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Evaluating some Rock-Physics Models for Carbonates
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, First EAGE Rock Physics Workshop in Latin America, Dec 2021, Volume 2021, p.1 - 6
Abstract
Summary
We test the Xu-Payne (X-P) rock physics model in a carefully selected database of carbonate rocks with a wide porosity range, where velocities were measured under dry conditions in the laboratory. We assess the model by using different stiff and compliant pore aspect ratio combinations and calculating the mean percent error (MPE) in model predictions. We also compare the X-P with the Vernik-Kachanov (V-K) model and some empirical models for S-wave velocity prediction.
The model fits the P-wave velocity reasonably well, but it tends to systematically overpredict the S-wave velocity, leading to underprediction of Vp/Vs ratio. We stress the non-uniqueness in the model application, such that numerous feasible pore aspect ratio combinations and their volume fractions result in the same velocity outcomes.
The V-K model for carbonates produces an excellent fit to the data in the entire porosity range, resulting in lower MPE values than the X-P for both Vp and Vs. The V-K model, which is based on more realistic pore shapes, is also easier to calibrate. The V-K model combined with the Gassmann modelling compares favorably against the purely empirical Greenberg-Castagna model for Vs prediction, with the added advantages of accounting for realistic pore microstructure and stress sensitivity.
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