Time-lapse full-waveform inversion with ocean-bottom-cable data: Application on Valhall field

Abstract

Knowledge of changes in reservoir properties resulting from extracting hydrocarbons or injecting fluid is critical to future production planning. Full-waveform inversion (FWI) of time-lapse seismic data provides a quantitative approach to characterize the changes by taking the difference of the inverted baseline and monitor models. The baseline and monitor data sets can be inverted either independently or jointly. Time-lapse seismic data collected by ocean-bottom cables (OBCs) in the Valhall field in the North Sea are suitable for such time-lapse FWI practice because the acquisitions are of a long offset, and the surveys are well-repeated. We have applied independent and joint FWI schemes to two time-lapse Valhall OBC data sets, which were acquired 28 months apart. The joint FWI scheme is doubledifference waveform inversion (DDWI), which inverts differenced data (the monitor survey subtracted by the baseline survey) for model changes. We have found that DDWI gave a cleaner and more easily interpreted image of the reservoir changes compared with that obtained with the independent FWI schemes. A synthetic example is used to demonstrate the advantage of DDWI in mitigating spurious estimates of property changes and to provide cross validations for the Valhall data results.

On the role of density and attenuation in three-dimensional multiparameter viscoacoustic VTI frequency-domain FWI: an OBC case study from the North Sea

“…From top to bottom, the depth slices intersect glacial sand channel deposits, a wide low-velocity zone intersected by scrapes left by drifting icebergs on the paleo-seafloor, the gas cloud and the base cretaceous reflector, respectively. These structures have been well documented by FWI in Sirgue et al (2010), Barkved et al (2010), Operto et al (2015), Yang et al (2016a) and Figure 11. FWI perturbation models (Q).…”

“…The subsurface target is a North Sea oil field in a 70 m depth shallow water environment (Barkved et al 2010;Sirgue et al 2010;Haller et al 2016;Yang et al 2016a). The overburden is characterized by soft sediments in the near surface and a low-velocity gas cloud above the chalk reservoir, which is located at around 2.5 km depth.…”

Interferometric full-waveform inversion

“…But in practice, we always generate extra nonreservoir updates because there are a finite number of iterations used for inverting the baseline model. Watanabe et al (2005), Asnaashari et al (2012), Yang et al (2016), and Kamei and Lumley (2017) use double-difference FWI (DDFWI) to invert for time-lapse velocity changes and show that DDWI provides a more accurate estimate for the time-lapse changes compared with the previously discussed strategies. In this strategy, the estimated baseline model is used as the initial model, but instead of inverting the monitor data as a whole, we invert the time-lapse differences between the baseline and monitor data sets.…”

Taming the divergent terms in the scattering series of Born by renormalization

“…Resolution analysis by random probing. Journal of Geophysical Research: Solid Earth 120 (8), 5549-5573. 15 Fichtner, A. and J. Trampert (2011a).…”

“…Time-lapse seismic is a widely used tool for the dynamic reservoir monitoring and assessing the reservoir changes due to production [2][3][4]. Recent studies have shown the applicability of the full waveform inversion for the timelapse seismic problem [5][6][7][8][9][10].…”