Influence factors of pop-in in the nanoindentation micromechanical property measurement of gas-bearing shale

Abstract

Studying the micromechanical properties of gas-bearing shale is very important for understanding it. In the nanoindentation measurement of gas-bearing shale, the load-displacement curve often shows pop-in at the loading stage, namely the change of load is small but the change of penetration depth is large. Pop-in can introduce a large error in the calculation of the mechanical parameter. To investigate the influence factors of pop-in, the maximum load, load rate and sample characteristics have been addressed. The results show that pop-in is related to cracks and pores in the shale. Due to the heterogeneity of shale, pop-in cannot be avoided, but can be reduced by choosing reliable load modes and test parameters. Pop-in can increase the maximum indentation depth and decrease the elastic modulus and hardness. The influence of pop-in on hardness is larger than on the elastic modulus. At a high load rate it is easy to induce pop-in. The influence of the load rate on pop-in is larger than that of the maximum load.

Application of Nanoindentation in the Characterization of a Porous Material with a Clastic Texture

“…On the other hand, the elastic modulus values were less scattered compared to the hardness values, with an average and one standard deviation of 24.54 ± 7.58 GPa (coefficient of variation of 31%), implying that the influence of the porous microstructure of plaster has a greater impact on the hardness than the elastic modulus. These observations match with the interpretations discussed by Wang et al [ 35 ] on the material properties of porous gas-bearing shales. These results correspond to cycle 1 of the nanoindentation tests on the plaster.…”

“…Shales are one of the most prominently tested porous geological materials to explore their mechanical properties through nanoindentation tests [ 6 , 7 , 31 , 32 , 33 , 34 ]. A recent work based on nanoindentation by Wang et al [ 35 ], on gas-bearing shale rocks particularly highlighted the development of pop-ins. The major outcomes of this work were that the pop-in events are directly related to the cracks and pores in the shale rock and the pop-in events influence the hardness values more pronouncedly compared with the elastic modulus.…”

Microscopic Pore Structures and Their Controlling Factors of the Lower Carboniferous Luzhai Shale in Guizhong Depression, China

“…Analyzed by MIP and LTNA, organic matter pores, intergranular pores, and microfractures are the main storage space of C 1 lz organic-rich shale in Guizhong Depression [28][29][30]. The pore sizes are mostly in the range of 17 nm~65 nm, with mesopores contributing the most to the shale pore volume, followed by micropores, and the lowest contribution of macropores.…”