Morphological characteristics of framboidal pyrite and their paleo-environmental significance in Longmaxi Formation of Weirong area, southern Sichuan Basin

ZHAO Guowei; DENG Mo; WANG Yuanzheng; JIANG Xiaoqiong; ZENG Huasheng; ZHANG Changjiang

doi:10.11781/sysydz2025020261

Volume 47 Issue 2

Mar. 2025

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Article Navigation > PETROLEUM GEOLOGY & EXPERIMENT > 2025 > 47(2): 261-272

ZHAO Guowei, DENG Mo, WANG Yuanzheng, JIANG Xiaoqiong, ZENG Huasheng, ZHANG Changjiang. Morphological characteristics of framboidal pyrite and their paleo-environmental significance in Longmaxi Formation of Weirong area, southern Sichuan Basin[J]. PETROLEUM GEOLOGY & EXPERIMENT, 2025, 47(2): 261-272. doi: 10.11781/sysydz2025020261

Citation:

ZHAO Guowei, DENG Mo, WANG Yuanzheng, JIANG Xiaoqiong, ZENG Huasheng, ZHANG Changjiang. Morphological characteristics of framboidal pyrite and their paleo-environmental significance in Longmaxi Formation of Weirong area, southern Sichuan Basin[J]. PETROLEUM GEOLOGY & EXPERIMENT, 2025, 47(2): 261-272. doi: 10.11781/sysydz2025020261

Citation:

ZHAO Guowei, DENG Mo, WANG Yuanzheng, JIANG Xiaoqiong, ZENG Huasheng, ZHANG Changjiang. Morphological characteristics of framboidal pyrite and their paleo-environmental significance in Longmaxi Formation of Weirong area, southern Sichuan Basin[J]. PETROLEUM GEOLOGY & EXPERIMENT, 2025, 47(2): 261-272. doi: 10.11781/sysydz2025020261

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Morphological characteristics of framboidal pyrite and their paleo-environmental significance in Longmaxi Formation of Weirong area, southern Sichuan Basin

doi: 10.11781/sysydz2025020261

ZHAO Guowei^{1, 2
,},
DENG Mo^{1, 2},
WANG Yuanzheng^{1, 2},
JIANG Xiaoqiong^{1, 2},
ZENG Huasheng^{1, 2},
ZHANG Changjiang^{1, 2}

1.
Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China
2.
SINOPEC Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi, Jiangsu 214126, China

Received Date: 2024-09-25
Rev Recd Date: 2025-01-23
Publish Date: 2025-03-28

Abstract

Abstract

The morphological characteristics of framboidal pyrite have important indicative significance for the shale sedimentary environments and shale gas enrichment. Taking the shale in the first member of the Longmaxi Formation from well WY1 in the Weirong area of southern Sichuan Basin as the study subject, argon ion scanning electron microscopic analyses and ImageJ image processing were conducted to obtain the morphological characteristics and particle sizes of framboidal pyrite and its microcrystals. By analyzing parameters such as trace elements, organic matter abundance, and gas content, the study explored the indicative role of framboidal pyrite morphology in paleo-water redox environments and shale gas enrichment. The results demonstrated that parameters such as the average particle size of framboidal pyrite, the average particle size of microcrystals, and the crystalline structures showed significant variations vertically. The average particle sizes of pyrite and its microcrystals were 4.02 μm and 0.45 μm, respectively. The particle sizes of both pyrite and its microcrystal gradually increased from bottom to top. The crystalline structure of microcrystals from the lower part was mainly truncated octahedrons, and the upper part featured truncated octahedrons, supplemented by octahedrons and truncated tetrahedrons. The roundness of microcrystals gradually decreased from bottom to top. The morphological characteristics of framboidal pyrite and its microcrystals indicated that the reducibility of the sedimentary water body in the first member of the Longmaxi Formation gradually weakened, transitioning from an euxinic and anoxic environment to a suboxic environment. This aligned well with the redox environment reflected by trace elements. Furthermore, contents of organic matter and desorbed gas showed a significant positive correlation with pyrite content, but a clear negative correlation with the particle sizes of framboidal pyrite and its microcrystals. The findings show that an euxinic and anoxic environment is favorable for the enrichment of organic matter and the generation, accumulation, and preservation of shale gas.
- framboidal pyrite,
- redox environment,
- sedimentary environment,
- shale gas,
- Longmaxi Formation,
- Weirong area,
- southern Sichuan Basin

All authors are employees of the sponsor of this journal. They did not take part in peer review or decision making of this article.
ZHAO Guowei provided research ideas and completed the writing and revision of the main content of the paper. DENG Mo participated in experimental design and data processing. WANG Yuanzheng completed image processing and data statistics. JIANG Xiaoqiong, ZENG Huasheng, and ZHANG Changjiang assisted in completing material and sample collection. All authors have read the final version of the paper and consented to its submission.

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Morphological characteristics of framboidal pyrite and their paleo-environmental significance in Longmaxi Formation of Weirong area, southern Sichuan Basin

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Morphological characteristics of framboidal pyrite and their paleo-environmental significance in Longmaxi Formation of Weirong area, southern Sichuan Basin

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