Sequence stratigraphy of the Burdigalian Rudeis Formation in Ras El-Ush oil field, Gulf of Suez: Application of gamma-ray analysis and biostratigraphy

Abstract

The Rudeis Formation represents one of the most important oil-producing reservoirs in the Gulf of Suez. This formation exhibits conspicuous lateral facies changes and therefore presents a complex exploration target due to tectonic activity. In the study area, it is composed largely of shale with a few limestone interbeds, but so far composed of fine-grained marl and sandstone. Here, we interpret the sequence stratigraphy of the Rudeis Formation at two onshore wells (Ras El-Ush-7 and Ras El-Ush 8) in the southernmost western shore of the Gulf of Suez via the integration of gamma-ray log and biostratigraphic data, in order to develop a high-resolution sequence stratigraphic model of these syn-rift rocks and determine their viability for hydrocarbon exploration. Using new biostratigraphic analysis of calcareous nannoplankton and planktic foraminifera, we verified the ages of the Rudeis successions. Our results suggest the occurrence of three Burdigalian depositional sequences (SQ1, SQ2 and SQ3), along with six stratigraphic surfaces delineating sedimentation cycles and were mainly deposited in inner shelf to upper slope settings. Each of the sequences typically contains a transgressive systems tract bounded above by a maximum flooding surface and a highstand systems tract bounded above by a sequence boundary. We further demonstrate that the variable timing in deposition and erosion of these depositional sequences were controlled by either local tectonism associated with Gulf of Suez rifting or eustatic sea-level changes.