Nuclear Magnetic Resonance Response to Textural Reservoir Changes

Abstract

Objectives/Scope: Carbonate reservoirs may have extensive secondary-porosity features that alter the character of the reservoir. Increased permeability is the result of the presence of these events, but characterizing them using logging devices has proven problematic. Imaging logs can generally identify the presence of these fractures and vugs, but their contribution to permeability cannot be evaluated. Methods, Procedures, Process: Nuclear magnetic resonance (NMR) logs were added to logging programs to assist in the direct identification of the quantity and quality of these alterations. NMR relaxation has been demonstrated to provide an indirect measurement of secondary porosity and a calculation for permeability. Results, Observations, Conclusions: A full core was taken in this carbonate reservoir. Significant secondary-porosity features were identified in the core. Most of these features were small events that were easily identifiable. The NMR logs were also capable of identifying these secondary-porosity events. Their addition to reservoir quality was also evaluated. Novel/Additive Information: This paper presents examples of core identification of secondary features in these reservoirs. At the same depths, NMR identification of the permeability enhancements is also observed. The additional information obtained from NMR secures a log product that provides a quantification of secondary-porosity reservoir properties without the expense of coring.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015