Rock physics-based analysis to discriminate lithology and pore fluid saturation of carbonate reservoirs: a case study

Rock physics templates (RPT) and modeling contribute significantly to accurately and fast characterization of hydrocarbon reservoirs. This study strives to characterize lithology and pore fluid saturation for a carbonate reservoir in southwest Iran using RPT by well-logging data in a zone with a thickness of almost 100 m. To discriminate lithology, Greenberg-Castagna and Gardner models were applied. Also, velocity ratio-Gamma-ray (GR) and density-GR templates were implemented to investigate more. Results show that the researched zone's lithology consists of a considerable amount of limestone, followed by dolomite, and a small amount of shale, without sandstone, which matches excellently with the lithology column and geophysical logs. For fluid discrimination, two different rock physical directions were impalement. Firstly, the rock physics model of the study area was built through Xu and Payne's model. Then, velocity ratio-acoustic impedance template (V-P/V-S-AI) was applied to modeled data scaled with resistivity and porosity and then successfully validated with oil and water saturation. Findings show that PRT organizes data concerning similar features (here, aspect ratio), causing easy, fast, and more accurate analysis, and fluid content in the study includes oil and water, which the figure for oil is much more. In different oil and water saturation, non-modeled data were investigated through V-P/V-S - V-S, V-S - V-P, and shear impudence (SI)-AI template supported by pore-pressure (PP) information to further research fluid distribution and its effect in the second direction. Regarding the rock physical analysis, the main reason for the decrease in seismic velocities and impedances is high pore pressure due to high oil saturation.