NMR log data was acquired on a well in a complex lithology reservoir in the North Sea. The entire gross reservoir interval had been cored, using low invasion core bit and tracer doped synthetic oil based mud for the purpose of providing core NMR and core water saturation data for log calibration. The reservoir is characterized by low-resistivity pay zones, high matrix densities and standard log and core porosities of about 35 PU. The reservoir sands are fine to very fine grained, well sorted with abundant iron-rich glauconite and chlorite. The microporous glauconite reduces the reservoir effective porosity. The main objectives of the NIMR log were to help identify mobile oil, quantify irreducible water saturation, effective porosity and bound fluid volume. Most of these objectives were achieved but during the course of the interpretation a number of other useful applications of NMR technology came to light. The demonstrated field specific applications related to the subject well include;
detection of tar within the hydrocarbon zone reflected by a NMR "signature" of missing porosity and shortened 12 decay;
determination of mobile fluid type through comparison of core calibrated NMR bound fluid volumes with water volumes computed from resistivity tools;
identification of glauconite and chlorite rich sands;
estimation of permeability through core calibrated NMR data; and
identification of gas by the density NMR indicator.
