Depositional Environments and Reservoir Characteristics of the Late Carboniferous-Permian Juwayl Member (Wajid Sandstone), Southwestern Saudi Arabia

Mohamed Ibrahim Mahgoub*, Osman M. Abdullatif, Ali Sahin, Mustafa Hariri, Gabor Korvin, and Waleed Abdulghani
KFUPM, Saudi Arabia
*[email protected]

This study was conducted to characterize the sedimentary facies, depositional environments and reservoir characteristics of the Juwayl Member of the Wajid Sandstone in southwestern Saudi Arabia. The facies analysis of the Juwayl Member revealed ten lithofacies and two main glacio-fluvial and braided river environments. The glacio-fluvial environment is characterized by pebbly to conglomeratic sandstone facies suggesting medium to high energy within a proximal depositional setting. In contrast, the braided river facies are dominated by medium to coarse grained trough- and planner cross-bedded sandstone facies. These lithofacies suggest a distal depositional environment characterized by laterally switching channels within an extensive braid plain system. The lithofacies, depositional environments and the stratigraphic positions indicate that Juwayl has similarities to the Unayzah B and C members in central Arabia. The Juwayl sandstone is classified as a quartz arenite with good to very good porosity and permeability. The cements, grain-size variation, quartz overgrowth, clay mineral types and matrix are the main factors controlling porosity and permeability in the member. Characterization of the hydraulic flow units indicates that it contains 15 such units. Relatively lower values of the Reservoir Quality Index and the Flow Zone Indicator correspond to the fluvial facies, whereas higher values correspond to the glacio-fluvial facies. Statistical analysis indicates a normal distribution for the porosity and a log-normal distribution for permeability in both the glacio-fluvial and fluvial facies. The reservoir heterogeneity analysis indicates that the Juwayl Member can be considered to be heterogeneous to very heterogeneous reservoir.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain