Fracture Characteristics and Change of Permeability Under the Influence of Natural Fractures: Experimental Study of Wufeng-Longmaxi Shale
- Authors
- Hai-Yan Zhu (Southwest Petroleum University) | Lei Tao (Southwest Petroleum University) | Qing-You Liu (Southwest Petroleum University and Xihua University) | Zheng-Dong Lei (RIPED, PetroChina) | Shu Jiang (China University of Petroleum (East China) and University of Utah) | John D. McLennan (University of Utah)
- DOI
- https://doi.org/10.2118/181842-PA
- Document ID
- SPE-181842-PA
- Publisher
- Society of Petroleum Engineers
- Source
- SPE Reservoir Evaluation & Engineering
- Volume
- 21
- Issue
- 02
- Publication Date
- May 2018
- Document Type
- Journal Paper
- Pages
- 225 - 237
- Language
- English
- ISSN
- 1094-6470
- Copyright
- 2018.Society of Petroleum Engineers
- Keywords
- shale gas reservoir, natural fracture, stimulated reservoir volume, triaxial compression experiment, fracture morphology
- Downloads
- 10 in the last 30 days
- 314 since 2007
- Show more detail
- View rights & permissions
| SPE Member Price: | USD 12.00 |
| SPE Non-Member Price: | USD 35.00 |
Summary
Currently, substantial shale gas reserves have been recognized in many countries, including China and the United States. An improved comprehension of the structure of these shale plays can lead to improved shale gas producibility. Gas is produced through natural fractures (NFs) and through hydraulically induced fractures, together creating the so-called stimulated reservoir volume (SRV). Although NFs are advocated as significantly influencing the size and shape of an SRV, the effects of NFs on fracturing and permeability changes are incomplete. This paper describes experimental studies performed on calcite-filled fractures from outcrops of Wufeng (O3w)-Longmaxi (S1l) shale. These samples are representative of Ordovician-Silurian productive shales in the Fuling Basin, near Chongqing City, China. Basic parameters, such as acoustic wave velocity, porosity, and permeability, were first measured on representative samples. Subsequently, permeability and acoustic emissions were measured during triaxial compression experiments through the post-peak domain. After these evaluations, the fracture modes and the fragment distribution were evaluated.
In the measurements made, the natural calcite-filled macroscopic fractures reduced the confined compressive strength of these shale samples from 26 to 47%. Permeability is also affected. During the triaxial compression experiments, different NF orientations affected the overall permeability differently. We divided the collected samples into three groups.
- Group 1 samples had axial fractures (AFs). The gas permeability reduced from 0.70 to 0.12 md. When the sample was broken, permeability increased to 2.0 md, whereas the axial stress dropped to zero.
- Samples in Group 2 had transverse natural fractures (TFs). When new fractures were generated, permeability increased to greater than 0.70 md.
- Because samples in Group 3 had no obvious, natural macroscopic fractures (NFs), permeability was too low to measure before catastrophic failure during triaxial compression. When these samples did fail in compression, significant fractures formed, and permeability increased, resembling Group 2.
There was a close relationship between the initial pattern of NFs and the subsequently generated fracture morphologies. For Group 1, the samples broke into several larger pieces along the original AFs. For Group 2, the samples broke into numerous small and relatively uniform pieces. For Group 3, the samples did not break completely, and the constituent fragments were nonuniform. Our results are helpful for understanding fracture-propagation mechanisms and the evolution of permeability under in-situ loading processes (long-term geologic loading, stress alteration during well construction and stimulation, and reservoir modification during depletion).
| File Size | 1 MB | Number of Pages | 13 |
References
Aybar, U., Eshkalak, M. O., Sepehrnoori, K. et al. 2014. The Effect of Natural Fracture’s Closure on Long-Term Gas Production From Unconventional Resources. Journal of Natural Gas Science and Engineering 21: 1205–1213. https://doi.org/10.1016/j.jngse.2014.09.030.
Cheng, W., Jin, Y., and Chen, M. 2015. Reactivation Mechanism of Natural Fractures by Hydraulic Fracturing in Naturally Fractured Shale Reservoirs. Journal of Natural Gas Science and Engineering 27: 1357–1365. https://doi.org/10.1016/j.jngse.2015.11.018.
