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3D Pre-Stack Previous HitDepthNext Hit Migration in Permafrost Transition, Point Thomson Field, North Slope, Alaska


N.C. Lian (Decipher GeoScience), J.R. Alldridge, J.R. Krebs, and J. Hefti (ExxonMobil)


One of the first full 3D Pre-Stack Previous HitDepthNext Hit Migrations (PSDM) on the North Slope of Alaska is in progress in the Point Thomson Field area. The Point Thomson Field lies under the transition zone where high-Previous HitvelocityNext Hit permafrost thins from onshore to offshore lagoon and thickens under barrier islands. Raypath distortion caused by rapid changes in permafrost thickness and Previous HitvelocityNext Hit has been a problem for seismic imaging and time-Previous HitdepthNext Hit conversion for many years. This talk concentrates on the impact of seismic acquisition geometry on processing for PSDM, the critical aspects of time pre-processing for PSDM, and on the approach to Previous HitvelocityNext Hit model building in this complex environment. Four 3D seismic surveys that image the main field area are being reprocessed through Pre-Stack Previous HitDepthNext Hit Migration.Variations in fold (30 vs. 60), offset distribution (10,149 ft vs. >20,000 ft), and azimuth (narrow vs. orthogonal vs. broad) between the four surveys significantly impact the data quality and Previous HitvelocityNext Hit analysis. The need to distinguish between small-scale statics-related variations and larger-scale Previous HitvelocityNext Hit model variations requires a dense Previous HitvelocityNext Hit grid of 0.25 mile for the time pre-processing. The Previous HitvelocityNext Hit grid for the PSDM Previous HitvelocityNext Hit model is 0.15 mile in the Previous HitdipNext Hit-oriented direction by 0.25 mile in the strike direction. The PSDM Previous HitvelocityNext Hit model is constrained Previous HitusingTop data from 23 wells, regional permafrost surfaces and a regional correlation surface along with the seismic data. Close interaction between the project interpreter and the seismic processors during all phases of the project is critical to identifying and solving these difficult data problems.



AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.