Confirmation of the Paleogene Source Rocks in the Northeast Java Basin, Indonesia, Based from Petroleum Geochemistry*

Confirmation of the Paleogene Source Rocks in the Northeast Java Basin, Indonesia, Based from Petroleum Geochemistry* Danis A. Wiloso1, Eddy A. Subroto2, and Eddy Hermanto3 Search and Discovery Article #10195 (2009) Posted June 9, 2009 *Adapted from extended abstract prepared for, and oral presentation at, AAPG International Conference and Exhibition, Cape Town, South Africa 1

Geology, Institute of Technology Adhi Tama Surabaya (ITATS), Surabaya, Indonesia (mailto:[email protected]) Dept. of Geology, Bandung Institute of Technology (ITB), Bandung, Indonesia 3 BPMIGAS, Jakarta, Indonesia 2

Introduction The research area is in the western part of the Northeast Java Basin, one of the biggest hydrocarbon producers in Indonesia. Significant oil and gas accumulation has been discovered in this basin both offshore and onshore. Despite the recent significant discoveries, there are still many uncertainties concerning aspects of petroleum geochemistry in the basin, especially in determining source rock(s) in the western part of this basin. It has been speculated that Ngimbang Formation is the hydrocarbon source rock in the whole basin. This speculation was mainly based by geological interpretation because only two wells were drilled in the eastern part of the basin that penetrated up to the formation. It should be noted that the condition of the samples for the formation in the two old wells are poor. In 1999, a well, namely Rembang-1, was drilled in the western part of the basin. This well has a total depth of 2134 meters and penetrated the Ngimbang Formation. Sediment samples from five old and new exploration wells, which include the Padi-1 whose total depth is 1296 meters (drilled in 2004) and which also penetrated the Ngimbang Formation, and from four oil seepages were used during this study. They were subjected to detailed geochemical analyses comprising organic carbon determination, maturity assessments based on pyrolysis and vitrinite reflectance techniques, and kerogen typing for the sediments and isotope study and biomarker assessments for both sediment and crude oil samples. Then, source rock assessment and oil to source correlation were made. The results indicate a positive correlation between the crude oils and the Ngimbang Formation. In addition, the Ngimbang Formation is relatively rich in organic matter and mature. Therefore, this study is a milestone in the Northeast Java Basin exploration history.

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Confirmation of the Paleogene source rocks in the Northeast Java Basin, Indonesia, based on petroleum geochemistry Danis Agoes Wiloso1) Eddy A. Subroto2) Eddy Hermanto3)

1) 2) 3)

Institute of Technology, Adhi Tama, Surabaya (ITATS)

Department of Geology, Bandung Institute of Technology (ITB)

Executive Agency for Upstream Oil and Gas Business Activities (BPMIGAS), Jakarta Cape Town, October 26- 29, 2008

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INTRODUCTION

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Research area

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(Satyana, 2005)

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Background:  Research area is located at western part of Northeast Java Basin that is one of the biggest hydrocarbon producers in Indonesia.  Significant oil and gas accumulation has been discovered in this basin both offshore and onshore.  Despite the recent significant discoveries, there are still many uncertainties concerning aspects of petroleum geochemistry in the basin, especially in determining source rock(s) at the western part of this basin.

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Objectives:  Identification

of rocks or formation(s) that may act as hydrocarbon source rocks in the western part of Northeast Java Basin.

 Identification

of the Ngimbang Formation as hydrocarbon source rock in the western part of Northeast Java Basin Cape Town, October 26- 29, 2008

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GEOLOGICAL SETTING

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There are two rift basin systems developed during EoceneOligocene times (Sribudiyani et al., 2003). The first rift system strikes NE-SW and the second system trends E-W direction, which is parallel to Rembang-Madura-Kangean (RMK) structural trend.

