Earth Resources Laboratory :: Abstracts

Nuclear Magnetic Resonance Logging

Howard Fred Sklar

Submitted to the Department of Earth, Atmospheric, and Planetary Sciences on May 23, 1997 in partial fulfillment of the requirements for the degree of Master of Science

Abstract

The application of nuclear magnetic resonance (NMR) in petroleum well logging is rapidly expanding. A new generation of pulsed NMR tools, similar in technology to devices in use in medical imaging, is gaining wide acceptance in petroleum exploration. However, methods of NMR data collection and interpretation are not as mature in this application as in medicine; refinement is needed, in particular to maximize the benefit of costly methodology. Herein is described a novel approach to formation evaluation in NMR well logging, enhanced by a nonconventional means of acquiring logging data. Heretofore, both NMR and conventional logs (e.g., acoustic, density, neutron, gamma-ray, spontaneous potential) were analyzed as input into a gross water-saturated model based on resistivity. In the new evaluative approach, in contrast , the NMR measurements—pore size, free fluid, capillary-bound water, effective porosity, and direct hydrocarbon imaging—are the key parameters; resistivity and other logs are input into the NMR model. The effectiveness of this evaluation has been enabled by the development of specific pulse sequences to improve direct hydrocarbon imaging through imaging of pour fluids. The technique, representing an extension of the differential spectrum method, exploits T1 and T2 relaxation methods used effectively to improve tissue contrast in medical magnetic resonance imaging. In practical application, the NMR evaluative model with use of pore size has described many prolific geologic formations deemed nonproductive or marginal by conventional saturation models and analyses. Example novel NMR logs and evaluations are provided, as is a review of NMR physics and previous NMR and conventional formation evaluation models.