Techniques used to calculate shale fractal dimensions involve uncertainties and imprecisions that require more careful consideration

Wood, David A.

doi:10.46690/ager.2021.02.05

Cited by 42 publications

(28 citation statements)

References 25 publications

(33 reference statements)

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“…Thus, the well development of mesopores is favorable for shale gas exploration. With the increase in pore size, the proportion of adsorbed gas decreases and the proportion of free gas increases, leading to the increased initial production of shale gas well [50][51][52].…”

Section: Ssa and Pv Characteristicsmentioning

confidence: 99%

Clarifying the Effect of Clay Minerals on Methane Adsorption Capacity of Marine Shales in Sichuan Basin, China

Wang

Zhou

Zhang³

et al. 2021

Energies

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The effect of clay minerals on the methane adsorption capacity of shales is a basic issue that needs to be clarified and is of great significance for understanding the adsorption characteristics and mechanisms of shale gas. In this study, a variety of experimental methods, including XRD, LTNA, HPMA experiments, were conducted on 82 marine shale samples from the Wufeng–Longmaxi Formation of 10 evaluation wells in the southern Sichuan Basin of China. The controlling factors of adsorption capacities were determined through a correlation analysis with pore characteristics and mineral composition. In terms of mineral composition, organic matter (OM) is the most key methane adsorbent in marine shale, and clay minerals have little effect on methane adsorption. The ultra-low adsorption capacity of illite and chlorite and the hydrophilicity and water absorption ability of clay minerals are the main reasons for their limited effect on gas adsorption in marine shales. From the perspective of the pore structure, the micropore and mesopore specific surface areas (SSAs) control the methane adsorption capacity of marine shales, which are mainly provided by OM. Clay minerals have no relationship with SSAs, regardless of mesopores or micropores. In the competitive adsorption process of OM and clay minerals, OM has an absolute advantage. Clay minerals become carriers for water absorption, due to their interlayer polarity and water wettability. Based on the analysis of a large number of experimental datasets, this study clarified the key problem of whether clay minerals in marine shales control methane adsorption.

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Section: Ssa and Pv Characteristicsmentioning

confidence: 99%

Clarifying the Effect of Clay Minerals on Methane Adsorption Capacity of Marine Shales in Sichuan Basin, China

Wang

Zhou

Zhang³

et al. 2021

Energies

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“…Liu et al presented a comparative study of all the FHH, Neimark, and Wang–Li fractal models applied to a suite of Bakken shales form the Williston Basin (USA), noting discrepancies in the results of the methods related to the PSDs of certain samples. Wood highlighted the uncertainties involved in the fractal values derived by each of the FHH, Neimark, and Wang–Li fractal models and illustrated the benefits of an integrated interpretation involving all three methods. This study compares the FHH, Neimark, and Wang–Li fractal determination methods applied to suites of organic-rich shale samples from the two India Permian basins (North Karanpura and Raniganj).…”

Section: Introductionmentioning

confidence: 97%

“…Most studies published to date have applied, in isolation, the FHH fractal determination method to N 2 gas adsorption isotherm data. ,,,,− Consequently, the two fractal dimensions ( D 1 and D 2 ) derived from the FHH method have been widely used to calculate the surface area and structures of the porous materials. − However, several studies have reported potential underestimation of pore fractal dimensions from N 2 adsorption isotherms when applying the FHH method, leading to uncertainty in pore texture interpretations of certain porous media. , It remains ambiguous as to whether the limited reach of N 2 gas to the micropores, is a key factor influencing the fractal dimension calculations. Important questions need to be answered regarding the relative merits of the FHH, Neimark, and Wang–Li fractal determination methods applied to organic-rich shales and the relationship of their derived fractal dimensions to PSD and thermal maturity.…”

