Anatomy of the ‘Lusi’ Mud Eruption, East Java

  Anatomy of the ‘Lusi’ Mud Eruption, East Java Mark Tingay Tectonics, Resources and Exploration (TRaX), Australian School of Petroleum University of Adelaide, SA 5005, Australia Mark.tingay@adelaide.edu.au

  Figure 1. Aerial view of the Lusi mud eruption looking southwest (photo taken late may 2007). The mud flow has covered 7km2 of the cisty of Sidoarjo and displaced approximately 40000 people. The main vent has been erupting continuously since the 29 th of May 2006 at rates of up to 170000 m

  Key words: Sidoarjo Mudflow, Lusi, Mud volcano.

  /day. The mud flow has now covered over 700 hectares of land to depths of over 25 meters, engulfing a dozen villages and displacing approximately 40000 people. In addition to the inundated areas, other areas are also at risk from subsidence and distant eruptions of gas. However, efforts to stem the mud flow or monitor its evolution are hampered by an overall lack of knowledge and consensus on the subsurface anatomy of the Lusi mud volcanic system. In particular, the largest and most significant uncertainties are the source of the erupted water (shales versus deep carbonates), the fluid flow pathways (purely fractures versus mixed fracture and wellbore) and disputes over the subsurface geology (nature of deep carbonates, lithology of lithological unit between shales and carbonates). This study will present the first balanced overview of the anatomy of the Lusi mud volcanic system with particular emphasis on these critical uncertainties and their influence on the disaster.

  3

  Early in the morning of the 29th of May 2006, hot mud started erupting from the ground in the densely populated Porong District of Sidoarjo, East Java. With initial flow rates of ~5000 cubic meters per day, the mud quickly inundated neighbouring villages. After almost four years, the ‘Lusi’ eruption has expelled over 73 million cubic meters of mud at an average rate of approximately 64000 cubic meters per day and at maximum rates of 170000m

  SUMMARY

  The issue of triggering of the mudflow is not simply of academic or legal interest, but has significant implications for the 40000 victims displaced by the disaster, most of whom have not received full or extensive compensation or relief aid. The company responsible for drilling the Banjar Panji-1 well (Lapindo Brantas) has provided partial compensation to residents of four villages affected by the mudflow, while the Indonesian government has provided some relief to other affected people and has assumed control of the disaster zone. However, Lapindo Brantas have halted further compensation to the disaster victims (claiming the disaster is natural and not their responsibility), while international aid agencies will also not provide needed relief and support (claiming the disaster is man-made and thus should be funded by Lapindo Brantas). Thus, whilst the triggering issue continues to be debated, many victims of the disaster have lived for almost 4 years in refugee villages and shanty towns built adjacent to the disaster zone. Furthermore, knowledge of the subsurface anatomy of the Lusi mudflow is essential for predicting the likely longevity of the disaster, the possible evolution of the region (in particular the ongoing subsidence of the area, the reactivation of faults and possibility of caldera collapse) and whether there may be potential engineering solutions to kill or control the mudflow.

  3 /day. Approximately 73 million m3 of mud was erupted in the first 3 years, approximately 1/7 th the volume of Sydney harbour.

  2006 Yogyakarta earthquake (Mazzini et al., 2007; Sawolo et al., 2009). However, despite numerous papers and public debates, the controversy remains unresolved, primarily due to the many unknowns in the subsurface anatomy of the mud volcano, the uncertainties surrounding events in the weeks prior and following the initial eruption and discrepancies over interpretation of petroleum engineering data from the Banjar Panji-1 well (Davies et al., 2010; Sawolo et al., 2010).

  The Sidoarjo mud flow, also known as ‘Lusi’ (a contraction of Lumpur Sidoarjo) is a unique geological disaster that has ignited widespread scientific and political controversy. The mud flow was first observed in a rice paddy in the Porong district at approximately 5am on the 29

  th

  6.3 May 27

  w

INTRODUCTION AND BACKGROUND

  of a major town and caused more than US$550 million in damages (Figure 1; Cyranowski, 2007). Lusi is an example of a mud volcano, a relatively common geological feature in which subsurface mud is extruded at the surface. However, Lusi is unusual in that it is the first recorded instance of the birth of a new mud volcano within an urban region and thus represents a new type of geological disaster (Davies et al., 2006). Furthermore, there has been intense scientific and political scrutiny over the triggering of Lusi, with some researchers suggesting the mudflow resulted from a blowout in the Banjar Panji-1 well located 150m away (Davies et al., 2008; Tingay et al., 2008), while a competing theory maintains the disaster was initiated by the M

