Geology topics

Joseph D. Seymour

Publications and source records attributed to Joseph D. Seymour.

3 recordsLinked to original sources

USGS2014

Simultaneous Gaussian and exponential inversion for improved analysis of shales by NMR relaxometry

Nuclear magnetic resonance (NMR) relaxometry is commonly used to provide lithology-independent porosity and pore-size estimates for petroleum resource evaluation based on fluid-phase signals. However in shales, substantial hydrogen content is associated with solid and fluid signals and both may be detected. Depending on the motional regime, the signal from the solids may be best described using either exponential or Gaussian decay functions. When the inverse Laplace transform, the standard method for analysis of NMR relaxometry results, is applied to data containing Gaussian decays, this can lead to physically unrealistic responses such as signal or porosity overcall and relaxation times that are too short to be determined using the applied instrument settings. We apply a new simultaneous Gaussian-Exponential (SGE) inversion method to simulated data and measured results obtained on a variety of oil shale samples. The SGE inversion produces more physically realistic results than the inverse Laplace transform and displays more consistent relaxation behavior at high magnetic field strengths. Residuals for the SGE inversion are consistently lower than for the inverse Laplace method and signal overcall at short T2 times is mitigated. Beyond geological samples, the method can also be applied in other fields where the sample relaxation consists of both Gaussian and exponential decays, for example in material, medical and food sciences.

Journal of Magnetic Resonance↗

USGS2013

NMR measurement of oil shale magnetic relaxation at high magnetic field

Nuclear magnetic resonance (NMR) at low field is used extensively to provide porosity and pore-size distributions in reservoir rocks. For unconventional resources, due to low porosity and permeability of the samples, much of the signal exists at very short T 2 relaxation times. In addition, the organic content of many shales will also produce signal at short relaxation times. Despite recent improvements in low-field technology, limitations still exist that make it difficult to account for all hydrogen-rich constituents in very tight rocks, such as shales. The short pulses and dead times along with stronger gradients available when using high-field NMR equipment provides a more complete measurement of hydrogen-bearing phases due to the ability to probe shorter T 2 relaxation times (<10 -5 sec) than can be examined using low-field equipment. Access to these shorter T 2 times allows for confirmation of partially resolved peaks observed in low-field NMR data that have been attributed to solid organic phases in oil shales. High-field (300 MHz or 7 T) NMR measurements of spin-spin T 2 and spin-lattice T 1 magnetic relaxation of raw and artificially matured oil shales have potential to provide data complementary to low field (2 MHz or 0.05T) measurements. Measurements of high-field T 2 and T 1 -T 2 correlations are presented. These data can be interpreted in terms of organic matter phases and mineral-bound water known to be present in the shale samples, as confirmed by Fourier transform infrared spectroscopy, and show distributions of hydrogen-bearing phases present in the shales that are similar to those observed in low field measurements.

Conference Paper↗

USGS2013

Low-field nuclear magnetic resonance characterization of organic content in shales

Low-field nuclear magnetic resonance (LF-NMR) relaxometry is a non-invasive technique commonly used to assess hydrogen-bearing fluids in petroleum reservoir rocks. Longitudinal T 1 and transverse T 2 relaxation time measurements made using LF-NMR on conventional reservoir systems provides information on rock porosity, pore size distributions, and fluid types and saturations in some cases. Recent improvements in LF-SNMR instrument electronics have made it possible to apply these methods to assess highly viscous and even solid organic phases within reservoir rocks. T 1 and T 2 relaxation responses behave very differently in solids and liquids, therefore the relationship between these two modes of relaxation can be used to differentiate organic phases in rock samples or to characterize extracted organic materials. Using T 1 -T 2 correlation data, organic components present in shales, such as kerogen and bitumen, can be examined in laboratory relaxometry measurements. In addition, implementation of a solid-echo pulse sequence to refocus some types of T 2 relaxation during correlation measurements allows for improved resolution of solid phase photons. LF-NMR measurements of T 1 and T 2 relaxation time correlations were carried out on raw oil shale samples from resources around the world. These shales vary widely in mineralogy, total organic carbon (TOC) content and kerogen type. NMR results were correlcated with Leco TOC and geochemical data obtained from Rock-Eval. There is excellent correlation between NMR data and programmed pyrolysis parameters, particularly TOC and S2, and predictive capability is also good. To better understand the NMR response, the 2D NMR spectra were compared to similar NMR measurements made using high-field (HF) NMR equipment.

Conference Paper↗