Characteristics of Natural Fractures and Their Influence on Oil and Gas Enrichment and Preservation of the Jurassic Continental Shale in the Yuanba Area, Northeastern Sichuan Basin

doi:10.19657/j.geoscience.1000-8527.2023.065

Abstract

Abstract:

Development of natural fractures is one of key factors affecting the enrichment and preservation of shale oil and gas with in the continental shale at the Yuanba area, northeast Sichuan Basin. This study investigated the distribution of the natural fractures in the Jurassic Da’anzhai shale and Qianfoya shale based on the core data, thin section, and scanning electron microscopic images. We further discussed the influence of fractures on the shale oil and gas enrichment and preservation. The results show that there are mainly tectonic fractures, lamellation fractures, cross-layer hydraulic fractures, and shrinkage fractures. The tectonic fractures include cross-layer shear fractures, layer-parallel shear fractures, and intra-layer aperture fractures. The lamellation fractures are the dominant natural fractures and the linear density is between 66 and 357 per meter with an average of 188 per meter. We concluded that the lamellation and shrinkage fractures are the storage space of shale oil and gas, as well as the migration channels to improve the reservoir and benefit the enrichment of shale oil and gas. The macroscopic fracture networks formed by tectonic fractures, cross-layer hydraulic fractures, and lamellation fractures are the channels for shale oil and gas emission, which has a great influence on the dissipation of shale gas in Da’anzhai Member, but has little influence on shale oil preservation in Qianfoya Formation. These results provide a fundamental reference for the exploration and development of continental shale oil and gas in the Sichuan Basin.

Key words: natural fracture, shale oil and gas, enrichment and preservation, Jurassic, Yuanba area, northestern Sichuan Basin

CLC Number:

JIANG Daiqin, LI Pingping, ZOU Huayao. Characteristics of Natural Fractures and Their Influence on Oil and Gas Enrichment and Preservation of the Jurassic Continental Shale in the Yuanba Area, Northeastern Sichuan Basin[J]. Geoscience, 2024, 38(02): 362-372.

Figures/Tables 9

Fig.1 Tectonic location (a), fault distribution (b), structural profile (c), and stratigraphic profile (d) in Yuanba

Fig.2 Characteristics of tectonic fractures from the cores of the Jurassic shale in Yuanba

Fig.3 Characteristics of nontectonic fractures from the cores of the Jurassic shale in Yuanba

Fig.4 Characteristics of nontectonic fractures from the thin sections of the Jurassic shale in Yuanba

Fig.5 Characteristics of microfractures from the FE-SEM images of the Jurassic shale in Yuanba

Fig.6 Gas content of different lithologies of Da’anzhai Member and Qianfoya Formation in Yuanba

Fig.7 Diagrams of relationship between gas content and fracture surface porosity of the Da’anzhai shale and Qianfoya shale in Yuanba

Fig.8 Display of oil and gas in the Jurassic shale from Yuanba

Fig.9 Migration, accumulation, and emission model of the Jurassic shale oil and gas in Yuanba

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