Sedimentary Characters and Flow Transitions of Reworked Carbonates: A Case Study of Cenomanian-Turonian Reworked Sediments in the Eastern Abu Dhabi, UAE

Abstract

Reworked carbonate caused by the major erosional event of the "Turonian Unconformity" is considered to be distributed around the eastern part of Abu Dhabi, UAE. During 2021-2022, new wells were drilled in a prospective area where the reworked carbonate was deposited. By using the new wells data (wireline logs and cores) and pre-existing wells data, we considered lateral changes in sedimentary character and flow transitions of the reworked carbonate. We conducted a well-well correlation, based on the wireline logs (GR, Neutron, Density, Resistivity and Sonic) of a total of 5 wells which were drilled in the prospective area. To understand the spaciotemporal changes of the reworked carbonate facies and properties, we conducted core observation and description, and routine core analysis (porosity and permeability) for the new wells. In addition, based on the distribution and flow direction of this reworked deposit, we considered the changes of flow regime towards the flow direction. The result of the well-well correlation and seismic interpretation suggests that the wells penetrated the same reworked carbonate body. We can recognize the variety of grain size, sorting, sedimentary structure, and a degree of the bioturbation between the wells: poorly sorted coarse-grained to pebbly carbonate is dominant around the depositional up-dip side, and sharp based well-sorted grainstone with sedimentary structures (grading and lamination) is dominant around the depositional down-dip side, with bioturbation being more intense especially at the upper part of these grading beds. These sedimentary characters suggest that the flow regime changed towards the flow direction: dense flow at the depositional up-dip side and dilute flow at the down-dip side. In addition, several grading beds in the same indicate that the flow repeated several times. Routine core analysis and log calculation (porosity and permeability) results suggest that the sediments in a middle body of the reworked sediments has better reservoir properties. There is remaining exploration potential for this new play concept (reworked carbonate reservoir) around Abu Dhabi. In this time, we drilled new wells to confirm this new play concept, and we suppose that the knowledge of this study may have a big impact to the future exploration.