Washover Fans: A Modern Geomorphologic Analysis and Proposed Classification Scheme To Improve Reservoir Models

Abstract Washover fan deposits are part of a much larger system of highly heterolithic barrier and shoreline-margin deposits which form notoriously hard to produce hydrocarbon reservoirs. This survey of modern fan morphologies identifies common fan geometries, considers the preservation potential and range of probable geometries of fan facies in subsurface datasets and outcrops, and aims to improve hydrocarbon recovery in barrier-island reservoir systems. We use satellite imagery to conduct a spatial analysis of 118 modern fans to quantify attributes of fans, including throat width, intrusion length, fan area, and barrier-island width. A new classification scheme for fans is proposed that refines the current fan model. In this classification, fans are initially divided into channelized and non-channelized fans. Channelized fans are subdivided according to the location of primary deposition: barrier depocenter or lagoonal depocenter. Non-channelized fans are subdivided based on morphology: dissipative, lobate, or apron-sourced. Quantitative cross-plots of morphologic parameters are analyzed to define geometric relations in fan morphologies. The probability of identifying fans in the subsurface is discussed. Our results indicate that the most commonly used model for a washover fan, the 52 km2 St. Joseph Island fan, is anomalous and does not reflect the most common sizes or geometries of washover fans. We suggest that our classification be used instead to capture the range of fan morphologies. Although our study encountered non-channelized, line-sourced, lobate washover fans with an area of less than 1 km2 more frequently than any other types of fans, washover fans exhibit diverse morphologies; therefore the entire range of washover fan morphologies should be considered when interpreting exploration data and looking to identify washover fans in the subsurface.

[1]  N. Plant,et al.  Two-dimensional time dependent hurricane overwash and erosion modeling at Santa Rosa Island , 2010 .

[2]  S. Dashtgard,et al.  Tidal Controls on the Morphology and Sedimentology of Gravel-Dominated Deltas and Beaches: Examples from the Megatidal Bay of Fundy, Canada , 2007 .

[3]  Magnus Larson,et al.  State of Knowledge on Measurement and Modeling of Coastal Overwash , 2006 .

[4]  D. Forbes,et al.  Storms and shoreline retreat in the southern Gulf of St. Lawrence , 2004 .

[5]  K. Pye,et al.  Sedimentology of coarse-clastic beach-ridge deposits, Essex, southeast England , 2003 .

[6]  Richard A. Davis,et al.  Stratigraphy of washover deposits in Florida: implications for recognition in the stratigraphic record , 2003 .

[7]  Orrin H. Pilkey,et al.  Global Distribution and Morphology of Deltaic Barrier Island Systems , 2002, Journal of Coastal Research.

[8]  S. Pemberton,et al.  Variability in Wave-Dominated Estuary Sandstones: Implications on Subsurface Reservoir Development , 2002 .

[9]  William E. Galloway,et al.  Terrigenous Clastic Depositional Systems: Applications to Fossil Fuel and Groundwater Resources , 1996 .

[10]  R. Dalrymple,et al.  Estuarine Facies Models: Conceptual Basis and Stratigraphic Implications: PERSPECTIVE , 1992 .

[11]  G. Zarillo,et al.  The interrelation and distinction between flood-tidal delta and washover deposits in a transgressive barrier island , 1987 .

[12]  S. Leatherman,et al.  Overwash and aeolian processes on a U.S. northeast coast barrier , 1987 .

[13]  Richard A. Davis,et al.  ORIGIN AND DEVELOPMENT OF ANCLOTE KEY, WEST-PENINSULAR FLORIDA , 1985 .

[14]  R. Schwartz.  Bedform and stratification characteristics of some modern small‐scale washover sand bodies , 1982 .

[15]  W. J. Cleary,et al.  Cyclic geomorphic patterns of washover on a barrier Island in southeastern North Carolina , 1977 .

[16]  D. K. Davies,et al.  Recognition of Barrier Environments , 1971 .

[17]  P. Andrews.  Facies and genesis of a hurricane-washover fan, St. Joseph Island, Central Texas Coast , 1970 .