Abstract
Estimating porosity and fluid bulk modulus is an important goal of reservoir characterization. Based on the model of fluid substitution, we first propose a simplified bulk modulus of a saturated rock as a function of bulk moduli of minerals and fluids, in which we employ an empirical relationship to replace the bulk modulus of dry rock with that of minerals and a new parameterized porosity. Using the simplified bulk modulus, we derive a PP-wave reflection coefficient in terms of the new parameterized porosity and fluid bulk modulus. Focusing on reservoirs embedded in rocks whose lithologies are similar, we further simplify the derived reflection coefficient and present elastic impedance that is related to porosity and fluid bulk modulus. Based on the presented elastic impedance, we establish an approach of employing seismic amplitude variation with offset/angle to estimate density, new parameterized porosity, and fluid bulk modulus. We finally employ noisy synthetic seismic data and real datasets to verify the stability and reliability of the proposed inversion approach. Test on synthetic seismic data illustrates that the proposed inversion approach can produce stable inversion results in the case of signal-to-noise ratio (SNR) of 2, and applying the approach to real datasets, we conclude that reliably results of porosity and fluid bulk modulus are obtained, which is useful for fluid identification and reservoir characterization.
Highlights
Identification of fluid type and prediction of porosity are important targets for reservoir characterization
Similar to acoustic impedance (AI), Connolly [11] presents an expression of elastic impedance (EI) that varies with the incidence angle
Given a two-layer model, we first verify the accuracy of the simplified reflection coefficient, and we verify the robustness of the proposed inversion approach using the synthetic seismic data of signal-to-noise ratio (SNR) of 2
Summary
Identification of fluid type and prediction of porosity are important targets for reservoir characterization. Based on the parameterized EI, partially incidence angle-stacked seismic data are employed to estimate EI datasets, and parameters of reservoir properties are extracted from the estimated EI [4, 10]. Based on the derived reflection coefficient and EI, different inversion approaches are established for employing amplitude variation with offset/angle (AVO/AVA) to estimate elastic parameters (e.g., P- and S-wave velocities, moduli, and density) and reservoir parameters (e.g., porosity, clay volume, and water saturation). Geofluids inversion approach, which involves the inversion of AVO/AVA data for EI datasets and the estimation of elastic parameters from inverted EI datasets, is well employed in hydrocarbon reservoir exploration and characterization. Based on the reflection coefficient and EI, we establish a two-step inversion approach involving (1) inversion of prestacked seismic data for EI and (2) estimation of new parameterized porosity and fluid bulk modulus from the inverted EI. Synthetic and real datasets are utilized to verify the stability and reliability of the inversion approach
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