Untitled - Jurnal LEMIGAS

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Figure 1

Oil seep distribution in South Central Java and

index map of Cipari oil seep location (modified from Armandita, et al., 2009).

Keywords : oil seep Cipari, Banyumas Sub-basin, heavy oil.

I. INTRODUCTION

Oil seepage in Cipari, Banyumas, Central Java (Figure 1), based on local information, has long been known since Dutch colonialism. Local people call this oil seep as “oli”, probably came from Dutch language “olie” which means oil. Several authors had reported and published studies regarding to this oil seep (Mulhadiyono, 1973; Subroto, et.al., 2005;

Armandita, et.al., 2009, Rizal, et. al., 2018).

However, none of them described in detail about the oil seep properties and characteristic. Therefore, this paper attempts to explore this oil seep properties and characteristic based on geological field observation, API gravity analysis, geochemical finger printing analysis Gas Chromatography (GC) & Gas Chromatography-Mass Spectometry (GCMS), and its relationship with geological feature in the surrounding areas.

The oil seep area is located near hot spring in Segaralangu Village, which belongs to Cipari Subdistrict, Cilacap Regency, Central Java Province

(Figure 2). The oil seep location is about 60 km to the West from Purwokerto City, or about 50 km to the Northwest from Cilacap City.

II. METHODOLOGY

In general, method used in this study is integration between field geology and laboratory analysis. The method begins with collecting several related published references and reports. The next step is to visit oil seep location, collection of oil seep sample, while conducting short field geological observation around the area. The oil seep sample is then submitted to the laboratory for physical properties and finger printing (GC & GCMS) analyses. The laboratory results integration with geological regional knowledge and field geology observation are then used to interpret the possible source rock depositional environment and present oil seep occurrence related to geological feature in the area.

Figure 1. Oil seep distribution in South Central Java and index map of Cipari oil seep location (modified from Armandita, et. al., 2009).

Halang volcanoclastic/volcanic formation distribution (Late miocene)

Kumbang volcanic formation distribution (Pliocene)

Oilseeps

Dominant direction of Paleocurrent

Pamanukan-Cilacap fault Interpretation from Gravity Map

the West from Purwokerto City, or about 50 km to the Northwest from Cilacap City.

DAtA AND MEtHODS

In general, method used in this study is the integration between field geology and laboratory analysis. The method begins by collecting several related published references and reports. The next step is to visit oil seep location, collection of oil seep sample, while conducting short field geological observation around the area. The oil seep sample is then submitted to the laboratory for physical properties and finger printing (GC & GCMS) analyses.

The laboratory results integration with geological regional knowledge and field geology observation are then used to interpret the possible source rock depositional environment and present oil seep occurrence related to geological feature in the area.

RESULtS AND DISCUSSION A. Field Geology

Banyumas Sub-Basin is a small Tertiary basin located in the west southern part of Central Java. This

basin as described by Bolliger & De Ruiter (1975), is a transition zone between the active volcanic arc of Java and the outer arc basin. Purwastriya, et al. (2018) stated that, based on paleo magmatic arc alignment, the Banyumas Sub-basin tectonic setting during Oligo-Miocene was back-arc basin, then after Plio-Pleistocene became fore-arc basin setting. This sub-basin was filled by transition to marine sediments which was influenced by volcanic material (Figure 3). The oldest sedimentary rocks are Paleogene sediment Karangsambung shale and Jatibungkus limestone followed by Oligo-Miocene Gabon volvanic and marine sediment that deposited during Middle Miocene to Pliocene. The last regional tectonic in Plio-Pleistocene time uplifted the whole area followed by sedimentation of Quaternary Alluvium deposit and deposition of erosional sediment from the oldest rocks. Several exploration well had been drilled within the basin, however none of them found commercial hydrocarbon accumulation (LEMIGAS, 2010).

Morphology of the Cipari area and surrounding is hilly area that formed by faulted anticline which bordered to the south by flat area which represents a depression. This anticline associated with NW-SE regional deep seated fault which extent from northern area of Majenang to Karangbolong. This fault probably

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163 (Jonathan Setyoko Hadimuljono and Desi Yensusnimar)

Figure 2 Location map of Cipari oil seep within topographic map of Cipari - Cilacap - Banyumas area.

