Investigation of Physical Properties of Hydrocarbons in Unconventional Mudstones
            Using Two-Dimensional NMR Relaxometry

Xie, Z. Harry; Gan, Zheng

doi:10.30632/t60als-2019_zzz

Cited by 8 publications

(8 citation statements)

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“…While this provides a good contrast mechanism for fluid typing and saturation estimates in organic-rich shale, the mechanism behind this observation is still not well understood. In some cases, 1 H− 1 H dipole−dipole relaxation is thought to be the dominant mechanism, 32,37,39,43,47,50,51 while in other cases surface paramagnetism is thought to be the dominant mechanism. 33,34,49,57 In order to shed light on this subject, we present MD simulations of T 1 and T 2 of n-heptane (henceforth simply heptane) in polymer−heptane mixtures, where the highviscosity polymer, a model for immature kerogen and bitumen, provides an organic "surface" and organic transient "pores" for heptane.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Aside from bulk fluids, another major conundrum in petrophysics is the origin of the NMR surface relaxation T 1S and T 2S of fluids confined in organic-rich shales. − For instance, Ozen and Sigal first reported that light hydrocarbons exhibit large ratios T 1S / T 2S ≳ 4 when confined in organic shale, while small ratios T 1S / T 2S ≃ 2 are found for water. While this provides a good contrast mechanism for fluid typing and saturation estimates in organic-rich shale, the mechanism behind this observation is still not well understood.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Critical Role of Confinement in the NMR Surface Relaxation and Diffusion of n-Heptane in a Polymer Matrix Revealed by MD Simulations

et al. 2020

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The mechanism behind the NMR surface-relaxation times (T 1S,2S) and the large T 1S/T 2S ratio of light hydrocarbons confined in the nanopores of kerogen remains poorly understood and consequently has engendered much debate. Toward bringing a molecular-scale resolution to this problem, we present molecular dynamics (MD) simulations of 1H NMR relaxation and diffusion of n-heptane in a polymer matrix. The high-viscosity polymer is a model for kerogen and bitumen that provides an organic “surface” for heptane. Diffusion of n-heptane shows a power-law dependence on the concentration of n-heptane (ϕC7) in the polymer matrix, consistent with Archie’s model of tortuosity. We calculate the autocorrelation function G(t) for 1H–1H dipole–dipole interactions of n-heptane in the polymer matrix and use this to generate the NMR frequency (f 0) dependence of T 1S,2S as a function of ϕC7. We find that increasing molecular confinement increases the correlation time, which decreases the surface-relaxation times for n-heptane in the polymer matrix. For weak confinement (ϕC7 > 50 vol %), we find that T 1S/T 2S ≃ 1. Under strong confinement (ϕC7 ≲ 50 vol %), we find that T 1S/T 2S ≳ 4 increases with decreasing ϕC7 and that the dispersion relation T 1S ∝ f 0 is consistent with previously reported measurements of polydisperse polymers and bitumen. Such frequency dependence in bitumen has been previously attributed to paramagnetism; instead, our studies suggests that 1H–1H dipole–dipole interactions enhanced by organic nanopore confinement dominate the NMR response in saturated organic-rich shales.

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Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Critical Role of Confinement in the NMR Surface Relaxation and Diffusion of n-Heptane in a Polymer Matrix Revealed by MD Simulations

et al. 2020

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations of NMR Relaxation and Diffusion of Heptane Confined in a Polymer Matrix

