Intelligent calculation method of relative sonic attenuation and its application to fracture evaluation in tight sandstone reservoir

Fractured tight reservoirs have widespread exploration and development prospects. For these types of reservoirs, fractures provide pathways for fluid flow and storage spaces for tight oil and gas, which play a significant role in increasing production. In order to explore a fine fracture evaluation scheme for tight reservoirs, we firstly proposed an intelligent calculation method for the relative sonic attenuation; and then developed a novel semi-quantitative evaluation approach for the equivalent fracture width based on relative sonic attenuation and physical experimental results of the effect of fracture on sonic attenuation. The acoustic experimental results of the models with fractures show that the S-wave relative attenuation coefficients have a good correlation with the fracture attribute parameters. This lays a foundation for the fine fracture evaluation based on attenuation information. Field application results of the intelligent calculation method for relative attenuation and the inversion method for fracture width have been validated by comparing them with results from image logging, S-wave anisotropy estimation, and production test data, which demonstrates the feasibility and correctness of the proposed methods. The investigation depth of the proposed fracture evaluation scheme based on acoustic attenuation is significantly larger than that of the image logging, which provides a new optional scheme for fine fracture evaluation, especially for effective fracture evaluation; and it makes up for the deficiencies of the image logging fracture evaluation method.