Possible pore structure deformation effects on the shale gas enrichment: An example from the Lower Cambrian shales of the Eastern Upper Yangtze Platform, South China

Ma, Yong; Ardakani, Omid H.; Zhong, Ningning; Liu, Honglin; Huang, Haiping; Larter, Steve; Zhang, Cong

doi:10.1016/j.coal.2019.103349

Cited by 62 publications

(69 citation statements)

References 65 publications

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“…Pore Types and PSD. The PSD information plays an essential role in the determination of reservoirs complexity, structures, and heterogeneity of the unconventional shales [76,[78][79][80]. Data from nitrogen isotherms for the different types of C7 shales are compiled in Figure 10.…”

Section: The Relationships Betweenmentioning

confidence: 99%

Geochemical Properties and Pore Structure Control on Oil Extraction of Shale

Liu

et al. 2021

Lithosphere

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Despite geochemical properties and pore structures for shale oil extraction, the interplay among shale chemistry, pore network, and hydrocarbon movability still is an open question. Here, by using hybrid experimental methods, including backscatter scanning electron microscopy, X-ray diffraction, adsorption/desorption isotherm, and nuclear magnetic resonance, we provide a general characteristic of geochemistry and pore structures of Chang 7 (C7) shale in Ordos basin and figure out how these properties impact the shale oil extraction. Our results confirmed that the C7 shale in Ordos basin could be divided into three types based on the mineral components with various pore structures, and the proportion of the pores that radius below 4.8 nm (from adsorption branch) or 3.8 nm (from desorption branch) play a dominant role in the determination of pore size distributions. The kerogen index that is derived from maceral types was the most significant geochemical indicator; high kerogen index was corresponding to large pore volumes and surface areas, but low pore diameters. We identify the pore structure mechanism—mesopores predominantly or micropores abundantly (increase free fluid index) and absence of inorganic or organic pores (decrease free fluid index)—responsible for the oil extraction capability and show that the unmovable fluid stained in the voids would lead to the slow rate decay of the curves, which caused the nonsignal disturbance. Our results demonstrate the powerful control of maceral components and pore diameters on shale oil extraction and show the markedly different flow behavior of various types of shale.

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Section: The Relationships Betweenmentioning

confidence: 99%

Geochemical Properties and Pore Structure Control on Oil Extraction of Shale

Liu

et al. 2021

Lithosphere

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“…Ramsay first analyzed the anticline fold and its internal strain characteristics, finding that the stratum above the neutral plane exhibits tensile stress and the stratum below the neutral plane exhibits compressive stress (Figure 9). During the process of stress extrusion to form an anticline, the part above the neutral surface of the Lujiaping shale will be subjected to strong tensile stress, which will change the composition of the shale [33][34][35][52][53][54]. As shown in Figure 6, under tensile stress, more ductile clay and OM are compact in the space around the brittle minerals and increase the heterogeneity of the shale.…”

Section: Fractal Characteristics Of Pores In Deformed Shalementioning

confidence: 99%

“…Characteristics. Tectonic stress may have destroyed the mesopores to macropores within the OM in the deformed area, while OM-hosted micropores are retained due to their greater mechanical resilience [33][34][35]54]. And tectonism also can cause the shale to develop a "mylonite structure" in the cleavage domains, which has a pore system composed of nanoscale intergranular gap, lamella gap aggregate, and pore network, thus greatly increasing the specific surface area and adsorption capacity of the shale [32].…”

