Correlation between rock physical properties, sedimentological, and diagenetic characteristics of late cretaceous carbonate rocks in the Middle East

This paper aims to establish correlations between petrophysical properties, sedimentological, and diagenetic characteristics of carbonate rocks from well cores of the Lower Cretaceous Thamama Group. A previous petrophysical study by Saleh, et al (2008) on the same well cores revealed that four plug samples out of 17 have a strong anisotropy relation of shear velocity (Vs) and permeability. Based on these results, we conducted a thorough sedimentological and petrographical study to explain the unique characteristics of these samples. We performed a full 170 feet core description of a vertical well to study the lithological and diagenetic background of the seventeen samples, It was assured that the core plug samples represent all types of lithofacies observed in the core description. Thin sections from the samples were also prepared and described, and well log data were analyzed. The well core description resulted in the identification of five lithofacies: bioclastic wackestone with low cementation, Bacinella floatstone, requieniid rudist floatstone/rudstone, highly cemented orbitolinid wackestone/packstone, and thin bedded shale. Three out of four samples, that have Vs and permeability anisotropy relationship, belongs to the bioclastic wackestone. The fourth sample belongs to the requieniid rudist floatstone/rudstone. It contains dominant matrix and scattered requieniid rudist fragments. Thin section description showed that samples with anisotropy relation of shear velocity and permeability are characterized by: a pore system that is homogenously distributed (microporosity), without significant influence of cementation, abundance of allochems, and other type of porosities, abundance of matrix, lack of skeletal and non-skeletal allochems, and low cementation, On the other hand, samples that have no clear anisotropy relationship have abundant bioclasts are highly cemented and have dominant intraparticle, interparticle, vuggy, or channel porosity. Crossplot analysis of well logs and core description gave the following results: • Core horizontal permeability and porosity correlation has three main trends interpreted according to different degrees of cementation. • In general, as horizontal permeability of core increases, the compressional wave velocity decreases twice as much as the shear wave velocity, taking into account the preferential permeability direction.