  2

  of May 2006 and has been erupting continuously ever since (almost 4 years at the time of writing). The mudflow has claimed 17 lives, displaced approximately 40000 people, inundated 7km

  th

REGIONAL GEOLOGY

  Hence, the stratigraphy under Lusi is herein revised to be: (i) Recent alluvium (alternating sands and shales; 0-290m); (ii) Pleistocene Pucangan Formation (alternating sands and shales; 290-900m); (iii) Pleistocene Upper Kalibeng undercompacted smectite-illite muds (900-1870m); (iv) Plio-Pleistocene low- porosity extrusive igneous rocks (1870-

  The mud being erupted from Lusi has varied slightly over the life of the mud volcano but can be broadly characterised as hot (70-100˚C) medium-grey slurry comprised of water (initially 60-80% water, but reducing over time and is currently 30-50% water) and a solid fraction comprised almost entirely of clays

  The major uncertainty surrounding the anatomy of the mudflow is the source (or sources) of the water component of the erupted mud and the pressures driving the mudflow. However, the origin of the solids being erupted at Lusi and the dominant shallow (<1200m) plumbing system is reasonably well constrained from surface measurements and is described in this section.

  Constrained Geological Aspects of the Lusi Mudflow

  One of the major contentious issues surrounding the Lusi mudflow is the nature of the subsurface plumbing system and the forces driving the eruption. Two significantly different models have been proposed for the subsurface anatomy of Lusi and these are, in turn, linked to the two competing theories on the triggering of the mudflow. One model, suggested by the proponents of the ‘drilling triggered’ theory, proposes that the Lusi mudflow is deep rooted and primarily driven by fluid escape from the deep carbonates (Davies et al., 2008; Tingay et al., 2008). The alternate model, suggested by the supporters of the ‘earthquake-trigger’ theory, proposes that Lusi is shallow-rooted and driven by fluid escape and liquefaction of the Upper Kalibeng clays (Mazzini et al., 2007; Istadi et al., 2009; Sawolo et al., 2009). Determination of the subsurface anatomy of Lusi thus has significant ramifications for determining the likely triggering mechanism for the Lusi eruption. However, prior to discussion of each of the proposed models for the anatomy of Lusi, it is necessary to first discuss aspects of the Lusi subsurface anatomy that are well constrained from surface measurements.

  LUSI’S SUBSURFACE PLUMBING SYSTEM

  ≈2833m) and (v) Miocene Tuban reefal carbonates ( ≈2833-≈3500m).

  2 This paper presents an overview of the geology of the Lusi

  disaster and, in particular, provides new information on the subsurface geology and highlights the key uncertainties in the anatomy of the mud volcano. Furthermore, all papers on the Lusi mudflow to date have supported a particular triggering mechanism and thus presented a subsurface geology that is somewhat biased towards that mechanism. This study attempts to provide the first unprejudiced summary of the anatomy of the Lusi mud volcano, presenting both proposed models of the subsurface geometry along with their pros and cons.

  3

  ρ=2.55-2.65 g/cm3; DT=160-120 µs/ft). The high density and fast p-wave velocity of these volcanic sequences indicates that these volcanic rocks have extremely low porosity (<5% assuming a grain density of 2.68 g/cm

  In addition to the younger reinterpretation of the carbonates, new evidence also suggests that the lithology of the reported volcaniclastic sands requires correcting. This unit had not been previously observed in hydrocarbon exploration and production wells in the area and was reported as being comprised of volcaniclastics by the on-site mud logging (and then in all publications examining the Lusi disaster). However, detailed reanalysis of the cuttings reveals that this unit is actually comprised of volcanic rocks (primarily dacites and welded tuffs) that had been ground into mostly sand-sized fragments by the drilling process and, thus, mistakenly interpreted as volcaniclastic sands by the mud logger. The new interpretation of these units as extrusive igneous rocks is supported by petrophysical log data collected in this interval that reveals a remarkably uniform, very dense and fast formation (

