Diagenetic Chlorite: Example of an Intra Sandstone Reservoir Seal – From Palaeocene Tyr Member Sandstone, Siri Canyon, Danish North Sea

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  • Afsoon Moatari Kazerouni, Danmark
  • Henrik Friis
  • Jens Peter Vind Hansen, Danmark
This study demonstrates the diagenetic evolution glaucony-rich deep water sandstones from
the Rau-1A well in the Siri Canyon, Danish North Sea. The major diagenetic phases in the studied well
are microquartz, large syntaxial quartz overgrowth, calcite and chlorite. Chlorite forms an intrareservoir
hydrocarbon seal, and our study demonstrates the influence of early diagenetic quartz on the
formation of the chlorite seal. Early opal and microquartz are precipitated close to shale contacts and
prevent the interaction between abundant detrital glaucony and pore-fluid and thus the formation of
grain-coating berthierine. It also preserves porosity and permeability in marginal and isolated parts of
the sandstone.In other parts of the sandstone grain coating berthierine precipitated. It was
transformed to chlorite with increased depth. A second phase chlorite is distinguished by its
morphology and slightly different diffraction pattern. It fills the porosity and reduced permeability in
the upper marginal part of the reservoir which had preserved porosity and permeability due to
microquartz cementation. The pore-filling chlorite acts as an impermeable seal to hydrocarbon
migration and prevents the topmost part of the reservoir to be oil filled. On basis of XRD data, it is
possible to demonstrate a slight shift of actual peak position in overlapping peaks of chlorite in the
studied samples. This variation indicates two facies of chlorite in different time. On basis of the SEM
studies, these facies are identified as an early grain coating chlorite and a later pore filling chlorite. The
change in diffraction pattern indicates that the relative amount of two types of chlorite varies in
relation to reservoir properties. The study demonstrates the conditions for formation of an intraformational
chlorite seal and relates its possible formation to high-porosity/high-permeability zones of
the reservoir. The study suggests that the formation of an intra-sandstone seal of diagenetic chlorite
relates to the distribution of early diagenetic microquartz (which preserve porosity and permeability),
and early diagenetic chlorite which reduces the permeability.
TitelSandstone: Geochemistry, Uses and Environmental Impact
RedaktørerAfsoon Moatari Kazerouni
Antal sider17
ForlagNova Science Publishers
ISBN (trykt)978-1-62948-382-5
ISBN (Elektronisk)978-1-62948-384-9
StatusUdgivet - 2013
SerietitelGeology and Mineralogy Research Developments

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