Petrophysical and geochemical evaluation of shales using magnetic resonance T_1 - T_2* relaxation correlation

摘要

Quantification of fluid and organic matter content of shale samples are principal goals of petrophysical and geochemical evaluation of shales that are essential to determine reservoir quality. While volumetric methods to characterize shales are cumbersome and destructive, H-1 magnetic resonance (MR) methods are robust, fast, and non-destructive. However, short-lived MR signal lifetimes of shale samples challenge existing MR methods and motivate the development of new MR methods.Two-dimensional (2D) MR T-1 - T-2 relaxation correlation is a powerful method to differentiate hydrogen-bearing species in porous materials. However, the experimental echo time limitation of the T-1 - T-2 method precludes acquisition of important short lifetime signal components. In addition, due to overlap of signal components in T-1 - T-2 correlations, quantification accuracy is impaired in shales. Here, we introduce the 2D MR T-1 - T-2(*) relaxation correlation measurement for quantitative determination of shale H-1 components.Liquid-rich shale samples from the Eagle Ford Formation were used in adsorption/desorption and evaporation experiments. 2D MR T-1 - T-2 and T-1 - T-2(*) correlations coupled with gravimetric measurements were performed to identify water, oil/bitumen, and kerogen peaks in the relaxation correlation maps. Peaks associated with shale components showed significant contrast in T-1 - T-2(*) correlations. This allowed quantitative measurement of water and oil content using the signal intensity of each peak.