| dc.description.abstract | Petrographic composition, diagenesis and reservoir properties of the Anisian Kobbe Formation within four wells located on the Bjarmeland Platform and in the Nordkapp Basin in the south-western part of the Barents Sea have been investigated. The study has focused on mineralogy, textural parameters, and porosity and permeability reducing factors. Petrographic analyses were performed on forty-four thin sections, and twenty-one of these were point counted, whereas five was examined by X-ray diffraction and electron microprobe analyses. The studied Kobbe Formation sandstones are generally fine grained (very fine to medium) and moderately to well sorted. The sandstone compositions are characterized by mineralogically immature lithic and arkosic arenites, which are dominated by quartz, plagioclase and lithic rock fragments.
Diagenetic alterations strongly control the porosity and permability of the Kobbe Formation sandstones. The main diagenetic processes identified were compaction, alteration, dissolution and precipitation of diagenetic cements such as chlorite, calcite, siderite, and quartz. The distribution of diagenetic cements is largely influenced by depositional facies. Pore-filling chlorite, clay-mineral aggregates, calcite and quartz overgrowths contribute to the low permeability in the tidal influenced deposits. Siderite occurs as abundant pore-lining cement in some samples, which is suggested to inhibit quartz overgrowths. The early diagenetic minerals found in the Kobbe Formation support the depositional model of a large-scale delta system in the Barents Sea during the Triassic, which has been proposed by numerous authors. | en |
