Abstract: Based on comprehensive analysis of the drilling core, thin section, FMI logging and other log data，the features of the Carboniferous volcanic fracture reservoirs in Hongshanzui oilfield of Junggar Basin were studied. According to contributing factors，the fractured reservoirswere divided into 4 categories, such as diagenesis fractures,structural fractures, weathered fractures, and dissolving fractures.Thediagenesis fractures were further divided intothree subclassesof condensation contraction fractures,gravel seam,intergranular fractures.The fractured reservoirswere also divided into4 categories, such as high-angle fractures, miter fractures, netted fractures and low-angle fractures according tofracture occurrence.With the FMI logging and other logging information,the scale logging by core method wasadopted,our study shows thatfracture intuffwas the most developed witha fracture density up to 11.46 count/m, followed by lava, fracture in sedimentary rock was the lowest level.The fracture thickness in the region about 300 m below weather crustwas accounted for 80.3% of the total thickness. Because of imaging logging is limited,the method of drilling wells trajectory calculated fracture trend was proposed. The fracture trendwas divided into two groups,NE and NW. The secondary pore-fracture formingand distribution werecontrolledby fracture systems, forming beneficial oil and gas migration system,the fracture system wasakey factor restricting oil and gas accumulation, and was crucial for volcanic rocks reservoirs.

Key words: Carboniferous, volcanic rocks, fracture, reservoirs, Hongshanzui oilfield, Junggar basin