Upper Palaeozoic carbonate reservoirs on the Norwegian Arctic Shelf: delineation of reservoir models with application to the Loppa High

The reservoir potential of the Upper Palaeozoic carbonates in the Barents S ea area is primarily controlled by early diagenetic processes. Upper Bashki rian to Asselian shallow platform carbonates deposited in warm, arid to sem i-arid climates were dominated by aragonitic organisms and mineralogically unstable aragonite and high-Mg calcite cements and mud. A reservoir model f or these carbonates involves extensive dolomitization and dissolution of me tastable carbonate during repeated subaerial exposure. The reservoir model is confirmed by drilling and is accordingly regarded as low risk. Artinskia n and Upper Permian shallow water carbonates deposited in a cold temperate climate were dominated by calcitic organisms and silica sponges, and associ ated with calcite cements and mud and chert. A reservoir model for these ca rbonates involves either preservation of primary porosity in carbonate buil d-ups or extensive dissolution of build-up marine cement during prolonged s ubaerial exposure. This model is not confirmed by drilling and is regarded as high risk.