Advances in NMR Logging

Abstract

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized to be experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Introduction This summary of the state of the art in nuclear-magnetic-resonance (NMR) well-logging technology is aimed at nonspecialists who would like to gain some knowledge of the formation-evaluation capabilities of NMR logging tools. The objective is to explain the basic measurement principles and interpretations needed to understand NMR formation-evaluation techniques and to discuss a few examples of these methods. Introduction of pulsed-NMR logging tools in the 1990s provided the industry with unique, even revolutionary, new methods for analyzing reservoir fluids, rocks, and fluid/rock interactions. The introduction of this technology came at an opportune time. It coincided with rapidly declining production after the 1970s drilling boom and the need for new tools to evaluate the more complex reservoirs being explored and developed. Pulsed-NMR logging tools brought a wealth of new and unique formation-evaluation applications, and this technology has grown rapidly since its inception. Today, major service companies (e.g., Baker Hughes, Halliburton, and Schlumberger) offer NMR logging services. Historical Perspective The potential value of NMR logging was first recognized in the 1950s, leading to development of nuclear-magnetic-logging (NML) tools in the early 1960s. NML tools had many limitations and eventually were retired from service in the late 1980s. In spite of these limitations, laboratory research conducted to support NML logging anticipated many formation-evaluation applications in use today. These applications include estimation of permeability, pore-size distribution, free-fluid volume, oil viscosity, and wettability. The modern phase of NMR logging can be traced to the initiation of an NMR borehole-logging research project at Los Alamos Natl. Laboratory in 1978. The goal of this project was, in part, to build and test a borehole NMR logging tool that would overcome the limitations of the NML tools. The Los Alamos experimental tool used strong permanent magnets and performed pulsed-NMR spin-echo measurements like those used in modern laboratory-NMR instruments. The value of these measurements is that they are extremely flexible and can be tailored to fit many different formation-evaluation applications.