Characterizing stratigraphically complex deepwater slope channel reservoirs for production optimization and better field management – A brown field example, offshore West Africa

Abstract

The dynamic relationship between field management and reservoir characterization has often been a puzzle, especially in complex deepwater channel systems. Reservoir management and infill drilling success cases were often due to improved understanding of deepwater depositional systems and geological controls on channel architecture and the general distribution of individual rock facies. For confined to weakly-confined slope channel complexes, some controls on the degree of channel avulsion and aggradation are the interplay between flow hydraulics, sediment calibre, depositional gradient, and the interaction of the flow with underlying substrate. This work aims at documenting the stratigraphic characterization of a Miocene deepwater channel system in a brownfield with focus on the historical evolution of the framework interpretation as well as applications of the recent updates in field management. The initial stratigraphic model (2005) was done using the layer cake concept with minimal incision, continuous shales and limited vertical connectivity based on observations from available seismic data (pre-baseline survey acquisition) and limited well control. This was modified in 2009 following acquisition of a 4D Monitor 1 seismic volume and 3 years production data from 20 wells to a more erosive model with compensationally stacked channel complexes of similar width. With new 4D Monitor 2 acquired in 2014, broadband processed seismic data in 2020, a total of 36 wells and 11 years of production, an updated framework has recently been built. In the new framework, two key fairways namely the Upper and the Lower Fairway were delineated, each comprising of 8 and 6 channel complexes, respectively. A conceptual basin-fill sequence was utilized, as well as a genetic classification of the channel complexes into erosional-confined systems, meandering systems, and levee-confined channel systems. The cut-and-fill behaviors of the individual complexes have been tied to changes in depositional gradient, sediment sand vs mud ratio, interaction of the flow with the substrate, and this has impacted the degree of channel amalgamation, avulsion and the degree of preservation of both internal and external levees. At flow unit scale, potential inter, and intra-reservoir connection pathways and compartments defined through integrated use of excess pressures, geobody attributes, well production and 4D data, have been very helpful in defining reservoir connection windows, injector – producer connectivity, and channel compartments. The implication is that this exercise or study has provided renewed insights into infill drill-well opportunities, well production performance as well as overall field management strategy.