geometry and volumetric. Nevertheless, their role in improving connectivity can be considered as relevant and should be taken into account for static and dynamic modeling.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery