Elastic Characterization of Shale at Microscale: A Comparison between Modulus Mapping, PeakForce Quantitative Nanomechanical Mapping, and Contact Resonance Method

Because of the extremely high resolution and little damage to the sample, micromechanical mapping methods have been widely used for elastic characterization of shale at microscale. However, few studies have investigated connections and differences among commonly used micromechanical mapping methods. The influencing factors of micromechanical tests, such as sample preparation, experimental set-up, and data processing, have not yet been sufficiently discussed. In the presented paper, three representative micromechanical mapping methods, including modulus mapping (MM), PeakForce quantitative nanomechanical mapping (PFQNM), and contact resonance (CR) method, were systematically compared from theory to application. The fundamental principles of the three methods were introduced, and connections in theoretical background were discussed. A shale sample from the Yanchang Formation in the Ordos Basin was selected for elastic characterization. Mechanical tests were performed on a fixed area on the sample surface by using different methods. The modulus distribution images obtained by the three methods intuitively exhibited microheterogeneity in shale. The influences of scanning frequen-cy, peak force frequency, and force setpoint were analyzed based on the test results. The comparison of the contact area revealed that MM possessed the lowest spatial resolution with the experimental setup, and the CR method was less sensitive to the surface condition than PFQNM. The effectiveness of the data processing method was demonstrated through scale dependency analysis, and the limitations of the test methods were discussed. This work may contribute to improved understanding and selection of micromechanical mapping methods and experimental design of elastic characterization of shale.