Understanding Fluvial to Shallow Marine Clastic Reservoirs From Modern Analogues Resolved by GPR and Drone Imagery

Abstract

Clastic deposition in the continental and near shore environment is widely recognized as complex, and is controlled by allogenic and autogenic processes that include eustasy, tectonics, 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 models utilized by exploration geologists. 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 and relationship to other passive margin deposits.

A series of GPR lines, fixed-wing drone surveys, and vibracore samples 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 drone imagery and vibracore data 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. Bedding packages are well imaged and can be used to predict the scale of reservoir units using empirical relationships. 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 will assist in locating and predicting the geometry, scale, and reservoir quality of these deposits in the subsurface.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018