Visible⁃light⁃photoredox catalysis has been recognized as a powerful technique to facilitate activation of organic molecules,enabling achievement of a wide variety of new chemical reactions.The combination of photoredox catalysis and nickel catalysis has shown even greater potential in promoting the cross⁃coupling reactions,owing to the advantages of low energy barrier,mild reaction condition and high selectivity.This review mainly focuses on the progress of carbon⁃carbon and carbon⁃heteroatom bond formation via the combination of photoredox catalysis and nickel catalysis in recently.The mechanisms of visible⁃light⁃photoredox catalyzed C-X (X＝C,N,O,P,S) bond formation are discussed in details.

Using the indoor experimental test, the intervals shale reservoir physical parameters, the rock mechanics parameters and the natural fracture distribution characteristic parameters were studied, and the constitutive models of stress fielddamage fieldseepage field coupling and the failure criteria of the defective rock mass in the process of riverfrac treatment were established. Through the finite element numerical simulation by the softwareComsol, the crack propagation law of formation respectively under tensile and compressive shear stress was analyzed, when the natural fracture system opens, hydraulic fracturing of shale reservoir artificial fracture network can be formed. When hydraulic fracture extended to natural fracture, there has been a marked increase the width of cracks, and hydraulic fracture direction changes, one of the wings extended along the natural fracture on the wing, the other one wing does not. There is obvious mutual interference between natural fracture. Process of multi cracks is developed from a small to a large crack fracture, the final number of cracks depends on the connectivity between the cracks; stress, natural fracture, perforation interval, perforation, dip, construction flow and liquid viscosity, are the main factors that influence the formation of multi cracks.