Sidoarjo mud flow located on terrain feature Java
Geological setting
Mud volcano systems are fairly common on Earth, and 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-pressured marine carbonates and marine muds. It forms an inverted extensional basin which has been geologically active since the Paleogene epoch. The basin started to become overpressured during the Oligo-Miocene period. Some of the overpressured 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, 200 km (120 mi) 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, 14 km south of Sidoarjo city, is known in the mineral industry as the Brantas Production Sharing Contract (PSC), an area of approximately 7,250 km2 which 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.