Seismic-based workflow for multi-scale and multi-stage fracture characterization in the Longmaxi Formation, Weiyuan Gas Field, Sichuan Basin

The Longmaxi Formation shale in the Weiyuan Gas Field of the Sichuan Basin has undergone multiple tectonic movements, resulting in fractures of various scales and stages. Characterizing fractures in shale reservoirs is critical for shale gas development and presents a challenge. We propose a workflow based on seismic data that incorporates multi-scale and multi-stage fracture characterization. First, a multi-scale fracture classification is established based on seismic forward modeling. Then, steerable pyramid processing is deployed for multi-scale decomposition of seismic data. Multi-scale fracture characterization is achieved by extracting various seismic attributes from the processed data on different scales. Finally, the fractures of each tectonic stage are characterized using a strike-constrained method and validated using drilling data. The results of field study indicate that fractures can be quantitatively classified into large-, medium-, and small-scale fractures based on their seismic response characteristics. These multi-scale fractures can be identified at different scales using various seismic attributes. The Weiyuan region has experienced four main episodes of tectonic movements, with four corresponding stages of fracturing. The fractures of the Himalayan period have had the most pronounced impact on gas production. The proposed workflow provides technical support for efficient development of shale reservoirs.