TopSeis™ is a next-generation marine towed-streamer acquisition solution, delivering a step-change in imaging for shallow to intermediate depth targets by providing massively increased near-offset coverage from a split spread with zero offsets. It is the most recent addition to our broadband portfolio and is the outcome of over eight years of technical collaboration between CGG and Lundin Norway AS, with additional funding from the Research Council of Norway. The first full scale commercial survey has been completed for Lundin in the Barents Sea and a new 5,000 km² multi-client survey will be start acquisition this summer.
TopSeis is a tailored solution, specifically designed to improve imaging of shallow and intermediate-depth targets by overcoming the lack of near-offset fold inherent in towed-streamer seismic. TopSeis achieves this by using an innovative source-over-spread acquisition configuration and proprietary processing algorithms.
Based ideas and continuous support from Lundin, TopSeis has been developed over the last four years by a multi-disciplinary team of CGG and Sercel Equipment, Marine Acquisition and Geoscience experts, using synthetic data and field trials to derive optimum configurations for specific targets and to develop methods to deploy these configurations safely. It capitalizes on CGG’s long-standing broadband capabilities, including deep-tow experience from acquiring over 500,000 km² of BroadSeis™, deployment of our broadband source (BroadSource™) and our recognized Subsurface Imaging excellence.
A full scale 3D survey of approximately 2,000km² was acuired for Lundin Norway in the Barents Sea in 2017. The survey was recorded without HSE incidents and with only 1% technical downtime. The TopSeis data shows considerable improvement over the legacy data. The deep-towed near offsets resulted in less swell noise and generally improved signal-to-noise ratios. The split-spread offset distribution including negative offsets, combined with near- and zero-offset coverage, smaller bins and higher fold, delivered higher-definition multiple models and improved multiple attenuation. Velocity and anisotropy model building has been improved by full 3D recording of the curvature of seismic events to provide better imaging.
Improvements can also be see in the depth slices
Following the acquisition of the Lundin survey, a small 24 x 3 km area was acquired over the Wisting field in the northern part of tthe Barents Sea for further evaluation of the technology. AVO analysis was performed on the TopSeis data to investigate the improvements obtained by the good angle range recorded. This area covers three wells, with the Central Well (7324/8-1, where the Wisting discovery was made) being located in the centre of the test area. This well was used in evaluation of the AVO. Four angle stacks, (0 - 10, 10 - 20, 20 - 30 and 30 - 40˚), were the input to the AVO analysis. As expected, AVO prediction was improved by the increased fold and the direct measurement of the intercept from recording zero-offset data. The TopSeis data showed a good match to the well data and also gave consistent AVO results, with both the seismic and well data showing negative intercepts and gradients.
A full deterministic elastic inversion of the four angle stacks was also performed, using amplitude-filtered well logs as an initialmodel. The outputs from this seismic inversion are 3D acoustic and elastic impedance volumes which should reflect the rockphysics properties of the target sands. A high correlation between the inverted attributes and well logs at both exploration wellswas observed. In addition, a distinct lateral variation in absolute Vp/Vs ratio amplitudes (from high to low values) is observed whenmoving towards the structural highs on the Top Stø formation. This is believed to be an indication of the transition from oil to gas in the reservoir. Several smaller prospective anomalies, as indicated by the red arrows, can also be observed, which should help in the positioning of future development wells.
The image quality is so good that it is revolutionary. It is like going from 720 to Ultra HD and 4K on your TV at home. - Per Eivind Dhelie, senior geophysicist in Lundin
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An innovative source-over-spread solution for imaging shallow reservoirs.