The characteristics and formation mechanism of a regional fault in shale strata: Insights from the Middle-Upper Yangtze, China

He, Jianglin; Wang, Jian; Milsch, Harald; Qiu, Zhen; Qian, Yu

doi:10.1016/j.marpetgeo.2020.104592

Cited by 10 publications

(4 citation statements)

References 57 publications

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“…Zhang et al studied shale gas accumulation in the syncline settings and found that shale gas escaped along the bedding is the dominant reason for the poor gas content of shale. Bedding fractures and detachment layers commonly developed at the bottom of the Longmaxi Formation are the main channels for shale gas to escape along the bedding direction. , Hence, the greater the dip angle of the formation, the less conducive to shale gas preservation, especially when the dip angle is greater than 20° . However, the Himalayan faults with a good sealing ability of the Mugan syncline can effectively block the escape channels of shale gas along the bedding direction, which is the primary reason for the difference in gas-bearing properties between the Pengshui syncline and the Mugan syncline (Figure a).…”

Section: Discussionmentioning

confidence: 99%

“…8,9 An open fault is a direct escape channel of shale gas; subsequently, the overpressured state of the reservoir is destroyed and the reservoir space is more easily transformed by tectonic stress, which is a mutually promoting process. 27,28 Hence, fault sealing is crucial, and its quantitative evaluation has gradually received attention. The main research methods include the mudstone smearing evaluation, 29 fluid inclusion analysis, 30 and fault plane stress analysis.…”

Section: Introductionmentioning

confidence: 99%

“…Fault is the key factor affecting the preservation of shale gas in complex structural areas outside the Sichuan Basin. ,− Small-scale faults with simple combination are the main faults in the Sichuan Basin and do not cut through the caprock, while large-scale faults develop intensively in complex structural areas outside the basin. , An open fault is a direct escape channel of shale gas; subsequently, the overpressured state of the reservoir is destroyed and the reservoir space is more easily transformed by tectonic stress, which is a mutually promoting process. , Hence, fault sealing is crucial, and its quantitative evaluation has gradually received attention. The main research methods include the mudstone smearing evaluation, fluid inclusion analysis, and fault plane stress analysis .…”

Section: Introductionmentioning

confidence: 99%

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Effect of Faults on Shale Pore Fracture and Shale Gas Preservation: A Case Study of the Wufeng-Longmaxi Formation in the Northeast Yunnan Area

et al. 2022

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The organic-rich shale of the Wufeng-Longmaxi Formation in the Northeast Yunnan area where faults develop has a considerable basis and potential for hydrocarbon generation. A total 16 core samples from well ZD2, which is affected by faults, and well ZY1, which is located in a residual syncline, were collected. The effect of faults on the shale pore fracture and shale gas preservation was investigated primarily through core fracture statistics, field emission scanning electron microscopy, nuclear magnetic resonance (NMR), and triaxial mechanical tests. The results show that high-angle shear and bedding fractures are more developed in well ZD2 than well ZY1, indicating that faulting promotes the development of both bedding and structural fractures. The pore types and morphology of samples affected by faults are significantly different in terms of the compaction of organic matter (OM) pores, reduction of interparticle (interP) pores, increase in dissolution pores and structural microfractures. NMR pore size distributions of the samples primarily show a bimodal distribution, and mesopores (2–50 nm) are the dominate pores. However, faulting can weaken the correlation of pore structure with total organic carbon and minerals content. Comparative studies reveal that the effects of faults on pore structure are manifested as an increase in porosity, a decrease in average pore size, and a leftward shift of the PSD curve. Strongly heterogeneous dissolution substantially increases shale porosity. Tectonic extrusion compacts the OM and interP pores, which reduces the average pore size. The triaxial compressive strength (σTCS) of the samples from well ZY1 is higher than the normal stress on the fault plane. However, considering the correlation between σTCS and mineral content, the Upper Longmaxi Formation has a better fault sealing ability compared to the Wufeng-Lower Longmaxi Formation. Together with the gas-bearing properties of the wells, the Himalayan faults have a good sealing ability in Mugan syncline. Hence, the Himalayan faults with satisfactory sealing can effectively block the escape channels of shale gas along the bedding in a syncline. The wings of gentle syncline covered by overthrusting Himalayan faults are a favorable structural style for shale gas enrichment.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of Faults on Shale Pore Fracture and Shale Gas Preservation: A Case Study of the Wufeng-Longmaxi Formation in the Northeast Yunnan Area

