One of the most widespread hypotheses for the origin of the present-day overpressure in the shale Post-Chalk section in the North Sea is the very rapid sedimentation from Neogene to present day. We tested this hypothesis by the means of numerical forward finite elements modelling and successfully simulated the overpressure build-up during the Cenozoic filling of the North Sea with relatively simple model set-up. Our model shows that overpressure of approximately 28% above hydrostatic developed in the Neogene, while during the Quaternary, it reached up to 36% above hydrostatic. At present day, the predicted onset of overpressure starts at about 800–1000 m below seafloor, while the maximum (magnitude about 1.36 sg, i.e. 36% above the normal hydrostatic pressure) is at approximately 2100 m. This overpressure profile fits reasonably well with data from wells drilled in the Central Graben. The exact magnitude of the overpressure depends on the used assumptions, the model set-up and the values of the input parameters. Especially the dynamic interaction between high sedimentation rates, clay permeability and low horizontal pressure gradient seems to be a key factor in the efficiency of dewatering of saturated clays during burial. The results indicate that, the assumption of horizontal stress isotropy results in nearly no horizontal fluid flow, despite the same magnitude for the vertical and the horizontal permeability. In these conditions, the vertical permeability plays much bigger role than the horizontal one in the effective de-watering of the sediments during burial. Further investigation is needed to explore the role of horizontal pressure gradient in fluid migration in passive sedimentary basins.

关于北海页岩后粉笔段现今超压成因的最广泛的假设之一是从新近纪到现今的快速沉积。我们通过数值正向有限元建模的方法验证了这一假设，并通过相对简单的模型设置成功地模拟了北海新生代充填过程中的超压形成。我们的模型显示，新近纪中的静水压力比静水压力高约28％，而在第四纪期间，它的静水压力高达静水压力的36％。目前，预计的超压开始于海床以下约800–1000 m，而最大压力（幅值约1.36 sg，即比正常静水压高36％）在约2100 m。该超压曲线与中格拉本中部钻井的数据非常吻合。超压的确切大小取决于所使用的假设，模型设置和输入参数的值。特别是高沉降速率，粘土渗透性和低水平压力梯度之间的动态相互作用似乎是埋藏过程中饱和粘土脱水效率的关键因素。结果表明，尽管垂直和水平渗透率的大小相同，但是假设水平应力各向同性几乎不会导致水平流体流动。在这种情况下，垂直渗透率在埋藏期间有效地使沉积物脱水方面比水平渗透率起更大的作用。