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 Netherlands in response to sediment loading in the recent geological past may contribute to the problem of land subsidence. Numerical modelling is used to study this process and to arrive at predictions of current compaction-driven land subsidence rates. This paper builds on previous work by addressing two issues: (1) the role of lateral drainage of formation water within the sandy layers of the sand-shale sequence, and (2) the importance of expected overconsolidation 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 model, incorporating a realistic representation of the distribution of sand and shale strata in the study area. Results show that lateral flow is a first-order control and can both subdue and enhance predicted compaction-driven subsidence rates, depending on the local stratigraphic architecture and permeability distribution. Overconsolidation is investigated by analysing well-log data. The analysis suggests that Tertiary shales in the north are not overconsolidated; instead, they appear to be not yet hydraulically equilibrated. (C) 2000 Elsevier Science B.V. All rights reserved.