Characterization and Correlation of Pore Structures and Mechanical Properties in Carbonate Mudrock Formations of Central Saudi Arabia

This comprehensive study aimed to analyze pore characteristics and mechanical properties of three carbonate mudrock units (Upper Marrat, Tuwaiq Mountain Limestone, and Hanifa formations) in Central Saudi Arabia. Employing a combination of petrographic thin section analysis, helium porosity measurements, X-ray diffraction, backscattered scanning electron microscopy with energy dispersive scanning, micro-computed tomographic scanning, Total Organic Carbon (TOC) analysis, nuclear magnetic resonance, and N2 adsorption analyses, the research identified various pore types and their abundance. Specific lithofacies were determined: three in Hanifa Formation Hawtah Member (LFH1, LFH2, LFH3), two in Tuwaiq Mountain Limestone mudstone (LFT1, LFT2), and two in Upper Marrat Formation (LFM1, LFM2). These lithofacies exhibited distinct pore types, including intra-skeletal, interparticle, and organic matter-hosted pores, linked to diagenetic processes and burial events. NMR-relaxation time and pore size distribution curves indicated variable pore abundances across these lithofacies, influencing fluid flow simulations for potential reservoir evaluation. The study also integrated lithofacies analysis with TOC, porosity, and mechanical property measurements to assess rock strength and elasticity. Textural and microstructural analyses suggested different depositional environments: lower shoreface intra-shelf basin for Hanifa and Tuwaiq formations, and peritidal low ramp setting for Upper Marrat Formation. Correlations between mechanical properties and porosity varied, with tensile strength showing a strong relation to porosity and mineral composition. Hard phase minerals exhibited a stronger correlation with elastic moduli. The study found significant differences in rock strength and stiffness across the formations, influenced by sedimentary layering and anisotropy. These findings are crucial for predicting rock brittleness in these Jurassic intervals and their global equivalents.