Developmental characteristics and dominant factors of natural fractures in lower Silurian marine organic-rich shale reservoirs: A case study of the Longmaxi formation in the Fenggang block, southern China

Gu, Yang; Ding, Wenlong; Tian, Qianning; Xu, Sheng; Zhang, Wei; Bai-ren, Zhang; Jiao, Baocheng

doi:10.1016/j.petrol.2020.107277

Cited by 29 publications

(7 citation statements)

References 24 publications

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“…The shale natural fractures are mainly structural fractures in southeastern Chongqing, which appear in groups with obvious alignment and regularity (He, 2018). The scale and complexity of the fractures are affected by the structural stress properties, stress strength and tectonic stages (Gu et al, 2020). According to the analysis of macroscopic fracture length in rock, fracture length distribution can be expressed by probability distribution functions, such as a uniform distribution, normal distribution and power-law distribution (Conny et al, 2013;Fadakar, 2014) or shale reservoirs (Gu et al, 2020;Li et al, 2021), log-normal distribution is selected to describe the distribution function of fracture length, which is a coincident distribution with both power law and normal distribution.…”

Section: Fracture Lengthmentioning

confidence: 99%

Numerical Modeling of Natural Fracture Distributions in Shale

CHEN

Shao

2023

Acta Geologica Sinica (Eng)

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The production efficiency of shale gas is affected by the interaction between hydraulic and natural fractures. This study presents a simulation of natural fractures in shale reservoirs, based on a discrete fracture network (DFN) method for hydraulic fracturing engineering. Fracture properties of the model are calculated from core fracture data, according to statistical mathematical analysis. The calculation results make full use of the quantitative information of core fracture orientation, density, opening and length, which constitute the direct and extensive data of mining engineering. The reliability and applicability of the model are analyzed with regard to model size and density, a calculation method for dominant size and density being proposed. Then, finite element analysis is applied to a hydraulic fracturing numerical simulation of a shale fractured reservoir in southeastern Chongqing. The hydraulic pressure distribution, fracture propagation, acoustic emission information and in situ stress changes during fracturing are analyzed. The results show the application of fracture statistics in fracture modeling and the influence of fracture distribution on hydraulic fracturing engineering. The present analysis may provide a reference for shale gas exploitation.

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Section: Fracture Lengthmentioning

confidence: 99%

Numerical Modeling of Natural Fracture Distributions in Shale

CHEN

Shao

2023

Acta Geologica Sinica (Eng)

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“…Some shale gas fields, including Jiaoshiba, Changning, Zhaotong, Weirong, and Luzhou, have been established. − The age-old over-mature shales in the Longmaxi Formation underwent multi-phase structural deformation; − thus, shale gas preservation conditions vary greatly from area to area. Owing to the dual effects of the Tethyan tectonic and Circum Pacific tectonic domains, the Sichuan Basin (especially the basin margin) experienced complicated structural evolution and severe structural deformation, giving rise to diverse structural styles, which led to various complicated preservation conditions. − There are many factors affecting shale gas preservation, and the most dominant factor is the occurrence of fractures (including faults and fractures). − The formation of fractures is governed by the mechanical properties and stress loads acting on rocks. In the absence of stress, rocks remain crack-free.…”

Section: Introductionmentioning

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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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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“… 14 For reservoirs, unfilled fractures can also provide channels for the migration of shale gas to increase the effectiveness of shale reservoirs apart from being effective reservoir spaces. 8 , 15 − 17 Regarding the preservation conditions, the self-closed property of shale might be destroyed by the excessively developed fractures, leading to vertical dissipation of shale gas. Fractures are tectonic weak surfaces that naturally occur, 18 − 20 which are expanded first in the hydraulic fracturing treatment of reservoirs, affecting the formation of artificial fracture networks.…”

Section: Introductionmentioning

confidence: 99%

“…Natural fractures play pivotal roles in the shale storage space, preservation conditions, and the morphology and expansion form of artificial fracture networks during fracturing and development, according to actual results of shale gas exploration in the Appalachian Basin of the United States and the Sichuan Basin of China. − Hence, the development of natural fractures should be considered in geological exploration of shale gas, drilling direction design of horizontal wells, and hydraulic fracturing methods . For reservoirs, unfilled fractures can also provide channels for the migration of shale gas to increase the effectiveness of shale reservoirs apart from being effective reservoir spaces. ,− Regarding the preservation conditions, the self-closed property of shale might be destroyed by the excessively developed fractures, leading to vertical dissipation of shale gas. Fractures are tectonic weak surfaces that naturally occur, − which are expanded first in the hydraulic fracturing treatment of reservoirs, affecting the formation of artificial fracture networks. ,, Also, more natural fractures are expected to drill in the drilling process of horizontal wells during drill design.…”

Section: Introductionmentioning

confidence: 99%

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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Developmental characteristics and dominant factors of natural fractures in lower Silurian marine organic-rich shale reservoirs: A case study of the Longmaxi formation in the Fenggang block, southern China

Cited by 29 publications

References 24 publications

Numerical Modeling of Natural Fracture Distributions in Shale

Numerical Modeling of Natural Fracture Distributions in Shale

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

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