Pore-type identification of a heterogeneous carbonate reservoir using rock physics principles: a case study from south-west Iran

The characterization of carbonate rocks is a challenging process compared to siliciclastics because of their more intricate pore-space structure. In this study, we applied rock physics methods to a heterogeneous carbonate reservoir located in south-west Iran to identify zones of various pore types, including inter-particle pores, stiff (vuggy and moldic) pores, and cracks, from geophysical measurements. We first constructed two rock physics templates (RPTs) using well logs and used them to quantitatively analyze the effect of various pore types on elastic properties. Using these RPTs, we then implemented an inversion algorithm to estimate the volume fractions of various pores using total porosity and P-wave velocity (V-p) derived from well logs. Next, we have compared the pore-type inversion results and the image log interpretation/core images at the corresponding depth intervals to validate inversion results. This comparison showed that the inversion results are consistent with the measurements. Also, we applied the introduced pore-type inversion algorithm on seismic data to achieve insight into pore-type distribution in the 3D framework of the reservoir under study. The results of these rock physics-based analyses indicate that the inter-particle pores are dominant in the pore-space, while there are stiff pores and dispersal cracks in some subzones of the studied depth interval. Additionally, employing the Xu and Payne rock physics modeling procedure, P- and S-wave velocities were estimated using pore-type inversion results at the location of several wells from the studied field. The calculated mean absolute error and the correlation coefficient indicate a high consistency between the measured and modeled velocities. This research may contribute to permeability prediction and analysis of the diagenetic processes' impact on reservoir properties.