Reservoir characterization and impacts of diagenesis on Upper Cretaceous sandstone formations in the Norwegian Sea, well 6707/10-1

Abstract

The study of deep marine sandstone is among the main research of hydrocarbon explorations now a days. The diagenetic alterations and impacts of diagenesis on reservoir quality of the deep marine sandstone are relatively poor explored in literature. The studied well on the Mid-Norwegian Margin within the Norwegian Sea consists of the Nise and Lysing Formations which are gas containing reservoirs. Twenty-five samples are used for petrophysical and petrographical analysis to determine the diagenetic alterations and their impact on reservoir quality. The main lithology of the reservoir is sandstone with some shale beds. The whole reservoir is divided into ten different zones from which six zones are hydrocarbon bearing zones. The average porosity values of the reservoir are 30%. Sandstone are texturally sub-mature to mature, angular and moderately sorted. Carbonate, quartz and clay cements are prominent. Clay coatings and the abundance of detrital quartz are the phenomenon which are preserving porosity in the whole reservoir. The medium to coarser-grained sandstones with little or no clay content have higher values of porosity as compared to fine to medium- grained sandstone which have a lot of clay content as a cement and matrix. Mechanical compaction doesn t have a major influence on the reservoir quality because of the quartz-feldspar rich detrital grains which are mechanical stable at the studied depths. Clay coatings present in the reservoir prevent the quartz overgrowth and hence increase the reservoir properties. Reservoir quality is good when there is only sandstone lithology. Reservoir quality changed dramatically in some zones when clay is present as a matrix and cement. The main lithology of the reservoir is sandstone with clay beds. These small clay beds are the zones where reservoir quality is not good but overall, the reservoir has good properties.