Improved Estimation of Shear-Wave Velocity by Ordered Weighted Averaging of Rock Physics Models in a Carbonate Reservoir

The aim of this paper is to improve estimation of shear-wave velocity in carbonate rocks. The region being studied is an oil field located in southwest Iran, where Upper Cretaceous carbonates act as the producing reservoir. These fracture bearing carbonates make the study of this reservoir complicated. Moreover, the accuracy and the precision of microstructure and pore type can affect the rock physics models by either directing or distracting these models from the typical models. The geological studies (thin sections, scanning electron microscope and core computer tomography scan) show that the reservoir mainly contains large pores with aspect ratios between 0.1 and 0.9. The existence of fractures is also demonstrated by a formation micro-imager and geological analyses. In this study, the applications of two rock physics models are investigated: (1) self-consistent approximation following the Gassmann equation and (2) Xu-Payne method, which has been carried out using the differential effective medium approach. In addition, for improving model predictions, these two rock physics models are fused by the ordered weighted averaging (OWA) aggregation operator that offers the most appropriate results. Furthermore, there are similarities between the three mentioned models based on the estimated values when compared to the measured dipole shear sonic imager log. Ultimately, the analysis and results demonstrate that the OWA model gives the best compatibility with the original well-log data. In other words, the reason why the OWA model provides the best results in the studied carbonates can be related to its optimization algorithm for defining model parameters.