Reservoir characterization of the Middle - Upper Triassic Kobbe and Snadd Formations in the southwestern Barents Sea: The role of chlorite coating
Deeply buried reservoirs represent interesting plays on the Norwegian Continental Shelf due to the efficiency of chlorite coatings as a porosity-preserving mechanism. This study investigates factors controlling reservoir quality of deeply buried middle – late Triassic sandstones in the Nordkapp Basi...
| Main Author: | |
|---|---|
| Format: | Master Thesis |
| Language: | English |
| Published: |
2016
|
| Subjects: | |
| Online Access: | http://hdl.handle.net/10852/49708 http://urn.nb.no/URN:NBN:no-53449 |
| Summary: | Deeply buried reservoirs represent interesting plays on the Norwegian Continental Shelf due to the efficiency of chlorite coatings as a porosity-preserving mechanism. This study investigates factors controlling reservoir quality of deeply buried middle – late Triassic sandstones in the Nordkapp Basin, Loppa High and Fingerdjupet Sub-basin in the southwestern Barents Sea. Special attention is given to the origin of the chlorite coating. Core material and well data from three wells was examined by sedimentological, petrographic and petrophysical methods. Sedimentological analysis was performed through core logging and facies division. Optical microscopy, X-ray diffraction and SEM provided the database for the petrographic analysis. Wireline logs were investigated during the petrophysical analysis. The sandstone of highest reservoir potential in the Kobbe Formation is interpreted as a tidally influenced fluvial channel in a protected, mesotidal estuary. Subaqueous infiltration of muddy water represents important emplacement of allogenic clay, of which a portion is adhered to the fine-grained detrital grains and forms a precursor clay coating. Small grain size is the major factor maintaining high IGV with increasing burial. Thin, iron-rich chlorite effectively prevents nucleation of quartz cement at greater depth intervals. The primary porosity is greatly reduced by the presence of pore filling clay matrix. Due to large volumetric potential and good petrographic properties, the interpreted intertidal bank deposits of the Snadd Formation show good reservoir quality. Mechanical clay infiltration in combination with subaerial exposure during low tide results in well-developed clay coatings around medium-sized detrital grains. High IGV is preserved with increasing burial due to the ductility of lithic rock fragments. Thick, continuous authigenic chlorite coating greatly reduces quartz precipitation and is thus crucial for preserving porosity at deep burial depths. Based on results from sedimentological, petrographic and petrophysical analyses, a sedimentological and diagenetic evolution of the Kobbe and Snadd Formation sandstones is proposed. This study concludes that initial mineralogy and texture have a crucial impact on the reservoir quality. As these factors reflect the provenance region, transport and processes occurring in the depositional environment, the importance of the sedimentological system is emphasized. |
|---|