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Depositional Environment and Reservoir Architecture of the Carboniferous Section in RKF Field, Berkine Basin, Algeria

N. Sabaou1, N. Connolly1, T. Bartrina2, A. Alaminos2, A. James1, N. Adamson1, G. Paintal1, and N. Alem3
1 Badley Ashton and Associates Ltd, Horncastle, Lincolnshire, United Kingdom
2 CEPSA, Spain
3 CRD-Sonatrach, Algeria

Sedimentological, diagenetic and palynological description of the Carboniferous section (RKF Sands) was carried out on one RKF well. This study allows an improved understanding of the depositional environments and the architecture of the reservoir, along with its quality (diagenetic effects) and age. These data will be important in 3D modelling.

The Rhourde El Krouf (RKF) oil Field was discovered in 1992 by the Sonatrach/Cepsa Association. It is situated in the Berkine Basin of eastern Algeria. This field has two reservoir units, the TAGI (Trias Argilo-Grèseux Inférieur), and the Carboniferous sections. The Carboniferous reservoir has been described as a multi-layer system of shallow marine sandstone beds interbedded with silty-shale intervals containing thin organic-rich shales. The sand sequences may constitute vertically isolated reservoir units with different hydrocarbon composition and hydrocarbon/water contacts. The main objective of the study was to capture the various oil and gas-condensate reservoirs within the Carboniferous RKF Sands to understand the reservoir architecture and possible quality of the different sand-bodies. The link between depositional environment and reservoir quality (diagenetic effects) is an important issue to allow effective 3D reservoir modelling.

The studied interval is considered to comprise bioturbated coastal shallow marine/estuarine deposits and offshore deposits. The cored section has been rationalised into 15 lithotypes that group into 9 facies associations.

The best reservoir quality is to be found where chlorite cementation is 'balanced' - enough chlorite to form sufficiently continuous and thin grain-coats, but not enough to fill pores or restrict pore throats too severely.