  New evidence indicates two major changes to this stratigraphy. Firstly, the reefal carbonates have been commonly described as the Kujung Carbonates, which is a major reservoir rock within the East Java Basin, particularly offshore in the Madura Strait (Sharaf et al., 2005). The Kujung Carbonate is an early-late Oligocene (22-28 Ma) transgressive reefal formation. However, a red algal fragment from the carbonates at the top of the nearby and stratigraphically equivalent carbonate build up in the nearby Porong-1 well (7 km ENE of Lusi) was dated by strontium isotope ratios as being formed in approximately 16 Ma (Kusumastuti et al., 2002). Hence, the carbonates underneath Lusi are not the Oligocene Kujung formation, but are most likely the Middle Miocene Tuban Formation (22-15 Ma; Sharaf et al., 2005). The known reservoir and fluid properties from other wells penetrating the Kujung Carbonates has been used for modelling possible longevity of Lusi as well as in arguments as to whether Lusi was triggered by drilling (Sawolo et al., 2009; Swarbrick et al., under review). However, the new evidence that the carbonates under Lusi are probably of the younger Tuban Formation renders these previous calculations using Kujung Formation data spurious.

  New Revisions to the Stratigraphy below Lusi

  ≈2833m) and (v) Oligocene Kujung reefal carbonates ( ≈2833-≈3500m).

  The Lusi mud volcano (7º 31’ 37.8”S, 112º 42’ 42.4”E) is located in the city of Sidoarjo, approximately 25 km south of Surabaya, the largest city in Eastern Java, Indonesia. Lusi is located within the East Java Basin, an E-W 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 of the East Java Basin in the region around Lusi are comprised of shallow marine clastics and carbonates, marine muds, volcaniclastic sediments and volcanic units from the nearby Penanggungan volcanic complex (located 15km to the SW of Lusi). The subsurface geology of Lusi was originally reported in many studies to be comprised of the following units (Davies et al., 2006; Mazzini et al., 2007; Davies et al., 2008; Tingay et al., 2008; Sawolo et al., 2009). (i) Recent alluvium (alternating sands and shales; 0-290m); (ii) Pleistocene Pucangan Formation (alternating sands and shales; 290-900m); (iii) Pleistocene Upper Kalibeng undercompacted smectite-illite muds (900-1870m); (iv) Pleistocene Upper Kalibeng volcaniclastic sands (1870-

  ) and, unless extensively fractured, are also likely to have low permeability. The reinterpretation of this unit as low porosity (and possibly sealing) volcanic rocks, rather than sand-sized (and likely permeable) volcaniclastics, has significant implications for the subsurface plumbing system in the region.

  3

  had been pumped from the holding ponds to the Porong River. Hence, the total volume of mud erupted by Lusi in its first three years was approximately 73 million m

  proposes that the main source of fluid for Lusi, and primary pressure drive of the eruption, is the deep Miocene carbonates (likely Tuban Formation). This model has primarily been suggested by authors supporting the hypothesis that Lusi was triggered by a blowout in the Banjar Panji-1 well (Davies et al., 2008; Tingay et al., 2008). Under this model, overpressured waters hosted by the carbonates escape upwards via the uncased section of the Banjar Panji-1 wellbore and, most likely, also via deep recently created or reactivated faults and fractures. The fluids pass through the Upper Kalibeng clays which, being highly thixotropic, are readily entrained creating the watery slurry that is erupted to the surface via the shallow feeder system (conical vent of intersecting conjugate fault zones).

  Model 1: Fluids Primarily from Deep Carbonates

  of August 2006, to a maximum of 155 bubblers in 2009 to, at the time of writing, 39 active bubblers at a maximum distance of 1.2 kilometres from the main vent (source: BPLS). Furthermore, there is a geometric distribution of the bubblers, with most occurring on two linear trends passing through the main vent (source: BPLS). The predominant trend is oriented approximately NE-SW, and has been proposed to be an extension of the fault proposed to have formed the nearby Watukosek escarpment, while the secondary trend is oriented NW-SE (Mazzini et al., 2007). The two dominant trends of secondary eruptions indicate the presence of a currently active NE-SW and NW-SE trending fault network underneath the Lusi mud volcano. Davies et al. (2006) initially proposed that the shallow feeder system under Lusi was comprised of a major newly initiated tensile fracture. However, this is inconsistent with the local NNE-SSW present-day maximum horizontal stress orientations for the region determined from by earthquake focal mechanism solutions (Tingay et al., 2010). Tensile fractures open against the least principal stress and would be expected to strike NNE- SSW near Lusi. However, the present-day maximum horizontal stress direction, and earthquake focal mechanism solution estimate of a strike-slip faulting stress regime, is consistent with the NE-SW and NW-SE fracture trends being approximately conjugate sub-vertical strike-slip fault zones.