Section: Effect Of Tectonism On Porementioning

confidence: 99%

Relationship between Tectonism and Composition and Pore Characteristics of Shale Reservoirs

et al. 2020

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Tectonism is one of the major controlling factors of shale gas accumulation and enrichment in China. To explore the relationship between tectonism and composition and pore characteristics of shale reservoirs, this research carried out mineralogy tests, organic geochemistry tests, field emission scanning electron microscopy (FE-SEM) experiments, and low-pressure gas adsorption (LPGA, N2 and CO2) experiments on the shale samples of various deformation intensities from Southwestern China. Based on the FE-SEM image analyses, it can be found that there are large differences in pore characteristics in shale samples with different deformation intensities. The samples with strong deformation have more organic pores, mainly related to the clay-organic aggregates and rigid grains. Tectonism can cause organic matter (OM) and clay minerals to be mixed or OM to fill in the clay layers, resulting in the retention of some organic pores. It is the presence of pressure shadows around the rigid grains that can resist tectonic extrusion and protect some organic pores. LPGA experiment results also show that micropore-specific surface areas and pore volumes of the samples with strong deformation are larger than those with weak deformation. The shale samples with strong deformation also have more microchannels and microfractures. Tectonism can also cause some micropores to become macropores; for example, tectonism can cause the rigid grains to slide and rotate, enlarging the dissolution pores at the edges of rigid grains. Shale samples with strong deformation have a smaller mesopore volume; but due to the presence of organic-clay aggregates, a larger mesopore-specific surface area embarks on these samples. According to fractal dimension calculations, it is found that in strong deformed shale, more multiple dimensions of the pore system tend to represent rougher pore surfaces and more irregular shapes. Besides, rougher pore surfaces are eager to provide more adsorption sites and enhance the adsorption capacity of the deformed shale. This study investigates the relationship between tectonism and composition and pore characteristics of shale reservoirs and may promote understanding of the accumulation of shale gas in highly deformed areas.

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“…In this process, solid matter migrates and redistributes in a given direction from macro to micro to adapt to the new tectonic environment (Liang et al 2017;Li et al 2019). In the case of plastic strain, the organic-rich shale can be regarded as a solid rheology that undergoes shear rupture and deformation (Ju et al 2018;Ma et al 2019). However, when under the effects of long-term, slow strain, the slip rheology will appear similar to that of liquid, and rheological folding often occurs.…”

Section: A Types and Characteristics Of Slip Rheological Deformatimentioning

confidence: 99%

Influence of differential structural deformation on shale reservoirs: a case study of the lower Silurian Longmaxi Shale in north Guizhou, Southern China

Gu¹,

Xu³

et al. 2020

Geol. Mag.

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Southern China is affected by multi-stage tectonic activities, with strong fold deformation, complex fault systems and poor shale gas preservation conditions. Here, we used shale samples from the lower Silurian Longmaxi shale in the complex tectonic area of Southern China, to study the relationship between differential structural deformation, and pore structure and adsorption capacity. According to the deformation mechanism of the shale, it is further divided into brittle-slip rheological deformation (BD) and ductile-slip rheological deformation (DD). The results show that all micro-fractures can be observed under scanning electron microscopy in deformed shale samples, but in shale samples with different types of rheological deformation, the micro-fractures have large differences in scale, fracture length and lateral connectivity. The micro-fractures developed in DD shales are small in scale and short in fracture length, but have strong local connectivity. In contrast, brittle minerals are more developed in BD shales, and interlayer shearing has formed micro-fractures with large fracture length and good lateral connectivity, which is beneficial for later fracturing. In these two types of deformed shales, pores in organic matter are rare, and sporadic organic pores have small pore size and poor connectivity. The total pore volume (1.8–2.4 × 10−2 cm3 g–1) of BD shale samples is higher than that of DD shale samples (0.8–1.6 × 10−2 cm3 g–1). There is a positive correlation between total pore volume and quartz content. In addition, the specific surface area (12–18 m2 g–1) of DD shale samples is larger than that of BD shale samples (6–12 m2 g–1).

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Possible pore structure deformation effects on the shale gas enrichment: An example from the Lower Cambrian shales of the Eastern Upper Yangtze Platform, South China

Cited by 62 publications

References 65 publications

Geochemical Properties and Pore Structure Control on Oil Extraction of Shale

Geochemical Properties and Pore Structure Control on Oil Extraction of Shale

Relationship between Tectonism and Composition and Pore Characteristics of Shale Reservoirs

Influence of differential structural deformation on shale reservoirs: a case study of the lower Silurian Longmaxi Shale in north Guizhou, Southern China

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