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Shanxi Formation Shan 23 Submember transitional shale in Eastern Ordos Basin is characterized by high TOC value, wide distribution, and large single-layer/cumulative thickness. In this study, based on section division of Shan 23 Submember, petrographic, mineralogical, and high-resolution geochemical analyses were integrated to reveal sedimentary environment, detrital influx, paleoclimate, paleosalinity, and paleoredox conditions. Results indicate that Shan 23 Submember is divided into four sections (Shan 23-1, Shan 23-2, Shan 23-3, and Shan 23-4). The upper part of the Shan 23-1 section is dominated by bay facies, which is characterized by high TOC value (2.75%–10.96%, avg. 6.98%), low detrital influx proxies (Zr, 97–527 ppm, avg. 310 ppm; Ti, 1985–7591 ppm, avg. 3938 ppm), relatively dry paleoclimate condition (CIA*, 41.96–92.58, avg. 75.55; Sr/Cu, 6.23–14.49, avg. 8.87), high paleosalinity proxies (Sr/Ba, 0.39–1.29, avg. 0.62), and relatively anoxic reduction condition (UEF, 0.83–3.00, avg. 1.67; MoEF, 3.95–27.00, avg. 15.56). By comparison, the other three sections are dominated by a combination of transitional facies, including barrier island, lagoon, tidal flat, and swamp. In this interval, shale is deposited in lagoon facies. The paleoclimate gradually tends to be warm and humid, which results in increasing the chemical weathering intensity. Meanwhile, the detrital influx increases, and the paleoredox condition tends to be oxic. The above conditions are not conducive to the preservation of organic matter in lagoon facies shale.

According to the damage evolution model of rock mass under stress-seepage coupling effect, the representative element theory is employed to describe the change law of rock mesostructure. Based on the theory of elasticity and Weibull distribution, the statistical damage constitutive model of rock mass and the finite element numerical algorithm are established, by adopting the COMSOL Multiphysics numerical software and MATLAB program. Besides, the validity of the statistical damage constitutive model of rock mass is verified by the triaxial compression test. Besides, the hydraulic fracturing processes of rock mass under equal and unequal in situ stresses are numerically simulated, and the mechanical behavior of rock mass during hydraulic fracturing in complex underground environment is also studied. Under the condition of equal in situ stress, the stress distribution of surrounding rock of circular hole is annular, which is similar to the elastic stress distribution of surrounding rock. Under the condition of unequal in situ stress, the stress distribution tends to be circular with the increase of lateral pressure coefficient, and the stress distribution along the diagonal decreases. The simulation results are in good agreement with the theoretical results, which indicates that the damage mechanical model and the numerical model have correlation and certain accuracy. By analyzing the size and direction of horizontal in situ stress, the shape and extension direction of cracks are judged, which provides an important theoretical basis for water inrush prediction and engineering protection.

Hybrid reactive power compensation (HRPC) which consists of series compensation and a stepped-controlled shunt reactor will see use in China's future ultra-high-voltage (UHV) transmission system. As a result, some new characteristics of the secondary arc during a single-phase-to-ground fault on UHV transmission lines with HRPC may be raised. In this paper, the secondary arc characteristics during the single-phase auto-reclosure (SPAR) operation have been simulated with regard to the UHV AC system installed with HRPC. Based on the UHV system model with HRPC and its secondary arc model, the influence mechanism of HRPC on secondary arc current is theoretically derived with the simulated waveforms and the Fourier analysis. Besides, the relationship among the secondary arc current, the arcing time with different HRPC compensation degrees, neutral reactance, as well as the grounding fault locations have been investigated in detail. Finally, an improved time sequential control strategy of bypass breaker and SPAR has been put forward. The research presented in this paper will provide necessary theoretical basis and technical support for the future application of HRPC in UHV transmission lines.