Geo-electric Surveying, a Useful Tool for Hydrocarbon Exploration

Abstract

The geo-electric method (GE) allows mapping Induced Polarization effects, often caused by epi-genetic micro-crystals of pyrite. A shallow halo-shaped mineralogical alteration zone is typically formed some distance above a hydrocarbon accumulation. The geo-electric surveying technique (DNME) makes it possible to acquire data in shallow water, where other EM methods are hampered by airwave energy (seabed logging or CSEM). GE method gives encouraging results in deeper water, transition zone and onshore domains. Geo-electric surveying visualizes anomalies in the electric potential response measured in the receiver. Inversion of the registered relaxation curve is done to establish a depth model. Various diagnostic GE attributes are here proposed. Acquisition and processing parameters are adjusted to the target depth, varying from very shallow to 5 km. GE surveys cover different geological settings (e.g. rifts, subsiding cratons, foredeeps). The success ratio for predicting hydrocarbon occurrences is high and some Russian companies incorporate the methodology already in their standard prospect evaluation toolbox. The GE technique helps to reduce risks related to drilling new prospects and allows a substantially better ranking at a reasonable cost.