Abstract:  Studying the characteristics and genetic mechanisms of structural fractures and predicting their distribution patterns are of great significance for guiding the exploration of volcanic gas reservoirs. This article focuses on the volcanic rocks of the Huoshiling Formation in Chaganhua subsag of Songliao basin. By comprehensively utilizing data of structural evolution, rock cores, imaging logging, rock physics experiments, and faults, the characteristics of structural fractures are analyzed to determine their formation periods. A three-dimensional geological model of the study area is established, and stress field simulation is carried out using the geostress module of Petrel software. The results show that structural fractures are mainly formed during the fault depression and inversion periods. Fractures formed during the fault depression period have high inclination angles and are mostly filled, they are mainly ineffective fractures. Fractures formed during the inversion period have low inclination angles and are partially filled, they are mainly effective fractures. Fractures formed during the inversion period cut through the fractures formed during the fault depression period. The maximum principal stress during the inversion period is horizontal principal stress, with a direction near east-west direction and a maximum stress value of 114.5 MPa. During the fault depression period, the maximum principal stress is vertical principal stress, with a direction near north-south direction. The stress field simulation results show that the current maximum horizontal principal stress direction is roughly east-west, consistent with the regional compressive stress direction. During the fault depression period, the maximum horizontal principal stress direction is roughly north-south, and the stress direction is basically consistent with the fault strike; The geostress is biased by the influence of faults. In areas with dense fault distribution, the stress direction is disorderly. In areas with sparse fault distribution, the stress direction is basically consistent with the principal stress direction. At the end of the fault, there is a clear phenomenon of stress concentration. It is concluded that effective fractures can be developed in areas with high maximum horizontal principal stress values, which can improve reservoir permeability. Therefore, drilling should be carried out in areas with high stress values and basically consistent stress directions.

Key words:  , structural fractures, tectonic stress field, volcanic rocks, tectonic periods, Chaganhua subsag, Songliao basin