Unraveling Reservoir Architecture of Complex Low Net: Gross Red-Bed Fluvial Sequence Using Palaeosoils and Chemostratigraphy

Andrea Moscariello
Dept of Geothecnology, Delft Technical University, Delft, Netherlands

The lack of stratigraphical markers and microfossils in continental, fluvial, low net-to-gross red-bed sequences, make conventional e-log based interwell correlations particularly challenging. Effective reservoir modelling and development of such reservoirs therefore rely on application of sedimentological concepts that set the basis for a robust correlation framework. This paper present a case study located offshore UK, where the sedimentary characteristics and reservoir architecture of a fluvial reservoir were re-evaluated by applying an multidisciplinary approach including pedofacies analysis and chemostratigraphy. This study developed an independent chronostratigraphic framework based on chemostratigraphy related primarily to a careful description and interpretation of “non-reservoir” facies. The innovative use of shear sonic to detect palaeosols in uncored sections, was also used for modelling channel distribution. This approach ultimately allowed the identification of meaningful stratigraphic units characterised by changes in the sequence of vertical stacking of pedofacies types. The latter were interpreted as the result of different depositional environments, hence reservoir architecture and connectivity.

The application of the pedofacies concept, the use of shear logs, associated with heavy-mineral analysis, allowed an independent validation of the chemostratigraphic correlation scheme, and provideed a framework for more sophisticated reservoir modelling. In particular, the recognition of the overall style of fluvial behaviour that may influence the style of channel sand-body stacking provided a predictive model to assess reservoir lateral and vertical connectivity. Also, indication of proximity to channel belts enabled identification of stratigraphical which are likely to be laterally connected to channels not penetrated in the wellbore.

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