Nuclear Magnetic Resonance and Pore Coupling in Clay-Coated Sandstones With Anomalous Porosity Preservation, Agua Grande Formation, Reconcavo Basin, Brazil

Jácomo, Marta Henriques; Trindade, R. I.; Lucas-Oliveira, Éverton; Leite, Carlson de Matos Maia; Montrazi, Elton Tadeu; Andreeta, Mariane; Bonagamba, Tito J.

doi:10.30632/pjv59n2-2018a2

Cited by 9 publications

(6 citation statements)

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“…For instance, [8] demonstrated that permeability estimations based on SDR model for different rocks could exhibit relative errors up to 15%. [20] shows that T 2 shifts to shorter times because of intermediate diffusion coupling between micro-and macro-pores in chlorite-coated sample leading to inaccurate permeability estimation. In addition, a pore-connectivity parameter, introduced for the Coates model, offers more precise permeability and movable fluid volume estimates in complex coupled pore geometry [21].…”

Section: Introductionmentioning

confidence: 99%

Numerical study of NMR relaxation responses in synthetic clayey sandstone by dual-scale modeling

2023

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Nuclear Magnetic Resonance (NMR) relaxometry is a common technique for petrophysical characterization of sedimentary rocks. The standard interpretation of NMR relaxation response assumes that the fast diffusion limit is valid for the whole pore space, allowing to translate transverse relaxation components into pore apertures. However, porous media naturally exhibit multiple length scales. The diffusion between different sized pores may modify the transverse relaxation rate, weakening the relationship with corresponding pore size populations. Focusing on sandstones, we investigate the impact of diffusion coupling on transverse relaxation depending on kaolinite amount, spatial distribution and temperature. A series of synthetic clayey sandstone models with different clay amounts and morphological distributions (pore-lining, pore-filling and laminated) are generated based on a micro-CT image of an actual Bentheimer sandstone. A dual-scale random walk NMR relaxation simulation with resolved multi-porosity kaolinite models is utilized to avoid problems in near to interface exchange regions typical for effective medium representations. Simulations provide spatially resolved dynamics of magnetization exchange between different porosity populations. The results indicate that increased temperature and kaolinite clay amount with lower micro-porosity allows higher magnetization exchange between micro- and macro- porous regions. Pore-lining clay demonstrates stronger diffusional coupling effects, leading to an overestimation of micro-porosity. We further discuss the impact of diffusion coupling on NMR-estimated permeability via SDR and Coates models.

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Section: Introductionmentioning

confidence: 99%

Numerical study of NMR relaxation responses in synthetic clayey sandstone by dual-scale modeling

2023

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“…Na técnica de RMN, os valores de porosidade são medidos em função das propriedades do fluido e do espaço poroso, neste caso, a matriz da rocha não tem uma influência substancial no parâmetro físico medido GE et al, 2015). Estudos tornaram as medições de RMN uma rotina em muitas aplicações petrofísicas, principalmente aquelas relacionadas às rochas siliciclásticas (EHRLICH et al, 1991;KENYON 1997;MARTINEZ e DAVIS, 2000;YAN et al, 2017;JÁCOMO et al, 2018).…”

Section: Introductionunclassified

NMR and Well Logs Petrophysical Characterization of Sandstone From the Maracangalha Formation, Bahia, Brazil

Penna

Batista

Vasconcelos

2021

RGNE

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The storage and production capacity of reservoir rocks can be estimated through some petrophysics characteristics involving the lithological identification of the constitute rocks, fluids nature in the porous space, porosity, permeability, saturation and clay content. The most popular tools for obtaining these petrophysical parameters are the conventional geophysical well logs. However, the determination of petrophysical parameters from tools based on the phenomenon of nuclear magnetic resonance (NMR) has gained prominence in recent decades. In this work, we analyzed rock samples from outcrops in Frades Island region, Bahia, Brazil, through laboratory NMR measurements, to estimate and evaluate the petrophysical properties of the Maracangalha Formation, one of the main hydrocarbons reservoirs in the Recôncavo Basin. The Sandstone samples were characterized in terms of porosity, permeability, saturation, and petrofacies. Finally, we calculated porosity, permeability, and clay content using data from gamma-ray, electrical and density logs, measured in a depth interval interpreted for Maracangalha Formation. These results corroborate with the obtained by NMR since, despite the effects of weathering and erosion on the samples used, the values of porosity and permeability obtained in NMR are in the range of values calculated from these profiles.

