AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Fluvial Stratigraphic and Reservoir Architectures Using Outcrop Analogs in the Cretaceous Straight Cliffs Formation, Southern Utah: Revised Depositional Models and Synthetic Seismic Modeling
(1) University of Utah, Salt Lake City, UT.
(2) KAUST, Thuwal, Saudi Arabia.
Measured sections, gamma logs, gigapans, and terrestrial lidar data constrain the vertical and lateral evolution of fluvial systems in the John Henry Member (JHM) of the Straight Cliffs Formation (southwest Kaiparowits Plateau, southern Utah). The ~230 m-thick section is divided into seven depositional units (DU) from stratigraphic base to top: DU-0, tidally influenced channel belts; DU-1, highly amalgamated, laterally accreting channel belts with tidally influenced channel belts in the upper section; DU-2, laterally extensive (>1.2 km wide), laterally accreting channel belts; DU-3, isolated channel belts (<150 m) embedded within thick floodplain muds; DU-4, clusters of laterally restricted (<500 m), laterally accreting channel belts and isolated channel belts; DU-5, laterally extensive, locally amalgamated, downstream accreting channel belts; and DU-6, highly amalgamated, downstream accreting channel belts. Reservoir quality of these depositional units and the fluvial sandstone bodies within were evaluated based on grain size, average porosity, net to gross estimates, channel belt size, internal connectivity (heterogeneity) and channel belt connectivity. Two trends in reservoir analog quality (upward decreasing and upward increasing) correspond to defining trends in fluvial architecture (upward fining and upward coarsening) and demonstrate that revised models of alluvial architecture deposition may be used to predict reservoir quality.
A lithologic cross section was created by ‘flattening’ a large outcrop section using gigapans, measured sections, and lidar. This model was then populated with rock and acoustic properties to create synthetic seismic sections of the John Henry Member. Synthetic experiments model 20, 40, 60, and 80 Hz frequency propagation, with high imaging resolutions of up to 41, 21, 14 and 10 m resolved layers, respectively. These resolutions were achieved with standard forms of prestack migration, allowing imaging capability analysis of real seismic experiments of similar geological sections at typical hydrocarbon's reservoir depths of 1km and shallower. Future improvements are expected using techniques of migration deconvolution, as a ‘deblurring’ operator applied to the seismogram, and 3-D Kirchhoff migration to visualize these capabilities in a 3-dimensional model space.