Parambathu,

Singer,

Hirasaki

et al. 2020

Preprint

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The mechanism behind the NMR surface relaxation and the large T1/T2 ratio of light hydrocarbons confined in the nano-pores of kerogen remains poorly understood, and consequently has engendered much debate. Towards bringing a molecular-scale resolution to this problem, we present molecular dynamics (MD) simulations of 1 H NMR relaxation and diffusion of heptane in a polymer matrix, where the high-viscosity polymer is a model for kerogen and bitumen that provides an organic "surface" for heptane. We calculate the autocorrelation function G(t) for 1 H-1 H dipole-dipole interactions of heptane in the polymer matrix and use this to generate the NMR frequency (f0) dependence of T1 and T2 relaxation times as a function of φC7. We find that increasing molecular confinement increases the correlation time of the heptane molecule, which decreases the surface relaxation times for heptane in the polymer matrix. For weak confinement (φC7 > 50 vol%), we find that T1S/T2S 1. Under strong confinement (φC7 50 vol%), we find that the ratio T1S/T2S 4 increases with decreasing φC7, and that the dispersion relation T1S ∝ f0 is consistent with previously reported measurements of polymers and bitumen. Such frequency dependence in bitumen has been previously attributed to paramagnetism, but our studies suggests that 1 H-1 H dipole-dipole interactions enhanced by organic nano-pore confinement dominates the NMR response in saturated organic-rich shales, without the need to invoke paramagnetism.

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“…Another possible relaxation mechanism in crude oils is enhanced 1 H-1 H dipole-dipole relaxation [1-5, 9, 13, 25, 30, 31, 43, 44], whereby the relaxation of the maltenes is enhanced by confinement from the transient nano-pores of the asphaltene macro-aggregates. Similarly, 1 H-1 H dipole-dipole relaxation is also postulated to dominate for light hydrocarbons in the organic nano-pores of kerogen [46][47][48][49][50][51][52][53]. In fact, crossed-linked asphaltenes have been shown to be a good model for kerogen when modeling of the equilibrium partitioning of hydrocarbons in nanoporous kerogen particles [54].…”

Section: Introductionmentioning

confidence: 99%

Elucidating the $^1$H NMR relaxation mechanism in polydisperse polymers and bitumen using measurements, MD simulations, and models

Singer¹,

Parambathu²,

Wang³

et al. 2020

Preprint

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The mechanism behind the 1 H NMR frequency dependence of T1 and the viscosity dependence of T2 for polydisperse polymers and bitumen remains elusive. We elucidate the matter through NMR relaxation measurements of polydisperse polymers over an extended range of frequencies (f0 = 0.01 ↔ 400 MHz) and viscosities (η = 385 ↔ 102, 000 cP) using T1 and T2 in static fields, T1 field-cycling relaxometry, and T1ρ in the rotating frame. We account for the anomalous behavior of the log-mean relaxation times T1LM ∝ f0 and T2LM ∝ (η/T ) −1/2 with a phenomenological model of 1 H-1 H dipole-dipole relaxation which includes a distribution in molecular correlation times and internal motions of the non-rigid polymer branches. We show that the model also accounts for the anomalous T1LM and T2LM in previously reported bitumen measurements. We find that molecular dynamics (MD) simulations of the T1 ∝ f0 dispersion and T2 of similar polymers simulated over a range of viscosities (η = 1 ↔ 1, 000 cP) are in good agreement with measurements and the model. The T1 ∝ f0 dispersion at high viscosities agrees with previously reported MD simulations of heptane confined in a polymer matrix, which suggests a common NMR relaxation mechanism between viscous polydisperse fluids and fluids under confinement, without the need to invoke paramagnetism. FIG. 1.Table of contents; graphical abstract.

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Investigation of Physical Properties of Hydrocarbons in Unconventional Mudstones Using Two-Dimensional NMR Relaxometry

Cited by 8 publications

References 0 publications

Critical Role of Confinement in the NMR Surface Relaxation and Diffusion of n-Heptane in a Polymer Matrix Revealed by MD Simulations

Critical Role of Confinement in the NMR Surface Relaxation and Diffusion of n-Heptane in a Polymer Matrix Revealed by MD Simulations

Molecular Dynamics Simulations of NMR Relaxation and Diffusion of Heptane Confined in a Polymer Matrix

Elucidating the $^1$H NMR relaxation mechanism in polydisperse polymers and bitumen using measurements, MD simulations, and models

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