By Mark Tingay, @Mark.Tingay
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| The Lusi Mud eruption in August 2006. Photo courtesy of Greenpeace. |
Introduction
Early in the morning of the 29th of May 2006, hot mud
started erupting from a rice paddy in the densely populated Porong District of
Sidoarjo, East Java. The ‘Lusi’ mud volcano (a contraction of Lumpur (mud)
Sidoarjo) rapidly flooded the city. The disaster has now buried an approximately
7km2 area in up to 40m of mud, displacing 40000 people and indirectly
causing 17 deaths. The Lusi mud volcano is still erupting today.
This unusual and controversial disaster has intrigued me
since it first began and I have authored 10 papers on the topic. So, to mark
the 10th anniversary of the disaster, I will be writing my first
ever blog – a three-part summary of the geology of the Lusi mud volcano and the
disaster’s hotly debated origins. Part 1 below presents a geological summary of
the Lusi mud volcano. The controversy about whether the earthquake was triggered
by the May 27th 2006 Yogyakarta earthquake, or by a blowout in the
nearby Banjar Panji-1 well, will be the subject of Parts 2 and 3 respectively.
Part 1: Geological Summary of the
Lusi Mud Volcano Disaster
Summary of the Disaster
The Lusi mud volcano (7° 31’ 37.8”S, 112° 42’ 42.4”E) is
located in the city of Sidoarjo, ~25 km south of Surabaya, the largest city in
Eastern Java, Indonesia. The mud flow was first noticed at sunrise (~5:30am) on
the 29th of May 2006 in a rice paddy surrounded by homes, factories,
farms and the main highway running south from Surabaya (Davies et al., 2007).
The eruption was comparatively mild at first, starting at ~5000m3/day,
but with sporadic rates – sometimes having violent bursts throwing mud 5-10m up
into the air, but other times gurgling out at a slow pace. While most of the
mud erupted from one point, later to be called the ‘Main Vent’ or ‘Big Hole’, mud
also erupted from 9 points spread out along an ~NE-SW 1km long line during the first
fortnight of the disaster (Mazzini et al., 2007).
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| The Lusi mud eruption on its first day in May 2006, erupting at rates of ~5000m3/day. The eruption increased dramatically on the 1st of August 2006, with rates ranging from 120000-180000m3/day. |
Significant damage had already been caused within the first
few weeks of the eruption, as the mud flow increased in rate to ~40000m3/day
and showed no signs of abating (Mazzini et al., 2007). The main tollway road
became flooded, as did some of the homes and factories located immediately adjacent
to the west and south of the main vent. However, the disaster took an unexpected
turn when, on the 1st of August 2006, the mud eruption increased
dramatically to ~120000m3/day (Mazzini et al., 2007), with some
estimates of flow rates up to 180000m3/day – enough to completely
fill an Olympic sized swimming pool every 20 minutes! Such huge flow rates
quickly inundated the city, destroying more villages and covering a
significantly expanded area. Ultimately, authorities were forced to simply try
and contain the mud flow within large earthen walls.
Today, 10 years later, the Lusi mud volcano is still
flowing, but has gradually reduced its flow rate to ~10000-30000m3/day.
I estimate that Lusi has erupted a total volume of between 0.15-0.19 km3
of mud in its first decade. The mud is held back by levees that can be over 10m
higher than the surrounding towns and farms, creating a giant mud lake covering
an approximately 2.4 by 3 km area, and which is known to be over 40m deep in
places. Buried under that lake are 12 villages, 11241 buildings and the homes
of 39700 people (McMichael, 2009). The disaster is believed to have caused
>US$600 million in lost property and >US$2.7 billion in total damages.
The mud is not just held in the giant lake, but is mixed with water and then
pumped and sluiced into the Porong River immediately south of the disaster
zone. All the sediment pumped into the Porong River has even resulted in the
formation of a new small island at the river mouth.
