Deepwater Shale Depositional Systems: Seismic Sedimentology
Seismic imaging and analysis have improved to the point that seismic lines resemble geologic cross sections and stratal slices mimic map views with all their potential for interpretation. Seismic attribute and geomorphological analysis allows characterization and prediction of lithology through evaluation of amplitude, frequency, continuity, velocity and other similar attributes. However, efforts to date have been focused on determining the distribution of reservoir facies and the facies architecture which determines reservoir performance. Recent work has demonstrated that shales, deposited in deep water depositional systems, display characteristic features that reflect distinct depositional and post-depositional processes that may be used to predict reliable and reproducible depositional facies distributions. Preliminary analysis of seismic data indicates that seismic sedimentology can be extended to the non-reservoir parts of the depositional system to produce generalized maps of the seal and flow barrier components of the system. The main controls on connectivity and permeability heterogeneity in deep-water reservoirs are permeability barriers and baffles, such as hemipelagic shales and marls, turbiditic drapes, debris-flow deposits, shale-clast breccia or mass transport complexes and cemented zones. Contrastingly, mappable permeability conduits including fractures, faults, fluid pipes and sand injections have a strong influence on hydrocarbon migration pathways through thick shale sequences. Such features present a complex and varied distribution. Seal, barrier and baffle 3D maps of the different architectural elements and of the limits among them can be enhanced by analogy to representative outcrops and well penetrations which can be used to complement seismic information.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009