The Sidoarjo mudflow (commonly known as Lumpur Lapindo, wherein lumpur is the Indonesian word for mud; and as Lusi (short for Lumpur Sidoarjo) is the result of an erupting mud volcano in the subdistrict of Porong, Sidoarjo, in East Java, Indonesia, that has been active since May 2006. It is the largest mud volcano in the world. Responsibility for the disaster was assigned to the blowout of a natural gas well drilled by Lapindo Brantas, although company officials contend it was caused by a very distant earthquake that occurred in a different province.
At its peak, the blowout spewed up to of mud per day. By mid-August 2011, mud was being discharged at a rate of per day, with 15 bubbles around its gushing point. This was a significant decline from the previous year, a rate of per day, with 320 bubbles. Initial estimates suggested that the flow would continue for 25 to 30 years. Although the Sidoarjo mud flow has been contained by levees since November 2008, resultant floodings regularly disrupt local highways and villages, and further breakouts of mud are still possible.Sidoarjo mud flow from NASA's Earth Observatory, posted 10 December 2008. This article incorporates public domain text and images from this NASA webpage.
Geological setting Mud volcano systems are fairly common, particularly in the Indonesian province of East Java. Beneath the island of Java is a half-graben lying in the east–west direction, filled with over-pressurized marine carbonates and marine muds. It forms an inverted extensional basin that has been geologically active since the Paleogene epoch. The basin started to become overpressurized during the Oligo-Miocene period. Some of the overpressurized mud escapes to the surface to form mud volcanoes, which have been observed at Sangiran Dome near Surakarta (Solo) in Central Java and near Purwodadi city, west of Lusi.
The East Java basin contains a significant amount of oil and gas reserves, therefore the region is known as a major concession area for mineral exploration. The Porong subdistrict, south of Sidoarjo city, is known in the mineral industry as the Brantas Production Sharing Contract, an area of approximately that consists of three oil and gas fields: Wunut, Carat, and Tanggulangin. As of 2006, three companies—Santos (18%), MedcoEnergi (32%), and PT Lapindo Brantas (50%)—had concession rights for this area; PT Lapindo Brantas acted as an operator.
Chronology On 28 May 2006, PT Lapindo Brantas targeted gas in the Kujung Formation carbonates in the Brantas PSC area by drilling a borehole named the "Banjar-Panji 1 exploration well". In the first stage of drilling, the drill string first went through a thick clay seam ( deep), then through sands, shales, volcanic debris, and finally into permeable carbonate rocks. The borehole was cased down to 1,091 m (3,579 ft). At 5:00 a.m. local time (UTC+7) on 29 May 2006, after the well had reached a total depth of , this time without a protective casing, water, steam, and a small amount of gas erupted at a location about 200 m southwest of the well. Two further eruptions occurred on the second and the third of June about 800–1,000 m northwest of the well, but these stopped on 5 June 2006. During these eruptions, hydrogen sulfide gas was released, and local villagers observed hot mud, thought to be at a temperature of around .
A magnitude 6.3 earthquake occurred in Yogyakarta at ~06:00 local time on 27 May 2006, approximately southwest of Sidoarjo. It has been suggested that a small (20 barrel) mud loss occurred in the Banjar Panji-1 well seven minutes after the earthquake (consistent with the time taken for the seismic waves to reach the Lusi location), though there is no clear report of these losses in the drilling data, and it has also been alternatively reported that these losses occurred one hour before the earthquake. The well suffered a complete loss of circulation at 12:50 p.m. local time on 26 May 2006, which was between 1.5 and 4.75 hours after three large aftershocks. A loss of circulation happens when drilling mud—necessary for maintenance of well bore stability—that is pumped down a shaft does not return to the surface but is lost into an opening or a fault system. This mud loss problem was finally stopped when "loss circulation material" was pumped into the well, a standard practice in drilling an oil-and-gas well. A day later, the well suffered a "kick", an influx of formation fluid into the well bore. The kick was reported by Lapindo Brantas drilling engineers as having been killed within three hours, though alternative interpretations of drilling records, specifically ongoing fluctuations in downhole drill-pipe pressure, indicate that the kick continued for at least 24 hours. Early the next day, on 29 May 2006, steam, water, and mud began erupting up to above the well, a phenomenon that is now known as the "Lusi mud volcano". Dense drilling mud and cement were pumped down the Banjar Panji-1 well at various times in the 48 hours after the mudflow started, in an attempt to kill the surface mud eruption. Lapindo Brantas daily drilling records state that "bubble intensity reduced and elapse time between each bubble is longer" after pumping dense drilling mud down the well, indicating direct communication between Banjar Panji-1 and the Sidoarjo mudflow.
Possible causes The Lusi eruption was a major disaster for the people living nearby, with the loss of homes, other properties, as well as livelihoods.