  rd

  /day) eruptions (termed ‘bubblers’) of water, mud or gas have occurred up to 4.5 kilometres from the main vent. The number of secondary eruptions has varied from 23 on the 3

  3

  Almost all of the mudflow has erupted from the main vent. However, a number of minor secondary sites of eruption have also occurred in the region. Three moderately-sized, but short- lived (lasting approximately one week), sand and mud eruptions occurred up to 1000m from the main vent in the days following the initial Lusi eruption. Since then, numerous very small (<10 m

  The shallow subsurface geometry of the main vent from the surface to the Upper Kalibeng clays is uncertain. Seismic images of major mud volcanoes in Azerbaijan commonly suggest that mud feeder pipes are conical in shape (Stewart and Davies, 2006). However, analysis of exposed Miocene- Pliocene mobile shale systems in Brunei indicates that mud volcano feeder systems may be comprised primarily of planar shale dykes entrained up faults or tensile fractures (Morley et al., 1998; Tingay et al., 2003). The 100 m wide circular main vent and the extremely high flow rate suggest that the feeder system under Lusi is either conical in shape or comprised of several very large open and intersecting fractures. Such an open pipe-like shallow feeder channel is consistent with measurements obtained during the 2007 attempt to stop Lusi by dropping sets of concrete balls tied together by heavy chain into the main crater. Whilst the attempt to drop these ‘balls and chains’ down the vent failed to stop or reduce the mud flow, cables attached to several of the concrete balls showed that some of the sets dropped down to depths of 800-1000 m. This indicates that a major feeder pathway is open to a width of at least 30cm down to a depth of 1000m.

  3 /day.

  /day over the first three years, and a significant reduction on the average and evolution (Istadi et al., 2009; Swarbrick et al., under review). Furthermore, flow rate, whilst fluctuating from day to day, has been gradually diminishing since September 2006 and, at the time of writing, is estimated as being approximately 20000-30000 m

  3

  (ignoring potential errors due to volume additions through rainfall and reductions due to evaporation and earlier unmonitored mud pumping and sluicing of mud into the river). This equates to an average flow rate of approximately 64000 m

  3

  3

  (solid fraction is 80-90% clays with minor silts and sand-sized grains). The mud has an original overall density of 1.3-1.4 g/cm

  and that approximately 8 million m

  3

  /day (Davies et al., 2006; Mazzini et al., 2007; Istadi et al., 2009). However, the Sidoarjo Mudflow Mitigation Agency (Badan Penanggulangan Lumpur Sidoarjo; BPLS) calculated in early June 2009 that the volume of mud contained in holding ponds at the time was approximately 65 million m

  3

  /day, with average rates previously estimated at 90000-100000 m

  3

  The solid fraction of the muds being erupted at Lusi is comprised primarily of illite, smectite and some chlorite, consistent with the sediments observed from 1341-1828m depth in the Banjar Panji-1 well (Mazzini et al., 2007). Furthermore, the erupted muds show vitrinite reflectances of 0.55-0.69% Ro, correlating with organic matter maturations of Ro>0.65% observed at depths of >1700m in Banjar Panji-1 (Mazzini et al., 2007). Finally, biostratigraphical analysis of the erupted mud reveals the presence of forams and nannofossils observed in cuttings collected from 1219-1828m depth in Banjar Panji-1. Thus, the solid fraction of the mud being erupted at Lusi can be well constrained as primarily coming from the Upper Kalibeng Clays from between 1219- 1828m depth (Mazzini et al., 2007). The eruption of mud from Lusi is predominately from one vent, termed the ‘main vent’ or ‘big hole’. The circular main vent is approximately 100 m in diameter and has been flowing at rates of up to 170000 m

  δD of -12.7‰ to -14.4‰) with respect to seawater. The temperature and geochemistry of the water indicates a source depth of >1700m (Mazzini et al., 2007).

