Permeability Estimation from NMR Time Dependent Methane Saturation Monitoring in Shales

Valori, Andrea; Berg, Sidney van den; Ali, Farhan; Abdallah, Wael

doi:10.1021/acs.energyfuels.7b00433

Cited by 19 publications

(10 citation statements)

References 15 publications

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“…Another (more recent) conundrum is the origin of the NMR surface relaxation for hydrocarbons confined in organic-rich shales, where large ratios T 1S / T 2S ≳ 4 for the hydrocarbons were previously reported, − as well as dispersion T 1S (ω 0 ) , for the saturating hydrocarbons. In order to shed light on this, we analyze the isolated heptane signal in the polymer–heptane mixes, and we interpret the heptane relaxation as surface relaxation T 1S and T 2S , where the polymer is considered as the “surface” for heptane.…”

Section: Introductionmentioning

confidence: 95%

Interpretation of NMR Relaxation in Bitumen and Organic Shale Using Polymer–Heptane Mixes

Singer¹,

Chen²,

Alemany³

et al. 2018

Energy Fuels

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One of the much debated mysteries in 1 H NMR relaxation measurements of bitumen and heavy crude oils is the departure from expected theoretical trends at high viscosities, where traditional theories of 1 H− 1 H dipole−dipole interactions predict an increase in T 1 with increasing viscosity. However, previous experiments on bitumen and heavy crude oils clearly show that T 1LM (i.e., log-mean of the T 1 distribution) becomes independent of viscosity at high viscosities; in other words, T 1LM versus viscosity approaches a plateau. We report 1 H NMR data at ambient conditions on a set of pure polymers and polymer−heptane mixes spanning a wide range of viscosities (η = 0.39 cP ↔ 334 000 cP) and NMR frequencies (ω 0 /2π = f 0 = 2.3 MHz ↔ 400 MHz) and find that at high viscosities (i.e., in the slow-motion regime) T 1LM plateaus to a value T 1LM> ∝ ω 0 independent of viscosity, similar to bitumen. More specifically, on a frequency-normalized scale, we find that T 1LM> × 2.3/f 0 ≃ 3 ms (i.e., normalized relative to 2.3 MHz), in good agreement with bitumen and previously reported polymers. Our findings suggest that in the high-viscosity limit T 1LM> and T 2LM> for polymers, bitumen, and heavy crude oils can be explained by 1 H− 1 H dipole−dipole interactions without the need to invoke surface paramagnetism. In light of this, we propose a new relaxation model to account for the viscosity and frequency dependences of T 1LM and T 2LM , solely based on 1 H− 1 H dipole−dipole interactions. We also determine the surface relaxation components T 1S and T 2S of heptane in the polymer−heptane mixes, where the polymer acts as the "surface" for heptane. We report ratios up to T 1S /T 2S ≃ 4 and dispersion T 1S (ω 0 ) for heptane in the mix, similar to previously reported data for hydrocarbons confined in organic matter such as bitumen and kerogen. These findings imply that 1 H− 1 H dipole−dipole interactions enhanced by nanopore confinement dominate T 1S and T 2S relaxation in saturated organic-rich shales.

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Section: Introductionmentioning

confidence: 95%

Interpretation of NMR Relaxation in Bitumen and Organic Shale Using Polymer–Heptane Mixes

Singer¹,

Chen²,

Alemany³

et al. 2018

Energy Fuels

View full text Add to dashboard Cite

show abstract

“…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%

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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“…This is in stark contrast to the 1 H-1 H dipole-dipole relaxation T 1RT which increases with T , for all hydrocarbons, including methane. Also of interest recently is the influence of pore confinement on the NMR response of methane [25][26][27][28][29][30][31][32][33][34], which has practical applications for characterizing the light hydrocarbons in the organic nano-pores of kerogen and bitumen in organic-rich shale. One of the current mysteries is why the T 1S /T 2S ratio for surface-relaxation of methane in organic-shale is typically T 1S /T 2S 2, while for higherorder alkanes it is typically higher T 1S /T 2S 4.…”

Section: Introductionmentioning

confidence: 99%

NMR spin-rotation relaxation and diffusion of methane

Singer

Asthagiri

Chapman

et al. 2018

The Journal of Chemical Physics

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The translational diffusion-coefficient and the spin-rotation contribution to the H NMR relaxation rate for methane (CH) are investigated using MD (molecular dynamics) simulations, over a wide range of densities and temperatures, spanning the liquid, supercritical, and gas phases. The simulated diffusion-coefficients agree well with measurements, without any adjustable parameters in the interpretation of the simulations. A minimization technique is developed to compute the angular velocity for non-rigid spherical molecules, which is used to simulate the autocorrelation function for spin-rotation interactions. With increasing diffusivity, the autocorrelation function shows increasing deviations from the single-exponential decay predicted by the Langevin theory for rigid spheres, and the deviations are quantified using inverse Laplace transforms. The H spin-rotation relaxation rate derived from the autocorrelation function using the "kinetic model" agrees well with measurements in the supercritical/gas phase, while the relaxation rate derived using the "diffusion model" agrees well with measurements in the liquid phase.H spin-rotation relaxation is shown to dominate over the MD-simulated H-H dipole-dipole relaxation at high diffusivity, while the opposite is found at low diffusivity. At high diffusivity, the simulated spin-rotation correlation time agrees with the kinetic collision time for gases, which is used to derive a new expression for H spin-rotation relaxation, without any adjustable parameters.

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Permeability Estimation from NMR Time Dependent Methane Saturation Monitoring in Shales

Cited by 19 publications

References 15 publications

Interpretation of NMR Relaxation in Bitumen and Organic Shale Using Polymer–Heptane Mixes

Interpretation of NMR Relaxation in Bitumen and Organic Shale Using Polymer–Heptane Mixes

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

NMR spin-rotation relaxation and diffusion of methane

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