Research on the Influence of Natural Fracture Development on the Deep Shale Gas Well Fracture Network Construction in Southern Sichuan

Abstract The Sichuan Basin, China's largest shale gas development region, encompasses the natural fracture-rich Luzhou Block. The high-density non-uniform natural fractures in this area significantly influence the construction quality and efficiency of deep shale gas horizontal wells. Research indicates that the mechanical properties and spatial distribution of these natural fractures affect the propagation and diversion of hydraulic fractures, but the governing laws remain to be fully elucidated. This study categorizes the Luzhou Block's naturally fractured areas into six types based on their development characteristics and relative positions to horizontal well sections. Furthermore, it introduces a method for morphological inversion of shale gas well fracture networks using microseismic monitoring data. This method was applied to 24 deep shale gas wells in the Block and combined with the six types of naturally fractured areas, the above underlying influence mechanism was derived. Then it reveals how naturally fractured areas with different characteristics influence the fracture network morphology and complexity and analyzes the relationship between fracture network quality and well production. The results demonstrate that during the hydraulic fracturing process in deep shale gas reservoirs, the development areas of natural fractures can capture or intercept the fracture network, obstructing its expansion behavior, reducing its area and complexity, and ultimately leading to a decrease in gas well production. In particular, when a small-angle, large-scale naturally fractured area develops near the wellbore, the hydraulic fractures will quickly propagate to this area. After activating and communicating the natural fractures, it may cause rapid fluid filtration and a sharp drop in the net pressure within the fractures, severely impacting stimulation performance. It suggests that adjusting construction parameters appropriately may mitigate the adverse impact of natural fractures on the fracturing effect. These findings clarify how naturally fractured areas with different development characteristics affect stimulation performance and offer insights and references for designing and optimizing deep shale gas well fracturing technology.