Abstract:

In the deep shale reservoirs of the southern Sichuan Basin, the development of fractures directly impacts the engineering construction and effective production of horizontal shale gas wells. Taking the shale cores in the Wufeng-Longmaxi Formation in the southern Sichuan Basin as a case study, rock physics experiments and numerical simulations were conducted to obtain the acoustic response characteristics of fractures at different scales, orientations, and fillings. The study analyzed the factors affecting the attenuation capability of acoustic waves on fractures and established a set of fracture identification and effectiveness evaluation methods for horizontal shale gas wells. The results showed that the amplitude attenuation of P-waves, S-waves, and Stoneley waves was influenced by both the fracture dip angle and fracture width, with attenuation capacity exponentially increasing with fracture width and decreasing with the dip angle. Stoneley waves were sensitive to fluid-filled fractures and could be used to identify and evaluate gas-bearing and water-bearing effective fractures. P-waves and dipole S-waves were sensitive to calcite-filled fractures, able to identify and evaluate ineffective calcite-filled fractures. The fracture identification results based on reflected wave imaging were consistent with the results obtained from imaging logging and core identification, verifying the reliability of the effectiveness evaluation method. The research findings were applied to the actual data from horizontal shale gas wells, thoroughly evaluating the fracture risk positions in horizontal shale gas wells and effectively ensuring the optimized and tailored design for fracturing segments.

Key words: fractures, deep shale, array acoustics, amplitude attenuation, effectiveness evaluation