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Insights From the First 4D Seismic over Valdemar Lower Cretaceous Chalk Field
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 80th EAGE Conference and Exhibition 2018, Jun 2018, Volume 2018, p.1 - 5
Abstract
New insights to Lower Cretaceous chalk production in the Danish North Sea have been provided by the first dedicated 4D monitor survey over the Valdemar field. Seabed subsidence and overburden time shifts indicated that compaction is occurring in both the Lower Cretaceous and overlying Upper Cretaceous reservoirs. Both reservoirs are being developed by depletion using horizontal wells. The 4D confirms that sand propped fracs are able to cross a barrier to vertical flow in the Lower Cretaceous. Regions of acoustic impedance increases, decrease and no change are observed in the vicinity of producing wells. Potential saturation and pressure change scenarios and the uncertainty in 4D prediction are explored to explain the observations. The observed 4D impedance change variations are interpreted to result from differences in the magnitude of competing gas saturation increase and pressure depletion effects. The trajectory of a planned well has been updated to avoid a region of potential pressure depletion. Analysis of the new survey has confirmed that valuable 4D signal can be recovered in Lower Cretaceous chalk and that a range of scenarios with associated 4D prediction uncertainties should be explored when interpreting time lapse seismic datasets.