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Understanding Fluvial to Shallow Marine Clastic Reservoir Heterogeneity From Modern Analogues Resolved by Core, GPR, and Drone Photogrammetry

Abstract

Clastic deposition in the continental and near shore environment is widely recognized as complex, and is controlled by allogenic processes such as eustasy and tectonics and autogenic processes influenced by fluvial discharge, and morphologic inheritance. The dynamic nature of the processes that drive fluvial to shallow marine deposition results in deposits that exhibit abrupt lateral and vertical discontinuities in facies that juxtapose porous and permeable units with impermeable ones. The complex geometries and stacking patterns that form the depositional architecture of preserved continental and near shore depositional systems represent significant obstacles to applying many of the conceptual and stochastic models utilized in exploration and reservoir modeling. Close examination of modern fluvial to shallow marine deposits of reservoir quality sand can assist in predicting the occurrence of these deposits in the subsurface, as well as understanding their internal structure. A series of vibracore samples, GPR lines, and fixed-wing drone surveys, were acquired in the coastal plain of South Carolina to investigate the internal structure and stratigraphy of a variety of fluvial to shallow marine sand deposits, to define the morphological expression of these features, and to estimate their reservoir characteristics. Strike and dip oriented reflection lines, as well as common midpoint surveys were collected in 100 and 200 MHz within fluvial channel belts, overbank sand bodies, barrier islands, and estuarine deposits. These data are integrated with vibracore data and drone imagery to resolve the geometry and internal structure of deposits, including bedform types and scales, as well as internal surfaces, such as unconformity, flooding, and accretionary surfaces. Stratigraphic units are differentiable on the basis of vibracores, as well as radar sections, with observed changes in radar velocity and facies correlative to structural and/or stratigraphic interfaces. The results establish the suitability of the imaged deposits as reservoir analogues for ancient continental to near shore equivalents. The high resolution imaging of modern deposits made possible by GPR and fixed-wing drones permit the construction of detailed 3D reservoir analogue models that can be used to condition subsurface reservoir models by defining internal geometries and estimating reservoir heterogeneity.