Velocity-depth Models from Towed-cable Refraction Data - a Southern North Sea Case-study

Vintage narrow-azimuth towed-cable data-sets from the southern North Sea generally suffer from a lack of near-offset cover, giving rise to poor near-surface velocity control. Near-surface chalk units present a problem for such data-sets because of their high-magnitude and laterally-variant velocity structure. We investigate the use of refracted arrivals (that would normally be filtered or muted in conventional processing flows) to derive shallow 3D velocity-depth models. Specifically, we tomographically invert first-break travel-times and compare the resultant models with well-derived velocities over the Thoresby field.