Cho, Y., Ozkan, E., and Apaydin, O. G. 2013. Pressure-Dependent Natural-Fracture Permeability in Shale and Its Effect on Shale-Gas Well Production. SPE Res Eval & Eng 16 (2): 216–228. SPE-159801-MS. https://doi.org/10.2118/159801-MS.
Damjanac, B. and Fairhurst, C. 2010. Evidence for a Long-Term Strength Threshold in Crystalline Rock. Rock Mechanics and Rock Engineering 43: 513–531. https://doi.org/10.1007/s00603-010-0090-9.
Fortin, J., Stanchits, S., Vinciguerra, S. et al. 2011. Influence of Thermal and Mechanical Cracks on Permeability and Elastic Wave Velocities in a Basalt From Mt. Etna Volcano Subjected to Elevated Pressure. Tectonophysics 503: 60–74. https://doi.org/10.1016/j.tecto.2010.09.028.
Gale, J. F. W., Reed, R., and Holder, J. 2007. Natural Fractures in the Barnett Shale and Their Importance for Hydraulic Fracture Treatments. American Association of Petroleum Geologists Bull. 91 (4): 603–622. https://doi.org/10.1306/110106061.
Gale, J. F. W., Laubach, S. E., Olson, J. E. et al. 2014. Natural Fractures in Shale: A Review and New Observations. American Association of Petroleum Geologists Bull. 98: 2165–2216. https://doi.org/10.1306/08121413151.
Gao, H. and Li, H. A. 2016. Pore Structure Characterization, Permeability Evaluation and Enhanced Gas Recovery Techniques of Tight Gas Sandstones. Journal of Natural Gas Science and Engineering 28: 536–547. https://doi.org/10.1016/j.jngse.2015.12.018.
Guo, T., Zhang, S., Qu, Z. et al. 2014. Experimental Study of Hydraulic Fracturing for Shale by Stimulated Reservoir Volume. Fuel 128: 373–380. https://doi.org/10.1016/j.fuel.2014.03.029.
Gutierrez, M., Øino, L. E., and Nyga°rd, R. 2000. Stress-Dependent Permeability of a De-Mineralized Fracture in Shale. Marine and Petroleum Geology 17: 895–907. https://doi.org/10.1016/S0264-8172(00)00027-1.
Gutierrez, M., Katsuki, D., and Tutuncu, A. 2015. Determination of the Continuous Stress-Dependent Permeability, Compressibility and Poroelasticity of Shale. Marine and Petroleum Geology 68: 614–628. https://doi.org/10.1016/j.marpetgeo.2014.12.002.
Jiao, K., Yao, S., Liu, C. et al. 2014. The Characterization and Quantitative Analysis of Nanopores in Unconventional Gas Reservoirs Using FESEM–FIB and Image Processing: An Example From the Lower Silurian Longmaxi Shale, Upper Yangtze Region, China. International Journal of Coal Geology 128–129: 1–11. https://doi.org/10.1016/j.coal.2014.03.004.
Jiang, T., Shao, J. F., Xu, W. Y. et al. 2010. Experimental Investigation and Micromechanical Analysis of Damage and Permeability Variation in Brittle Rocks. International Journal of Rock Mechanics and Mining Sciences 47 (5): 703–713. https://doi.org/10.1016/j.ijrmms.2010.05.003.
King, G. E., Haile, L., Shuss, J. A. et al. 2008. Increasing Fracture Path Complexity and Controlling Downward Fracture Growth in the Barnett Shale. Presented at the SPE Shale Gas Production Conference, Fort Worth, Texas, USA, 16–18 November. SPE-119896-MS. https://doi.org/10.2118/119896-MS.
Laubach, S. E. 2003. Practical Approaches to Identifying Sealed and Open Fractures. American Association of Petroleum Geologists Bull. 4: 561–579. https://doi.org/10.1306/11060201106.
Laubach, S. E., Olson, J. E., and Gale, J. F. W. 2004. Are Open Fractures Necessarily Aligned With Maximum Horizontal Stress? Earth and Planetary Science Letters 222: 191–195. https://doi.org/10.1016/j.epsl.2004.02.019.
Liang, C., Jiang, Z., Yang, Y. et al. 2012. Shale Lithofacies and Reservoir Space of the Wufeng-Longmaxi Formation, Sichuan Basin, China. Petroleum Exploration and Development 39: 736–743. https://doi.org/0.1016/S1876-3804(12)60098-6.