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| Satellite pictures of the Lusi disaster location taken shortly before the eruption began (left) and after over 9 years of the eruption (right). The Lusi mud flow has covered ~7 square kilometres and buried 12 villages. Images from CRISP and Google Earth. |
Video footage of the Lusi mud volcano during peak eruption rates in August and September 2006. Image courtesy of Greenpeace and used with permission.
What is Lusi?
Lusi is an example of a mud volcano, which is the general
name for a range of features in which mud (mixture of water, clay, other
sediment and gas) erupts at the surface. Mud volcanoes are a relatively common
feature in sedimentary basins, particularly those that have been rapidly
deposited or are in tectonically active areas (Kopf, 2002). Mud volcanoes
essentially represent the release of high pore fluid pressures (overpressures)
that can build up underground, and are basically the exterior expression of an
underground plumbing system that transmits high pressure water, mud and gas
from a source rock, up through faults, fractures or vents, to the surface
(Tingay et al., 2003).
It is unknown exactly how many mud volcanoes exist on Earth,
as most occur underwater, but there are over 1000 known mud volcanoes on land
(with over 400 in Azerbaijan alone), and mud volcanoes have even been proposed to
exist on Mars (Kopf, 2002; Oehler & Allen, 2010)! Mud volcanoes are usually
quite small and benign features – they mostly gurgle and burp out mud sedately
from little lakes (salses) and small cones (gryphons). However, mud volcanoes
are also known to sometimes erupt violently for brief periods of time (several
days to weeks), with eruption rates of >1 million m3/day in some
cases (Davies et al., 2007), and can even spontaneously ignite to form huge
fireballs (such as this 2012 example in Azerbaijan: http://videoday.az/view=ccj59eiu ).
What makes Lusi so unusual is that it has maintained an extremely high average
eruption rate for a long length of time, but also that it is the only time in
known history that we have witnessed the birth of a brand new major mud
volcano, and right in a highly populated area.
Lusi Geology
Lusi is in the East Java Basin, an east-west trending
inverted back-arc basin that underwent extension during the Paleogene and was
reactivated during the early Miocene-Recent (Kusumastuti et al., 2002; Shara et
al., 2005). The Miocene-Recent sequences of the East Java Basin, in the region
around Lusi, are composed of shallow marine clastics and carbonates, marine
muds, volcaniclastic sediments and volcanic units from the nearby Penanggungan
volcanic complex (located 15 kilometres to the south-west of Lusi). However,
despite the many geological studies of the Lusi mud volcano (for example,
Davies et al., 2007; Mazzini et al., 2007; Istadi et al., 2009; Tingay, 2010),
there are numerous variations and uncertainties with regards to the subsurface
geology. Hence, in 2015, I published a new summary of the subsurface geology,
in which careful examination of geological data and mud logs was used to
resolve many of the geological uncertainties and common geological errors
propagated in the literature (Tingay, 2015).
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BJP-1 lithology, formations, casing points and available
petrophysical data, as well as available petrophysical data from the Wunut
Field and Porong-1 well, all located within 7km of the Lusi mud volcano (Tingay,
2015). All depths are in meters TVD RT. Petrophysical data has been carefully
processed, checked and corrected for significant errors caused by the poor logging
conditions. Density data has been estimated for some sections from p-wave
velocity data, as per the Gardner (1979) relationship, and is a good match to
measured data from BJP-1 and offset wells. Shallow shear wave sonic slowness
data has been estimated using four standard methods, and provides a reliable
match to measured shear wave data.
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(i) Holocene alluvium composed of alternating sands, shales and volcaniclastics (0-290m, <0.6 Ma).
(ii) Pleistocene-Holocene Pucangan Formation composed of alternating sands, silts and shales from 290 to ~520m and then shales with rare thin sands from 520-900m (0.6-1.1 Ma).
(iii) Pleistocene Upper Kalibeng smectite-illite blue clays (900-1870m) with rare thin siltstones and dolomitic siltstones (1.1-1.7 Ma).