Research area

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Tectonic Elements

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SEDIMENTATION

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(Manur and Barraclough, 1994)

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STRATIGRAPHY

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WELL CORRELATION

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Padi-1, Rembang-1, and Rembang-2 Rembang-2

Rembang-1

Padi-1

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(Lundin, 2004)

WELL CROSS SECTION

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Padi-1 Rembang-2

Rembang-1

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(Lundin, 2004)

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CROSS SECTION Tengis-1 Well

(Lundin, 2007) Cape Town, October 26- 29, 2008

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DISCUSSION

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RI CHNESS Well

Formation

TOC (%)

Rembang-1

Lidah/Mundu Tuban Kujung CD Ngimbang

0.22-0.39 0.26-1.95 0.23-2.69 1.06-5.09 0.40-71.88

Padi-1

Lidah Tuban Kujung (Prupuh) Kranji CD Ngimbang

0.13-0.24 0.29-1.89 0.70 0.67-1.81 0.09-3.26 1.27-58.16

Ngawi-1

Early Pliocene Globigerinid Marl (equivalent Ledok or Mundu Formation) Banyak Kerek

0.58-0.76 0.20-1.00 0.05-1.14

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Padi-1

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Rembang-1 Well

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MATURITY Padi-1 Well

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Padi-1 Well

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Rembang-1 Well

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Rembang-1 Well

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CORRELATION

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OIL-OIL CORRELATION Legend:

A

B

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hopane

Ngimbang Formation AAPG International Conference and Exhibition Depth 4901 feet m/z 191

Norhopana

Tm

Rembang-1 Well

Ts

OIL-SOURCE CORRELATION Hopane

Kedung Jati Oil seep m/z 191 Norhopane

Tm Ts

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Ngimbang Formation AAPG International Conference and Hopane Exhibition Depth 5500 feet

Norhopane

m/z 191 Ts

Rembang-1 Well

Tm

Hopane

Galeh Oil Seep m/z 191 Norhopane

Ts Tm

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Oil Seep Legend

Source rocks Legend

A

B

A

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B

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CONCLUSIONS •

•

The correlation studies suggest that the crude oils found as seepages (Kedung Jati and Galeh) in western part of the Northeast Java Basin were most likely to be derived from the Ngimbang source rocks. This study reconfirms that Ngimbang Formation is the source of the NE Java Basin crude oils based on the geochemical correlation. Cape Town, October 26- 29, 2008

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ACKNOWLEDGEMENTS The authors would like to thank: • BPMIGAS for permission to publish the results. • Lundin for providing the data. • Total Indonesie and CPI (Chevron Pacific Indonesia) for sponsoring the speaker to attend this AAPG International Conference.

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Selected References Lundin, B.S., 2004, Petrology of Central American tertiary ignimbrites: M.S. Thesis, University of Rhode Island, 220 p. Manur, H. and R. Barraclough, 1994, Structural control on hydrocarbon habitat in the Bawean Area, East Java Sea: 23rd Annual Convention Proceedings, v. 1, p. 129-144. Satyana, A.H., 2005, Petroleum geology of Indonesia: Current concepts (pre-convention course): Indonesian Association of Geologists 34th Annual Convention Proceedings, Surabaya, Indonesia, November 2005. Satyana, A.H, and M.E.M. Purwaningsih, 2003, Geochemistry of the East Java Basin: New observations on oil grouping, genetic gas types and trends of hydrocarbon habitats: Proceedings Indonesian Petroleum Association, 29th Annual Convention and Exhibition, October 2003. Sribudiyani, M.N., R. Ryacudu, T. Kunto, P. Astono, I. Prasetya, B. Sapiie, S. Asikin, A.H. Harsolumakso, and I. Yulianto, 2003, The collision of the East Java microplate and its implication for hydrocarbon occurrences in the East Java Basin: Proceedings Indonesian Petroleum Association 30th Annual Convention & Exhibition. Waples, D.W., 1985, Geochemistry in Petroleum Exploration: International Human Resources Development Corporation, Boston, 232 p.