Figure 2 . Lo cation map of Cip ar i oil see p withi n top ogra phi c map of Cip ar i – Cila ca p - Ban yu m as ar ea II I. DISCUSS IO N AN D RES ULTS II I.a. Field Geology Ban yum as Sub -B asin is a sm all Tertiary b asi n lo cat ed in the w est sout hern p art of Central Java. This ba sin as des cribed by B olliger & d e Ruit er (1975), is a transiti on zo ne be tween the acti ve vo lc an ic arc of Ja va an d th e ou te r arc ba sin . Pu rw as tri ya , e t. al . ( 20 18 ) s ta te d th at , b as ed o n pa le o m ag m at ic a rc a lig nm en t, th e Ba ny um as S ub -b as in te ct on ic s et tin g du rin g O lig o- M io ce ne w as b ac k- ar c bas in, th en afte r Pli o-P leis toce ne b ec am e fo re- ar c ba sin setting. Thi s s ub-bas in w as fi lle d by tr an sit io n to m arine se di m ents which was in flu en ce d by vo lc an ic m at er ia l ( Fi gu re 4 ). Th e o ld es t s ed im en ta ry rocks are Pal eogene sedi m en t Kar angs ambu ng sh al e an d Ja tib ungkus lim eston e fo llo wed by O lig o- M io ce ne G ab on v ol van ic a nd m ar in e se di m en t t ha t de po sited du ring M iddle Mio cen e to Pliocene. The la st reg io na l te cto nic in Pl io -P le isto ce ne tim e up lif te d th e w ho le ar ea fo llo w ed b y se di m en ta tio n of Q ua te rna ry A lluv ium dep os it an d de po sitio n of er os io na l s ed im en t fro m t he o ld es t r oc ks . Se ve ra l exp loration well had b een dr ill ed w ith in th e ba sin , howev er non e of them fo un d commercia l hy dr oc ar bo n ac cu m ula tio n (L em ig as , 2 01 0) . Mo rpho log y of th e Cipa ri are a and surrounding is hilly a rea that f or m ed by f aulted an tic lin e w hi ch b or de re d to th e so ut h by f la t ar ea which represent s a dep res sion. This anticline as so ci at ed wi th N W -S E re gi on al d ee p se at ed f au lt which exten t fro m nort hern area of Majenang to K ar ang bo long . T hi s fa ult pr ob ab ly b ec om e the m ain mi gr ation pat hway fo r the se veral oil se ep ag es in th e M aj en an g an d Ba ny um as r eg io ns ( se e Figure 1 ). Geo log ical m ap of Ci pari – Jatilawang a rea s in Ba ny um as de sc rib e se ve ra l N E- SW tre nd in g anticli nes, w hich ass oc iat ed with f ault s ( Figu re 5 ) such as Ci pali Anticli ne trend an d Bany um as anticli ne trend. The southern part of the Cipal i Anticli ne is a depressi on , whi ch is kn own as Citandu y Basin (Lun t, et. al., 2009). The anticli ne s were dis sected by sever al nor m al fau lts and t he no rth ern p art possi bl y bo unded by thrus t fau lt.

Cipari Oil seep Besuki Oil seep Jatilawang gas seep

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Figure 4. General stratigraphy of Banyumas and Southern Java area (Satyana, 2005).

Figure 5. Geological map showing the occurrence of anticline and fault which associated

with several oil & gas seepages (modified from Purwasatriya & Waluyo, 2012).

The Cipari oil seep occurs within the Cipari anticlinal trend. It slowly flows from a fracture within cliff of a creek in Segaralangu village (Figure 6). The oil has brownish to greenish black

colour, strong smell, and relatively viscous. It flows mixed with water. It is possible that the oil flows out by water driving mechanism, especially during rainy session.Near the oil seep location, about 200 m to

Figure 3

General stratigraphy of Banyumas and Southern Java area (Satyana, 2005).

Figure 4

Geological map showing the occurrence of anticline and fault which associated with several oil & gas seepages (modified from Purwasatriya & Waluyo, 2012).

Figure 4. General stratigraphy of Banyumas and Southern Java area (Satyana, 2005).

Figure 5. Geological map showing the occurrence of anticline and fault which associated

with several oil & gas seepages (modified from Purwasatriya & Waluyo, 2012).

