Stratigraphic Architecture in the Cretaceous Pinda Fm; Block 0, Offshore Angola

The Pinda Formation, offshore Angola, was deposited as a mixed carbonate-clastic coastal system. We present a regional stratigraphic framework constructed from detailed analysis of over 30,000 ft of core combined with well-log data from 200+ wells and block-wide 3D seismic.

The Albian Pinda reaches thicknesses of over 3000' and contains a series of regressive-to-transgressive mixed lithology wedges that record long-term coastal retreat. Each wedge comprises marine, marginal-marine and fluvial depositional environments, the youngest of which is capped regionally by a thick (hundreds of feet) shelf limestone.

Marine and marginal-marine depositional environments comprise interbedded (decimeter to meter scale) siliciclastic and carbonate strata deposited in a strandplain to barrier-island coastal setting. Both carbonate and clastic rocks are found in high energy (shoreface, tidal inlet) and low energy (lagoon, tidal flat) environments. These environments can be dominated by either lithology or a mix of the two. Most carbonates are detrital (>95%); little evidence has been recovered suggesting the presence of in situ reef deposits.

Despite the fine-scale interbedding of environments and complex lithology mix, the larger-scale stratigraphic architecture of the Pinda reveals insights into the sub-regional distribution of these lithologies. After reconstructing the stratigraphic architecture, we note that periods of coastline transgression comprise greater proportions of carbonate material; many transgressive erosional surfaces are lined with shell debris and/or capped with meter-scale limestone deposits. Regressive architectures are commonly associated with greater proportions of siliciclastics.

The Albian was deposited contemporaneously with active salt movement in the underlying Aptian Loeme evaporites. Large growth faults that sole in the Loeme salt produced syn-depositional accommodation centers as reflected in massively expanded (4-5X) Pinda-aged growth sections. Post-Pinda displacement along these growth faults created "rafted" blocks of Pinda separated by growth sections of younger sediments. Structural controls such as these make it challenging to characterize reservoir architectures within individual fields.