Sedimentology, Geochemistry, and Mechanical Stratigraphy of an Early Kimmeridgian Carbonate Mudstone in an Arabian Intrashelf Basin

This study integrates sedimentology, geochemistry, and geomechanics to define relationships among lithofacies, elemental compositions, and mechanical properties of five cores from an Early Kimmeridgian carbonate mudstone in an Arabian intrashelf basin. Core logging and description were used to define lithofacies heterogeneity and well-to-well variability, including texture, sedimentary features/structures, and bioturbation index (BI). A non-destructive hand-held energy-dispersive X-ray fluorescence spectrometer (ED-XRF) was employed to acquire elemental compositions with high stratigraphic resolution. Further, open-system pyrolysis was employed to evaluate organic richness, kerogen type, generation potential, and thermal maturity. Mechanical characterization was established through the employment of core (Micro-Rebound Testing (MRT) on 700 ft of the core at 0.5 ft resolution), log-based methods (Young’s modulus (E*), Poisson’s ratio, and UCS), and automated scanning (impulse-hammer and ultrasonic wave velocities), and scratch testing. Twelve lithofacies have been identified through detailed core descriptions, thin section petrography, and XRF elemental analyses. A combination of lithologic characteristics, geochemistry, and geomechanical properties aided in defining six clusters that were grouped into four zones. Zone 1: high TOC, low BI, suspension-dominated beds, high Ca-calcite, low terrigenous elements, brittle and high Vp, E, and HLD. Zone 2: high to the medium TOC, sparse to no bioturbation, fine laminations, suspension with traction deposition, lower Ca-calcite, increased terrigenous elements (Al, Fe), low Vp, E, HLD, and ductile. Zone 3: high BI, dominated by bioturbation and traction depositional processes, low Ca-calcite, increased terrigenous-associated elements, low TOC, and Mo. Zone 4: mostly in the distal well with low TOC, bioturbation and suspension dominated, increase Ca, low terrigeneous element, brittle and high Vp, E, and HLD.