Formation Stagesabout Structural Fractures of Xujiahe Formation in Fault-Fold Belt of Central Yuanba Area, Northeast Sichuan

The reservoir of Xujiahe Formation in Fault-Fold Belt of central Yuanba area are mainly structural fractures, which serve as the main percolation channels and reservoir spaces in tight sandstone reservoirs.The structural fractures in this studying area are mainly dominated by low-and high-angle shearing cracks.These cracks have wide changing range in length and narrow width, with large spacing and low density.And these cracks are mainly filled by calcite, muddy and carbonaceous fillings through the full-and semi-filling methods, without high filling degree but with better overall effectiveness.Without considering the diagenetic fracture, three stages of structural fractures are developed in this studying area.The first stage fractures are formed in Late Yanshanian tectonic movement, developing with orientation strikes in NE(30°±5°), NW (315°±5°)trending.The second stage fractures are formed in early-middle Himalaya tectonic movement, with orientation strikes in NEE(75°±10°)and SN(0°±5°)trending.The third stage fractures are formed in late-Himalaya tectonic movement, with orientation strikes in NWW(290°±10°)trending.