DISTRIBUSI ZONA OVERPRESSURE DAN PENYEBAB TERJADINYA OVERPRESSURE DI DAERAH BLORA DAN SEKITARNYA CEKUNGAN JAWA TIMUR
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Date
2012
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Abstract
ABSTRACT
Research area are included into Blora Regency, Tuban Regency and
Bojonegoro Regency, Central Java Province and East Java Regency.
Geographically the research area are located in 6° 54` 51.68" - 7° 17` 50.41"
South Latitude and 111° 12` 31.45" - 111° 48` 54.756" East Longitude. There are
13 exploration well in the research area which consists of Banyubang – P1,
Banyuasin – P1, Gabus – P1, Jambaran – 1, Jepon – A, Kedunglusi – 1,
Kedungtuban – 1, Metes – P1, Ngronggah Timur – 1, Semanggi – 2,
Randublatung – 1, Tapen - 1, and Tiung Biru – 01.
Base on drilling, the research area consists of formations from younger to
elder which consists of Turi Formation, Lidah Formation, Mundu Formation,
Ledok Formation, Wonocolo Formation, Bulu Formation, Ngrayong Formation,
Tawun Formation, Tuban Formation, Prupuh Formation, and Kujung Formation.
Geological structure in the research area consists of Tuban Half Graben, Blora
Graben, Bojonegoro Graben, dan Metes Horst.
In Turi Formation, Lidah Formation, Mundu Formation, and Ledok
Formation, the distribution of pore pressure tend around hydrostatic gradient. In
the research area, overpressure are started in Wonocolo Formation, Ngrayong
Formation, Bulu Formation, and Tawun Formation. The end of overpressure in
the research area is occurred in Kujung Formation.
Overpressure zone in the research area consists of Wonocolo – Ngrayong
Zone, Bulu Zone and Tawun Zone. Generally overpressure zone are dominated by
claystone, shalestone and siltstone which are affected by smectite – illite
transformation, and also sandstone and limestone which are isolated by seal
layers.
Overpressure in the research area is caused by smectite – illite
transformation process. This process cause the fluids are released from
claystone, shalestone and siltstone, and also increasing fluids in sandstone and
limestone. This condition causing the pore pressure increase until overpressure.
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Keywords
OVERPRESSURE, BLORA, PEMBORAN