Deformation Differences in Complex Structural Areas in the Southern Sichuan Basin and Its Influence on Shale Gas Preservation: A Case Study of Changning and Luzhou Areas

He, Shun; Qin, Qirong; Li, Hu; Wang, Shilin

doi:10.3389/feart.2021.818534

Cited by 20 publications

(12 citation statements)

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“…The gas‐bearing capacity of the shales is a key metric for evaluating a shale reservoir. It indirectly reflects the abundance of gas in the shales and is a key tool for assessing the commercial exploitation value of gas‐bearing shales (He et al, 2020; He, Qin, Li, & Wang, 2022; He, Qin, Li, & Zhao, 2022; Hu et al, 2018; Jiang et al, 2022; Li, Qin, Li, et al, 2013). In the study area, the degree of gas saturation in the shales ranges from 65% to 80% in the Longyi 1 1 – 1 3 sublayers and averages 56.6% and 61.4% in the Longyi 1 4 sublayer and the WF Fm, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, many liquid hydrocarbon inclusions can also be seen distributed primarily in a linear or banded pattern along the fractures in the calcite minerals (Zhang et al, 2018; Li, Li, Yang, et al, 2023). The homogenization temperatures for the inclusions were analysed to determine the characteristics of fluid activity in the SG reservoirs during multiple periods (He, Qin, Li, & Wang, 2022). On this basis, the SG preservation conditions in the Luzhou block during multiple periods of tectonic evolution and superposition were identified.…”

Section: Resultsmentioning

confidence: 99%

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Intensive geological alteration and gas accumulation in Longmaxi Formation shales at moderate and great depths: A case study of the Luzhou area in the southern Sichuan fold zone, China

Jiang¹,

Tang²,

Zhong³

et al. 2023

Geological Journal

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In recent years, significant efforts have been directed towards extracting deep shale gas (SG) in Luzhou. Understanding the factors influencing the accumulation and preservation of SG in the section extending from the Upper Ordovician Wufeng (WF) Formation (Fm) through the Lower Silurian Longmaxi (LMX) Fm is crucial for its large‐scale, profitable development. The shale layers in the LMX Fm located in the Luzhou‐Zigong area in the southern part of the Sichuan Basin have undergone unique geological processes, including deep deposition, intensive uplift, erosion and deformation. The Luzhou block, situated in the low‐fold zone in southern Sichuan between the southern slope of the paleo‐uplift in central Sichuan and the down‐warping fold zone in south‐eastern Sichuan, was studied using seismic, well‐log, drilling and core analysis and test data to understand its tectonic, sedimentary, reservoir and fracture characteristics and identify the principal factors controlling gas accumulation in this area. The study found that SG in the Luzhou block is primarily distributed in the WF Fm through the Longyi1 sub‐member. Class I continuous reservoirs, 2.6–20.3 m in thickness, are mainly found in the Longyi11–13 sublayers and those with large continuous thickness produced high yields during tests. Gentle anticlinal zones and wide, gentle tectonic structures with relatively high‐pressure coefficients have formed in this area. High‐angle fractures (HACs) in this area tend to accumulate free gas and, therefore, facilitate the accumulation and production of SG. The study concludes that the continuous thickness of Class I reservoirs and natural HACs controlled by the centre of the deep‐water continental shelf are the primary factors controlling SG accumulation in the Luzhou block.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Intensive geological alteration and gas accumulation in Longmaxi Formation shales at moderate and great depths: A case study of the Luzhou area in the southern Sichuan fold zone, China

Jiang¹,

Tang²,

Zhong³

et al. 2023

Geological Journal

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“…Diagenesis is an important factor affecting reservoir quality. Reservoir types with different pore structures and physical properties result from distinct diagenetic sequences, diagenetic stages, and diagenetic evolution (Zhu et al, 2009;He et al, 2022b;Wang et al, 2022). Based on the assemblage of diagenetic minerals of deep low-permeability Gaoshangpu reservoirs, it Frontiers in Earth Science frontiersin.org can be preliminarily determined that the sequence of diagenetic minerals or diagenesis is as follows: Microcalcite-silica I stage overgrowth-weak dissolution of feldspar, debris-silica II stage overgrowth-kaolinite precipitationlarge-scale feldspar, and lithic dissolution-silica III stage overgrowth-intergranular pores filled with quartz-(ironbearing) calcite filling-dolosparite-weak dissolution.…”

Section: Diagenetic Sequencementioning

confidence: 99%

Densification mechanism of deep low-permeability sandstone reservoir in deltaic depositional setting and its implications for resource development: A case study of the Paleogene reservoirs in Gaoshangpu area of Nanpu sag, China

Wang

Yang²,

Lu³

et al. 2022

Front. Earth Sci.

