Extended Azimuthal Elastic Impedance (EAEI) calculation for fluid indicator in fractured reservoirs

Huaizhen Chen, Kristopher A. Innanen

Inversion of seismic data for estimating fracture and fluid properties is an important task in reservoir characterization. Fracture and fluid indicators estimated using data of seismic amplitude variation with incidence angle and azimuth (AVAZ) provide evidence for fracture and fluid prediction. Selecting the tangential fracture weakness as fracture indicator and fluid bulk modulus as fluid indicator, we derive PP-wave reflection coefficient and azimuthal elastic impedance (AEI). Based on the derived AEI, we proposed an inversion method and workflow of using azimuthal partially incidence-angle-stacked seismic data to estimate multi-parameters that involve P- and S-wave moduli, density, fracture and fluid indicators. To improve the accuracy of seismic inversion for multi-parameters, we propose a method of using pre-stacked seismic attributes (AVA intercept, isotropic and anisotropic gradients) to generate initial models of fracture and fluid indicators. In the case of building fluid indicator initial models, we propose a novel extend AEI (EAEI) to relate pre-stacked seismic attributes to fluid indicator. We employ an approximate Hessian matrix calculated using the first- and second-order derivatives of AEI to further improve the accuracy of multi-parameter inversion. Using noisy synthetic seismic data, we verify the robustness of the proposed inversion method. Applying the proposed inversion method to real data acquired over fractured reservoirs, we obtain reliable fracture and fluid indicator results that match well logging data. It illustrates that the proposed inversion method is a valuable tool for providing reliable fracture and fluid indicators for characterization of potentially hydrocarbon-bearing fractured reservoirs.