Land subsidence due to compaction in the coastal area of The Netherlands: the role of lateral fluid flow and constraints from well-log data

Compaction of thick Cenozoic sediments in the coastal area of The Netherlan ds in response to sediment loading in the recent geological past may contri bute to the problem of land subsidence. Numerical modelling is used to stud y this process and to arrive at predictions of current compaction-driven la nd subsidence rates. This paper builds on previous work by addressing two i ssues: (1) the role of lateral drainage of formation water within the sandy layers of the sand-shale sequence, and (2) the importance of expected over consolidation by the continental ice-sheet, which covered the northern half of the country during the Saalian glacial. The first issue is investigated by carrying out a sensitivity analysis for lateral flow in the numerical m odel, incorporating a realistic representation of the distribution of sand and shale strata in the study area. Results show that lateral flow is a fir st-order control and can both subdue and enhance predicted compaction-drive n subsidence rates, depending on the local stratigraphic architecture and p ermeability distribution. Overconsolidation is investigated by analysing we ll-log data. The analysis suggests that Tertiary shales in the north are no t overconsolidated; instead, they appear to be not yet hydraulically equili brated. (C) 2000 Elsevier Science B.V. All rights reserved.