Characterization of glaciogenic reservoirs using high-resolution quantitative mineralogical and textural analysis of drill cuttings. 9th Middle East Geosciences Conference, GEO 2010.

In the past decade Palaeozoic glaciogenic deposits in North Africa and the Middle East have been recognised as important reservoirs for hydrocarbons. However, the sedimentary system associated with glaciers and ice-sheets is highly complex and still poorly understood. This often results in large exploration and development risks due to potentially large uncertainties in the reservoir stratigraphy, facies and 3-D architecture. Glaciogenic reservoirs are often associated with deeply incised valleys (i.e. tunnel valleys). These are formed under ice-sheets by overpressured meltwater and can reach up to 600 meters in depth, tens of kilometers in length and 5 kilometers in width. As the sedimentary mechanisms and depositional environments can be highly variable, the subsequent infill of the valleys is vertically and laterally extremely heterogeneous. The heterogeneity of the sedimentary infill often results in problematic subsurface correlation. This is made even more difficult by the absence of biomarkers or marker beds that can be traced on a regional scale. Under the Pleistocene ice-sheets of NW Europe, tunnel valleys with similar characteristics to those from the Palaeozoic age were formed. In the city of Hamburg (NW Germany) there is good understanding of the architecture and lithology of the infill of the Pleistocene tunnel valleys due to a database of ca. 17,000 boreholes that were mainly drilled for geotechnical investigations. This study presents the results of a detailed sedimentological and mineralogical study of one of these boreholes. 170 cuttings samples were analysed using QEMSCAN®. This automated instrument uses a combination of backscattered electron imaging and energy dispersive X-ray spectroscopy to mineralogically and texturally quantify samples. Mineralogical and textural trends were identified and correlated with the available wireline logs. Grain-size was compared with the reconstructed density and porosity logs and used to differentiate potential reservoir flow units. Mineralogical composition provided an indication of the provenance at different stratigraphical intervals. Diagenetic minerals such as clay and secondary cement infills were also investigated to assess whether such elements could be used for correlative purposes. This study highlighted the compositional heterogeneity of tunnel valley infill and confirmed the potential of QEMSCAN® as a tool to unravel complex stratigraphy and quantify reservoir potential.