Seismic Interpretation and Reprocessing Over the Wadi Field NC149, Sirte Basin, Libya

Geophysics, Petroleum geology

Ghrouda, Fathi Mohamed Ahmed

University:University of Glasgow

关键词: Geophysics, Petroleum geology;   

Others  :  http://theses.gla.ac.uk/78399/1/11011466.pdf

来源: University of Glasgow

【 摘 要 】

The Wadi field is located in the Hagfa Trough, where exploration targets are very deep, compared with the other exploration targets on the platform. Seismic data are poor for the deep horizons, and the deepest horizon for reliable mapping is the top Upper Cretaceous Zmam Formation. Twelve wells have been drilled within the Wadi field structure, the main reservoir being penetrated by eleven wells. Five wells have a check shot survey (D6, D7, D8, D9, and K1-149). The field is seismically defined on the basis of a 2-D seismic survey. One line (V07-85) has been reprocessed using the uphole static correction. The uphole static has improved the image in the area where the elevation changes markedly. The check shot surveys from wells D6, D7, D8, D9, and Kl-149 are used to identify the reflectors. Eight reflectors have been picked on the seismic sections. Times picked from four horizons (top Gargaf, Nubian, Zmam and Zelten respectively) have been contoured. The maps show that the structure is subdivided into a number of interlinked grabens and half-grabens, separated by structurally high horst or footwall highs formed by normal faults trending NW-SE, with at least one likely growth fault. The isochron maps for the Gargaf-Nubian, Nubian-Zmam and Zmam-Zelten intervals all show thinning on the crest of the structure, and thickening on the flank of the structure towards the grabens. The tilting is responsible for the entrapment of the oil in the main reservoir (Nubian sandstone) against the Socna shale. To understand the timing of faulting in the study area, the back-stripping technique has been used. Wells D6 and D7-149 show an average velocity decrease with depth at Heira (Palaeocene) and Socna (Upper Cretaceous) horizons. D9-149 shows velocity decrease with depth at the Socna (Upper Cretaceous) Cretaceous) reflector. The average velocity calculated using the relation between average and interval velocities is unreliable for the depth conversion. All the average velocities calculated using the time from the seismic lines are used for the depth conversion. The structure map for the top Nubian shows the structure subdivided into four blocks (A, B, C, D).