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North East Java Basin Petroleum Geology Fieldtrip AAPG UGM – SC May 30, 2012

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The participants of North East Java Basin petroleum geology fieldtrip with 2 instructures accompanying during the fieldtrip

North East Java Basin petroleum geology fieldtrip which was held by AAPG UGM SC on 24 – 27 May 2012, as many 15 representative member of AAPG UGM-SC had participated in this fieldtrip. This fieldtrip was sponsored by : Bp Migas, Mobile Cepu Ltd., Pertamina EP cepu, Pertamina Hulu Energy, and Badan Kerjasama Blok Cepu and instructured by : Mr. Wartono Rahardjo and Mr. Didit Hadi Barianto  (These instructures had led for similiar fieldtrip with Santos and Premier Oil ).

On the first day, at 06.00 am, all participants of  North East Java Basin fieldtrip had arrived at Grafika Kampus ( Geological Engineering Dept. ) to prepare their self going through this fieldtrip. Before starting the trip, all participants of  North East Java Basin petroleum geology fieldtrip had briefing and prayed with the instructures ( Mr. Wartono Raharjdo and Mr. Didit Hadi Barianto ) to make sure everything was ready and well-prepared during the trip. Then, the participants of fieldtrip started their trip to Sangiran Museum ( which is located about 15 km from Surakarta ). At Sangiran Museum, the participants were explained about the history of the earth and the development of ancient Human – Being and Antrolopogical study which is related to geological age. Many replicas of Homo Erectus with life size diorama had well-made there, so that it could reflect the history of life.

Life Size Diorama in Sangiran

After visiting Sangiran Museum, the participants of fieldtrip continued their trip to Kedung Ombo, the trip took around 1 -1,5 hours to reach the location. Kedung Ombo is the place of biggest artificial lake in Central Java with area of 6,576 hectare. This artificial lake had been conducted since ‘Orde Baru’ where beneath of this artificial lake have many structural geology composing this artificial lake, because this artificial lake is exactly located on Kendeng Zone. After observing and having discussion around 30 – 45 minutes, the participants took the rest to pray and have their lunch there before starting to reach the next destination ( Bledug Kuwu ). After taking around 2 hours during the trip, the participants reached Bledug Kuwu ( which is located in Kuwu Village ). The participants had a big curiosity about the origin of the Bledug Kuwu, because Bledug Kuwu erupts salty mud every 1 – 1,5 minutes. It had been known that the Kuwu generates the active mud volcano, because this location is composed of many geological structure especially: faults  , so that the fluid which is beneath of its mud generates the pressure to erupt periodically to the surface.

Bledug Kuwu at Kuwu Village

The following day of North East Java Basin petroleum geology fieldtrip, the activities was started at 06.30 am by doing briefing between the lectures and all participants of North East Java Basin petroleum geology fieldtrip of AAPG UGM –SC. The first destination where would be reached was Sambong River section. There was a section of Selorejo Member outcrop consisted of interbedded between clean to glauconitic foraminifera packstone / grainstone and sandy limestone. All participants were asked to observe its location by the lectures based on its morphology, lithology, geological structure and its potential for geological resources. At the first time, the participants were a bit confused because the section was not too ideal to be observed, however, the lecture  gave some clues and datas supporting the characteristics of its deposits, so that, the participants were able to conclude and describe the outcrop ( based on depositional environment, lithology and fossil content of its location ).

After having well – explanation of Selorejo Formation, the participants  of north east Java Basin petroleum geology fieldtrip moved to Pollaman Quarry to observe main reservoir of Cepu Oil Field ( Ngrayong Formation ). The participants were explained about the depositional environment of this outcrop which had been uplifted, caused by found the oxidation of sandstone overlying at Pollaman Quarry. After observing marine –  intertidal environment deposit at Pollaman Quarry, All participants of North East Java Basin petroleum geology fieldtrip was shown shallowing upward sequence at Gunem River Section lying from north to south. In this section, the participants found abundant microfossil of marls indicating the outcrop was deposited in marine. Then, the participants continued the trip to North Beach which is located around Lasem, after taking some hours during trip, finally, the participants of fieldtrip reached the last destination of  North East Java Basin petroleum geology fieldtrip at second day ( Lasem ).  In this location, the stop site of observation was divided into 2 stop sites, at the first stop site, the participants observed the beach and its surrounding, in this location,  the participants were explained about transitional deposits and beach deposits and its usage of reservoir rock in petroleum system.  After taking around 30 – 45 minutes for the explanation and discussion, the participant moved to the outcrop where its location is near to the beach, this outcrop was explained as Volcanic Deposits origin. In this outcrop, participants was demanded to distinguish between Lahar Deposits and Breccia and Conglomerate composing this Lasem Hills.