The Pleistocene-Holocene clastic sequences in BJP-1 are underlain by a unit commonly misreported as being Upper Kalibeng “volcaniclastic sands” that extends from 1870m to ~2830m depth. However, detailed reanalysis of sidewall cores and drill cuttings reveals that this unit is actually predominately composed of fractured extrusive igneous rocks (primarily andesites, dacites and welded tuffs) that were mistakenly interpreted as volcaniclastic sands in mud logs. In addition, there are some interpreted volcaniclastics, possibly due to lahar deposits. This unit also becomes increasingly calcareous from approximately 2600m depth, and the bottom 220m of the unit are interpreted as calcareous volcaniclastics. Hence, this unit is now interpreted to be rapidly-formed (approximately 1.7-3.0 Ma) low porosity Pliocene-Early Pleistocene volcanics and volcaniclastics (Tingay, 2015).
It is interesting to note that this volcanic and
volcaniclastic sequence has not been previously reported in any offset wells,
with the Upper Kalibeng clays in the nearby Porong-1 well (7 km ENE of Lusi and
a ‘sister well’to BJP-1) extending right down to the underlying carbonates (Kusumastuti
et al., 2002). Furthermore, the volcanic sequences observed under Lusi are not
obviously different in seismic character (on low quality 2D seismic; Figure 2)
to the equivalent shales and silts observed under Porong-1, despite having anomalously
high densities and fast velocities.
The target reservoirs for the BJP-1 well were reefal
carbonates, originally (and often since) misreported as the Oligocene ‘Kujung’
carbonates. The Kujung carbonates are the common reservoir units in the
prolific offshore East Java Basin, and are typically not overpressured
(Kusumastuti et al., 2002; Ramdhan et al., 2013). However, the carbonates under
Lusi are actually one of a linked series of highly overpressured reefal
carbonate build-ups, along a ENE-WSW trend, that have previously been
penetrated by the Porong-1, Kedeco-11C, Kedeco-11E and BD wells (Kusumastuti et
al., 2002). Red algal fragments from carbonates at the top of the nearby, and
stratigraphically equivalent, carbonate build up in the Porong-1 well were
dated by strontium isotope ratios as being formed at ~16 Ma (Kusumastuti et
al., 2002). Hence, the carbonates underneath Lusi cannot be the Oligocene
Kujung formation, but are most likely the Middle Miocene Tuban Formation, and
possibly equivalents of the Rancak limestone (22-15 Ma; Tingay, 2015). The
carbonates encountered in the bottom 54m of Porong-1 well were dolomitized
limestone (with minor mudstone and packstone), light grey in colour, consisting
of bioclasts in a grey matrix. Porosity ranged up to 25%, but averaged 15%, and
was occasionally vuggy to moldic. The limestones encountered in Porong-1
contained 50% residual oil saturations, whilst the Miocene carbonates in the
Kedeco wells, and presumably BJP-1 (due to no evidence of significant hydrocarbons
erupting from Lusi), were fully water saturated (Kusumastuti et al., 2002).
It is not actually known whether the Miocene carbonates were penetrated by the BJP-1 well. The drillers were intending to penetrate these limestones prior to running casing (an extremely odd and dangerous plan, but more on that in Part 3!). However, the well had a total loss of circulation at 2833m, and no cuttings were returned in the bottom four meters of the well following a bottoms-up circulation at 2829m (Sawolo et al., 2009). Some authors interpret the sudden loss of returns as being indicative of the carbonates being encountered (Davies et al., 2007), while others argue that carbonates were yet at some deeper depth (Istadi et al., 2009). Daily drilling reports note that 25 ppm H2S was observed when drilling at 2813m depth early on the 27th May 2006, which was followed by 500 ppm H2S during the kick on the 28th of May (Tingay et al., 2015). As the carbonates are the only known source of significant H2S concentrations in the East Java Basin, this early H2S release, and subsequent large amounts of H2S during the kick, likely indicates that the base of the well was very close to the carbonates, if not inside them (Tingay et al., 2015). Regardless, there is general agreement that the BJP-1 well either penetrated, or was very close to the Miocene carbonates when total loss of circulation occurred at 2833m depth. Hence, I assume the Miocene carbonates to be located at ~2833m depth (terminal depth of the BJP-1 well). Seismic data suggests these deep carbonates extend to approximately 3500m depth and are underlain by the Eocene Ngimbang shales.