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A better understanding of reservoir densification mechanisms is very important for petroleum exploration and controlling the reservoir quality distribution in low-permeability reservoirs. Low porosity and low permeability, difficult reconstruction, and economic infeasibility are important factors restricting its efficient production. Systematic analysis was performed to study the evolution of different microfacies in the deltaic depositional setting of the Paleogene deep low-permeability Gaoshangpu reservoir, define their genetic mechanisms, delineate the dominant facies belts, and define the favorable diagenetic sequences that are important for exploration of high-quality reservoirs. To understand the tight genesis of the low-permeability reservoirs, we analyzed the sedimentological and diagenetic evolution characteristics of various microfacies (i.e., underwater distributary channel, distributary bay, mouth bar, and front sheet sand) using core data and physical property analysis of the reservoir sand body. The results show the underwater distributary channel and estuary bar sand body with medium-to fine-grained and poor–medium sorting. The diagenesis is dominated by strong compaction, calcareous, argillaceous cementation, and dissolution during stage B in early diagenesis and stage A in middle diagenesis. In the fan delta environment, the weak anti-compaction resistance of low-permeability reservoirs is mainly due to the large content of plastic particles, finer grain size, and medium–poor sorting, with an average porosity reduction rate of 65%. This is a key factor for densification of reservoirs above 3000 m. Comparison among different sandstone microfacies of the deltaic setting shows that the sand body of the underwater distributary channel with low shale content has slightly stronger compaction resistance. The porosity reduction is not obvious at the depth of 3,000–4,000 m, but the loss of permeability at this depth section is significant, and the reservoir improvement from later dissolution is most obvious at this depth section. Calcareous cementation is the cause for densification of some mouth bars in the early stage and of underwater distributary channels in the middle and late stage. Under the influence of strong compaction and calcareous-filling pore throat, the sand body of the mouth bar has been basically densified at 3,000 m, resulting in limited reservoir transformation from later dissolution. The study shows that compaction is the main cause of reservoir densification, argillaceous and calcareous cementation is the secondary cause, and later dissolution is another main cause of reservoir enhancement. The research results can provide a reference and direction for reservoir development and search for the high-quality sweet spot in the deep and low-permeability reservoir.

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“…Meanwhile, its exploration and development march into the “deeper, older, and wider”domain. 1 − 3 The Wufeng–Longmaxi Formation shale in the southern Sichuan Basin has become a major stratum for shale gas exploration and development because of its high total organic carbon (TOC) content, highly brittle mineral content, high maturity, large effective thickness, and contiguous distribution. 4 , 5 Shale is widely perceived as combining “source, reservoir, and coverage” due to its features of “low porosity and low-to-extra-low permeability”.…”

Section: Introductionmentioning

confidence: 99%

“…With production increased year by year, shale gas becomes the most important composition of unconventional oil and gas exploration. Meanwhile, its exploration and development march into the “deeper, older, and wider”domain. − The Wufeng–Longmaxi Formation shale in the southern Sichuan Basin has become a major stratum for shale gas exploration and development because of its high total organic carbon (TOC) content, highly brittle mineral content, high maturity, large effective thickness, and contiguous distribution. , Shale is widely perceived as combining “source, reservoir, and coverage” due to its features of “low porosity and low-to-extra-low permeability”. , In addition, the free state occurring in pores, adsorbed on the surfaces of organic matters and mineral particles in the adsorbed state, and a small amount of dissolved state are the occurrence states of hydrocarbon gas in shale. − …”

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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Deformation Differences in Complex Structural Areas in the Southern Sichuan Basin and Its Influence on Shale Gas Preservation: A Case Study of Changning and Luzhou Areas

Cited by 20 publications

References 70 publications

Intensive geological alteration and gas accumulation in Longmaxi Formation shales at moderate and great depths: A case study of the Luzhou area in the southern Sichuan fold zone, China

Intensive geological alteration and gas accumulation in Longmaxi Formation shales at moderate and great depths: A case study of the Luzhou area in the southern Sichuan fold zone, China

Densification mechanism of deep low-permeability sandstone reservoir in deltaic depositional setting and its implications for resource development: A case study of the Paleogene reservoirs in Gaoshangpu area of Nanpu sag, 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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