Natural tectonic fractures and their formation stages in tight reservoirs of Permian Lucaogou Formation, Jimsar Sag, southern Junggar Basin, NW China

Kong, Xianjing; Zeng, Jianhui; Tan, Xianfeng; Ding, Kun; Luo, Qun; Wang, Qianyou; Wen, Ming; Wang, Xin; Wang, Maoyun

doi:10.1016/j.marpetgeo.2021.105269

Cited by 13 publications

(10 citation statements)

References 62 publications

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“…Fractures in the Longmaxi Formation shales with a linear density of 3.0–8.0/m account for 50.3%, followed by fractures with a density less than 3/m, accounting for 31.4%, and of 8/m, accounting for 18.3% (Figure B), regardless of folds and faults. Fracture spacing refers to the distance between two neighboring fractures at the same observation point. , Fractures with a spacing < 1.0 m account for 67.4%, mainly occurring in mudstones. Fractures with a spacing of 1.0–3.0 and 3.0–6.0 m account for 20.6 and 10.3%, respectively.…”

Section: Resultsmentioning

confidence: 99%

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Multi-scale Fractures and Their Influence on Shale Gas Deliverability in the Longmaxi Formation of the Changning Block, Southern Sichuan Basin, China

Zhao

Zheng²,

Liu³

et al. 2023

ACS Omega

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The capacity and deliverability of shale gas are closely linked to the presence of multi-scale fractures, including fractures and faults, within organic-rich shales. This study aims to investigate the fracture system of the Longmaxi Formation shale in the Changning Block of the southern Sichuan Basin and quantify the influence of multi-scale fractures on shale gas capacity and deliverability. The fracture system was analyzed through outcrop, core observations, and 3D seismic interpretation. Criteria for fault classification were established based on the horizon, throw, azimuth (phase), extension, and dip angle. The Longmaxi Formation shale mainly comprises shear fractures that form under multi-phase tectonic stress, characterized by large dip angles, small extensions, small apertures, and high density. The high content of organic matter and brittle minerals in the Long 1-1 Member facilitates the occurrence of natural fractures, which somewhat enhance shale gas capacity. Reverse faults with a dip angle of 45−70°e xist vertically, while laterally, there are early-stage nearly E-W faults, middle-stage NE faults, and late-stage NW faults. Based on the established criteria, faults that cut upward through the strata in and above the Permian with a throw greater than 200 m and a dip angle greater than 60°have the greatest influence on shale gas preservation and deliverability. These results provide important guidance for shale gas exploration and development in the Changning Block and contribute to our understanding of the relationship between multi-scale fractures and shale gas capacity and deliverability.

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Section: Resultsmentioning

confidence: 99%

“…Fracture spacing refers to the distance between two neighboring fractures at the same observation point. 46 , 47 Fractures with a spacing < 1.0 m account for 67.4%, mainly occurring in mudstones. Fractures with a spacing of 1.0–3.0 and 3.0–6.0 m account for 20.6 and 10.3%, respectively.…”

Section: Resultsmentioning

confidence: 99%

Multi-scale Fractures and Their Influence on Shale Gas Deliverability in the Longmaxi Formation of the Changning Block, Southern Sichuan Basin, China

Zhao

Zheng²,

Liu³

et al. 2023

ACS Omega

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“…Then, 5−6 g of broken sample was selected and placed in an agate grinder, and the sample was ground to about 300 mesh for the XRD test. During the experiment, the weight of the powder sample was kept above 50 mg, the voltage of the instrument was gradually increased to 40 scanning was carried out with the general qualitative analysis degree (2θ > 3°), and the scanning step was 0.016 (°/step). The whole experiment was carried out at room temperature.…”

Section: Samples and Methodsmentioning

confidence: 99%

“…Shale has lower matrix porosity and permeability in comparison to conventional reservoirs, 39 and microfractures are essential for the increase of effective pore storage and deep flow capacity. 40 A large number of microscopic fractures are developed in the Wufeng–Longmaxi shale, mostly in clay minerals and quartz, according to SEM results. These fractures are mostly nonstructural fractures, including organic matter contraction fractures, clay mineral interlayer fractures, mineral intercrystalline fractures, and corrosion fracture.…”

