Seismic prediction method for fractured gas-bearing reservoirs based on high-order amplitude variation with angle and azimuth attributes
Zhan Wang, Xingyao Yin, Zhengqian Ma, Yaming Yang, Wei Xiang · Interpretation · 2025
Abstract Subsurface medium information is directly reflected in the seismic amplitude variation with angle and azimuth (AVAZ), making the AVAZ attribute a common technique for directly evaluating reservoir lithology, fractures, and fluid type. However, conventional AVAZ attributes for fracture azimuth prediction often suffer from 90° ambiguity and difficulty in decoupling fracture and fluid type information. To address these issues, a seismic prediction method for fractured gas-bearing reservoirs based on high-order AVAZ attributes is developed. First, according to the Ruger equation for horizontal transverse isotropic media, a more concise reflection coefficient approximation is obtained, which reduces the parameters to four at the expense of accuracy at large angles. Condition number analysis indicates the effectiveness of our equation. Second, an iterative solution algorithm alternating between AVAZ attributes and fracture azimuth is developed to estimate high-order AVAZ attributes, overcoming the 90° ambiguity stably. Third, analyzing the AVAZ attributes of different lithologies and fluid models, a fractured “fluid line” that can classify four classes of fractured gas-bearing reservoirs is presented. An improved gas-bearing indicator attribute is constructed by introducing AVAZ strength to directly identify fractured gas-bearing reservoirs and characterize high-fracture zones that are difficult to predict due to fluid influence. Numerical experiments and field data demonstrate that our method overcomes the 90° ambiguity of conventional fracture azimuth prediction, improving the stability and effectiveness of fracture azimuth and gas-bearing prediction based on AVAZ attributes.