Seismic Challenges in the East-Med: Edison’s Experience and Lessons Learned
Since 2013, Edison E&P has operated acreages in excess of 10000 km2 which cover two prolific petroleum provinces of the East Med; the Nile Delta cone and the Levantine basin. Significant investments in seismic activities have been made in order to accurately assess the exploration potential of the acreage. The legacy seismic coverage included only a few 2D lines and some vintage 3D. Currently, the area is fully covered by 3D seismic as a result of Edison’s seismic activities, including the Acquisition/Processing of more than 6000km2 of new 3D broadband seismic and the reprocessing of around 4000km2 of 3D. The main exploration targets identified are the Mio-Oligocene clastic sequence, extension of Levantine basin floor fan plays, the typical Nile delta slope channel plays, and the recently-recognized Cretaceous isolated carbonate plays lying at 4km to 6 km depth. Two main geophysical challenges characterized Edison’s area: the presence of a thick (1-2km) structured Pliocene Nile delta anisotropic sequence and a thick (0.5 to 2 km) salt sequence of Messinian age with the presence of steeping diapirs and salt walls. Seismic wave propagation is strongly affected by such a complex geological environment overlying the target intervals. Such behaviors become less prominent westward towards the rest of the Levantine basin. The lack of well control on the acreage presented an additional obstacle to the proper addressing of velocity trends and to the prediction of seismic response at the target depth. The seismic acquisitions have been designed to obtain the broadest possible frequency range and a proper illumination of the targets. Two different contractors have been involved. Different streamer configurations have been selected to achieve the goals, especially to reduce the ghost-notch impact and to enhance the low frequency response. During the various processing/reprocessing projects, different workflows and techniques have been applied producing some key lessons learned. In the time pre-processing, a proper sequence of deghosting/demultiple has been setup. Strong efforts were also made to understand and remove a PSP mode-converted wave present immediately below the base salt. A key element addressed during the imaging phase has been the assessment of Pliocene anisotropy, incorporated during tomographic velocity updates to correctly determine and define the Top & base salt. Accuracy on salt and post-salt velocity estimation had an important impact for the target zone imaging. Kirchhoff migration was used as basic flow while RTM was used in the zone with high salt movement. FWI has been tested but not run due to timing constraints: it will be considered in the post-drilling phase as soon as some additional knowledge is obtained from the well data. Challenges and lessons learned during the acquisition and processing phases have been incorporated in the seismic quantitative interpretation phase due to the strong impact on visibility/detectably of reservoir, reliability of DHI/AVO results and strength of structural trap.