Magnetic resonance characterization of shale rocks
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Date
2023-02
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University of New Brunswick
Abstract
Magnetic Resonance (MR) techniques are foremost among shale characterization methods since they probe in-situ fluids directly and non-invasively. However, the shale MR signal (i) is short-lived, largely precluding quantitative signal acquisition and MR imaging and (ii) is multicomponent, requiring signal differentiation. The T1-T2 MR relaxation correlation method is well-known for signal differentiation for shales. This method, however, suffers from poor signal resolution, limiting its application to fluid typing for shales. In this dissertation, the 2D T1-T2 * relaxation correlation method was developed for shale rock characterization to differentiate, identify, and quantify the shale MR signal at high and low magnetic fields.
The T1-T2 * MR relaxation correlation method was used to determine shale rock petrophysical and geochemical properties. A methodology was presented for quantification of water and oil content in shales, involving water adsorption/desorption and evaporation experiments. It was shown that the MR signal resolved using the T1-T2 * measurement is directly proportional to the shale species content. The short transverse magnetization lifetime signal was dominated by kerogen content in shales. Hydrogen content of kerogen was quantified to determine kerogen hydrocarbon generation potential. It was shown that the FID – the simplest MR measurement – is capable of resolving and quantifying kerogen signal in shales.
The SPRITE MR imaging method was adapted for shale rocks, allowing direct quantitative image acquisition of fluids in shales non-invasively. Using this MR imaging technique, separate images of oil and water in shales were acquired on a macroscopic scale, for the first time. 1D and 3D images of oil and water revealed shale macroscopic heterogeneity features, such as oil and water-rich layers, macro-fractures, and low porosity layers. The oil and water-rich layers were the most common feature in the shale rocks studied and were linked to spatial variation of wettability in shales.
Shale characterization using MR techniques developed in this research advances laboratory core analysis and wellsite evaluations of shales. These MR methods also provide a powerful experimental tool for investigation of fluid flow and storage in shales. Application of these methods lead to environmental-friendly development of shale reservoirs and economic petroleum production, thereby contributing to the energy security.