Electrofacies analysis - a possible use in Paleogeographic understanding of a North Sea reservoir

Abstract

The study area is centered around the B prospect, which is situated in block 34/6, in the northern part of the Tampen Spur area, northern North Sea. In the study area, lateral changes in reservoir properties of the Lower Jurassic Cook Formation have been observed as well as the need to understand the overall trend and lateral continuity of the lithology within the depositional environments. Understanding of the paleogeography is crucial for prediction and evaluation of the reservoir qualities. Electrofacies could be a possible tool for reconstructing paleogeographic settings. The study is based on eight wells drilled on the Cook formation, using basic log data as input (Gamma Ray, Density, Neutron Porosity Logs), and as additional logs like Sonic, Deep Induction and the Density-Neutron Separation computation. Existing petrophysical interpretation is also incorporated, together with information from cores and sedimentological analysis, to link electrofacies associations with depositional environment. The final electrofacies model is then propagated in wells without core data as well as in areas lacking detailed sedimentological analysis. The results are used to understand the paleogeographic distribution of the identified lithofacies from one well to another in the area of interest and its possible implication in terms of: - reservoir presence and facies typing, - formation and layer tops correlation - lateral variation and regional continuity. Finally, this study can be used for possible future well locations.