Five cores from a late Jurassic (Kimmeridgian) carbonate mudstone succession from Saudi Arabia were evaluated for sedimentologic, stratigraphic, organic geochemical, and geomechanical properties. A broad range of data allowed a comprehensive characterization of this potential source-rock interval that was deposited in a basinal setting during Kimmeridgian time in the Jafurah basin of eastern KSA.
Twelve lithofacies were identified through centimeter-scale core descriptions, standard petrography, and XRD and XRF characterization. Lithofacies are grouped into two distinct facies associations based on similarities in sedimentological and geochemical properties. Organic-rich facies of calcareous and mixed-calcareous mudstones with low bioturbation indices, high-redox sensitive elements, medium to high paleo-productivity indices, and good to excellent TOCs, corresponded to anoxic to dysoxic oxygen levels. In contrast, calcareous- and silica-rich mudstones with high bioturbation indices, light coloration, poor TOC values, and low redox-sensitive elements were deposited in more oxygenated water in a more proximal setting. Based on multiple data sets, a high-resolution sequence stratigraphic interpretation will be discussed.
The twelve lithofacies have also been characterized by their organic richness and hydrocarbon potential. Organic richness and hydrocarbon generation potential are good to excellent in the more anoxic facies association. Thermal maturity estimates from pyrolysis Tmax and maturity related biomarker ratios suggest a medium- to high-maturity source rock, analogous to the mature oil and wet-gas windows. Analyses of slabbed core samples were used to develop a high-resolution mechanical stratigraphy using micro-rebound testing, impulse hammer measurements, scratch testing, and ultrasonic velocity measurement methods. Calculated Leeb Hardness values range from 300 to 800 HLD, with low values associated with increased TOC and clay content. Techniques were used to compare/calibrate measured elastic properties with wireline logs.
Dr. John D. Humphrey is Chairman of the Geosciences Department, College of Petroleum Engineering and Geosciences, KFUPM. He received his B.S. degree in Geology at the University of Vermont, and his M.Sc. and Ph.D. degrees from Brown University in Geological Sciences. He was on the faculty of Geosciences at the University of Texas at Dallas from 1986 to 1991. Beginning in 1991, Dr. Humphrey served on the faculty of Geology and Geological Engineering at Colorado School of Mines, where he was Department Head from 2006 to 2013. He joined KFUPM in 2017 and has been Chairman since 2020. He is director of the KFUPM-CPG Isotope Facility. His areas of specialization include carbonate diagenesis and geochemistry, carbonate sedimentology and stratigraphy, carbonate reservoir characterization, unconventional carbonate reservoirs, stable isotope geochemistry, and paleoclimatology.