Distinct Petrographic Changes Across the Triassic-Jurassic Boundary in the Southwestern Barents Sea — Implications for Predicting Reservoir Quality
Distinct petrographic changes across the Triassic-Jurassic boundary in the
southwestern Barents Sea - Implications for predicting reservoir quality
Lina Hedvig Line (UiO), Helge Hellevang (UiO) and Jens Jahren (UiO)
A major challenge for reservoir quality predictions in the southwestern Barents Sea is the
complex uplift and erosion history that have complicated the thermal trends of the sediments.
Sandstone reservoirs are currently not located at their maximum burial depths, and
disappointing drilling results are often associated with unexpected poor reservoir quality.
Because seismic and acoustic inversion methods fail to distinguish high-quality from low-
quality sandstone reservoirs, we attempt to attribute reservoir properties to depositional
setting and diagenetic evolution by coupling petrography with sedimentary facies and basin
analyses. Triassic and Jurassic sandstones are the major stratigraphic targets for hydrocarbon
prospecting in the SW Barents Sea, and marked contrasts in texture and mineralogy are
observed between the geological periods. This provides an opportunity to understand how
different initial petrophysical properties change with increasing burial depth and temperature.
Channelized sandstone deposits of Triassic age are expected to have high potential for
preserving porosity with deep burial due to extensive development of chlorite coatings.
However, high concentrations of mechanically weak lithic fragments produce low
intergranular volumes during burial, which often result in poor reservoir quality. Conversely,
textural and mineralogical maturity characterize the Jurassic sandstones in the southwestern
Barents Sea. This petrographic contrast has been related to hinterland rejuvenation and
decreased subsidence rates, followed by extensive sediment reworking in the Jurassic. As
opposed to the Triassic sandstones, the potential for preserving porosity with deep burial is
lower in the Jurassic sandstones due to limited distribution of grain coatings. Jurassic
reservoirs are thus prone to chemical compaction if burial temperatures exceed 70C. Future
exploration campaigns should target Jurassic sandstone reservoirs with maximum burial
depths of less than 2 - 2.5 km. Reworked sediments from both provenance regions have
potential for preserving good reservoir properties.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019