Fracture Distribution in Reverse-Faulted Carboniferous Volcanic Reservoirs, Dinan Uplift, Junggar Basin

More than 300 m of core from 18 wells, 4931 m of fullbore electrical image logs from 11 wells, and 3D seismic data were integrated to characterize fracture distribution in Carboniferous volcanic reservoirs of the Dinan Uplift, Junggar Basin. Five eruptive cycles, seven stages, and three volcanic-edifice types were identified. Thirty-three volcanic-edifice intervals from 10 wells (4052 m) were compared by structural position, fault distance, volcanic-edifice type, and facies-belt position. Tectonic fractures strike NW-SE to NNW-SSE and are parallel to reverse faults, with hanging-wall intervals showing a narrower orientation range than footwall intervals. Fracture line density (Dline) is weakly related to fault distance, with R2 values of 0.03 and 0.24 for hanging-wall and footwall intervals, and this relationship differs among volcanic-edifice types. Lava-plateau edifices have the highest pooled Dline, whereas pyroclastic-cone edifices show the largest proximal–distal contrast. Core data indicate higher fracture densities in lavas and coarse heterogeneous pyroclastic rocks than in fine tuffs. Later reverse-fault deformation is expressed more consistently in fracture orientation than abundance, whereas fracture abundance varies among volcanic-edifice, facies-belt, and lithologic settings. Fracture distribution is therefore best understood by considering fault-related structural position together with inherited volcanic architecture rather than by applying a uniform distance-to-fault relationship.