Detecting Hydraulic Fracture Hits Using Low-Frequency DAS Data in Deep Shale Gas Reservoirs of the Sichuan Basin

ABSTRACT: This study evaluates the fracture geometry and well interference in a deep shale gas pad in the Sichuan Basin, China, using low-frequency Distributed Acoustic Sensing (DAS) technology. Four horizontal wells with varying well spacings were analyzed—two wells were fractured using the zip-fracturing method, while the other two were equipped with fiber-optic cables for real-time fracture monitoring. The DAS data revealed strain corridors, providing insights into both fracture length and height propagation. In particular, the strain corridor observed in well W3 showed a significant horizontal propagation, likely influenced by the high density of bedding planes in the basin. Fractures in well W2 exhibited an average strain corridor length of 610 meters, while those in well W4 reached 485 meters. Fracture arrival times from W2 to W3 averaged 47.5 minutes, indicating more complex propagation compared to W4's 28.7-minute arrival time. These results highlight the importance of real-time monitoring and optimized well spacing for effective resource extraction in complex geological settings like the Sichuan Basin. 1. INTRODUCTION Hydraulic fracturing has been a critical technique for unlocking the potential of unconventional reservoirs for decades. However, as well designs evolve—with increased lateral lengths and reduced cluster spacing—the challenges in understanding fracture propagation and accurately estimating final subsurface fracture geometry have become more pronounced (Wang et al., 2021). Accurate knowledge of how fractures propagate is essential for optimizing well completion designs and determining well spacing, which in turn maximizes resource recovery. In particular, the ability to assess the final fracture geometry is a key factor in improving hydraulic fracture efficiency and overall reservoir performance. Recent advances in Distributed Acoustic Sensing (DAS), particularly at low frequencies, have revolutionized our ability to monitor and measure the geometric characteristics of hydraulic fractures in real time. DAS technologies, through fiber optics, have proven highly effective in capturing detailed strain responses, providing valuable data on both fracture length and height propagation (Jin and Roy, 2017; Liu et al., 2020; Wu et al., 2021; Tan et al., 2021). This technology allows for a detailed understanding of fracture behavior during stimulation and the interactions between hydraulic and natural fractures. Specifically, DAS is known for detecting "heart-shaped" tensile zones ahead of hydraulic fracture tips, which can help predict the arrival of hydraulic fractures before fluid reaches the monitoring well. While this method has been successfully applied in various shale plays, the unique geological conditions of the Sichuan Basin, China, characterized by dense networks of natural fractures and faults (Yong et al., 2019; Zeng et al., 2021; Wu et al., 2023, 2024), pose additional challenges that complicate fracture monitoring and analysis.