![]() Rutherford and Williams determined gas sands based on the normal-incidence reflection coefficient and the contrast in Poisson’s ratio. and the pseudo-Poisson’s ratio reflectivity to define the fluid factor in the form of the weighted difference between the P- and S-wave velocity reflectivities. Smith and Gidlow initially incorporated the mudrock line of Castagna et al. A lot of efforts are taken to study various fluid indicators from prestack seismic records for reservoir prediction and fluid discrimination. Second, the instability and inaccuracy of the traditional elastic parameters, such as the P-wave velocity and S-wave velocity estimated by prestack seismic inversion, may magnify the uncertainty of the fluid indicators. First, the fluid indicators are very likely to provide ambiguous results for fluid identification due to the mixed effects of the fluid and rock porosity. The major challenge is the uncertainties in geofluid discrimination associated with two factors. Estimation of the rock-physical property directly from seismic records is a better way to differentiate the geofluid filled in reservoirs. However, the qualitative interpretation, such as the bright-spot, dim-spot, and flat-spot techniques, has difficulties in discriminating the geofluid in complicated lithologic reservoirs. Qualitative interpretation and direct quantitative estimation for rock properties are two main methods to discriminate different pore-fluid types. Introductionįluid discrimination plays an important role in seismic exploration and reservoir description. The synthetic and field data tests illustrate the accuracy and feasibility of the proposed fluid modulus inversion approach for geofluid discrimination. Model examples demonstrate the accuracy of the proposed linearized AVO approximation compared with the exact Zoeppritz equation and Aki-Richards approximate equation. Meanwhile, we introduce the Bayesian inference with multivariable Cauchy prior to the fluid modulus inversion for a stable and high-resolution solution. ![]() Convoluting this linearized AVO approximation with seismic wavelets, the forward modeling is constructed to combine the prestack seismic records with the fluid modulus. In terms of the new linearized equation of the fluid modulus, we derive a novel linearized amplitude variation with offset (AVO) approximation to avoid the complicated nonlinear relationship between the fluid modulus and the reflectivity series. ![]() On the one hand, the linearized relationship can decouple the fluid bulk modulus from the mixed fluid/rock term on the other hand, the decoupled terms are more stable especially in low-porosity situations compared with previous approaches. We combine the empirical relations with deterministic models to form a new kind of linearized relationship between the mixed fluid/rock term and the fluid modulus. ![]() Compared with other fluid indicators, the effective pore-fluid bulk modulus is more sensitive to the property of fluid contained in reservoirs. Geofluid discrimination plays an important role in reservoir characterization and prospect identification. ![]()
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