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Mineralogy and Illite/Smectite Mixed-Layer Expandability of Rudies Formation and Its Relation to Maturation of Organic Matter, in the Southern Sector of the Gulf of Suez, Egypt
(1) Egyptian Petroleum Research Institute, Cairo, Egypt.
The X-ray diffraction analysis of 29 bulk samples and 21 clay fractions samples derived from Rudies Formation, that present in Gabal El-Zeit and Morgan basins in the southern part of the Gulf of Suez, are used to define the mineralogic composition of this formation. This rock unit is composed mainly of quartz, dolomite and calcite associated with minor amounts of phyllosilicates, such as kaolinite and illite/smectite mixed-layer, as well as traces of K and Na feldspars, and hematite. The analysis of clay fraction of the studied samples indicated that, illite/smectite mixed-layer is the main mineral component in Gabal El-Zeit Basin, followed by kaolinite, in which kaolinite is the main clay mineral, followed by illite/smectite mixed-layer in El-Morgan basin. Illitization of illite/smectite mixed-layer is the main process in this study, which indicated that the random interstratification (R=0) of illite/smectite mixed-layer is present in two stages of organic matter maturation at Gabal El-Zeit Basin smectite percentage (S%) ranges between 85 and 80%, present in temperature range from 28 to 46 °C indicating immature stage. whereas random interstratification in Morgan basin are situated in with smectite percentage ranged between 60 and 50 and temperature range 90 to 91°C, reflects mature source rock.
The ordered interstratification (R=l) has S% ranged between 40 and 25 % present at depth range from 2413 to 3055m and temperature range 94 to 103°C is also detected. While (R=3) illitization stage is identified with S% ranged between 15 and 10 %, is present at depths 3250 and 3480m and have temperature range of 115-137 °C which reflecting end of oil generation stage, whereas R≥3 illitization stage with S% of 10% or less is present at depth ranged from 3445 to 3550m and temperature from 139 to 143°C which indicating wet gas stage. Generally, these illitization stages and temperature ranges show that, the organic matter content of Rudeis Formation at Gabal El-Zeit Basin is present in immature stage, whereas the organic matter in Rudeis Formation at Morgan basin is attending in a range of oil window and wet gas stage.