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Summary Amplitude versus offset/angle (AVO/AVA) inversion recovers elastic properties of subsurface media and thus is an essential tool in oil and gas exploration. The exact Zoeppritz equation has high accuracy in reflection coefficient modelling, but the amplitude inversion based on the exact Zoeppritz equation is highly nonlinear. In this abstract, we propose a hybrid quantum genetic algorithm (HQGA) for the nonlinear AVO inversion using the exact Zoeppritz equation. Compared with the conventional genetic algorithm (GA) and quantum genetic algorithm (QGA), HQGA includes a self-adaptive rotating strategy, quantum mutation, and quantum catastrophe. The self-adaptive rotating strategy improves the flexibility and efficiency of a quantum revolving gate, and quantum mutation and quantum catastrophe enhance the local and global search capabilities respectively. Numerical tests show that compared with GA and QGA, HQGA requires fewer searches to converge to a global optimal solution, and the inversion results of HQGA have higher accuracy, higher efficiency and greater robustness than that of GA and QGA. A field data application verifies that there is a good consistency between the inverted parameters and real logs.

Summary The Lower Silurian shale-gas formation in the Sichuan Basin shows a property of transverse isotropy with vertical axis of symmetry (VTI). We present a case study of seismic inversion and quantitative interpretation of the target shale-gas reservoir formation. An AVO inversion method for VTI media is applied to estimate three elastic parameters (the acoustic impedance - A, the shear modulus weighted by an anelliptical anisotropy parameter - B, and the approximated horizontal P-wave velocity - C). Statistical rock-physics and machine learning are applied to the inverted parameters for the characterization of the reservoir formation. Brittleness-related shales can be successfully discriminated from surrounding formations using the attribute pair A-C, and the organic-rich gas-bearing shale can be successfully identified using the attribute pair A-B. Estimated TOC results using statistical rock-physics and support vector regression (SVR) method show highly consistent with the each other. Comparison between the prediction results and well logs demonstrates the feasibility of the inversion and quantitative interpretation approaches.

Nano-sized copper powder with an average size of 50 nm fabricated by chemical reduction method of hydrazine hydrate was consolidated using spark plasma sintering (SPS) method. The relationship between the sintering temperature and relative density of the nanocrystalline bulk copper was studied, the microstructure and the mechanical properties were examined, and the sintering mechanism was discussed. It was concluded that the nanocrystalline copper with a relative density greater than 99% and the yield strength of nearly 650 MPa could be fabricated by SPS process with the holding pressure of 600 MPa, sintering temperature of 350 °C, holding time of 5 min, and heating rate of 100 °C/min. Both refinement of the grains and formation of the extensive nanoscale twins in the NC bulk copper are the main factors to strengthen the metal.

The instability and non-linear dynamics of a slender rotating shaft with a rigid disk at the mid-span are analyzed. The shaft is simply supported at both ends and is made of a viscoelastic material. The stability criteria are determined from the linear equations of motion based on the small strain assumption. The bifurcation of the double zero eigenvalue point on the stability boundaries in the parametric space is analyzed by using center manifold theory on the non-linear equations of motion, for which a large transverse displacement of the shaft is assumed. Analytical expressions for the radius of synchronous whirling and the radius and precession rate of non-synchronous whirling near the double zero eigenvalue point are obtained explicitly. The behaviors of the parameteric points away from the stability boundaries are analyzed numerically. The general effects on the precession rate for these points are somewhat different from those for the parametric points in the vicinity of the double zero eigenvalue.