To explain what triggered the mud volcano, three hypotheses have been suggested, though none has won universal support: Drilling-induced fracturing or fault reactivation (reflecting a human-made event) Earthquake-triggered fault reactivation (reflecting a natural event) Geothermal processes (reflecting geothermal heating)
Drilling-induced fracturing From a model developed by geologists working in the UK, the drilling pipe penetrated the overpressurized limestone, causing entrainment of mud by water. Whilst pulling the drill string out of the well, there were ongoing losses of drilling mud, as demonstrated by the daily reports stating "overpull increasing", "only 50% returns", and "unable to keep hole full". The loss of drilling mud and associated drop in downhole mud weight eventually resulted in a drilling kick, with over 365 barrels of fluid erupting at the Banjar Panji-1 wellhead. Blowout preventers were closed to help kill the kick, which resulted in a spike in downhole pressure within the wellbore. The drilling-induced triggering model proposes that the increase in pressure within the wellbore was sufficiently high to induce a large hydraulic fracture in the formation. The extra pressure caused the hydraulic fractures to propagate 1–2 km to the surface and emerge 200 m away from the well. The lack of protective casing in the bottom 1,742 m of the borehole is considered a key reason why the drilling kick could not be controlled and why pressures during the kick were high enough to initiate hydraulic fracturing. Alternatively, it has also been suggested that the increased fluid pressure in the borehole, due to the kick, may have triggered reactivation of a nearby fault system, rather than hydraulic fracturing (in a similar manner to how fluid injection can induce seismicity). Though steel casing is used to protect the well bore in oil or gas exploration, this can only be applied in stages after each new section of the hole is drilled; see oil well.
The relatively small distance, around , between the Lusi mud volcano and the Banjar Panji-1 well may not be a coincidence, as less than a day before the start of the mudflow, the well suffered a kick. Lapindo's analysis suggests that the well has a low resistance to a kick. Similarly, a NE–SW crack in the surface in the drill site may be evidence of an underground blowout. The well may have suffered an underground blowout that resulted in a surface breach.
Earthquake-induced fault reactivation The relatively close timing of the Yogyakarta earthquake, the problems of mud loss and kick in the well, and the creation of the mud volcano continue to interest geoscientists. Experts from Norway, Russia, France, and Indonesia have suggested that the shaking caused by the earthquake may have induced liquefaction of the underlying Kalibeng clay layer, releasing gases and causing a pressure change large enough to reactivate a major fault nearby (the Watukosek fault), creating a mudflow path that caused Lusi.
They have identified more than ten naturally triggered mud volcanoes in the province of East Java, with at least five near the Watukosek fault system, confirming that the region is prone to mud volcanism. They also showed that surface cracks surrounding Lusi predominantly run NE–SW, the direction of the Watukosek fault. Increased seep activity in the mud volcanoes along the Watukosek fault coincided with the 27 May 2006 seismic event. A major fault system may have been reactivated, resulting in the formation of a mud volcano.
Geothermal process Lusi is near the arc of volcanoes in Indonesia where geothermal activity is abundant. The nearest volcano, the Arjuno-Welirang complex, is less than 15 km away. The hot mud suggests that some form of geothermal heating from the nearby magmatic volcano may have been involved.
Investigations Cause Controversy exists around what triggered the eruption and whether the event was a natural disaster or not. According to PT Lapindo Brantas, it was the 2006 Yogyakarta earthquake that triggered the mudflow eruption, and not their drilling activities. Two days before the mud eruption, an earthquake of moment magnitude 6.3 hit the south coast of Central Java and Yogyakarta provinces, killing 6,234 people and leaving 1.5 million homeless. At a hearing before parliamentary members, senior executives of PT Lapindo Brantas argued that the earthquake was so powerful that it had reactivated previously inactive faults and also created deep underground fractures, allowing the mud to breach the surface, and that their company presence was coincidental, which should exempt them from paying compensation damage to the victims. If the cause of the incident was determined to be natural, then the government of Indonesia had the responsibility to cover the damage instead. This argument was also recurrently echoed by Aburizal Bakrie, the Indonesian Minister of Welfare at that time, whose family firm controls PT Lapindo Brantas.
However, a UK team of geologists downplayed Lapindo's argument and concluded "...that the earthquake that occurred two days earlier is coincidental". While it could have generated a new fracture system and weakened strata surrounding the Banjar-Panji 1 well, it could not have been the cause of the formation of the hydraulic fracture that created the main vent away from the borehole. Additionally there was no other mud volcano reported on Java after the earthquake, and the main drilling site is away from the earthquake's epicenter. The intensity of the earthquake at the drilling site was estimated to have been only magnitude 2 on the Richter scale, the same effect as a heavy truck passing over the area.
In June 2008, a report released by British, American, Indonesian, and Australian scientists concluded that the volcano was not a natural disaster but the result of oil and gas drilling.
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