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“…Pore-filling clays like non-swelling kaolinite, Al 2 Si 2 O 5 (OH) 4 , or illite, (K,H 3 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH) 2 ,(H 2 O)], and swelling type clays like smectites (e.g., montmorillonite, (Na,Ca) 0.33 (Al,Mg) 2 (Si 4 O 10 )(OH 2 )· n H 2 O, or willemseite, Ni 3 Si 4 O 10 (OH) 2 ·4H 2 O), are known to reduce both porosity and permeability. − It is worth mentioning that the previous chemical compositions of the clays are not standard, and clays can exist in different forms …”

Section: Introductionmentioning

confidence: 99%

“…Conversely, chlorite, (Mg,Fe) 3 (Si,Al) 4 O 10 (OH) 2 ·(Mg,Fe) 2 (OH) 2 , coating of siliciclastic grains can serve as a physical barrier retarding the quartz overgrowth allowing for anomalous porosity preservation in deeply buried sandstones …”

Section: Introductionmentioning

confidence: 99%

The Effect of Clay Content on the Spin–Spin NMR Relaxation Time Measured in Porous Media

et al. 2020

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Clays, hydrous aluminous phyllosilicates, have a significant impact on the interpretation of physical measurements and properties of porous media. In particular, the presence of paramagnetic and/or ferromagnetic ions like iron, nickel, and magnesium in clays can complicate the analysis of nuclear magnetic resonance (NMR) data for porous media characterization. This is due to the internal magnetic field gradient induced by the clay minerals. In this study, we aim to investigate the impact of clay content on spin–spin relaxation time (T 2), which is strongly influenced by the pore surface chemistry. Seven rock core plugs, characterized with variable clay content, were used for this purpose. The clay mineralogy and volume were determined by means of quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN). The T 2 relaxation time was measured using a Carr–Purcell–Meiboom–Gill (CPMG) sequence with variable echo spacing (T E). The maximum percentage difference in dominant T 2 values (MRDT 2) between shortest and longest echo spacing was subsequently correlated with clay content obtained from QEMSCAN. Our results show that the reduction in T 2 distribution with increasing echo time T E is more significant in samples characterized by higher clay contents. The MRDT 2 was found to be strongly correlated with clay content. An analytical equation is presented expressing MRDT 2 as a function of clay content providing a quick and non-destructive approach for clay content estimation. Moreover, the MRDT 2–clay content relationship showed a nonlinear behavior: MRDT 2 increases drastically as the clay content increases up to 15%, beyond which the rate of MRDT 2 change with clay content diminishes. This behavior could be attributed to the clay distribution. At higher clay contents (above 15%), it is more likely for clay to form clusters (structural clays), which will not significantly increase the clay surface in contact with the pore fluid. Further, experimental data suggests that ignoring the impact of clay on internal magnetic gradients and T 2 signal may result in considerable underestimation of the actual pore size distribution.

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Nuclear Magnetic Resonance and Pore Coupling in Clay-Coated Sandstones With Anomalous Porosity Preservation, Agua Grande Formation, Reconcavo Basin, Brazil

Cited by 9 publications

References 0 publications

Numerical study of NMR relaxation responses in synthetic clayey sandstone by dual-scale modeling

Numerical study of NMR relaxation responses in synthetic clayey sandstone by dual-scale modeling

NMR and Well Logs Petrophysical Characterization of Sandstone From the Maracangalha Formation, Bahia, Brazil

The Effect of Clay Content on the Spin–Spin NMR Relaxation Time Measured in Porous Media

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