Naturally occurring underpressure – a global review

Abstract

Several mechanisms have been suggested as drivers of naturally occurring underpressure. However, the phenomenon is largely underrepresented in literature. Previous studies have focused on individual cases in North America, where challenges due to topography and defining hydrostatic gradients exist. More recent publications from underpressured basins have emerged from other parts of the world, where settings are arguably more favourable to studying the phenomenon. Based on a total of 29 underpressured locations, it is apparent that the magnitudes and depths of underpressure are similar throughout the world. Pressures of up to 60 bar blow hydrostatic are common in sedimentary basins of North America, China, Russia, and Europe and typically occur at shallow depths (<2500 m). All occurrences of underpressure occur in areas that have been geologically recently uplifted and is predominantly confined to low permeability rocks. Although rarely tested, it appears that mudstone intervals are susceptible to developing underpressure. Given the shallowness, low permeability, and recent uplift of the cases, it seems that underpressure is typically a geologically short-lived phenomenon.