PETROGRAPHIC 3D-IMAGING AND DIAGENETIC MODELLING OF SILICICLASTIC RESERVOIRS

The Utsira High (Southern Norwegian North Sea) has been a petroleum exploration target since late 1960s. It is a large basement high (about 200x50 km) located 190 km west of Stavanger, flanked by the Viking Graben to the West.

The southern part of the Utsira High complex (“Haugaland High”) gained new interest when in 2007 Lundin Norway AS discovered commercial hydrocarbons reservoirs in Permo-Triassic to Early Cretaceous formations (Edvard Grieg field).

Several detailed mineralogical and sedimentological studies have been carried out on these rocks; including sedimentological core logging, and petrographical analyses such as optical mineralogy, X-ray powder diffraction (XRD) and scanning electron microscope (SEM).

The present study focuses on the application of high-resolution 3D micro-CT scans in order to provide new insights of the heterogeneous core material (Edvard Grieg field). The core samples exhibit a range of clastic and diagenetic phases (particularly quartz, feldspar, and clays) and display significant primary and secondary porosity. The non-destructive high-resolution 3D micro-CT technique may improve our knowledge of the evolution of inter-connectivity of primary and secondary porosity through time.

The development of micro-CT methods has advanced greatly the last years, enabling us to get detailed petrographical information across multiple scales (cm- to nm-scale). While the grey scale micro-CT tomograms can provide sufficient information regarding pore and rock-matrix structures, they alone are insufficient to distinguish mineralogy. Complementary information is required from other imaging and analytical techniques, such as 2D BSEM or optical thin-section analysis. Polished rock surface of the corresponding region of the micro-CT image, are subsequently scanned by SEM-EDS producing a quantified representation of the minerology. The 2D mineral map can then be registered to the corresponding slice of the micro-CT scan. This approach gives more accurate quantification of mineral and diagenetic phases in the micro-CT data. To characterize nanoscale micropores, additional sub-plugs (4 mm diameter) were extracted from appropriate locations and imaged at higher resolution, down to 1.65μm per voxel. The project goal is better prediction of reservoir characterization through time.