Subsurface structure:
Anatomy of the Lusi Mud Volcano
The mud erupting from Lusi is a hot (85-95°C) mixture of
clays and water, with ratios that have varied over time (initially 20-40% clay,
but thickening over time to be 50-70% clay in 2010; Tingay, 2010). The clays (solid
phase) have been accurately identified from foraminifera as being from the
upper Kalibeng shale formation (Mazzini et al., 2007). Furthermore, it is well
established that the mud travels from the Kalibeng clays to the surface via a
deep vent, that is likely along a fault zone (termed the Watukosek Fault Zone).
The initial eruption along a NE-SW line of vents strongly indicates flow up a
shallow fault or fracture zone. Furthermore, experiments demonstrated that the
subsurface mud vent was at least 50cm wide right down to 800m depth, as this
was the maximum measured depth they were able to drop sets of concrete balls,
chained together, during a 2007 attempt to clog up and stop the mud eruption. However,
there is still significant uncertainty about the source of the water
(liquid phase) erupting from Lusi, and also whether this may have changed over
time.
Initial Source of
Water
The two competing hypotheses for the triggering of the Lusi
mud flow each have different models for the initial source of water feeding the
eruption (May 29th – 31st July 2006). The
earthquake-triggering hypothesis argues that the initially erupted waters are primarily
sourced from the Upper Kalibeng clays, which are proposed to have undergone
extensive liquefaction before flowing to the surface via a nearby fault
(Mazzini et al., 2007; Lupi et al., 2013). However, the drilling-triggering
hypothesis proposes that the water is primarily sourced from the deeper Miocene
carbonates, and flowed to the surface via a combination of the BJP-1 borehole
and fractures or faults, mixing with and entraining the Kalibeng clays en route
(Davies et al., 2008; Tingay et al., 2008). Recent geochemical analysis has
demonstrated that there are signatures of deep gases (deeper than the Kalibeng
clays) in the early erupted muds from Lusi, and data from BJP-1 indicates no
pre-existing charging of deep gases/fluids into the Kalibeng clays, which all
support the hypothesis that initially erupted waters for Lusi have come
primarily from the deep Miocene carbonates (Tingay et al., 2015).
Evolution of the
Lusi Plumbing System
The 3-4 times increase in Lusi eruption rates on the 1st
of August likely represents a significant change in the subsurface plumbing
system feeding the mud volcano (and makes it difficult to reliably use later
measurements of geological events and geochemical data in the triggering controversy).
Possible causes for this eruption rate increase include:
1)
Formation of new fluid pathways, particularly
through the volcanics/volcaniclastics. This could be due to propagating
fractures or faults downwards over time, eventually enabling fluids from the Miocene
carbonates to flow into the Lusi shallow vent/fracture system by pathways other
than (or in addition to) the BJP-1 borehole (Tingay, 2010).
2)
The onset of a new additional fluid source
transmitted up a fault zone, such as deep hydrothermal fluids from the Ngimbang
Formation or deeper (Mazzini et al., 2012).
3)
Some sort of ‘unblocking’ of the initial Lusi
plumbing system, such as the creation of subsurface voids, or the movement of
debris within the BJP-1 borehole. This is often observed in borehole blowouts,
where the well can become partially or completely ‘bridged’ by debris, which
then shifts allowing increased flow (analogous to an artery becoming clogged
and then the blockage shifting or disaggregating).
The sudden increase in eruption rate in August 2006, regardless
of its cause, appears to be primarily increased fluid flow from the deep
carbonates (and possibly deeper formations), and likely indicates the
initiation or reactivation of faults and fractures in the subsurface. Indeed, there
has been reports from the local mudflow mitigation agency (BPLS) that some
fossils and rocks from the Ngimbang Formation have recently been found in Lusi
erupted material, which supports the recent modelling of InSAR data that
proposes that significant mass has been removed from both the Kalibeng clays
(source of most solids) and either the deep carbonates or Ngimbang formation
(Shirzaei et al., 2015).
