Reservoir spaces in tight sandstones: Classification, fractal characters, and heterogeneity

Huang, Wenbiao; Lu, Shuangfang; Hersi, Osman Salad; Wang, Min; Deng, Shouwei; Lu, Rui-Jing

doi:10.1016/j.jngse.2017.07.006

Cited by 69 publications

(37 citation statements)

References 22 publications

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“…Previous studies show that the pore type is superior to the transition type, while the transition type further overmatches the throat type from perspectives of hydrocarbon exploration and development. 7 It has been demonstrated that physical properties of poretype rocks are not necessarily better than those with throat-type ones with large void space. Therefore, this paper did not focus on the shape classification of constant-rate mercury injection-based capillary pressure curves.…”

Section: Constant-rate Mercury Injectionmentioning

confidence: 99%

“…1,3 Exploration and development in such reservoirs are hindered by extreme heterogeneity owing to the fine pores and complex pore characteristics including size, shape, location and connectivity of pores and throats. [4][5][6][7] As one of the most primary factors controlling the exploitation of tight gas sandstones, the pore-throat structure of fine pores has been extensively studied. It is generally believed that the pore-throat structure directly impacts the fluid flow through the reservoir and thus further affects the hydrocarbon recovery.…”

Section: Introductionmentioning

confidence: 99%

“…mercury injection, gas adsorption and nuclear magnetic resonance). 14,[19][20][21][22][23] Mercury injection test is a well-proved effective approach to characterize the pore-throat structure of sandstones, 11,12,24 and constant-rate mercury injection data can distinguish pores from throats 7,25 and reflect their respective fractal features. 7 However, studies regarding individual effects of pore and throat fractal features on gas flow in tight gas sands are rare.…”

Section: Introductionmentioning

confidence: 99%

“…The microscopic pore-throat structure of tight sandstone gas reservoirs is just such a complex system with fractal features. 7 According to the complexity of pore-throat structure of tight sandstone gas reservoir in the three-dimensional space, the structure fractal dimension should be between 2 and 3. Therefore, fractal characteristics of the spatial distributions of pores and throats can be respectively described based on distinction of them.…”

Section: Introductionmentioning

confidence: 99%

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Pore-Throat Structure and Fractal Characteristics of Shihezi Formation Tight Gas Sandstone in the Ordos Basin, China

et al. 2018

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In order to better understand the impact of fractal features of pore-throat structures on effective physical properties of tight gas sandstones, this paper carried out constant-rate mercury ‡ ‡ Corresponding authors. This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited. 1840005-1Fractals 2018.26. Downloaded from www.worldscientific.com by 13.66.222.141 on 04/01/19. Re-use and distribution is strictly not permitted, except for Open Access articles. H. Huang et al.injection tests, gas-water permeability analyses, helium-based porosity and nitrogen pulse decay permeability measurements, and SEM and casting thin-section analyses on 20 sandstone samples of the Shihezi Formation from 16 wells of the Sulige Gas Field in the Ordos Basin, China. The fractal dimensions of pores corresponding to two pore radius ranges, namely fractal dimensions D p2 and D p3 , and those of throats also corresponding to two throat radius ranges, namely fractal dimensions D t1 and D t2 , were then calculated using the constant-rate mercury injection data. Fractal dimensions D p2 and D p3 are negatively correlated with the average pore radius and pore volume as well as quartz content, and they are positively related to contents of clay minerals and lithic fragments. Compared with pore fractal dimensions, throat fractal dimensions have lower correlations with throat structural parameters, and show vague relations with mineral compositions. Although the effects imposed by mineral compositions upon throat structures are similar to those upon pore structures, the flake-like and curved shapes of throats result in irregularity of fractal dimensions. Tight gas sandstones, with smaller fractal dimensions D p2 and D p3 , have larger effective porosity, indicating that more gas volumes can be replaced by liquids. As for tight gas sandstones with lower fractal dimensions D p3 and D t2 , the effective gas permeability is relatively high. In such cases, gas can flow more easily through the reservoir.