Section: Developmental Characteristics Of Fractures In Coresmentioning

confidence: 99%

“…Shale has lower matrix porosity and permeability in comparison to conventional reservoirs, and microfractures are essential for the increase of effective pore storage and deep flow capacity . A large number of microscopic fractures are developed in the Wufeng–Longmaxi shale, mostly in clay minerals and quartz, according to SEM results.…”

Section: Developmental Characteristics Of Fractures In Coresmentioning

confidence: 99%

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Natural Fracture Development Characteristics and Their Relationship with Gas Contents─A Case Study of Wufeng–Longmaxi Formation in Luzhou Area, Southern Sichuan Basin, China

Qin

Qin³

et al. 2022

ACS Omega

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Natural fractures are critical factors that should be considered in shale reservoir evaluation, storage condition analysis, horizontal well design, and fracturing stimulation, which also play a non-negligible role in the occurrence state of shale gas in the reservoir. This paper discussed the influence of fracture development on gas-bearing properties based on the analysis results of core observation, scanning electron microscopy, mineral composition, and gas-bearing properties after the development characteristics of fractures and their longitudinal variation law were clarified. In this way, the development characteristics of organic-rich marine shale fractures in the Longmaxi Formation in the 203 well area of the Luzhou member of the Sichuan Basin and their effects on the gas-bearing properties can be analyzed. The results show that the Longmaxi Formation shale develops shear fractures, extensional fractures of tectonic origin, bedding fractures, dissolution fractures, and abnormally high-pressure fractures of nonstructural origin. Specifically, interlayer fractures, intercrystalline fractures, organic matter contraction fractures, and fractures between clay layers are microfractures. Fracture development is characterized by short longitudinal extension, small opening, high degrees of composite filling, and large density changes, with calcite and pyrite as the filling materials. The fracture density has a “three-stage” variation pattern longitudinally, and the bottom is dominated by thin siliceous shale development, together with a small amount of shale mixed with calcareous and calcareous materials. Moreover, the fracture is dominated by “splitting” and “shearing” failure, crossing stratification with the fracture density. The highest fracture density was found in the 2 sub-layer, featuring the joint development of horizontal and vertical fractures, which form the mesh fracture system through mutual cutting and restriction. The lithofacies in the 4 sub-layer are dominated by clay siliceous shale with a small amount of mixed shale of calcareous and siliceous materials. The formation of fractures always expands along the lamellation direction, which has concentrated development members of top and bottom fractures, with the development of horizontal fractures dominated and vertical fractures less developed. Furthermore, a synergistic effect can be found among the total organic carbon (TOC) content, fracture density, and gas-bearing property of the shale in Longmaxi Formation. It is worth noting that a high TOC content and siliceous content are conducive to the formation of microfractures, while the development of fracture contributes to the total gas-bearing property, especially to the increase in free gas content. To be concrete, the free gas content in the fracture development member accounts for more than 55% of the total gas content, thanks to a channel provided by fractures for the desorption of shale gas.

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Shale oil migration across multiple scales: A review of characterization methods and different patterns

Gao,

Bai,

et al. 2024

Earth-Science Reviews

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Natural tectonic fractures and their formation stages in tight reservoirs of Permian Lucaogou Formation, Jimsar Sag, southern Junggar Basin, NW China

Cited by 13 publications

References 62 publications

Multi-scale Fractures and Their Influence on Shale Gas Deliverability in the Longmaxi Formation of the Changning Block, Southern Sichuan Basin, China

Multi-scale Fractures and Their Influence on Shale Gas Deliverability in the Longmaxi Formation of the Changning Block, Southern Sichuan Basin, China

Natural Fracture Development Characteristics and Their Relationship with Gas Contents─A Case Study of Wufeng–Longmaxi Formation in Luzhou Area, Southern Sichuan Basin, China

Shale oil migration across multiple scales: A review of characterization methods and different patterns

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