XOM Returns To Shoot Yoho

The American major Tenders For 3D Survey APSDM In OML 104 Seven years after a carpet seismic coverage, spanning 1,230km2 full fold, ExxonMobil(XOM) is returning to the Oil Mining Lease(OML) 104, offshore Nigeria, for a Strategic Imaging Project. The work, this time, is largely a rigorous processing of the data acquired in 2003. The company is looking at a combination of anisotropic pre-stack depth migration APSDM, combined with advanced velocity model and tomographic techniques, “to improve fault sag and fault shadow imaging problems in OML 104 and ultimately reduce the structural deeper (>10,000ft) exploration leads as well as at Yoho and adjacent fields”. Fault surfaces will need to be depth interpreted and become surfaces that separate velocity contrasts within the model. Anisotropic parameters will need to be constrained by available well control and checkshots (Vl and Walkaway) as well as geological surfaces. “Finding the proper combination of depth imaging algorithms and model building will require some trial and error testing’ XOM declares.

ExxonMobil wants a collaborative effort in technology breakthrough with contractors that work in this kind of area. “Success will require strong collaboration between specialized experts from the contractor and MPN(the Nigerian shallow water subsidiary of ExxonMobil)”.

The 2003 vintage data was acquired in a 10 streamer dual source configuration in an East West direction, into 12.5 xline bins with 6km streamers with a1-8-7-m-fIip flop source yielding 80 fold. Due to surface obstructions in the area, some 1500m offset box-in-data was also acquired in 2003. Additional vintage streamer data(different shooting direction) will also be used to supplement near offset gaps around obstructions. The imaging programme area includes the entire 2003 3D survey extent(1230km2 full fold. “Based on technical and business needs, a priority area of ‘262 km2 full fold(”125 km2 image area) is planned to be branched off later in the velocity model building phase.

The entire workscope can then be broken down into three categories:

• High end preprocessing from navigation merged field taps. Noise mitigation, multiple suppression and signal enhancement are critical, particularly in fault shadow areas. Bin and regularlisation of data prior to migration.

• Iterative Anisotropic Velocity Model Building to accurately resolve lateral velocity contrasts across faults for the entire OML 104 block. Contractor must have a full suite of proven prestack depth migration algorithms (Kirchoff, Beam, WEM, RTM) as

well as proven tomography with ability to constrain input rays based on model surfaces. Contractor must have the ability to incorporate the geological surfaces and other geophysical data into the velocity/anisotropic model

• Hi end post-migration processing and noise reduction as required with a suite of angle stacks and specialized derivative volumes.

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