  18 O=9.0‰) and depleted in deuterium (

  δ

  18 O (

  , but has been slowly increasing as the amount of solids has increased (Mazzini et al., 2007). The waters being erupted are approximately 61% the salinity of seawater (11300 ppm chloride, 7300 ppm sodium; Mazzini et al., 2007) and are enriched in

  3

  This model has several supporting pieces of evidence. Firstly, the adjacent and stratigraphically identical Porong and Kedeco-11C carbonate mounds (located on a trend to the ENE from Lusi) both contain extensive circular collapse structures with faults propagating out of the crest of the carbonate mounds (Kusumastuti et al., 2002). These large collapse structures are over 1 km wide and 300m deep and, though not

2 S, which is

2 S release may indicate penetration of, or connection

  w

  /day). However,

  3

  /day for over three years. There is no known mechanism by which such vast amounts of shale could continuously undergo liquefaction over such a long period of time. Finally, Lusi is the only mud volcano ever recorded that has had such large flow rates for a sustained period of time (Kopf, 2002; Davies et al., 2006). Natural mud volcanic systems have never been reported to behave in such a manner. Natural mud volcano systems worldwide tend to flow at rates of only a few tens to hundreds of cubic metres per day, but can occasionally have eruptions that are short-lived (1-14 days) and extremely violent (100000-1000000 m

  3

  /day and to sustain average flow rates of 64000 m

  3

  2006 Yogyakarta earthquake and thus is it uncertain as to why only the Yogyakarta earthquake triggered the mudflow (Tingay et al., 2008; Davies et al., 2008). There is also the improbability and likely impossibility for largely impermeable shales, even undergoing liquefaction, to flow at rates of up to 170000 m

  th

  This model is supported by analogue models that reveal that active faults can cause thixotropic shales to become mobile and erupt along a fault zone (Mazzini et al., 2009). Furthermore, large earthquakes (>Mw7.5) have remotely triggered increases in mud volcano flow rates in Iran and Azerbaijan (Kopf, 2002; Mellors et al., 2007). In addition, there is, as yet, no direct evidence suggesting any involvement of fluids from the deep carbonates in the mud volcanic system. For example, no fragments of Miocene limestone, nor Plio- Plesitocene volcanic rocks have been found in the erupted muds (although these lithologies are less prone to erosion and large fragments of these lithologies are unlikely to be carried to the surface). Furthermore, a three month micro-seismicity survey only reported only one event from deeper than 2km depth (though only a few dozen micro-seismic events were recorded and these indicated no spatial trend and failed to provide conclusive evidence of an active subsurface fault network; source: BPLS). Finally, the Banjar Panji-1 well suffered minor losses (20 barrels) seven minutes after the Yogyakarta earthquake, suggesting that the passage of seismic waves may have opened up some fractures intersecting the wellbore (Sawolo et al., 2009). There are also several issues concerning the model in which all of the mud is derived from the Upper Kalibeng clays. Firstly, it is not known how the Yogyakarta earthquake could trigger fault reactivation under Sidoarjo 250 km away. Analysis of all known methods for triggering of fault reactivation and clay liquefaction via remote seismicity (dynamic stress changes due to direct shaking, co-seismically induced static stress changes; post-seismic relaxation of static stress changes, and; poroelastic rebound effects) indicate that the Yogyakarta earthquake was at least an order of magnitude too small to have triggered fault reactivation under Sidoarjo. earthquake were in the order of +33 kPa (smaller than tidal forces), whilst pressure changes due to the kick in Banjar Panji-1 were over three orders of magnitude greater (Tingay et al., 2008; Davies et al., 2008). Furthermore, there have been several recorded earthquakes that were larger and nearer to Sidoarjo than the May 27

  6.3 Yogyakarta earthquake 250 km away (Mazzini et al., 2007; Sawolo et al., 2009). The highly thixotropic nature of the Upper Kalibeng clays makes them extremely susceptible to liquefaction if ‘disturbed’ by shaking or fault motion. Furthermore, fault zones are often extremely permeable during the moment of rupture, providing a pathway for liquefied and mobile shales to escape to the surface. In addition, sonic and density logs from Banjar Panji-1 indicate that the Upper Kalibeng Clays are significantly undercompacted and have porosities approximately 5-12% greater than would be predicted under normal compaction. Undercompaction in clays typically indicates that the shales are overpressured by means of disequilibrium compaction (Osborne and Swarbrick, 1997) and thus these high fluid pressures may add further driving force to the mud volcanic system. Mazzini et al., 2007 suggest that even greater overpressures may have been generated in the Upper Kalibeng clays by the release of inter-layer bound water during the diagensis of smectite into illite. However, smectite to illite transition has been largely dispelled as an overpressure generation mechanism (Osborne and Swarbrick, 1997) and thus is unlikely to provide any further increase the pore fluid pressures driving Lusi.

