Abstract
We have investigated the tectonic and erosion features of the Upper Triassic (Mulussa F Formation) and Lower Cretaceous (Rutbah Formation) sediments in the Euphrates graben area and analysed their influence on changes in the thickness and zonal distribution patterns of these sediments. In this study, the geological modeling software of Petrel Schlumberger is used to model the regional geological structure and stratigraphy from the available geological and geophysical data.The Upper Triassic and Lower Cretaceous sediments (in total, almost 800 m thick) are the major hydrocarbon reservoirs in the Euphrates graben, which contain approximately 80 to 90 % of the total hydrocarbon reserve in this area. These sedimentary zones experienced variable changes in thickness and zonal distribution due to erosion processes caused by the two major regional unconformities, the Base Upper Cretaceous (BKU) and Base Lower Cretaceous (BKL) unconformities. The maximum thickness of the Upper Triassic sediments amounts to 480 m in the central parts of the Euphrates graben and along the NW-SE trend, i.e. in the dip direction of the Upper Triassic Mulussa F Formation. Towards the NE flank of the graben near the Khleissia uplift and the SW flank near to the Rutbah uplift, the thickness of the Upper Triassic sediments is gradually decreased due to their partial or total erosion caused by the BKL unconformity, and also due to a less space for sediment accumulation near the uplifts. The thickness of the Lower Cretaceous sediments increases in the northern, NW and NE flanks of the graben. Their maximum thickness is about 320 m. The BKL unconformity is the major cause of erosion of the Lower Cretaceous sediments along the southern, SE and SW flanks of the graben. In the Jora and Palmyra areas towards the NW flank of the Euphrates graben, the Upper Triassic and Lower Cretaceous sediments show no changes in thickness. In these areas, there was more space for sediment accumulation, and the sediments were less influenced by the BKL and BKU unconformities and thus less eroded.
Highlights
Based on the data collected during two decades of inten sive hydrocarbon exploration, production and field develop ment activities in the Euphrates graben area of East Syria (Fig. 1), it is emphasized that the availability of structural geology datasets and a proper knowledge of the geome chanics is the basis for improving the structural geological understanding of the graben system in the study area
The BKL unconformity formed during the Late Triassic to Jurassic period when a tilted block dipping towards the northwest existed along the Euphrates graben area
The BKL soil horizon in most of the Euphrates graben fields can be regarded as a barrier for hydrocarbons flows between the reservoir layers of the Upper Triassic Mulussa F Formation and the overlying sediments of the Lower Cretaceous Rutbah For mation
Summary
Based on the data collected during two decades of inten sive hydrocarbon exploration, production and field develop ment activities in the Euphrates graben area of East Syria (Fig. 1), it is emphasized that the availability of structural geology datasets and a proper knowledge of the geome chanics is the basis for improving the structural geological understanding of the graben system in the study area. The definitions of the tectonism, regional unconformities, erosion processes, zonal geometries and distribution of the Upper Triassic and the Lower Cretaceous sediments along the graben area have proven to be very critical to the geometrical integrity of the geological and geophysical models. In the static geological models of the Upper Triassic and the Lower Cretaceous sediments over the Euphrates graben fields, the thickness changes and zonal distribution of the reservoir layers of these sedi ments are mainly controlled by faults, erosion, and the re gional unconformities complex [Yousef et al, 2016]. Geological modeling software of Petrel Schlumberger, we have attempted to obtain a better understanding of the in fluences of erosion processes caused by the regional uncon formities on the zonal distribution and thickness changes of the Upper Triassic and Lower Cretaceous sediments in the study area
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