Paper submitted to SEG FWI Beyond Structure Interpretation Workshop, by Milos Cvetkovic, Martin Widmaier, Marc Rocke, Curt Schneider, Carsten Udengaard, David Brookes, Simon Baldock, Greg Nash, Richard Huang and Ashish Misra (TGS) 

Summary

Extended-frequency sources or point sources developed in the last two decades, such as Wolfspar® (Dellinger et al., 2016), the Tuned Pulse Source (TPS) (Ronen and Chelminski, 2017), and Gemini (Brittan et al., 2020), have been primarily designed to provide lower frequency data for Full Waveform Inversion (FWI). These new sources also allow for better imaging of deeper targets in salt and volcanic basins, and have other advantages in processing (Rocke et al., 2024). However, because of highvolume chambers they need longer refill times and have other operational characteristics that restrict survey design compared to most traditional air-gun arrays.

In this abstract we will show how we iterate standard survey design practices when working with operational requirements for the Gemini source in exploration settings. We first show a sparse OBN survey in Gulf of Mexico or Gulf of America (GoM / GoA) where we try to maximize shot sampling in the field with quad-tow sources, while still acquiring long offset and full azimuth data without increasing survey duration and cost. We start with modeling on real and synthetic data to propose node and source spacing, and offsets needed to improve existing models with FWI up to source rock and basement level. We then get quad-tow extended source in-field refill times with available vessels and other operational parameters, that we use to adjust our shooting and dithering scheme. We run another pass of modeling, low frequency FWI and imaging on synthetic data to validate final acquisition parameters. The proposed survey is the first sparse OBN survey with an extended-frequency source in quad-tow configuration with relatively dense shot grid of 75 m x 75 m.

For streamer projects with Gemini sources, we have seen several configurations deployed in various salt basins offshore West Africa and Mediterranean (Donaldson et al., 2024, Ibanez et al., 2025). We will present details and results for ½ WAZ acquisition offshore Angola where we deploy 2 triple-source Gemini. We balance the long offsets (10 km) and azimuthal coverage (½WAZ), while maximizing shot spacing that is operationally permitted.