Section: Introductionmentioning

confidence: 99%

Pore Properties in Organic-Rich Shales Derived Using Multiple Fractal Determination Models Applied to Two Indian Permian Basins

et al. 2021

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The pore geometry of shale reservoirs plays an important role in the storage and transportation of petroleum in these unconventional resources. Intrinsic surface roughness, indicated by fractal dimensions and contrasting pore size distributions of shales are primary factors that influence shale's fluid flow and resource volume characteristics. The Frenkel−Halsey−Hill (FHH) derived fractal dimensions are widely applied for evaluating the pore structural complexities of shales. In this work, for a suite of shales samples collected from two Permian basins, India, with distinct maturities, low pressure nitrogen gas adsorption−desorption has been employed to elucidate the pore structural framework. Three alternative fractal calculation methods (FHH, Neimark, and Wang−Li) are compared to provide further insight into the fractal characteristics of the shales. Ambiguities are revealed in the selection of the most appropriate fractal values. Fractal dimensions calculated by the FHH and Wang−Li methods are in relatively close agreement (ranging between 2.5 and 2.8) and the small systematic differences between their values can be explained in terms of fitting errors and assumptions associated with both methods. However, the Neimark fractal values are unreasonable (>3 for all the samples). Thermal maturity is a key controlling feature of the pore structural facets and fractal dimensions of the Raniganj basin samples (T max = 431−463 °C) but not for North Karanpura (T max = 434−442 °C) samples. Strong correlations exist between calculated fractal dimensions and specific surface area, pore volume, and average pore radius for all samples. However, systematic differences in these values between the samples from the two basins are most likely explained in terms of their mineralogical differences, specifically the higher kaolinite content of the Raniganj samples.

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“…Fractal geometry is a powerful analytical tool for the characterization of complex materials. Fractal geometric parameters measured directly from pore scale images can also be volume-averaged, which thus reveal the influence of pore structure on macroscale parameters like permeability [24][25][26][27]. Fractal dimension is a scale-invariant parameter that characterizes the extent of complexity of pore space geometry [28].…”

Section: Introductionmentioning

confidence: 99%

Characterization of Two-Phase Flow from Pore-Scale Imaging Using Fractal Geometry under Water-Wet and Mixed-Wet Conditions

Zou

Xie

et al. 2022

Energies

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High resolution micro-computed tomography images for multiphase flow provide us an effective tool to understand the mechanism of fluid flow in porous media, which is not only fundamental to the understanding of macroscopic measurements but also for providing benchmark datasets to validate pore-scale modeling. In this study, we start from two datasets of pore scale imaging of two-phase flow obtained experimentally under in situ imaging conditions at different water fractional flows under water-wet and mixed-wet conditions. Then, fractal dimension, lacunarity and succolarity are used to quantify the complexity, clustering and flow capacity of water and oil phases. The results show that with the wettability of rock surface altered from water-wet to mixed-wet, the fractal dimension for the water phase increases while for the oil phase, it decreases obviously at low water saturation. Lacunarity largely depends on the degree of wettability alteration. The more uniform wetting surfaces are distributed, the more homogeneous the fluid configuration is, which indicates smaller values for lacunarity. Moreover, succolarity is shown to well characterize the wettability effect on flow capacity. The succolarity of the oil phase in the water-wet case is larger than that in the mixed-wet case while for the water phase, the succolarity value in the water-wet is small compared with that in the mixed-wet, which show a similar trend with relative permeability curves for water-wet and mixed-wet. Our study provides a perspective into the influence that phase geometry has on relative permeability under controlled wettability and the resulting phase fractal changes under different saturations that occur during multiphase flow, which allows a means to understand phase geometric changes that occur during fluid flow.

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Techniques used to calculate shale fractal dimensions involve uncertainties and imprecisions that require more careful consideration

Abstract: Wood, D. A. Techniques used to calculate shale fractal dimensions involve uncertainties and imprecisions that require more careful consideration. Advances in

Cited by 42 publications

References 25 publications

Clarifying the Effect of Clay Minerals on Methane Adsorption Capacity of Marine Shales in Sichuan Basin, China

Clarifying the Effect of Clay Minerals on Methane Adsorption Capacity of Marine Shales in Sichuan Basin, China

Pore Properties in Organic-Rich Shales Derived Using Multiple Fractal Determination Models Applied to Two Indian Permian Basins

Characterization of Two-Phase Flow from Pore-Scale Imaging Using Fractal Geometry under Water-Wet and Mixed-Wet Conditions

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