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Gulf of Mexico Four Point

Narrow-azimuth broadband 3D survey data

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The Four Point narrow-azimuth broadband 3D multiclient survey spans 417 Outer Continental Shelf blocks across three protraction areas and includes some of the most prospective acreage in the Norphlet play of the Gulf of Mexico. Primary exploration targets in this area are at depths of 20,000 to 35,000 ft, above a complex and highly variable autocthonous salt.

Understanding stratigraphic variability at the Norphlet level, which resulted from lateral variations in accommodation space caused by early salt movement, is a critical component of both exploration and appraisal activities in the play.

Survey challenges, processing, and interpretation

  • Deep Norphlet play targets overlying autochthonous salt
  • Poor seismic resolution at play depth
  • Multiples
  • Anisotropic velocity model building
Map showing 3D broadband survey area.
Exploration targets depths of 20,000 to 35,000 ft, above a complex and highly variable salt structure.
Map showing 3D broadband survey area.

Understanding stratigraphic variability at the Norphlet level is a critical component of both exploration and appraisal activities in the play.

Acquisition technology and technique

Sliding-notch broadband acquisition and imaging optimizes recorded bandwidth via slanted streamers and proprietary deghosting and is compatible with narrow-, wide-, and full-azimuth acquisition geometries. The technique addresses imaging issues that are common to this play by recording broader bandwidth data, optimizing the resolution required for deeper targets.

The Four Point broadband 3D multiclient survey data was acquired using this technique, employing

  • a single vessel equipped with a point-receiver marine seismic system
  • variable streamer depth, increasing from the near-offset to the farthest offset
  • eight 12-km steerable streamers.

Processing highlights

Advanced data processing technologies used to address the geophysical challenges present include

  • true-azimuth 3D GSMP general surface multiple prediction and attenuation
  • well-controlled provision of initial tilted transverse isotropy (TTI) anisotropic parameters
  • benchmarking of well velocities and depths throughout data processing
  • 3D prestack acoustic full-waveform inversion (FWI) using wave equations to produce high-resolution velocity models
  • FWI iterations performed on the supersalt sediments, salt body, intrasalt velocity variation, and the subsalt
  • accurate imaging in presence of structural and velocity complexities through two-way prestack wave equation reverse-time migration (RTM)
  • monitoring of imaging improvement and refinement of salt body interpretation throughout processing with RTM.

Full-Waveform Inversion

High-resolution velocity models

Derive high-resolution velocity and anisotropy models from seismic data using a two-way wave equation.

Reverse Time Migration

Advanced two-way wave-equation prestack migration

Accurately image in and below areas with great structural and velocity complexity.

3D GSMP

General surface multiple prediction

Preserve double bounces and other complex primary events for removal with complementary techniques.

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