عنوان مقاله [English]
Nowadays there are many attempts to exploring stratigraphic traps all over the world. Because of existing Sarvak reservoir rock Formation in central Persian Gulf which consists of carbonate with various lateral changes in the terms of lithology, there is high probability to form of these stratigraphic traps in this region. The main aim of this research is to recognize the oil and gas stratigraphy traps by using seismic attributes and petrophysical and geological logs in the Bahregansar oil field, NW of Persian Gulf basin. In order to reconnaissance these regions, petrophysical logs (density, acoustic, neutron and gamma) and seismic reflection data from three wells have been studied. On the other hand, the obtained data have been interpreted with some seismic volume attributes such as momentary frequency, domain and acoustic impedance, reflection coefficient, normalized amplitude and envelope amplitude attributes to show the situation of hydrocarbon basin in the study area.
By using seismic attributes and compare with geological information we can infer reliable interpretation because of some reasons. The first reason is seismic velocity allow us to understand the situation of lithology, fluid content and abnormal pressure or temperature. The second reason is lateral amplitude changes permit the inference of geological situation such as changes in porosity, existence of hydrocarbon and thickness of lithology. The third reason is seismic trace morphologies or interpretation sections allow us to recognize depositional environments or faults and fractures. Finally, changes in measurements direction permit to deduce velocity anisotropy, or fracture orientation.
The software which used in this study was Petrel. Density log is creating with using neural network method by application of well No.3 in this oil field. The petrophysical study of gamma log shows well identity of formation boundaries in sections. Also the use of cross plot graph of density-neutron logs applied to well recognized of the efficient zones in Gurpi-Ilam, Sarvak and Kazhdumi-sand Formation. The Turonian epirogenic event is caused erosion of top of the Sarvak Formation and on the other hand Santonian epirogenic is caused hiatus stratigraphic trace in the lower part of Gurpi and Ilam Formation. By seismic volume attributes interpretation a number of the stratigraphy traps detected over some seismic sections. Furthermore, recognizing a main fault which exists in the western part of Hendijan oil field has main role in the changing of lithological effect in continuity quality of seismic reflection.
In order to increase interpretation accuracy, some seismic inversion has been made on considered sections and the obtained data have been compared with petrophysical logs and seismic attributes. By doing this research and interpretation of sections two type of stratigraphic traps recognized. The first type is oil trap related to the top of Turonian unconformity (truncation) which exists in the eastern part of fault. The second is relation to narrowing part which is belonging to the above of the reservoir layer (pinch out) under Turonian unconformity in the western part of seismic section. Meanwhile the study shows that there is an oil trap as hydrocarbon accumulation in the upper part of Kazhdumi sand formation seismic subunit acting like stratigraphy trap in the above unconformity. In general, all of oil traps recognized in this study were composed of anticline structural dip and on the other hand existence of faults has a main role of geological structure in this region. The obtained results clearly demonstrated the shape and the geological situation of the existing structural traps in the studied area.