*4.1. Structure*

In the late Cretaceous, the Hong-Che Fault Zone tilted and the overall structure tilted to the south. The structural pattern of the Carboniferous changed from high in the south and low in the north to high in the north and low in the south. At this time, the oil and gas, which were in the traps in the middle and south migrated along the fault to the north and formed mixed-source oil and gas reservoirs in the north. The Carboniferous oil and gas in the Hong-Che Fault Zone are mainly concentrated in the north, and oil and gas mainly accumulated at the high part of the structure [38,39].

At the same time, the Carboniferous volcanic reservoirs in the Hong-Che Fault Zone were greatly affected by faults. Most of the reservoirs are distributed in strips and blocks along the Hong-Che Fault Zone. The controlling e ffect of faults on hydrocarbon accumulations is reflected in three ways. The first is the openness of the faults. During periods of fault activity, the faults acted as migration channels for oil and gas and the main migration directions along the faults were north-south and vertical. The second consideration is sealing. When fault zones were in relatively static stages, the faults acted as sealing zones for oil and gas accumulations [40–45]. The third factor is the e ffect of fractures, which were derived from faults. During active fault periods, large numbers of cracks were produced due to stress release. Fractures connected the storage spaces of various pores and fractures, greatly improved reservoir property and permeability, and even increased the permeability of rocks by several orders of magnitude. There is a positive correlation between fracture density and oil well productivity. The greater the fracture density, the higher the oil well productivity [46].
