Mechanical properties of organic matter in shales mapped at the nanometer scale |
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| Affiliation: | 1. Institute of Earth Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem, 91904, Israel;2. Shell International Exploration and Production Inc., Shell Westhollow Technology Center, R1004B 3333 Highway 6, South Houston, TX, 77082, USA;1. College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), D11, Xueyuan Road, Beijing 100083, PR China;1. Structural Dynamics, Sandia National Laboratories, Albuquerque, NM, 87123, USA;2. LGM Consultants Engineering Services, Tarrytown, NY, 10591, USA;3. Department of Civil, Construction, and Environmental Engineering, Campus Box 7908, North Carolina State University, Raleigh, NC, 27695, USA;4. CSIRO Energy, Ian Wark Laboratory, Bayview Avenue, Clayton, Victoria, 3169, Australia;5. Australian Resources Research Centre, 26 Dick Perry Avenue, Kensington, Western Australia, 6151, Australia;6. Department of Chemical and Biomolecular Engineering, Chemical Engineering #1, University of Melbourne, Parkville, Victoria, 3010, Australia;1. College of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China;2. Sinopec Petroleum Exploration and Production Research Institute, Sinopec Corporation, Beijing, 100083, China;3. College of Geoscience, China University of Petroleum (East China), Qingdao 266580, China;4. Energy & Geoscience Institute, University of Utah, Salt Lake City, UT 84102, USA |
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| Abstract: | The mechanical properties of organic matter strongly affect the way shales deform and fracture. However, the way organic matter responds to mechanical stresses is poorly understood, representing a critical obstacle to assessing oil and gas production in shale formations. Little is known about the mechanical properties of organic matter in fine grained rocks primarily because it often occupies tiny nanometer-scale voids between the mineral grains which cannot be accessed using standard mechanical testing techniques. Here, we use a new atomic force microscopy technique (PeakForce QNM™) to map the mechanical properties of organic and inorganic components at the nanometer scale. We find that the method is able to distinguish between different phases such as pyrite, quartz, clays, and organic matter. Moreover, within the organic component Young's modulus values ranged from 0 to 25 GPa; in 3 different samples – all of which come from thermally mature Type II/III source rocks in the dry gas window – a modal value of 15–16 GPa was measured, with additional peaks measured at ≤10 GPa. In addition, the maps suggest that some porous organic macerals possess a soft core surrounded by a harder outer shell 50–100 nm thick. Thus, our results demonstrate that the method represents a powerful new petrographic tool with which to characterize the mechanical properties of organic-rich sedimentary rocks. |
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| Keywords: | Bitumen Kerogen Mudrocks Young's modulus |
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