Low-field NMR laboratory measurements of hydrocarbons confined in organic nanoporous media at various pressures

Thern, Holger; Horch, Carsten; Stallmach, Frank; Li, Baoyan; Mezzatesta, Alberto; Zhang, Hao; Arro, Roberto

doi:10.1016/j.micromeso.2017.11.047

Cited by 11 publications

(7 citation statements)

References 6 publications

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“…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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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 difficulty in the characterization of shale reservoirs is the quantitative description of micropore and mesopore structures. A variety of experiments have been used to study the pore structure, including scanning electron microscopy (SEM) [15][16][17], atomic force microscopy (AFM) [18,19], small-angle X-ray (SAXS) [20,21], small-angle/ultra-small-angle neutron scattering (SANS/USANS) [22][23][24][25][26], nuclear magnetic resonance (NMR) [27][28][29][30], high-pressure mercury intrusion (HMIP) [31][32][33][34] and low-temperature liquid nitrogen/carbon dioxide adsorption (LP-N 2 /CO 2 GA) [23][24][25]31,35]. Among these, LP-N 2 /CO 2 GA analysis has been proven to be an effective method in characterizing the pore size distribution of micropores and mesopores [23][24][25]31].…”

Section: Introductionmentioning

confidence: 99%

Fractal Characteristics of Micro- and Mesopores in the Longmaxi Shale

2020

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To better understand the variability and heterogeneity of pore size distributions (PSDs) in the Longmaxi Shale, twelve shale samples were collected from the Xiaoxi and Fendong section, Sichuan Province, South China. Multifractal analysis was employed to study PSDs of mesopores (2–50 nm) and micropores (<2 nm) based on low-pressure N2/CO2 adsorption (LP-N2/CO2GA). The results show that the PSDs of mesopores and micropores exhibit a multifractal behavior. The multifractal parameters can be divided into the parameters of heterogeneity (D−10–D10, D0–D10 and D−10–D0) and the parameters of singularity (D1 and H). For both the mesopores and micropores, decreasing the singularity of the pore size distribution contributes to larger heterogeneous parameters. However, micropores and mesopores also vary widely in terms of the pore heterogeneity and its controlling factors. Shale with a higher total organic carbon (TOC) content may have a larger volume of micropores and more heterogeneous mesopores. Rough surface and less concentrated pore size distribution hinder the transport of adsorbent in mesopores. The transport properties of micropores are not affected by the pore fractal dimension.

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“…Fortunately, MD studies and experimental results demonstrate that oil viscosity is closely related to relaxation time, and the relationship holds even at nanoscale. , The relaxation time is heavily dependent on molecule–surface interactions, which can be understood as the complexity to reach the stable state, that is, the energy-minimization state . As for the case of the bulk state oil molecule, the relaxation time of the long-chain oil will be prolonged more than the relatively small-chain molecules.…”

Section: Model Constructionmentioning

confidence: 99%

Comprehensive Model for Oil Transport Behavior in Nanopores: Interactions between Oil and Pore Surface

Lei

Lai

Sun

et al. 2020

Ind. Eng. Chem. Res.

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A clear knowledge of fluid flow at the nanoscale will greatly contribute to recovery of unconventional oil/gas reservoirs. The distinction of nanoconfined fluid flow behavior with that of the bulk phase stems from strong fluid–surface interactions, which favor the emergence of slip phenomenon as well as spatial variation of viscosity and further affects transport capacity. However, elaboration of the above essential relationship remains challenging nowadays. Oil possesses a complex molecular structure and therefore leads to fruitful technical content regarding oil–surface interplay, posing a huge resistance to gaining a good understanding. Furthermore, the physical properties of tight oil reservoirs exhibit a wide variation range, including rock wettability, pore dimensions, and temperature, and their influences on oil transport are fascinating for in-depth investigation. The aim of this research is to establish a physics fully coupled model for nanoconfined oil transport behavior, which is capable of quantifying the contribution of each influential factor. The excellent agreement against the collected data from published literature claims the reliability of the proposed model. Results indicate the following: (i) A wide pore size can effectively suppress the nanoscale-induced influence on the oil flow behavior, including slip boundary and spatial viscosity variation features. (ii) The velocity distribution characteristic exhibits a plug-like shape as a result of a relatively large slip length by tuning surface wettability. (iii) Slip length shows a negative correlation with increasing temperature, and the feasibility of thermal recovery for tight oil reservoirs is not beneficial compared with that applied in conventional heavy oil reservoirs.

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Low-field NMR laboratory measurements of hydrocarbons confined in organic nanoporous media at various pressures

Cited by 11 publications

References 6 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

Fractal Characteristics of Micro- and Mesopores in the Longmaxi Shale

Comprehensive Model for Oil Transport Behavior in Nanopores: Interactions between Oil and Pore Surface

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