Interwell Interference Characteristics and Multisource Connectivity Diagnosis for Vertically Stacked Deep Shale Gas Development in the Daan Area, Western Chongqing

Interwell interference has become a routine engineering concern in closely spaced, vertically stacked shale gas development, yet pressure responses observed in offset wells do not necessarily represent direct hydraulic or fluid communication. This study investigates the DH21 deep shale gas pad in the Daan area, western Chongqing, by integrating fracturing records, continuous offset-well pressure monitoring, three-dimensional well geometry, geomechanical information, natural-fracture interpretations, and gas/water tracers. Clear pressure responses are identified in 316 of 334 reviewed, evaluable events (94.61%), indicating frequent pressure communication within the documented event dataset. Response occurrence generally decreases with increasing three-dimensional separation, but spacing alone does not explain the marked variability among well pairs. Same-layer responses generally become established earlier than cross-layer responses, and this contrast remains in receiver-adjusted sensitivity analysis, highlighting the importance of vertical geological and mechanical heterogeneity. Most responses are initiated during the early stage of treatment, whereas observed pressure maxima commonly occur after pumping, demonstrating that interference diagnosis should cover both early treatment and post-pumping pressure evolution. Treatment intensity does not translate directly into stronger offset-well responses; instead, source loading is selectively transmitted through spatial, stratigraphic, and fracture-controlled pathways. Accordingly, pressure monitoring is most effective for real-time disturbance identification, natural-fracture interpretation for screening potential preferential pathways, and tracers for verifying actual mass transport. These findings support a source–path–receiver framework for monitoring prioritization, interference warning, and post-treatment connectivity assessment in vertically stacked shale gas development. The quantitative relationships are derived from a single pad and, therefore, require local validation before application to other shale gas developments.