Nanoindentation is a powerful tool to characterizing rock mechanical properties. Using nanoindentation on Longmaxi sidecore samples can provide reliable values for Young's modulus, and hardness. The load-displacement obtained from nano-indentation measurements can be used to calculate fracture toughness through energy method. Experiment results show the measured average Young's modulus varied from 41.13 to 44.97 GPa, the measured average hardness varied from 2.31 to 2.87 GPa and the average fracture toughness varied from 4.05 to 6.12 MP•m^0.5 for Longmaxi Shale. The shale heterogeneity is considered as the basic reason for mechanical data diversion. Longmaxi show good brittleness and can be regarded as good completion target. Further work will focus on time dependent behavior at nano scale and the upscaling of nano scale measurements to meso scale and core scale measurements.
Silurian Longmaxi marine shale play is regarded as an important natural gas resources in China, which offers China's most shale gas potential. Previous geological assessment of reservoir quality and gas accumulation show Longmaxi marine shale is estimated recoverable resources of up to 8.1~1012 m3. The Lower Silurian Longmaxi marine shale yielded about 1.8~108 m3 gas in 2013, which demonstrates large amount shale gas is of economic potential. Currently, many shale gas blocks in the Sichuan Basin have been reported to produce good shale gas from the Silurian Longmaxi shale after multi-stage hydraulic fracturing with horizontal well. This area has experienced several tectonic events: such as the Paleozoic Caledoniane Hercynian, Triassic Indo-China and Jurassic-Cretaceous Yanshan and Cenozoic Himalayan activities controlled the tectonic evolution of the southeast Sichuan Basin (Guo, 1996; Chen et al., 2015, Jiang et al., 2016). Therefore, In order to develop shale gas commercially, horizontal multi-stage fracturing design is essential for developing shale gas reservoirs in complex geological conditions. The deformation and fracture properties of shale depend on the mechanical properties of its basic constituents, understanding the mechanical behavior of shales is significant to have a successful hydraulic fracturing treatments. Shales are highly heterogeneous sedimentary rocks that composed of kerogen and different minerals, such as quartz, clay and carbonate. Moreover, the existence of large amounts of nano and meso pores can affect shale mechanical properties. Conventional mechanical measurements generally evaluated by compression or extension experiments are inadequate to provide information for mechanical properties at the small-scale while results are not repeatable. Also, the collection of shale samples that are large enough to coring cylindrical specimens is difficult because of the chemical and physical instability of shale.