The Cipari oil seep occurs within the Cipari anticlinal trend. It slowly flows from a fracture within cliff of a creek in Segaralangu village (Figure 6). The oil has brownish to greenish black

colour, strong smell, and relatively viscous. It flows mixed with water. It is possible that the oil flows out by water driving mechanism, especially during rainy session.Near the oil seep location, about 200 m to

Artificial well found oil (Tipar and Prapagan) gas seep

(Karangwelas Jatilawang) Fault dependent anticline

Possible thrust/reverse fault Cipari Oil Seep

Location

PRE - TERTIARY EOCENEOLIGOCENEMIOCENE

PLIOCENE QUATERNARY

EPOCH ^LETTER_ZONES ^OFFSHORE ^{GABON HIGH} ^BANYUMAS ^KARANGBOLONG KEBUMEN LUK ULO

KULON PROGO HIGH

YOGYA-

KARTA JIWO

HILLS

become the main migration pathway for the several oil seepages in the Majenang and Banyumas regions (see Figure 1). Geological map of Cipari

- Jatilawang areas in Banyumas describe several NE-SW trending anticlines, which associated with faults (Figure 4) such as Cipali Anticline trend and

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Figure 5

Oil seepage location in Segaralangu village, Cipari Sub-district, Cilacap regency.

GPS location: 108^◦45’54 E, 7^◦25’41.63 S. Oil seep slowly flows from cliff of the creek (A) and accumulated into a small pond (B). The oil seep sample is taken from this small pond.

Figure 6

Cipari hot spring tourism area.

the Southeast, there is a hot spring that is utilized for tourism purposes (Figure 7).

Figure 6. Oil Seepage location in Segaralangu Village, Cipari Sub-district, Cilacap Regency. GPS location : 108

^◦

45’54 E, 7

^◦

25’41.63 S. Oil seep slowly flows from cliff of the creek (A) and accumulated into a small pond (B). The oil seep sample is taken from this small pond.

Figure 7. Cipari hot spring tourism area.

III.b. Laboratory Analysis result

The oil sample was analysed at Lemigas Laboratory facility (Lemigas, 2020) for oil properties and finger printing analysis. Picnometer

analysis of the oil samples resulted in 12° API gravity, which means that the oil seep sample can be classified as heavy oil (Meyer et. al., 1998). The result of Gas Chromatography (GC) analysis reveals that the Cipari oil seep sample have lost all their

the Southeast, there is a hot spring that is utilized for tourism purposes (Figure 7).

Figure 6. Oil Seepage location in Segaralangu Village, Cipari Sub-district, Cilacap Regency. GPS location : 108^◦45’54 E, 7^◦25’41.63 S. Oil seep slowly flows from cliff of the creek (A) and accumulated into a small pond (B). The oil seep sample is taken from this small pond.

Figure 7. Cipari hot spring tourism area.

III.b. Laboratory Analysis result

The oil sample was analysed at Lemigas Laboratory facility (Lemigas, 2020) for oil properties and finger printing analysis. Picnometer

analysis of the oil samples resulted in 12° API gravity, which means that the oil seep sample can be classified as heavy oil (Meyer et. al., 1998). The result of Gas Chromatography (GC) analysis reveals that the Cipari oil seep sample have lost all their

A B

Banyumas anticline trend. The southern part of the Cipali Anticline is a depression, which is known as Citanduy Basin (Lunt, et al., 2009). The anticlines were dissected by several normal faults and the northern part possibly bounded by thrust fault.

The Cipari oil seep occurs within the Cipari anticlinal trend. It slowly flows from a fracture within

cliff of a creek in Segaralangu village (Figure 5).

The oil has brownish to greenish black colour, strong smell, and relatively viscous. It flows mixed with water. It is possible that the oil flows out by water driving mechanism, especially during rainy session.

Near the oil seep location, about 200 m to the South- east, there is a hot spring that is utilized for tourism purposes (Figure 6).

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Figure 7

Chromatogram of GC analysis of Cipari oil seep describing that all alkanes fraction has been lost.

alkane fraction including isoprenoid pristane and phytane (Figure 8), which indicate that the oil had been biodegraded.

Chromatogram of GCMS analysis (Figure 9) describes triterpana distribution (m/z 191) of oil seep sample appears to be dominated by bicadinane resins whereas the hopane compounds are not well detectable. This condition indicates that there has been a very intensive degradation of the oil that is predicted to be due to biodegradation or thermal.

