Abstract: The Qixia Formation gas reservoir in the Shuangyushi structure, the first large-scale gas reservoir discovered in the Longmenshan foothill belt, is characterized by extremely developed faults and complex structural patterns, where structural features are a key factor influencing reservoir development. Considering that the structure in this area is jointly controlled by multi - stage tectonic movements and multi - detachment layers, while the existing studies have insufficient discussion on the controlling effect of the multi - detachment system, this paper adopts a progressive technical route of “physical simulation - numerical simulation - geological verification”. By designing models with different properties and thicknesses of detachment layers, the controlling mechanism of multi - detachment layers on structural deformation is revealed. Combined with actual drilling data, the simulation results are verified to guide the development and deployment of the gas reservoir. The results show that: ① Three sets of detachment systems are developed in the Shuangyushi area, namely the Cambrian (deep main detachment layer), Triassic (shallow main detachment layer), and Silurian (local secondary detachment layer). The “upper-lower double detachment” combination is the key to forming the thrust imbricate - steep fold structure in this area; ② The properties of detachment layers significantly affect structural styles: weak detachment layers tend to form continuous imbricate thrust structures, while strong detachment layers enhance the deformation complexity of overlying strata and weaken the continuity of imbricate structures; ③ The thickness of detachment layers controls structural evolution: thin detachment layers are characterized by “fold-dominated, fault-secondary”, mediumthick detachment layers form compartmental box folds - imbricate fan structures, and thick detachment layers develop “detachment layerdominated” giant fold - thrust systems, with thick plastic detachment layers having better sealing performance; ④ Based on the differences in structural styles, development models are proposed: the “sparse well pattern + high - angle well” model for the pop - up structure area, the “long horizontal section horizontal well (deployed at the high point)” model for the monocline anticline area, and the “high - angle well + horizontal well combination” model for the faulted anticline area. The research results clarify the structural formation mechanism under the control of multi - detachment layers and provide theoretical support and technical reference for the exploration and development of similar gas reservoirs in the Longmenshan piedmont belt.

Key words: Shuangyushi structure, Qixia Formation gas reservoir, detachment layer, physical simulation, numerical simulation, structural style