Keynote; Sedimentology and Depositional Environments from Image Logs and Cores. Examples from the Gargaf Gp. and the Sarir Sandstone of the Eastern Sirte Basin

Deciphering the depositional settings of a reservoir is a crucial step in predicting its characteristics, which are necessary for an optimal field development. In this sense, integrated core and image log studies led to the sedimentological and depositional interpretation of several reservoirs. Examples are provided for two reservoirs from the Wintershall concessions in the Eastern Sirte Basin. The Early Paleozoic Gargaf reservoir shows a transition from deltaic environments to fluvial systems with varying density of channel stacking patterns. The major part of the reservoir consists of units sedimented by northerly-directed braided river systems. The top of the reservoir includes units deposited by braid deltas within a shallow water embayment. The Early Cretaceous Sarir series represents a complex interfingering of fluvial systems, shoreface/deltaic systems, and a lacustrine environment. The deposition was controlled by palaeogeography and variations of the base-level. These integrated studies improved the understanding of the reservoirs at different scales: depositional facies and facies associations, sediment geometries, palaeogeographical context (palaeocurrent directions and sediment fairways, areas of non-deposition, possible flooding surfaces, etc.). The image logs, once calibrated with cores, provided a powerful tool for interpretation of facies and palaeocurrents. Regional changes in palaeocurrents identified in wells also provided markers, which could support the well correlations.