Internal structure and sealing properties of the volcanic fault zones in Xujiaweizi Fault Depression, Songliao Basin, China

Through outcrop observation of the internal structure of volcanic fault zone and in combination with fault sealing mechanism research and lithology juxtaposition evaluation, this paper analyzes the internal structure and lateral fault sealing of a volcanic fault zone of the Xujiaweizi Fault Depression. The “binary structure” of damage zone and fault core is developed inside the volcanic fault zone. The fault does not have the sealing property basically at the juxtaposition of volcanic rock. Lithologic juxtaposition sealing is formed at the juxtaposition of the volcanic rock reservoir stratum and the overlying conglomerate bed and mudstone bed. By improving the traditional Knipe diagram (single-well triangle diagram), a dual-well triangle map is drawn to indicate the influence of strike-slip fault on the lithology juxtaposition. Modeling is established with the dual-well triangle diagram and in combination with the fault lithology juxtaposition diagram to evaluate the fault sealing property. Research showed that the gas pools in the Xujiaweizi Depression are almost in the upside of faults; in the longitudinal, gas-water contract is almost at the most shallow position of volcanic juxtaposition and the horizontal distribution of gas pools around faults is just like the curve “sine” as the result of the “dolphin effect” of the Xuzhong strike fault.