An integrated approach for de‐risking hydrocarbon prospects using induced polarization anomalies in highly conductive media

Abstract

An offshore electrical investigation was carried out in the eastern Russia adopting the differentially normalized electromagnetic or DNME method. Such workflow is useful in de-risking hydrocarbon prospects. The main aim is to document the presence of diagnostic induced polarization (IP) anomalies related to HC occurrences in highly conductive media. First the response of a known hydrocarbon accumulation was examined and IP anomalies were outlined. No anomalies coincide with the non-productive wells. A local high resistivity layer was detected and mapped on a depth of 2000 – 2500 m, caused by the presence of an oilproducing reservoir. Often a typical epigenetic mineral alteration zone occurs in a halo above deeper-seated hydrocarbon fields. It coincides with a significant change in pyrite content around productive wells. The leakage and pyrite growth at a shallower level depends on geological age and various medium properties. This working model has been confirmed by careful analysis of well data. Inversion of the geoelectric dataset allows separation of the IP field component from the electromagnetic response above the high conductive medium. The first and second potential differences of the transient field measurements over several source-receiver distances are inverted simultaneously. Several IP anomalies were determined via the 1D inversion, that are attributed to different geoelectrical layers. 3D modeling allows verification of the anomalies, with a proper distinction between genuine anomalies and the artificial ones related to the non-horizontal seabed. Resistivity and chargeability anomalies are outlined that derisk the prospectivity of seismically defined structures and moreover to detect a few new prospects of nonanticlinal nature.