  4

  yet studied in detail with respect to Lusi, are possibly Lusi- type mud eruptions that occurred during the Quaternary and were sourced by these adjacent and slightly shallower reefal mounds. Further supporting evidence for a deep carbonate primary source for the waters erupted at Lusi comes from the very high pore fluid pressures (18.5 MPa/km) and the high porosity and permeability observed in these carbonates in the adjacent Porong-1 well, making the carbonates appear to be the ideal and best suited primary source of water erupted at Lusi.

  of September 2006, which may indicate changing to a plumbing system primarily flowing up faults and fractures) and the wellbore is likely to have been eroded larger over time. Furthermore, and quite significantly, all discussions of this model to date ignore the additional contribution of fluids from the Upper Kalibeng clays. Entraining large volumes of clays (the mud was initially 20-40% clay and has thickened over time to a current consistency of 50-70% clay) also involves the adding of pore fluids within the clays into the mud erupted at the surface. Hence, under this model, the erupted fluids will be primarily sourced from the carbonates but must also contain a significant (and increasingly dominant) amount of pore waters from the Upper Kalibeng clays.

  st

  /day on the 1

  3

  /day to over 100000m

  3

  However, under the deep carbonate sourced model it is not necessary for all fluids to flow via the wellbore (Lusi suddenly increased from <50000m

  3 /day observed at Lusi (Sawolo et al., 2009).

  with, the carbonates, there was no instantaneous kick suggesting very high magnitude overpressures. Furthermore, it is not certain whether a 12.25” wellbore would be able to achieve sufficient flow rates to explain the up to 170000m

  routinely released from carbonate mounds drilled in the area, erupted from Banjar Panji-1 when it kicked and from the Lusi main vent in its first few days). While this loss of circulation and H

  There are also several issues that make this model highly uncertain. First, it is not known whether the Banjar Panji-1 well intersected the deep carbonates (Sawolo et al., 2009). No cuttings were returned from the bottom several meters of the wellbore when there was a complete loss of circulation and drilling was halted (although large amounts of H

  The second model proposed for the geometry and driving forces of the Lusi mud flow is that both the water and solids erupted from Lusi are entirely derived from the Upper Kalibeng clays. Under this model the Lusi eruption was the result of liquefaction of the Upper Kalibeng clays caused by reactivation of a pre-existing NE-SW oriented fault zone (often termed the Watukosek Fault), with the reactivation being triggered by the May 27 2006 M

IMPLICATIONS OF REVISED LUSI ANATOMY

  5

  /day (rather than 90000-100000 m

  The Lusi mud eruption and, in particular, the debate over the triggering of the disaster is a significant social, political and legal issue. The author has publicly argued in several previous publications that Lusi was most likely triggered by a underground blowout in the Banjar Panji-1 well. However, the purpose of this study is to provide a balanced and unbiased overview of the geology and plumbing system underneath Lusi. Thus, I have, wherever possible, avoided discussion on the theories for the triggering of the mud flow. The information presented herein is aimed at reducing the

  Determination of the subsurface geology and plumbing system of the Lusi mud flow is an essential first step towards predicting the evolution of the mud volcano, likely duration of the eruption and for resolving the long-running debate on triggering of this unique geological disaster.

  The existing data set is insufficient to unequivocally evidence that supports it, but also has currently unexplained criticisms. (xi)

  The alternate model proposes that the mud is entirely derived from the Upper Kalibeng clays, which have been remobilised due to remote triggering of pre- existing faults underneath Sidoarjo. (x)

  (vii) The main uncertainty regarding the anatomy of the Lusi mud volcano is the source of the water component of the erupted mud. The temperature and chemistry of the waters indicate a source depth of >1700 m. Two models for the anatomy of Lusi have been suggested, each genetically linked to a proposed trigger for the disaster. (viii) One model proposes that fluids are primarily derived from the overpressured deep carbonates, which flow up the Banjar Panji-1 wellbore and reactivated faults, entraining the Upper Kalibeng clays (and further pore fluid water) en route to the surface. (ix)

  (vi) There are a large number of minor secondary eruption sites (water, mud and gas) that is being feed by a currently active NE-SW and NW-SE conjugate strike- slip fault system, with the two fault zones intersecting near the main Lusi vent.

