A New Method for Comprehensive and Quantitative Characterization of Shale Microfractures: A Case Study of the Lacustrine Shale in the Yuanba Area, Northern Sichuan Basin

Pingping Li (), Qianshen Li, Lei Li and Huayao Zou
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Pingping Li: State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China
Qianshen Li: College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China
Lei Li: College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China
Huayao Zou: State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China

Energies, 2023, vol. 16, issue 15, 1-15

Abstract: Microfractures can connect isolated pores within shale, significantly increasing the shale’s storage capacity and permeability, and benefiting shale gas exploitation. Therefore, the quantitative characteristics of microfractures are important parameters for shale reservoir evaluation. In this paper, taking the Jurassic Da’anzhai Member (J 1 z 4 ) lacustrine shale in the Yuanba area of the northern Sichuan Basin as an example, we propose a method for comprehensive and quantitative characterization of shale microfractures that combines rock thin section (RTS) and scanning electron microscopy (SEM) observations. The different magnifications of RTSs and SEM images lead to the identification and characterization of microfractures of different scales using these two methods. RTSs are mainly used to characterize microfractures with widths larger than 10 μm, while SEM is mainly used to characterize microfractures with widths smaller than 10 μm. These techniques can be combined to comprehensively and quantitatively characterize microfractures of different scales in shale. The microfracture characterization results show that the average total porosity of the J 1 z 4 shale is 4.46%, and the average microfracture surface porosity is 1.20% in the Yuanba area. The calculated average percentage of microfracture porosity to total porosity is 21.09%, indicating that the J 1 z 4 shale reservoir space is dominated by pores and has the conditions for stable shale gas production and potential for shale gas exploration. However, the percentage of microfracture porosity to total porosity of shale near faults and fold zones approaches or exceeds 50%, which may lead to the loss of shale gas. The new method proposed in this study is also useful for quantitative characterization of shale microfractures in the Sichuan Basin and other basins.

Keywords: microfracture characterization; rock thin section; scanning electron microscopy; shale; Sichuan Basin (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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