oa Modelling of Pyrite Anomalies above Hydrocarbon Accumulations Due to Persistent Leakage Across a Non-perfect Top Seal

The geo-electric method detects Induced Polarization anomalies in the subsurface. In sedimentary rocks these anomalies are often situated in a halo above a deeper-seated hydrocarbon occurrence. An epigenetic alteration halo is stimulated by small but persistent leakage from the trap, due to diffusion and/or porefill perculation processes. Hence locally a reducing chemical condition is established below an effective regional seal, where in-situ pyrite crystals can grow. These crystals are easily polarized and detected by geo-electric investigation techniques. Mathematical modelling permits simulation of the micro-leakage and the geochemical processes triggered in the overburden. The influence of various rock physical parameters is examined. The consequences for the geo-electric evaluation method is demonstrated on the DNME dataset across the Severo-Gulyaevskaya oil-and-gas field, located on the Barents Sea shelf in NW Russia, as well as on a hydrocarbon occurrence in the Kaliningrad region.