AAPG Bulletin, V. 83 (1999), No. 1 (January 1999), P. 114-127.

Application of NMR Logging to Reservoir Characterization of Low-Resistivity Sands in the Gulf of Mexico¹

M. A. Hodgkins² and J. J. Howard³
 

©Copyright 1999.  The American Association of Petroleum Geologists.  All Rights Reserved
 

¹Manuscript received April 14, 1997; revised manuscript received March 23, 1998; final acceptance April 15, 1998.
²Amoco Canada Petroleum Company Ltd., 240-4 Avenue SW, P.O. Box 200, Station M, Calgary, Alberta T2P 2H8, Canada; e-mail: [email protected]
³Phillips Petroleum Company, 116 Geoscience Building, Bartlesville, Oklahoma 74004.
 

We wish to acknowledge the laboratory assistance of D. E. Langley. Helpful comments were provided by R. Wiley and members of the Amoco Petrophysics Program. Editorial comments from John Doveton and an anonymous reviewer were also very helpful in clarifying portions of the text. Permission to publish this paper was granted by the management of Amoco USA and Phillips Petroleum Company. 

ABSTRACT

Nuclear magnetic resonance (NMR) technology from laboratory data and well logs is rapidly gaining acceptance as a petrophysical tool for evaluating reservoir quality. The evaluation of laboratory NMR data as a core analysis technique shows that NMR relaxation time distributions match independent estimates of pore-size distributions. These other pore-size estimates come from grain-size analyses, pore-throat distributions from mercury porosimetry, thin-section petrography, and permeability values. Irreducible water-saturation estimates from NMR-based pore-size distributions also correspond well with independent measures of irreducible water from special core flood tests.

In this study, we look at the relaxation time distributions extracted from laboratory and downhole NMR measurements to determine pore geometry and volumetrics within a reservoir. This understanding leads to a better overall reservoir characterization. Both core and log NMR data are used to demonstrate that there is a direct connection between NMR relaxation time distributions and the fundamental property of pore size in sandstones. This description of pore-size distributions allows us to estimate permeability and irreducible water saturation. Additionally, the NMR logs accurately characterize the NMR core (lab) measurements and provide important information that enhances the description of low-resistivity pay.