Effect of Lateral Confining Pressure on Shale’s Mechanical Properties and Its Implications for Fracture Conductivity
Abstract
:1. Introduction
2. Materials and Methods
2.1. Samples and Sample Preparation
2.2. Unconfined Compression Testing
2.3. Microindentation Testing
3. Results
3.1. Indentation Load–Displacement Curves
3.2. Young’s Modulus and Brinell Hardness
3.3. Fracture Toughness
4. Discussion
4.1. Enhancement Mechanisms of Shale’s Mechanical Characteristics under Confining Pressure
- (1)
- Compression of micropores and fractures: The application of confining pressure on shale leads to the compression of micropores and fractures, resulting in a reduction in their size and volume. This compression effect increases the density of the rock and decreases the number and size of micropores, thereby enhancing the shale’s strength and stiffness [39,40]. Therefore, this compression improves the fracture toughness of the shale while reducing its deformability.
- (2)
- Uniform stress distribution: The application of confining pressure in shale samples ensures a more homogeneous distribution of applied stress [41]. Without confining pressure, external loading can result in stress concentration. However, by applying confining pressure, the stress is more evenly distributed across the sample, reducing stress concentration and enhancing overall strength.
- (3)
- Particle contact: Through the application of confining pressure, the particles within the shale come into closer contact and undergo compaction [42]. This densification process leads to increased interparticle interaction, resulting in the enhanced strength and hardness of the shale. Furthermore, the denser particle arrangement reduces microscale particle displacement, effectively reducing the deformability of the shale. The promotion of particle contact under confining pressure contributes to improved mechanical properties and reduced deformation in the shale.
4.2. Effect of Lateral Confining Pressure on Proppant Embedment
4.3. Effect of Lateral Confining Pressure on Fracture Conductivity
5. Conclusions
- The load–displacement curves obtained from the microindentation tests under various confining pressures demonstrate a decreasing trend in ultimate displacements with higher levels of confining stress. This observation indicates that the depth of the proppant embedment decreases when taking reservoir confining pressure into consideration;
- Young’s moduli, Brinell hardness, and fracture toughness exhibit a direct linear correlation with increasing confining pressure, suggesting that applying confining pressure enhances the strength and hardness of the shale;
- Considering the effects of confining pressure, the decrease in proppant embedment is proportional to Young’s modulus of the shale. Regarding fracture conductivity, for larger-sized proppants (e.g., D = 2.50 mm), the influence of confining pressure on fracture conductivity is relatively minor. However, when using smaller-sized proppants (e.g., D = 1.00 mm), especially in scenarios where prolonged shale–hydraulic fracturing fluid interaction results in significant shale debris swelling, there is a noticeable improvement in fracture conductivity when confining pressure is taken into account. Overall, previous computational models have tended to overestimate the depth of proppant embedment while underestimating the assessment of fracture conductivity.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Samples | Mineral (wt%) | |||||||
---|---|---|---|---|---|---|---|---|
Quartz | Orthoclase | Albite | Calcite | Dolomite | Pyrite | Chlorite | Illite | |
Shale | 12.9 | 0.2 | 2.4 | 15.5 | 55.5 | 0.4 | 2.6 | 10.6 |
Shale Samples | UCS (MPa) | E (GPa) | ν |
---|---|---|---|
1# sample | 101.38 | 40.03 | 0.25 |
2# sample | 99.38 | 39.98 | 0.25 |
3# sample | 104.60 | 40.10 | 0.25 |
Average values | 101.79 | 40.04 | 0.25 |
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Song, J.; Liu, Y.; Luo, Y.; Yang, F.; Hu, D. Effect of Lateral Confining Pressure on Shale’s Mechanical Properties and Its Implications for Fracture Conductivity. Appl. Sci. 2024, 14, 5825. https://doi.org/10.3390/app14135825
Song J, Liu Y, Luo Y, Yang F, Hu D. Effect of Lateral Confining Pressure on Shale’s Mechanical Properties and Its Implications for Fracture Conductivity. Applied Sciences. 2024; 14(13):5825. https://doi.org/10.3390/app14135825
Chicago/Turabian StyleSong, Jinliang, Yuan Liu, Yujie Luo, Fujian Yang, and Dawei Hu. 2024. "Effect of Lateral Confining Pressure on Shale’s Mechanical Properties and Its Implications for Fracture Conductivity" Applied Sciences 14, no. 13: 5825. https://doi.org/10.3390/app14135825
APA StyleSong, J., Liu, Y., Luo, Y., Yang, F., & Hu, D. (2024). Effect of Lateral Confining Pressure on Shale’s Mechanical Properties and Its Implications for Fracture Conductivity. Applied Sciences, 14(13), 5825. https://doi.org/10.3390/app14135825