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Open AccessArticle

Brittleness Evaluation in Shale Gas Reservoirs and Its Influence on Fracability

by Yapei Ye 1,2,3, Shuheng Tang 1,2,3,* and Zhaodong Xi 1,2,3
1
School of Energy Resources, China University of Geosciences, Beijing 100083, China
2
Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Enrichment Mechanism, Ministry of Education, Beijing 100083, China
3
Key Laboratory of Strategy Evaluation for Shale Gas, Ministry of Land and Resources, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Energies 2020, 13(2), 388; https://doi.org/10.3390/en13020388
Received: 23 December 2019 / Revised: 8 January 2020 / Accepted: 9 January 2020 / Published: 13 January 2020
(This article belongs to the Section Geo-Energy)
The brittleness index (BI) is a key parameter used to identify the desirable fracturing intervals of shale gas reservoirs. Its correlation with fracability is still controversial. There have been a variety of methods proposed that can estimate BI. The brittleness evaluation method based on stress-strain curves according to the energy-balanced law is the most suitable and reliable in this study. Triaxial compression test, optical microscopy and scanning electron microscopy (SEM) observation, and X-ray diffraction analysis (XRD) were performed on nine drill core samples from well SY3 located in the peripheral regions of Sichuan Basin, China. These tests further evaluated several commonly used methods (brittleness indices based on rock elastic parameters, rock mineral compositions) and determined the relationship between brittleness, rock elastic parameters, and the content of minerals. The results obtained indicate that for sedimentary rocks, a higher Young’s modulus reduces the brittleness of rock, and Poisson’s ratio weakly correlates with brittleness. Excessive amounts of quartz or carbonate minerals can increase the cohesiveness of rock, leading to poor brittleness. Furthermore, the most suitable fracturing layers possess a high brittleness index and low minimum horizontal stress. View Full-Text
Keywords: brittleness; brittle minerals; Young’s modulus; Poisson’s ratio; fracability; in-situ stress brittleness; brittle minerals; Young’s modulus; Poisson’s ratio; fracability; in-situ stress
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Ye, Y.; Tang, S.; Xi, Z. Brittleness Evaluation in Shale Gas Reservoirs and Its Influence on Fracability. Energies 2020, 13, 388.

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