Ekofisk life-of-field seismic: Operations and 4D processing

Abstract

In 2010, the world's largest optical permanent reservoir monitoring (PRM) system was installed in the southern part of the Norwegian North Sea at Ekofisk. The life-of-field seismic (LoFS) system consists of 3966 seabed multicomponent sensors along 200 km of mostly trenched fiber-optic seismic cables and covering about 60 km 2 of Ekofisk field. Seismic data are acquired via a topside recording unit and a containerized source operated on a supply vessel. Six vintages of data were acquired between the end of 2010 and fall 2013. Different aspects of seismic operations at Ekofisk include seismic source, recording system, data transfer, quality control, and processing. One of the key factors in achieving the full value of a PRM system is to handle such operations in a safe, integrated, and efficient manner to deliver high-quality seismic volumes for interpretation with rapid turnaround. Key aspects of the 4D processing sequence include robustness and optimal turnaround. Integration of the different operational phases of the LoFS project and integration of expertise between client and contractor play a key role in delivering clean, well-resolvable 4D signals and low residual 4D noise with NRMS as low as 5%. The high-quality data delivered by operations and processing are now routinely used in well planning and reservoir-management workflows.

Review Paper: Post‐stack 4D seismic time‐shifts: Interpretation and evaluation

“…; Ekofisk field: Guilbot and Smith ; Bertrand et al . ) over 5–10 years. Some of the most challenging fields are in the Southern Gas Basin, where imaging difficulties arise due to the overlying Zechstein carbonate sequence combined with a weak noisy signal.…”

“…6 (>3km) reservoirs over a short time period of several years (e.g. Curlew-D and Skua fields) to the more dramatic 24 ms or more for compacting chalk reservoirs (Valhall field: Barkved et al 2005;Hall et al 2005; Ekofisk field: Guilbot and Smith 2002;Bertrand et al 2014) over 5-10 years. Some of the most challenging fields are in the Southern Gas Basin, where imaging difficulties arise due to the overlying Zechstein carbonate sequence combined with a weak noisy signal.…”

Reservoir characterization based upon the onset of time-lapse amplitude changes

“…New approaches allowing for more frequent seismic monitoring have appeared recently. For example, permanent, life-of-field, and continuous oceanbottom seismic arrays are increasingly common (van Gestel et al, 2008;Berg et al, 2012;Bertrand et al, 2014). These advancements should lead to improved reservoir monitoring and better signal-tonoise (Landro and Skopintseva, 2008).…”

Intra‐survey reservoir fluctuations – implications for quantitative 4D seismic analysis

“…Whilst reservoir monitoring with ocean‐bottom nodes is not restricted by large streamer or cable dimensions, nevertheless such surveys can still take a few weeks to a few months to cover a much smaller but higher fold area of 20–143 km 2 (Bertrand et al . ; Eriksrud ; Farmer et al . ) due to weather and operational restrictions.…”