et al. 2022

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“…For example, shrinkage fractures and abnormally high-pressure fractures account for a small proportion and are mostly filled by later mineralization [22][23][24], so they have little impact on the enrichment and preservation of shale gas. However, interlayer shear fractures, bedding detachment fractures, interlayer expansion fractures, and interlayer fractures have a greater impact on gas enrichment and preservation [25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Types and Quantitative Characterization of Microfractures in the Continental Shale of the Da’anzhai Member of the Ziliujing Formation in Northeast Sichuan, China

et al. 2021

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A number of wells in the Sichuan Basin of China have tested industrial gas flow pressure arising from the shale of the Da’anzhai section of the Ziliujing Formation, revealing good exploration potential. Microfractures in shales affect the enrichment and preservation of shale gas and are important storage spaces and seepage channels for gas. In order to increase productivity and to reduce the risks associated with shale gas exploration, the types, connectivity, and proportion of microfractures in the Da’anzhai Member have been studied in this work by core and thin section observations, micro-CT, scanning electron microscopy, nitrogen adsorption, and high-pressure mercury intrusion. The results show that four types of fractures have developed in the shale of the Da’anzhai section: microfractures caused by tectonic stress, diagenetic shrinkage fractures of clay minerals, marginal shrinkage fractures of organic matter, and microfractures inside mineral particles. Among these, structural fractures and organic matter contraction fractures are the main types and are significant for shale reservoirs and seepage. The structural microfractures are mainly opened and are well-developed in the shale, with a straight shape, mainly between bedding, with the fracture surface being curved, fully opened, and mainly tensile. Organic matter fractures often develop on the edge of the contact between organic matter and minerals, presenting a slit-like appearance. The fractures related to bedding in the shale are particularly developed, with larger openings, wider extensions, intersecting and expanding, and forming a three-dimensional interconnected pore-fracture system. Based on image recognition, generally speaking, microfractures account for about 20% of the total pore volume. However, the degree of the microfractures’ development varies greatly, depending upon the structural environment, with the proportion of microfractures in fault-wrinkle belts and high-steep zones reaching 40% to 90% of the total pore space. On the other hand, micro-fractures in areas with underdeveloped structures account for about 10% of the total pore space.

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Depositional environment changes and organic matter accumulation of Pliensbachian-Toarcian lacustrine shales in the Sichuan basin, SW China

Qiu

2022

Journal of Asian Earth Sciences

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The characteristics and formation mechanism of a regional fault in shale strata: Insights from the Middle-Upper Yangtze, China

Abstract: Shale is a type of fracture-prone rock, but few regional faults are observed in shale strata. Here, we investigate a regional detachment fault in the Middle-Upper Yangtze (MUY) to understand the formation mechanism of a special regional fault in shale strata.

Cited by 10 publications

References 57 publications

Effect of Faults on Shale Pore Fracture and Shale Gas Preservation: A Case Study of the Wufeng-Longmaxi Formation in the Northeast Yunnan Area

Effect of Faults on Shale Pore Fracture and Shale Gas Preservation: A Case Study of the Wufeng-Longmaxi Formation in the Northeast Yunnan Area

Types and Quantitative Characterization of Microfractures in the Continental Shale of the Da’anzhai Member of the Ziliujing Formation in Northeast Sichuan, China

Depositional environment changes and organic matter accumulation of Pliensbachian-Toarcian lacustrine shales in the Sichuan basin, SW China

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