  (v) The mud feeder system to the main vent, which extends down to at least the Upper Kalibeng clays, is either a approximately conical pipe or formed by the intersection of two main fault zones and is at least 30 cm wide down to a depth of 1000 m.

  3 /day).

  /day) and has been reducing over time (currently 20000-30000 m

  3

  3

  such major mud eruptions are only ever recorded on deep- rooted mud volcanic systems that are primarily driven by large overpressured sources and thus the flow rates observed in Lusi are not consistent with a shallow-rooted liquefaction mechanism.

  Average flow rate for Lusi is significantly lower than what has been previously reported by scientific publications and in the media. Average flow rates over the first 3 years are approximately 64000 m

  The solid fraction of the mud erupted by Lusi is sourced from the Upper Kalibeng clays at between 1219-1828m depth (Mazzini et al., 2007). (iv)

  The deep carbonates are overlain by extrusive igneous rocks (dacites, andesites, welded tuffs) that have very low porosities (<5%) and are likely to have low permeabilities (not permeable volcaniclastic sands). (iii)

  Kujung carbonates). (ii)

  The main issues and conclusions from this study are summarised below. (i) The deep carbonates underneath Lusi are Miocene in age and likely to be the Tuban Formation (not the Oligocene

  This study provides an up-to-date overview of the geology of the Lusi mud flow and is also the first paper to provide a balanced and unbiased summary of the main anatomical models for this unique geological disaster. Whilst the triggering debate is not covered in any detail herein, the revised stratigraphy, summary of the geology extrapolated from surface measurements and the discussion of both models for Lusi’s subsurface plumbing system have implications for the triggering debate and for the possible evolution and longevity of this disaster.

  SUMMARY

  /day are impossible up at 12.25’ borehole. Furthermore, the original casing design for the Banjar Panji-1 well assumed the target carbonates would have relatively mild overpressures, as this is routinely observed in the offshore Kujung carbonate reservoirs. However, the neighbouring carbonate mound penetrated by Porong-1 7 km away encountered very high overpressures. More recently, Swarbrick et al. (under review) attempted to calculate the likely duration of the Lusi mud flow assuming the well established, but now inappropriate, flow rates, porosities and permeabilities of the Kujung carbonates. Given the potential legal and social significance of the Lusi disaster, prior use of information from the Kujung carbonates cannot be considered as valid. The new reinterpretation of the unit overlying the carbonates and underlying the Upper Kalibeng clays being comprised of low porosity and tight extrusive igneous rocks, rather than permeable volcaniclastic sediments has major implications for the hydrodynamics of the region. The model in which the fluids are primarily derived from the deep carbonates is not feasible unless the carbonates are sealed, and thus was not likely under the initially proposed stratigraphy. Furthermore, in the clay liquefaction model, it has been proposed that the long term high flow rates are the result of additional aquifer drive from the previously considered volcaniclastic sands. Yet, this theory is unlikely under the revised stratigraphy.

  3

  The revision of the stratigraphy underneath Lusi has some significant implications. All studies to date on the Lusi mud flow have considered the deep carbonates to be the Kujung Formation and have made assumptions based on the known properties of this unit. For example, Sawolo et al. (2009) use the well established flow rates from existing production wells in the Kujung Formation to argue that flow rates of 170000 m

  This study provides an up-to-date overview of the geology of the Lusi mud flow and also is the first paper to provide a balanced, and hopefully unbiased, summary of the main anatomical models for this unique geological disaster. Whilst the triggering debate is not covered in any detail herein, the revised stratigraphy, summary of the geology extrapolated from surface measurements and the discussion of both models for Lusi’s subsurface plumbing system have implications for the triggering debate and for the possible evolution and longevity of this disaster.

AUTHORS NOTE

• – implications for shale injection. In: Van Rensbergen, P., Hillis, R.R., Maltman, A.J., and, Morley, C.K. (eds.) London Special Publication, London, 216, 369-379. Tingay, M., Heidbach, O., Davies, R., and Swarbrick, R.E., 2008, Triggering of the Lusi mud eruption: earthquake versus drilling initiation: Geology, 36, 639-642. Tingay, M., Morley, C.K., King, R.E., Hillis, R.R., Hall, R., and, Coblentz, D., 2010, The Southeast Asian Stress Map: Tectonophysics, 482, 92-104.

