Cretaceous petroleum-bearing rock types—their diagenesis and significance in the Gulf of Suez area, Egypt

Abstract

Detailed petrographic studies of cores of Cretaceous sediments from the Gulf of Suez area, from both productive and non-productive fault blocks, reveal the rock types, their petrophysics, the nature and distribution of their cements and the effect of diagenesis on hydrocarbon migration and accumulation. An understanding of the petrographic and sedimentologic characteristics of these clastic and non-clastic sediments helps in a valid interpretation of their depositional history and their significance in petroleum exploration. This study is important because of the observed complexity of the virtually unexplored areas and sections of buried Cretaceous rocks in the Gulf of Suez petroleum province, caused by the combined effects of sedimentation and tectonic movements that shaped the Gulf as an intercontinental juncture. There are four petrographic groups, arenite, micrite, wackestone, and claystone. Each group is subdivided into main types and subtypes that reflect the environmental changes within the shallow, fluctuating basin of deposition in the Gulf and related areas. In order to elucidate the porosity changes, the dolomitization process and the clay fractions were investigated. It appears that a post-compactional mechanism is responsible for providing the medium with the Fe 2+, Mg 2+ and K + needed for dolomite formation. Consequently, a porosity decrease may arise from the effect of argillaceous-rich carbonate portions. Also, the decrease of porosity of the Matulla Formation (Lower Senonian sandstone) as compared to the pre-Cenomanian sandstone is the result of increasing overgrowth of secondary silica. Significant dolomitization has increased the porosity of the Lower Seronian—Turonian sediments. This is due to the difference in ionic radii between calcite and dolomite crystal packing. Thus, the petrographic variability of the studied sediments and their diagenesis reflect the variability of their capacity as petroleum-bearing rocks, both laterally and vertically.