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Quantitative Characterization of the Architecture of Shallow-Marine Clastic Parasequences: Applications to Reservoir Studies

Abstract

The recognition of parasequence organization is routinely attempted when performing well correlations in clastic shallow-marine reservoirs, as it provides the basis for predicting geometry and connectivity of net volumes and therefore planning field development.

The architecture of clastic parasequences is commonly thought to be influenced by rates of creation of accommodation, rates of sediment supply to a shoreline, and by autogenic behaviors. However, a systematic assessment of these factors has been, to-date, lacking. This study combines data from several published case studies, with the aims of undertaking a quantitative characterization of parasequences and determining how allogenic controls on their architecture are recorded, in part to enable predictions of likely subsurface architecture.

Data on 40+ shallow-marine successions containing 700+ parasequences have been coded in a relational database (the Shallow Marine Architecture Knowledge Store, SMAKS), which includes outcrop and subsurface datasets, both ancient and Quaternary examples, and that covers the preserved records of both river-dominated deltas and wave-dominated coasts.

The role of accommodation (A) and sediment supply (S) in determining parasequence architecture is assessed through analysis of relationships between proxies of these variables at different scales (rates of aggradation and progradation, facies-tract shoreline trajectories, systems-tract type, parasequence-set stacking patterns, parasequence progradation angle, size of delta catchment areas) and morphometric parameters of parasequences and parasequence-scale sandstone bodies. Statistical analysis of database outputs indicates the significance of proxies of A/S ratios as predictors for parasequence architecture (thickness, sandstone thickness and lateral extent, top type), and the existence of scaling relationships between parasequence geometry and measures of sediment-delivery rates. However, results also highlight biases in the ability to resolve parasequences consistently, especially where temporal control is available.

The resulting insight allows predictions of likely reservoir geometry and compartmentalization to be made on the basis of constraints of accommodation and sediment supply, typically arising from studies based on regional seismic stratigraphy and source-to-sink analysis. These predictions might find application to the estimation of likely net-reservoir volumes and definition of field-development strategies.