Correlation and modelling of a fluvial depositional system

Abstract

The Huesca fluvial fan contains a low gradient fluvial system with well-exposed, 3D outcrops. An outcrop study of low-sinuous deposits aims to provide a deterministic reservoir model that predicts correlation lengths, nesting and reservoir potential of thin-bedded fluvial reservoir sandstone in an overall low net-to-gross setting. To correlate the study area, centimetre accurate dGPS measurements of paleosols have been collected to calculate the tectonic dip. This was used to correlate lithostratigraphic logs of the area. Correlation lengths between wells are dependent on how spatial and continuous a paleosol has developed. Photo panels of the outcrop were analysed for net-to-gross ratio and distribution of channel and floodplain deposits. A clear distinction between high and low net-to-gross regions can be observed in the panels, which causes a lateral heterogeneity. This can be explained by the nesting of a river channel. Nesting can be caused by local avulsions triggered by crevasse splays of the river channel in combination with avulsion by annexation. The lateral heterogeneous character can have major implications on reservoir potential. The reservoir volume is dependent on the connectivity between the higher and lower net-to-gross regions. The heterogeneity also has an impact on reservoir modelling as there only is a limited subsurface expression from wells. Therefore, it cannot be known whether the higher or lower net-to-gross zones are being looked at for that particular fluvial system which makes estimates about reservoir volume difficult and inaccurate.