Sequence Stratigraphic Organization of Architectural Elements

Flint, Stephen¹, David Hodgson¹ (1) University of Liverpool, Liverpool, United Kingdom

Architectural elements control fluid flow in reservoirs and many datasets exist on likely geometries and (less commonly) shapes. Datasets include both modern and ancient outcrop examples and, under optimal conditions, high resolution shallow seismic examples. However, a crucial and sometimes forgotten aspect of architectural element applications to reservoir modelling is the degree of preservation of original depositional geometries. We argue that these datasets must be collected within a robust high resolution sequence stratigraphic framework, so that correct analogues are used. Long term accommodation trends impose a predictable control on the nature of high frequency sequences such that in fluvial reservoirs, long term base level fall results in very net:gross but ‘leaky' reservoirs, with many elements not preserved. Periods of long term base level rise produce less incision at high order sequence boundaries hence reduced vertical connectivity and preservation of a wider range of elements. Deepwater basin floor fan reservoirs are commonly composite lowstand bodies of high order sequences that stack in a predictable forward-stepping to aggradational to landward-stepping manner. Different mixes of architectural elements are preserved in the different stacking positions and this architecture strongly affects vertical/horizontal connectivity. Accurate linking of architectural elements of position in sequence and in sequence hierarchy allows for forward prediction of proportions of element types and preservation of these elements, thus allowing a greater degree of determinism in 3-D reservoir models.