Nonstretch moveout correction of long-offset multichannel seismic data for subbasalt imaging: Example from the North Atlantic

Abstract

We have developed a pragmatic new processing strategy to enhance seismic information obtained from long-offset multichannel seismic data. The conventional processing approach, which treats data on a sample-by-sample basis, is applied at a coarser scale on groups of samples. Using this approach, a reflected event and its vicinity remain unstretched during the normal moveout correction. Isomoveout curves ͑lines of equal moveout͒ in the time-velocity panel are employed to apply a constant moveout correction to selected individual events, leading to a nonstretch stack. A zigzag stacking-velocity function is introduced as a combination of segments of appropriate isomoveout curves. By employing a zigzag velocity function, stretching of key events is avoided and thus information at far offset is preserved in the stack. The method is also computationally cost-effective. However, the zigzag stacking-velocity field must be consistent with target horizons. This method of horizon-consistent nonstretch moveout has been applied to a wide-angle data set from the North Atlantic margin, providing improved images of the basement interface, which was previously poorly imaged.

Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

“…These difficulties are compounded at OCCs such as Atlantis Massif by the presence of high velocities and large lateral velocity gradients immediately below the seafloor [ Canales et al ., ; Henig et al ., ]. Previous reflection imaging of Atlantis Massif has used either dip‐moveout (DMO)‐based filtering [ Canales et al ., ; Kent et al ., ] or wide‐angle stacking [ Singh et al ., ; Masoomzadeh et al ., ] to reduce the influence of seafloor scattering, but has still concentrated on shallow subsurface events such as the D reflector [ Canales et al ., ]. A benefit of creating an accurate velocity model through waveform inversion is that it can be used as the input for reverse time migration (RTM) [ Baysal et al ., ], a form of prestack depth migration that implicitly filters much seafloor scattering, and can better resolve deeper structure [e.g., Arnulf et al ., ].…”

Coal seismic surveying over near-surface basalts: Experience from Central Queensland, Australia

“…This is a simple extension to conventional seismic surveying and can be implemented in the field with only a nominal increase in cost. This approach has been suggested by many authors (Ryu, 1997;Emsley et al, 1998;Fruehn et al, 1998;Wombell et al, 1999;Fliedner and White, 2001;Fruehn et al, 2001;Hu et al, 2003;Lau et al, 2007;Spitzer et al, 2008;Gallagher and Dromgoole, 2008;Masoomzadeh et al, 2010). Long-offset recordings are less affected by shot noise and forward modeling indicates large amplitude reflection events are generated at long offsets (Wombell et al, 1999;Dobson et al, 2003).…”

“…Long-offset recordings are less affected by shot noise and forward modeling indicates large amplitude reflection events are generated at long offsets (Wombell et al, 1999;Dobson et al, 2003). To deal with the increased normal moveout (NMO) stretching that occurs at long offsets, special processing strategies have been developed (Masoomzadeh et al, 2010). The use of low-frequency sources further increases the likelihood for success.…”

Improving resolution of NMO stack using shaping regularization

“…Trickett's results tend to be higher frequency but noisier than a conventional stack. Multiple other algorithms have been proposed that aim to reduce NMO-stretching effects (Byun and Nelan, 1997;Hicks, 2001;Hilterman and Schuyver, 2003;Rupert and Chun, 1975;Perroud and Tygel, 2004;Masoomzadeh et al, 2010;Zhang et al, 2013;Kazemi and Siahkoohi, 2011). Shatilo and Aminzadeh (2000) proposed a constant NMO-correction strategy, which applies a constant NMO shift within a finite-time interval that is equal to the wavelet length of a trace.…”