The ongoing Lusi eruption has also been associated with
significant surface deformation, such as widespread subsidence (covering an
area of ~22km2) and the development of numerous small surface
faults, some with clear strike-slip offsets, in a wide area around the Lusi mud
volcano. Subsidence is a particularly significant issue, as areas near the main
crater have been measured to be subsiding at rates of 3-5cm a day (with occasional
sudden shifts of up to 1m), while areas even 3km away from Lusi are dropping at
2-3cm/month. The subsidence has caused dams to sometimes break, flooding nearby
houses, and was also responsible for the breaching of a nearby gas pipeline
that ignited and claimed 13 lives. Subsidence has also caused a number of small
shallow gas vents to appear, often around homes – though these have commonly
been ignited and put to good use as natural cooking fires!
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| Schematic evolution of the Lusi mud volcano from Roberts et al., 2011. |
The large-scale eruption of deep fluids, widespread
subsidence, and ongoing faulting all indicates that the Lusi mud volcano is
evolving in a manner similar to other major mud volcano systems, like those
widely studied in Azerbaijan (Stewart & Davies, 2006). Hence, it is thought
that the Lusi mud volcano system now comprises of a main vent, up which water
from the Miocene carbonates (and possibly deeper) flows, entraining Kalibeng
mud and water en route. However, a series of extensional faults has also
developed, forming a gradually growing elliptical collapse graben around the
entire mud volcano system (Roberts et al., 2011). Indeed, it is interesting to
note that the neighbouring Porong reefal mound displays a series of extensive
normal faults propagating from its crest that form a large (1km wide), circular,
300m deep depression in the overlying sedimentary sequence. This structure
overlying the Porong reefal mound is often considered to represent a previous
Lusi-like eruption that likely occurred 0.5-1.0 Ma, and is thought to be an
indicator of how Lusi will eventually evolve as it continues to erupt over the years,
or decades, to come.
Brief Notes on BJP-1
Drilling, Petrophysical and Pore Pressure Data
In my studies of the Lusi mud volcano disaster I have found
a large number of errors and inconsistencies in both published data and reports,
in addition to the usual variety of interpretations that can be made from data.
Errors and inconsistencies are particularly rife in the data from the BJP-1
well, and greatly add to the difficulties associated with studying this
disaster. I will document and explain some of the major inconsistencies and
claims made about drilling of the BJP-1 well in Part 3 of this blog. However, I
have also noticed significant errors in both the petrophysical and pore
pressure data associated with BJP-1.
In 2014 I spent a lot of time carefully compiling, reprocessing
and QC’ing all available drilling, petrophysical and pore pressure data, in
order to help understand Lusi’s origins, monitor its evolution and predict its
longevity. These datasets were published as part of Tingay (2015), and I am
more than happy to provide this data to anyone wishing to study the disaster.
References
Davies, R. J., R. E. Swarbrick, R. J. Evans, and M. Huuse, 2007, Birth of a mud
volcano: East Java, 29 May 2006: GSA Today, 17, 4–9.
Davies, R., M. Brumm, M. Manga, R. Rubiandini, R. Swarbrick,
and M. Tingay, 2008, The east Java mud volcano (2006 to present): an earthquake
or drilling trigger?: Earth and Planetary Science Letters, 272, 627-638.
Istadi, B., G. Pramono, and P. Sumintadireja, 2009, Modeling
study of growth and potential geohazard for LUSI mud volcano: East Java,
Indonesia: Marine and Petroleum Geology, 26, 1724–1739.
Kopf, A. J., 2002, Significance of mud volcanism: Reviews of
Geophysics, 40, 1005, doi: 10.1029/2000RG000093.
Kusumastuti, A., P. van Rensbergen, and J. Warren, 2002,
Seismic sequence analysis and reservoir potential of drowned Miocene carbonate
platforms in the Madura Strait, East Java, Indonesia: AAPG Bulletin, 86,
213-232.
