WASHOVER FANS: A MODERN GEOMORPHOLOGIC ANALYSIS AND PROPOSED CLASSIFICATION SCHEME TO IMPROVE RESERVOIR MODELS

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 km(2) 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 km(2) 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.