Shale fracture prediction using integrated seismic methods

A casing deformation incident occurred in the Longmaxi Formation during shale gas production at Platform H1 in the southern Sichuan Z215 well block. Based on the monitoring and analysis of microseismic signals, preliminary analysis suggests the hydration of NW-trending fractures generated by hydraulic fracturing. The deeper shale layers of the Longmaxi Formation (3500 m) are complicated to interpret seismically because they are poorly resolvable with weak fracture responses, such that traditional seismic attributes cannot effectively recognize microfaults and microfractures. This has hampered additional production in the Z215 well block. To enhance seismic resolution and accurately describe fracture distribution in this area, we applied an integrated approach combining seismic forward modeling, spectral decomposition, 3D U-Net convolutional neural networks, ant colony algorithm, seismic inversion, and microseismic signal monitoring for comprehensive fracture prediction. Fracture prediction from this method demonstrates high consistency with microseismic data and shows a fault-fracture network that is governed by NE-trending major faults and limited NW-trending fractures. Casing deformation at Platform H1 was associated with composite deformation comprising NE-trending major faults, EW-trending minor faults, and NW-trending fractures. This study shows that the integrated method proposed in this paper can predict fractures in the Z215 well block reliably; this may be a reference for shale fracture prediction in other regions.