Brittle minerals, mechanical properties and fracability evaluation of shales

Abstract

The brittleness of shales is critical to hydraulic fracturing since rock with high brittle minerals are more likely to fracture and maintain open fractures. Shale rocks have a wide range of constituting components, and different minerals display distinct elastic behavior. The microscale measurements of mechanical properties indicate that pyrite has the highest Young’s modulus, followed by quartz and feldspar. Organic matter was commonly recognized as the soft component, and has very low Young’s modulus. Alkaline minerals show similar Young’s modulus values to quartz and feldspar, and can be grouped into brittle minerals. The relative content, source and structure of brittle minerals can affect rock brittleness from multiple scales. Understanding the relationship between mineral compositions and geomechanical properties is beneficial for fracability estimation in engineering applications for shales.

Document Type: Perspective

Cited as: Xu, S., Wen, J., Liu, K., Shi, X., Dong, T. Brittle minerals, mechanical properties and fracability evaluation of shales. Advances in Geo-Energy Research, 2024, 14(1): 8-11. https://doi.org/10.46690/ager.2024.10.03

References

Baruch, E. T., Kennedy, M. J., Lōhr, S. C., et al. Feldspar dissolution-enhanced porosity in Paleoproterozoic shale reservoir facies from the Barney Creek Formation (McArthur Basin, Australia). AAPG Bulletin, 2015, 99(9): 1745-1770.

Cui, Q., Zhao, Y., Zhang, L., et al. A semianalytical model of fractured horizontal well with hydraulic fracture network in shale gas reservoir for pressure transient analysis. Advances in Geo-Energy Research, 2023, 8(3): 193-205.

Ding, W., Li, C., Li, C., et al. Fracture development in shale and its relationship to gas accumulation. Geoscience Frontiers, 2012, 3(1): 97-105.

Dong, T., Harris, N. B., Ayranci, K., et al. The impact of rock composition on geomechanical properties of a shale formation: Middle and Upper Devonian Horn River Group shale, Northeast British Columbia, Canada. AAPG Bulletin, 2017, 101(2): 177-204.

Dowey, P. J., Taylor, K. G. Extensive authigenic quartz overgrowths in the gas-bearing Haynesville-Bossier Shale, USA. Sedimentary Geology, 2017, 356: 15-25.

Jarvie, D. M., Hill, R. J., Ruble, T. E., et al. Unconventional shale-gas systems: The Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment. AAPG Bulletin, 2007, 91(4): 475-499.

Liu, K., Jin, Z., Zeng, L., et al. Alteration in the mechanical properties of the Bakken during exposure to supercritical CO2. Energy, 2023, 262: 125545.

Liu, S., Dong, T., Hu, D., et al. The impact of silica diagenesis on shale rock mechanical properties: An example from the Upper Ordovician-Lower Silurian Wufeng-Longmaxi formations, Southeast Sichuan Basin, South China. Marine and Petroleum Geology, 2024, 162: 106736.

Li, Z., Li, L., Li, M., et al. A numerical investigation on the effects of rock brittleness on the hydraulic fractures in the shale reservoir. Journal of Natural Gas Science and Engineering, 2018, 50: 22-32.

Milliken, K. L., Day-Stirrat, R. J., Papazis, P. K., et al. Carbonate lithologies of the Mississippian Barnett Shale, Fort Worth Basin, Texas, in Shale reservoirs-Giant resources for the 21st century, edited by J. A. Breyer, AAPG, Tulsa, pp. 290-321, 2013.

Milliken, K. L., Ergene, S. M., Ozka, A. Quartz types, authigenic and detrital, in the Upper Cretaceous Eagle Ford Formation, South Texas, U.S.A. Sedimentary Geology, 2016, 339: 273-288.

Milliken, K. L., Olson, T. Silica diagenesis, porosity evolution, and mechanical behavior in siliceous mudstones, Moway Shale (Cretaceous), Rocky Mountains, U.S.A. Journal of Sedimentary Research, 2017, 87(4): 366-387.

Peng, J., Milliken, K. L., Fu, Q., et al. Grain assemblages and diagenesis in organic-rich mudrocks, Upper Pennsylvanian Cline shale (Wolfcamp D), Midland Basin, Texas. AAPG Bulletin, 2020, 104(7): 1593-1624.

Thyberg, B., Jahren, J., Winje, T., et al. Quartz cementation in Late Cretaceous mustones, northern North Sea: Changes in rock properties due to dissolution of smectite and precipitation of micro-quartz crystals. Marine and Petroleum Geology, 2010, 27(8): 1752-1764.

Wei, C., Dong, T., He, Z., et al. Major, trace-elemental and sedimentological characterization of the upper Ordovician Wufeng-lower Silurian Longmaxi formations, Sichuan Basin, south China: Insights into the effect of relative sea-level fluctuations on organic matter accumulation in shales. Marine and Petroleum Geology, 2021, 126: 104905.

Wang, Z., Dong, L., Jin, Z. Efforts to untie the multicollinearity knot and identify factors controlling macropore structures in shale oil reservoirs. Advances in Geo-Energy Research, 2024, 11(3): 194-207.

Zeng, W., Zhang, J., Ding, W., et al. Fracture development in Paleozoic shale of Chongqing area (South China). Part one: Fracture characteristics and comparative analysis of main controlling factors. Journal of Asian Earth Sciences, 2013, 75: 251-266.

Zhao, J., Jin, Z., Jin, Z., et al. Mineral types and organic matters of the Ordovician-Silurian Wufeng and Longmaxi Shale in the Sichuan Basin, China: Implications for pore systems, diagenetic pathways, and reservoir quality in fine-grained sedimentary rocks. Marine and Petroleum Geology, 2017, 86: 655-674.