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Section: Constant-rate Mercury Injectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pore-Throat Structure and Fractal Characteristics of Shihezi Formation Tight Gas Sandstone in the Ordos Basin, China

et al. 2018

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“…It not only describes pore heterogeneity qualitatively, but also characterizes pore roughness quantitatively. 19,20 Fractal theory has been widely implemented in the field of petroleum exploration and development, especially in the study of reservoir micro-pore structure. It has developed into a Fractal Nature of Porosity in Volcanic Tight Reservoirs simple and effective way to quantitatively characterize the heterogeneity and complexity of pore structure in low permeability reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Fractal Nature of Porosity in Volcanic Tight Reservoirs of the Santanghu Basin and Its Relationship to Pore Formation Processes

Wang

Chen

et al. 2018

Fractals

Self Cite

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In this paper, in a case study of Santanghu Basin in China, the morphological characteristics and size distribution of nanoscale pores in the volcanic rocks of the Haerjiawu Formation were investigated using the results of low temperature nitrogen adsorption experiments. This research showed that within the target layer, a large number of nanoscale, eroded pores showed an "ink bottle" morphology with narrow pore mouths and wide bodies. The fractal dimension of pores increases gradually with increasing depth. Moreover, as fractal dimension increases, BET-specific surface area gradually increases, average pore diameter decreases and total pore volume gradually increases. The deeper burial of the Haerjiawu volcanic rocks in the Santanghu Basin leads to more intense erosion by organic acids derived from the basin's source rocks. Furthermore, the internal surface roughness of these corrosion pores results in poor connectivity. As stated above, the corrosion process is directly related to the organic acids generated by the source rock of the interbedded volcanic rocks. The deeper the reservoir, the more the organic acids being released from the source rock. However, due to the fact that the Haerjiawu volcanic rocks are tight reservoirs and have complicated pore-throat systems, while organic acids dissolve unstable minerals such as feldspars which improve the effective reservoir space; the dissolution of feldspars results in the formation of new minerals, which cannot be expelled from the tight reservoirs. They are instead precipitated in the fine pore throats, thereby reducing pore connectivity, while enhancing reservoir micro-preservation conditions.

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Pore structure of tight sandstones with differing permeability: The He 8 Member of the Middle Permian Lower Shihezi Formation, Gaoqiao area, Ordos Basin

Chen,

Zhu,

Wang

et al. 2023

Energy Science & Engineering

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Tight sandstone has strong pore heterogeneity and complex pore structure, and the pore structure of tight sandstone varies with different permeability. To study the differences in the pore structure of tight sandstone with different permeability, this study investigated the tight sandstone of the He 8 Member in the Gaoqiao area of the Ordos Basin. Factors influencing pore formation are analyzed through experiments utilizing methods, such as distinguishing casting thin sections, scanning electron microscopy, high‐pressure mercury intrusion, and low‐temperature nitrogen adsorption. The results indicate that in this area, the pores of the tight sandstone are primarily dissolution and intercrystalline pores, with occasional intergranular pores and microcracks. Type Ⅱ samples (permeability > 0.2 × 10−3 μm2) are primarily composed of dissolution and intercrystalline pores, with a few visible intergranular and microcracks. In contrast, Type Ⅰ samples (permeability < 0.2 × 10−3 μm2) mainly consist of micropores and intercrystalline pores, where microcracks are observed locally. Pore size research demonstrates that Type Ⅰ samples have pore size under 1000 nm, with peaks primarily at 4–5 nm. There are also peaks between 10–1000 nm, but without a consistent pattern. For Type Ⅱ samples with sizes smaller than 1000 nm, pore distribution is evident. Peak values when the pore size exceeds 1000 nm. Type Ⅰ samples have fewer micron‐level pores, while Type Ⅱ samples are primarily dissolution pores. The nanopores of Type Ⅰ samples consist of flat pores with good connectivity, whereas those of Type Ⅱ samples are mainly blind pores with poor connectivity. Type Ⅰ samples have larger pore fractal dimensions, more intricate pore morphology, and rougher and irregular pore throat surfaces compared to Type II samples. Hence, the sedimentary environment, diagenesis, and mineral composition affect the pore distribution in tight sandstone. The research findings highlight the variations in the pore structure of tight sandstone with varying permeability, providing crucial guidance for classifying and assessing pore structure in tight sandstone reservoirs.

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Reservoir spaces in tight sandstones: Classification, fractal characters, and heterogeneity

Cited by 69 publications

References 22 publications

Pore-Throat Structure and Fractal Characteristics of Shihezi Formation Tight Gas Sandstone in the Ordos Basin, China

Pore-Throat Structure and Fractal Characteristics of Shihezi Formation Tight Gas Sandstone in the Ordos Basin, China

Fractal Nature of Porosity in Volcanic Tight Reservoirs of the Santanghu Basin and Its Relationship to Pore Formation Processes

Pore structure of tight sandstones with differing permeability: The He 8 Member of the Middle Permian Lower Shihezi Formation, Gaoqiao area, Ordos Basin

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