In the third day, the participants continued our trip to Pegat Quarry as the first site of the day. In this site, the participants were served by the beautiful scenery of the quarry with fabulous phenomenal geological things such as fault, joint. Here the participants were learning the characteristic of carbonate reservoir. This quarry shows an outcrop of upper Mundu formation which  acts as a gas reservoir beneath the Cepu Town named Balun reservoir.

Pegat Quarry well-known as Balun Reservoir

Then the second site was Kabuh village. It is located in north of Ploso, Jombang. Here, the participants found the contact between Pucangan formation and Kabuh formation. The Kabuh itself consists of interbedded or crossbedded sandstone, lenses of conglomerate and yellow tuff. Both of formations which was shown here is predicted as marine product. The last site of the day drove us to the Trowulan in Mojoagung, the historical site of Majapahit. In this site, the participants tried to know the ancient life of Majapahit including the artifacts, ceremonial activities, rituals, sanctuaries, industrial activities, water canals and reservoirs. Mojoagung itself was a part of capital of the biggest ancient Hindu-Buddha monarchy in the country.

The last day of fieldtrip, 27 may 2012. The participants went to first site of the day, North Ngawi. Here the participants were shown the Kerek formation in the edge of Bengawan Solo river. The participants learned more about the systematics of meandering river including its deposition products and the part of the meandering river itself and the turbiditic product systems as this formation is a thick turbidite sequence product. Here, the participants also saw many geological structures composing this area, such as fault and fold which is characterized the Kerek formation. The second site of last day was at Ngrahu, Watujago, Ngawi. In this site the participants saw the contact of Kalibeng and Kerek formation. The outcrop here is lying in Northeast-Southwest. The participant felt a bit confused to determine the dipping of Marl composing this formation. In this area, there are too many geological structure which is not easily to be recognized here. Then,  Continuing the trip, the participants arrived at the third site, Sadang Village. At this location The participants had a contact between Pucangan Formation at the bottom and Kabuh Formation at the top. Here the participants started to observe seeing the Pucangan Formation at the bottom and then the participants walked away parallel to the dip , so there would be found the Kabuh formation lying above the Pucangan Formation. Kabuh Formation here, in Sadang village, was composed of conglomerate beds with cross bedding structures. Beside that, the instructure of this fieldtrip explained to the participants  about the appearance of the fluviatil sediment products, meandering river product one, which is good as reservoir, because at this stage meandering river would make a clean sand or clean conglomerate sedimentation which have a good porosity and good for being the reservoir. The crevasse splay were occured here beside the meandering products, it consisted of clean sand. In this location, one of the participant found a vertebrate fossil lied in the conglomerate.

Fluvial Deposit at Sadang Village

The last site of this trip is in the Dawung village, in the river, which showed the contact between Kalibeng formation and Klitik formation. Both of formation showed an unconformity relations which was shown by the oxidation in the top of Kalibeng formation. The participants also found the paleokars here in the Klitik formation. As the last site finished, it was the end of this fieldtrip, after explaining about this site, then there was a momento given to the instructures of this fieldtrip, Mr. Wartono Rahardjo and Mr. Didit Hadi Barianto as the trip leader and the trip mentor and ended with a photo session in this site.

Last but not least, We are from committee of North East Java Basin petroleum geology fieldtrip would like to thank to our sponsors : BP MIGAS, Mobil Cepu ltd., Pertamina EP Cepu, Badan Kerjasama PI Blok Cepu, and Pertamina Hulu Energy which had supported for this fieldtrip.

This fieldtrip was sponsored by :

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