Paper submitted to EAGE Annual 2026
Summary
Standard 4D time-lapse acquisitions require extensive planning, specialized navigation equipment and strict repeatability for both source and receivers. Milne et al. (2024) demonstrated that multi-client datasets can be used in an opportunistic way to improve understanding of reservoir production. In 2025, a new monitor was acquired with a design focused on maintaining the repeatability achieved in previous dedicated surveys. This case study compares the results obtained from an opportunistic 4D approach with those from a dedicated 4D acquisition.
The Ærfugl field is approximately 60 km long and 2-3 km wide, with a stratigraphic pinch-out to the East (Figure 1). A test producer P1 drilled in 2013 proved the presence of gas before start-up of the first regular producer in 2020. In total, 6 wells were set on production in the period 2019 to 2021. Prior to the 2025 new monitor, two conventional 4D surveys were acquired, in 2005 and 2017 respectively. Only minor water flooding effects were interpreted on the 2017 data. However as most of the production started after 2017, it is expected to see some hardening in the south where water is replacing gas and some softening along the gas-water contact. In the north area, some hardening is expected as wells are producing water. Gas cap expansion is expected to be a major contributor to the 4D signal. Additionally, gas out of solution in aquifer could be a potential 4D signal.