Types of Low Resistivity Layer and Genesis Analysis of the Lower Interval of Guantao Formation in Gudong Oil-field

Lower interval of the Guantao Formation, a fluvial reservoir with overall good physical properties, has long been thought to have poor oil - bearing properties as the resistivity is much lower than the upper interval. Reinter-pretation and production test reveal that part of the reservoir is highly productive oil layers with low resistivity. Based on genesis analysis of the low resistivity layers in the interest area, it is believed that the low resistivity in the lower interval are mainly caused by high salinity, small amplitude of structure and high irreducible water saturation. The low resistivity layers are divided into low permeability type, high permeability type and thin layer type according to the genesis and geological features. The study achievements provide a basis for interpretation of the low resistivity layers in Gudong oilfield and new methods for adding reserves to mature blocks.