Application of NMR logging to reservoir characterization of low-resistivity sands in the Gulf of Mexico

Nuclear magnetic resonance (NMR) technology from laboratory data and well l ogs is rapidly gaining acceptance as a petrophysical tool for evaluating re servoir quality. The evaluation of laboratory NMR data as a core analysis t echnique shows that NMR relaxation time distributions match independent est imates of pore-size distributions. These other pore-size estimates come fro m grain-size analyses, pore-throat-distributions from mercury porosimetry, thin-section petrography, and permeability values. irreducible water-satura tion estimates from NMR-based pore-size distributions also correspond well with independent-measures of-irreducible water from special core flood test s. In this study, we look at the relaxation time distributions extracted from laboratory and downhole NMR measurements to determine pore geometry and vol umetrics within a reservoir. This understanding leads to a better overall r eservoir characterization. Both core and log NMR data are used to demonstra te that there is a direct connection between NMR relaxation time distributi ons and the fundamental property of pore size in sandstones. This descripti on of pore-size distributions allows us to estimate permeability and irredu cible water saturation. Additionally, the NMR logs accurately characterize the NMR core (lab) measurements and provide important information that enha nces the description of low-resistivity pay.