  6

  widespread variations or inaccuracies in the reported geology under Lusi and to summarize, without preference, the two main models for Lusi’s plumbing system and source of erupted water. This study is not designed to prove or disprove either theory or model, but rather to give a review of the current state of knowledge of this disaster.

  ACKNOWLEDGMENTS

  This summary has been written following discussions with numerous researchers. Particular thanks go to Richard Davies, Dick Swarbrick, Bambang Istadi, Rocky Sawolo, Soffian Joyopranoto, Handoko Wibowo, Adriano Mazzini, Michael Manga and Oliver Heidbach.

  REFERENCES

  Cyranoski, D., 2007, Indonesian eruption: Muddy waters: Nature, 445, 812–815. Davies, R.J., Swarbrick, R.E., Evans, R.J., and Huuse, M., 2007, Birth of a mud volcano: East Java, 29 May 2006: GSA Today, 17, 4–9. Davies, R., Brumm, M., Manga, M., Rubiandini, R., Swarbrick, R., and Tingay, M., 2008, The east Java mud volcano (2006 to present): an earthquake or drilling trigger?: Earth and Planetary Science Letters, 272, 627-638. Davies, R.J., Manga, M., Tingay, M., Lusianga, S., and Swarbrick, R., 2010 (in press), DISSCUSSION: Sawalo et al. (2009) The LUSI mud volcano controversy: Was it caused by drilling?: Marine and Petroleum Geology, 27, doi:10.1016/j.marpetgeo.2010.01.019. Istadi, B.P., Pramono, G.H., Sumintadireja, P., and Alam, S., 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, v. 40, doi: 10.1029/2000RG000093. Kusumastuti, A., van Rensbergen, P., and Warren, J., 2002, Miocene carbonate platforms in the Madura Strait, East Java, Indonesia: AAPG Bulletin, 86, 213-232. Mazzini, A., Svensen, H., Akhmanov, G.G., Aloisi, G., Planke, S., Malthe-Sørenssen, A., and Istadi, B., 2007, Triggering and dynamic evolution of LUSI mud volcano, Indonesia: Earth and Planetary Science Letters, 261, 375–388. Mazzini, A., Nermoen, A., Krotkiewski, M., Podladchikov, Y., Planke, S., and, Svensen, H., 2009, Strike-slip faulting as a trigger mechanism for overpressure release through piercement structures. Implications for the Lusi mud volcano, Indonesia: Marine and Petroleum Geology, 26, 1751-1765. Mellors, R., Kilb, D., Aliyev, A., Gasanov, G., and Yetirmishli, G., 2007, Correlations between earthquakes and large mud volcano eruptions: Journal of Geophysical Research, 112, B04304. Morley, C.K., Crevello, P., and Ahmad, Z.H., 1998, Shale tectonics and deformation associated with active diapirism: the Jerudong Anticline, Brunei Darussalam: Journal of the Geological Society, London, 155, 475-490. Osborne, M. J., and Swarbrick, R.E., 1997, Mechanisms for generating overpressure in sedimentary basins: a reevaluation: AAPG Bulletin, 81, 1023-1041. Sawolo, N., Sutriono, E., Istadi, B.P., and Darmoyo, A.B., 2009, The LUSI mud volcano triggering controversy: Was it caused by drilling?: Marine and Petroleum Geology, 26, 1766- 1784. Sawolo, N., Sutriono, E., Istadi, B.P., and Darmoyo, A.B., 2010 (in press), Was LUSI caused by drilling? – Authors reply to discussion: Marine and Petroleum Geology, 27, doi:10.1016/j.marpetgeo.2010.01.018. Shara, E., Simo, J.A., Carol, A.R., and Shields, M., 2005, Stratigraphic evolution of Oligiocene-Miocene carbonates and siliciclastics, East Java basin, Indonesia: AAPG Bulletin, 89, 799-819. Stewart, S.A., and Davies, R.J., 2006, Structure and emplacement of mud volcano systems in the South Caspian Basin: AAPG Bulletin, 90, 771-786. Swarbrick, R.E., Mathias, S.A., Davies, R.J., and Tingay, M., under review, Probabilistic longevity estimate for the LUSI mud volcano, East Java: Geophysical Research Letters. Tingay, M., Hillis, R., Morley, C., Swarbrick, R., and, Okpere,

  E., 2003, Pore pressure/stress coupling in Brunei Darussalam