Martin, C. D. 1997. Seventeenth Canadian Geotechnical Colloquium: The Effect of Cohesion Loss and Stress Path on Brittle Rock Strength. Canadian Geotechnical Journal 34: 398–725. https://doi.org/10.1139/t97-030.
Pan, Z., Ma, Y., Connell, L. D. et al. 2015. Measuring Anisotropic Permeability Using a Cubic Shale Sample in a Triaxial Cell. Journal of Natural Gas Science and Engineering 26: 336–344. https://doi.org/10.1016/j.jngse.2015.05.036.
Paterson, S. 1978. Experimental Deformation of Rocks: The Brittle Field. Berlin: Springer.
Singh, K. K., Singh, D. N., and Ranjith, P. G. 2015. Laboratory Simulation of Flow Through Single Fractured Granite. Rock Mechanics and Rock Engineering 48: 987–1000. https://doi.org/10.1007/s00603-014-0630-9.
Souley, M., Homand, F., Pepa, S. et al. 2001. Damage-Induced Permeability Changes in Granite: A Case Example at the URL in Canada. International Journal of Rock Mechanics and Mining Sciences 38: 297–310. https://doi.org/10.1016/S1365-1609(01)00002-8.
Sun, J., Zou, A., Sotelo, E. et al. 2016a. Numerical Simulation of CO2 Huff-N-Puff in Complex Fracture Networks of Unconventional Liquid Reservoirs. Journal of Natural Gas Science and Engineering 31: 481–492. https://doi.org/10.1016/j.jngse.2016.03.032.
Sun, J., Zou, A., and Schechter, D. 2016b. Experimental and Numerical Studies of CO2 EOR in Unconventional Liquid Reservoirs With Complex Fracture Networks. Presented at the SPE Improved Oil Recovery Conference, Tulsa, 11–13 April. SPE-179634-MS. https://doi.org/10.2118/179634-MS.
Wu, K., Olson, J. E., and Balhoff, M. T. 2015. Study of Multiple Fracture Interaction Based on an Efficient Three-Dimensional Displacement Discontinuity Method. Presented at the 49th U.S. Rock Mechanics/Geomechanics Symposium, 28 June–1 July, San Francisco. ARMA-2015-279.
Wu, K. and Olson, J. E. 2015. A Simplified Three-Dimensional Displacement Discontinuity Method for Multiple Fracture Simulations. International Journal of Fracture 193: 191–204. https://doi.org/10.1007/s10704-015-0023-4.
Yan, W., Ge, H., Wang, J. et al. 2016. Experimental Study of the Friction Properties and Compressive Shear Failure Behaviors of Gas Shale Under the Influence of Fluids. Journal of Natural Gas Science and Engineering 33: 153–161. https://doi.org/10.1016/j.jngse.2016.04.019.
Zhang, R., Ning, Z., Yang, F. et al. 2015. Impacts of Nanopore Structure and Elastic Properties on Stress-Dependent Permeability of Gas Shales. Journal of Natural Gas Science and Engineering 26: 1663–1672. https://doi.org/10.1016/j.jngse.2015.02.001.
Zhu, H. Y., Deng, J. G., Liu, S. et al. 2014. Hydraulic Fracturing Experiments of Highly Deviated Well With Oriented Perforation Technique. Geomechanics and Engineering 6: 153–172. https://doi.org/10.12989/gae.2014.6.2.153.
Zhu, H. Y., Deng, J. G., Jin, X. et al. 2015. Hydraulic Fracture Initiation and Propagation From Wellbore With Oriented Perforation. Rock Mechanics and Rock Engineering 48: 585–601. https://doi.org/10.1007/s00603-014-0608-7.
Zhu, H. Y., Tao, L., and Liu, Q. Y. 2016. Multiscale Change Characteristics of Chinese Wufeng Shale Under Supercritical Carbon Dioxide. Presented at the SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. SPE-181369-MS. https://doi.org/10.2118/181369-MS.
Zou, C., Dong, D., Wang, Y. et al. 2016. Shale Gas in China: Characteristics, Challenges, and Prospects (II). Petroleum Exploration and Development 43: 182–196. https://doi.org/10.11698/PED.2016.02.02.
