AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Depth Imaging Strategy for Low Relief Carbonate Platform Giant Oil Field Offshore Abu Dhabi, United Arab Emirates
(1) ExxonMobil Upstream Research Company, Houston, TX.
(2) ZADCO, Zakum Development Company, Abu Dhabi, United Arab Emirates.
An offshore Abu Dhabi low relief carbonate platform giant oil-field is characterized by various structural complexities that significantly affect reservoir and deeper level intervals. Inter-bedded clastics and carbonates within the overburden produce rapid velocity inversions and lateral variations that cannot be explicitly accommodated by time migration algorithms. Imaging challenges due to shallow geology, such as presence of faulting and small scale features of about 500m or smaller in diameter. Project goal was to determine the potential uplift to interpretation of depth imaging over conventional time migration, including the time stretched to depth technique. The depth imaging velocity model created as a result of this project accounts for both the long and the short wavelength velocity anomalies and was constructed by explicitly including all available well data information, interpretation and seismic velocity information. Due to seismic data high amplitude coherent and random noise, strategic data conditioning flows were applied to ensure that high frequency data was retained in the stack, to attenuate the noise, mitigate acquisition footprint and some of the overburden effects. To limit the migration noise and to better account for the effects of the small scale structures, hybrid time/depth imaging scheme was created which utilizes 3D dynamically corrected DMO sub bin stacks, followed by zero offset wave equation migration. This was determined to be more effective than a conventional Kirchhoff approach. The migration of each individual offset group with a velocity model that honors the 3D complexity found in the overburden allows each offset group to focus differently, thus providing uplift over the post-stack depth migration, without sacrificing the benefits of signal-to-noise enhancement through sub-stack. To accurately evaluate the potential interpretation uplift of prestack over post stack depth imaging and time imaging, it was necessary to implement a fairly exotic post-migration processing flow to ensure that the depth imaging products had similar signal-to-noise, wave-shaping and de-multiple characteristics as the time migrated products. Results from time-to-depth stretching, time migration, post-stack depth migration, prestack depth migration, and conventional Kirchhoff prestack time (or depth) migration comparisons will be demonstrated and discussed.