Assessment of the Multiphase Mechanical Properties of the Longmaxi Formation Shale Using Nanoindentation Tests

Abstract

Mechanical properties are some of the most important parameters for understanding well drilling and hydraulic fracturing designs in unconventional reservoir development. As an effective tool, nanoindentation has been used to determine the mechanical properties of rocks at the nanoscale. In this study, the Longmaxi Formation shale samples from the Yibin area of China were collected and analyzed to obtain the multiphase mechanical properties. The mineral compositions and organic geochemistry of the shale samples were studied using X-ray diffraction, energy-dispersive X-ray spectrometry, and a carbon/sulfur analyzer. The pore structures of the shale samples at the micro- and nanoscales were characterized by field-emission scanning electron microscopy. The mechanical parameters of the shale samples, such as the hardness and elastic modulus, were investigated using the nanoindentation method to identify three mineral phases: brittle minerals, soft matters, and complex minerals at the interfaces between brittle minerals and soft matters. The uncertainty characteristics of the mechanical parameters of the three mineral phases were evaluated using the Weibull model, and the factors interfering with the mechanical parameters were analyzed for the different shale samples. The results showed that the brittle minerals had the largest recovered elastic deformations and the smallest residual deformations, while the soft matters had the largest residual deformations and the smallest recovered elastic deformations. The analysis results of the coefficients of variation and the Weibull modulus both confirmed that the scatter of the hardness was higher than that of the elastic modulus because of the uncertain contact area, and the hardness and elastic modulus of the soft matters had the highest uncertainty among the three mineral phases. The elastic modulus increased nonlinearly with increasing hardness according to a power function for the whole shale sample. The elastic modulus and hardness both had a favorable linear relationship with the total organic carbon (TOC) content, illustrating that the TOC content was one of the significant factors that affected the mechanical parameters of the shale samples.

Using Nanoindentation to Characterize the Mechanical and Creep Properties of Shale: Load and Loading Strain Rate Effects

“… 13 − 17 This technique uses only small sample volumes (cuttings are acceptable) and can quickly generate large amounts of mechanical data. It therefore greatly aids the analysis of the micromechanical properties of shale; examples include the calculation of the mechanical parameters of individual phases in shales, such as minerals 16 − 19 and organic matter, 14 , 15 , 20 − 23 the relationships between mineralogy and bulk mechanics of shale, 14 , 15 , 24 the elastic anisotropy of shale, 17 , 25 , 26 and the methods for the prediction of the macromechanical properties of shale. 23 , 26 , 27 Besides, nanoindentation can also be used to study shale creep.…”

“…Conventional uniaxial/triaxial compression tests can reveal the macroscopic mechanical properties and creep behavior of shale. − However, these tests are generally time-consuming and require high-quality samples comprising a large volume free from fracture, which is generally difficult to obtain in field sampling. − Therefore, nanoindentation has been introduced as an alternative technique to characterize the mechanical properties of shale. − This technique uses only small sample volumes (cuttings are acceptable) and can quickly generate large amounts of mechanical data. It therefore greatly aids the analysis of the micromechanical properties of shale; examples include the calculation of the mechanical parameters of individual phases in shales, such as minerals − and organic matter, ,,− the relationships between mineralogy and bulk mechanics of shale, ,, the elastic anisotropy of shale, ,, and the methods for the prediction of the macromechanical properties of shale. ,, Besides, nanoindentation can also be used to study shale creep . Wick reported that nanoindentation gave results that were comparable with those of conventional uniaxial compression testing for creep behavior; thus, they believed that nanoindentation measurements were reliable in determining the creep behavior of shales .…”

Seepage Characteristics of Broken Carbonaceous Shale under Cyclic Loading and Unloading Conditions

“…The total organic carbon content varies from 2 to 4%, with a high proportion of micropores . In addition, the samples are mainly composed of quartz and clay minerals (about 70%), presenting brittle and hard lithology and strong heterogeneity …”

“…33 In addition, the samples are mainly composed of quartz and clay minerals (about 70%), presenting brittle and hard lithology and strong heterogeneity. 34 Shale samples were taken from massive carbon shale and further crushed in the laboratory. The broken shales were classified according to the particle size.…”

Achieving excellent mechanical and electrical properties in transition metal oxides and rare earth oxide‐doped KNN‐based piezoceramics

“…The nanoindentation technique has been extensively adopted for probing the mechanical properties of materials at the nanoscale, such as contact stiffness, Young's modulus, and hardness. Nanoindentation hardness and modulus of KNN-based ceramics and PZT-based ceramics (Pb 0.5 Sr 0.05 Zr 0.54 Ti 0.46 O 3 -1 wt% Sb 2 O 3 , abbreviated as PSZT) were calculated using Oliver and Pharr method by fitting the unloading curve to the power-law relation 36 :…”