Lupi, N., E. H. Saenger, F. Fuchs, and S. A. Miller, 2013,
Lusi mud eruption triggered by geometric focusing of seismic waves: Nature
Geoscience, 6, 642-646.
McMichael, H., 2009, The Lapindo mudflow disaster:
environmental, infrastructure and economic impact: Bulletin of Indonesian
Economic Studies, 45, 73-83.
Mazzini, A., H. Svensen, G. Akhmanov, G. Aloisi, S. Planke,
A. Malthe-Sørenssen, and B. Istadi, 2007, Triggering and dynamic evolution of
Lusi mud volcano, Indonesia: Earth and Planetary Science Letters, 261, 375–388.
Mazzini, A., G. Etiope, and H. Svensen, 2012, A new
hydrothermal scenario for the 2006 Lusi eruption, Indonesia. Insights from gas
geochemistry: Earth and Planetary Science Letters, 317, 305-318.
Oehler, D. Z., and C. C. Allen, 2010, Evidence for pervasive
mud volcanism in Acidalia Planitia, Mars: Icarus, 208, 636-657.
Ramdhan, A. M., F. Hakim, L. M. Hutasoit, N. R. Goulty, W.
Sadirsan, M. Arifin, F. Bahesti, K. Endarmoyo, R. Firmansyah, R. M. Zainal, M.
Y. Gulo, M. Sihman, P. H. Suseno, and A. H. Purwanto, 2013, Importance of
understanding geology in overpressure prediction: the example of the East Java
Basin: Proceedings of the 37th Annual Convention and Exhibition of the
Indonesian Petroleum Association, May 2013, IPA13-G-152.
Roberts, K. S., R. J. Davies, S. A. Stewart, and M. Tingay,
2011, Structural controls on mud volcano vent distributions: examples from Azerbaijan
and Lusi, east Java: Journal of the Geological Society, 168, 1013-1030.
Sawolo, N., E. Sutriono, B. P. Istadi, and A. B. Darmoyo,
2009, The LUSI mud volcano triggering controversy: Was it caused by drilling?:
Marine and Petroleum Geology, 26, 1766-1784.
Shara, E., J. A. Simo, A. R. Carol, and M. Shields, 2005,
Stratigraphic evolution of Oligiocene-Miocene carbonates and siliciclastics,
East Java basin, Indonesia: AAPG Bulletin, 89, 799-819.
Shirzaei, M., M. L. Rudolph, and M. Manga, 2015, Deep and shallow
sources for the Lusi mud eruption revealed by surface deformation: Geophysical
Research Letters, 42, 5274-5281.
Stewart, S.A., and R. J. Davies, 2006, Structure and
emplacement of mud volcano systems in the South Caspian Basin: AAPG Bulletin,
90, 771–786.
Tingay, M., R. Hillis, C. Morley, R. Swarbrick, and E.
Okpere, 2003, Variation in vertical stress in the Baram Basin, Brunei: tectonic
and geomechanical implications: Marine and Petroleum Geology, 20, 1201-1212.
Tingay, M., O. Heidbach, R. Davies, and R. E. Swarbrick,
2008, Triggering of the Lusi mud eruption: earthquake versus drilling
initiation: Geology, 36, 639-642.
Tingay, M., 2010, Anatomy of the ‘Lusi’ mud eruption, East
Java: Australian Society of Exploration Geophysicists 21st International
Conference and Exhibition, 1-6, doi:10.1071/ASEG2010ab241.
Tingay, M., 2015, Initial pore pressures under the Lusi mud
volcano, Indonesia: Interpretation, 3(1), SE33–SE49,
doi:10.1190/INT-2014-0092.1.
Tingay, M., M. L. Rudolph, M. Manga, R. J. Davies, and C.-Y.
Wang, 2015, Initiation of the Lusi mudflow disaster: Nature Geoscience,
doi:10.1038/ngeo2472.
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