Petrophysical, seismic structural and facies analysis of the Miocene reservoirs of East Morgan oil field, Gulf of Suez, Egypt

Abstract

The Gulf of Suez is characterized by the presence of many hydrocarbon-bearing fields including reservoirs ranging in age from the Palaeozoic to the Tertiary. East Morgan oil field is one of the promising oil fields which are located in the southern part of the Gulf of Suez and tapping hydrocarbon deposits and potentials of the Miocene age. The purpose of this work is to evaluate the Miocene sediments of the Asl and Hawara Formations in East Morgan oil field (western sub-basin) through carrying out an integrated petrophysical, seismic structural and sequence stratigraphy study. Quantitative well logging analyses are carried out over Asl and Hawara Formations to throw light over their hydrocarbon potentiality. Good oil saturation is exhibited by the sand sections of Asl Formation, and fair to good are assigned for those of Hawara Formation in the Belayim dip province. On the other hand, a little hydrocarbon saturation is represented by both formations to the south of the study area in the Morgan accommodation zone (MAZ). The estimated petrophysical parameters of Asl reservoir throughout the study area range between 4 % and 10 % for effective porosity, 18 % and 89 % for shale volume and 2 % and 48 % for hydrocarbon saturation. Meanwhile, the ranges of 1–8 %, 20–98 % and 2–32 % are given for Hawara Formation for effective porosity, shale volume and hydrocarbon saturation, respectively. The lateral distribution maps show that the central and the western parts of the MAZ attain the best petrophysical parameters and hydrocarbon potentiality. Seismic facies analysis, structural framework and depositional history of the study area were studied through interpreting the seismic reflection data of 27 seismic profiles. A number of geo-seismic cross sections are constructed and interpreted to investigate the structural setting of the study area and clarify the main structural elements that affect the hydrocarbon bearing reservoirs. A group of simple NW–SE step-like normal faults, parallel to the Clysmic trend, is found cutting through the reservoir rocks at the bottom layers of the section (Rudeis Formation) and extending upwards to overlying layers (Zeit Formation). Some graben- and horst-shaped structures are found and usually bounded by two sets of oppositely dipping normal step-like cross faults. The seismic facies and sequence analysis revealed that the Miocene rocks are subdivided into two major third-order depositional sequences (S1 and S2), separated by two major depositional sequence boundaries (DSB1 and DSB2). The first sequence (S1, Lower–Middle Miocene rocks) is of prime interest, as it encounters the main hydrocarbon reservoirs in the study area (Asl and Hawara Formations that are equivalent to Rudeis Formation). The seismic facies of this sequence are characterized by low to moderate amplitude, discontinuous horizons and bounded by the depositional sequence boundary (DSB1) at the top. The reflection geometry at the cycle boundaries is considered as erosional truncation, toplaps and even concordant along the upper boundary of the cycle. The external form of these sediments is considered as sheet-like and wedge-shaped units. The entrapment of hydrocarbons seems to be of a combined effect of the stratigraphic and structural elements. It appears clear that both of the step-like structural fault system and the lateral variation of facies are the key parameters that control the accumulation of hydrocarbon in this area and in East Morgan field as a whole.