Fluid transport properties and estimation of overpressure at the Lusi mud volcano, East Java Basin (Tanikawa et al., 2010)

摘要

The Lusi mud volcano in Sidoarjo, East Java, started to erupt on May 29th 2006 and has displaced 13,000 families. Controversy surrounds whether the mud volcano was caused by drilling of the Banjar Panji 1 gas exploration well (Davies et al., 2007; Manga, 2007; Davies et al., 2008; Tingay et al., 2008) or due to the Yogyakarta earthquake that occurred at 05:54 am on the 27th May 2006 (Mazzini et al., 2007; Sawolo et al., 2009). Constraining (a) pore pressure in sedimentary strata prior to drilling; (b) changes in pore pressure that occurred due to drilling the Banjar Panji 1 well and the earthquake, and; (c) potential routes for fluid to the surface are critical for resolving this debate. These areas are tackled in the recent paper by Tanikawa et al. (2010), who model pore pressure development during burial of sedimentary strata at the site of the eruption and measure the permeability and porosity of outcrop samples of formations of equivalent age and lithology as those penetrated by the well. From this analysis, they conclude that overpressure developed within specific successions, in particular the Upper Kalibeng clays and a deep carbonate formation. They go on to argue that the overpressure made the clay-rich unit susceptible to liquefaction as a result of cyclic deformation during the Yogyakarta earthquake, and that this initiated the mud volcano. In this discussion we begin by summarising the main conclusions made by Tanikawa et al. (2010) and then consider the validity of their most important conclusion that Lusi is a natural disaster. Lastly, we reiterate the compelling evidence (Davies et al., 2008; Tingay et al., 2008) that Lusi is man-made and was caused by an underground blowout at the Banjar Panji 1 well.