Oil and gas resevoir characteristics and petrogenetic evolution of the Carboniferous volcanic lava in Xiquan area, Junggar Basin

Junggar Basin is an important area for the exploration and development of volcanic lava in western China. 16 volcanic lava wells were selected for core observation, ordinary thin-section and cast thin-section identification and quantitative statistic analysis under microscope, scanning electron microscopy and X-ray diffraction experiments to study petrological characteristics, pore types, combination characteristics, similarities and differences of basalt, andesite and dacite which are characterized by relative lack of research data on the characteristics of the volcanic lava reservoirs and petrogenetic evolution processes in the Xiquan area, eastern Junggar Basin. Besides, diagenetic evolutionary sequence of volcanic lavas was built and the influence of diagenesis on the pore evolution of volcanic lava was explored. The results show that andesite has a large reservoir space, and its pore types and pore combinations are complex and diverse, which include stoma+phenocryst solution pore+matrix solution pore+dissolution fracture combination, and stoma+phenocryst solution pore+matrix solution pore+dissolution fracture+structural fracture combination. Pore types and combinations of dacite are stoma+phenocryst solution pore+matrix solution pore and stoma+phenocryst solution pore+matrix solution pore+dissolution fracture. Pore types and combinations of basalt are simple, which include structural fracture+dissolution fracture combination, structural fracture+matrix solution pore combination, and stoma+dissolution fracture combination. Volatilization controls the development of original gas hole in volcanic lava. Dissolution, weathering, leaching, and tectonic fracture have greatly improved the reservoir performance of volcanic lava. Post-magmatic hydrothermal and filling have destroyed the reservoir space of volcanic lava. Overall, it is considered that andesite in the weathering and erosion-leaching belt at the top of the Carboniferous in Xiquan area (0-20 m from the top of the Carboniferous) is the most advantageous segment of hydrocarbon accumulation.