Upper Lekhwair (Lower Cretaceous) Depositional System and Reservoir Characterization in a Frontier Area, Southeastern Abu Dhabi

Abstract The Lekhwair Formation, a prominent geological unit within southeastern Abu Dhabi, has recently been established as an oil-bearing reservoir outside of the traditional giant fields in the region. This study utilizes petrography and petrophysical evaluation to understand the Upper Lekhwair relationship between the reservoir quality and depositional environment. Variability in the thin Upper Lekhwair units creates challenges in predicting reservoir quality while drilling horizontal wells, identifying prospects, and optimizing hydrocarbon recovery efforts. This study will expand on the regional understanding of the Upper Lekhwair depositional system and reservoir characteristics to an oil-bearing area not previously investigated. The Lekhwair Formation was deposited on a wide carbonate ramp setting, with depositional environments ranging from proximal mid-ramp to intertidal. Well log observations across the area show variability in porosity and thickness in most of the reservoir units but little variability in the intraformational seals known as ‘Dense’ zones. Reservoir variability is predominately related to the dynamic nature of the inner-ramp shoal system, which has sub-regionally displayed rapid facies changes between grainstones and mud-dominated packstones within the same zone over short distances (e.g. 2 km). The study noted high abundance of laterally inconsistent grainstones and rudists in the upper most reservoir units. The relationship between these rapid lateral changes between inner ramp mud-dominated and grain-dominated sediment is likely related to local build-ups on the inner ramp. Unlocking this relationship will unlock new exploration strategies.