Many basins in Indonesia such as the North Sumatra, South Sumatra and Lower Kutai are highly overpressured. As a result, some wells have experienced drilling problems resulting in termination. In the literature, an empirical relationship such as Eaton has historically often been used to interpret pore pressure. In this paper, we take an alternative approach, one based on deterministic models.

Herein, we use Bowers’ and Dutta's equations to calculate the contributions of loading and unloading to the overall overpressure. Due to the advantages of the density log, the contributions of loading and unloading can be discriminated. By applying these methods, we suggest that in the North Sumatra Basin, unloading is caused by clay diagenesis. In the others, gas generation is significant.

The analysis also reveals that the unloading parameter (U) in the North Sumatra and South Sumatra basins is different than that of U in the Lower Kutai Basin. This suggests that mudrock in the overpressure zone in the Sumatran basins is more elastic than that in the Lower Kutai Basin, which appears to be more plastic in behaviour.

Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure

印度尼西亚的许多盆地，如北苏门答腊、南苏门答腊和下库台，都处于高度超压状态。结果，一些井遇到了导致终止的钻井问题。在文献中，历史上经常使用诸如伊顿之类的经验关系来解释孔隙压力。在本文中，我们采用了另一种方法，一种基于确定性模型的方法。

在这里，我们使用 Bowers 和 Dutta 方程来计算加载和卸载对整体超压的贡献。由于密度测井的优势，可以区分加载和卸载的贡献。通过应用这些方法，我们认为在北苏门答腊盆地，卸载是由粘土成岩作用引起的。在其他情况下，气体产生很重要。

分析还表明，北苏门答腊和南苏门答腊盆地的卸荷参数（ U ）与下库台盆地的卸荷参数（ U ）不同。这表明苏门答腊盆地超压区的泥岩比下库台盆地的泥岩更具弹性，后者似乎更具塑性。

专题合集：本文是 Geopressure 合集的一部分，可在以下网址获得：https://www.lyellcollection.org/cc/geopressure