The result of the process causes those left in the oil are only high resistance compounds to the degradation process, such as bikadinana resin (W,T) and oleanane (OL). Oleanane in crude oils is a marker for both source input and geologic age. The

oleananes originates from betulins that are produced by angiosperms (flowering land plants). Angiosperm first became prominent in the Late Cretaceous (Peter

& Moldovan, 2005). Oleanane and related compounds are best preserved in deltaic rocks. The Sterane chromatogram (m/z 217) show diasteranes and regular sterane distribution pattern with interference of bicadinanes compounds, which in turn was difficult to identify (Figure 9). These compounds are typical of terrigenous higher plant organic matter deriving from dipterocarpaceae species. In the m/z 217 sterane ion chromatograms, they predominantly appear as four distinctive peaks labelled W, T, T’ and R.

Figure 8. Chromatogram of GC analysis of Cipari oil seep describing that all alkanes fraction has been lost.

2.00 4.00 6.00 8.00 10.0012.0014.0016.0018.0020.0022.0024.0026.0028.00 200000

250000 300000 350000 400000 450000 500000 550000 600000 650000

Time Response_

Signal: 204001 cpr.D\ FID1A.CH

650000 600000 550000 500000 450000 400000 350000 300000 250000 200000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 26.00 28.00 Signal: 204001 cpr:D\FID1ACH

Response_

Time

Figure 6 Oil Seepage location in Segaralangu Village, Cipari Sub-district, Cilacap Regency. GPS location : 108^◦45’54 E, 7^◦25’41.63 S. Oil seep slowly flows from cliff of the creek (A) and accumulated into a small pond (B). The oil seep sample is taken from this small pond.

B. Laboratory Analysis Result

The oil sample was analysed at LEMIGAS Laboratory facility (LEMIGAS, 2020) for oil properties and finger printing analysis. Picnometer analysis of the oil samples resulted in 12° API gravity, which means that the oil seep sample can be classified as heavy oil (Meyer, et al., 2007).

The result of Gas Chromatography (GC) analysis reveals that the Cipari oil seep sample have lost all their alkane fraction including isoprenoid pristane and phytane (Figure 7), which indicate that the oil had been biodegraded.

Chromatogram of GCMS analysis (Figure 8) describes triterpana distribution (m/z 191) of oil seep sample appears to be dominated by bicadinane resins whereas the hopane compounds are not well detectable.

This condition indicates that there has been a very intensive degradation of the oil that is predicted to be due to biodegradation or thermal. The result of the process causes those left in the oil are only high

resistance compounds to the degradation process, such as bikadinana resin (W,T) and oleanane (OL).

Oleanane in crude oils is a marker for both source input and geologic age. The oleananes originates from betulins that are produced by angiosperms (flowering land plants). Angiosperm first became prominent in the Late Cretaceous (Peters &

Moldowan, 2005). Oleanane and related compounds are best preserved in deltaic rocks. The Sterane chromatogram (m/z 217) show diasteranes and regular sterane distribution pattern with interference of bicadinanes compounds, which in turn was difficult to identify (Figure 9). These compounds are typical of terrigenous higher plant organic matter deriving from dipterocarpaceae species. In the m/z 217 sterane ion chromatograms, they predominantly appear as four distinctive peaks labelled W, T, T’

and R.

The occurrence of bicadinane (W, T) and oleanane within the oil sample indicated that the biomarkers derived from higher plant, which was probably deposited in deltaic/transition environment.

Ternary diagram based on the composition C27-C28- C29 sterane (Figure 9) indicates that the hydrocarbons in Cipari oil sample originated from fluvio-deltaic depositional environment where the main organic matter influx was dominated by higher plants.

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Figure 8

Chromatogram of Gas Chromatography Mass Spectometry (GCMS) of Cipari oil seep shows high resistance compounds to the degradation process, such as bikadinana resin (W,T) and oleanane (OL).

Figure 9. Chromatogram of Gas Chromatography Mass Spectometry (GCMS) of Cipari oil seep shows high resistance compounds to the degradation process, such as bikadinana resin (W,T) and oleanane (OL)

The occurrence of bicadinane (W, T) and oleanane within the oil sample indicated that the biomarkers derived from higher plant, which was probably deposited in deltaic/transition environment. Ternary diagram based on the composition C27-C28-C29 sterane (Figure 10) indicates that the hydrocarbons in Cipari oil sample originated from fluvio-deltaic depositional environment where the main organic matter influx was dominated by higher plants

III.c. Discussion

Oil seepage in Cipari based on laboratory analysis can be classified as heavy oil (12° API gravity) and also severe biodegraded (level 5-6) based on the table conducted by Head et al (2013).

The 5-6 levels biodegradation describes that all alkanes and isoprenoid pristane phytane are lost, while Hopane compounds from the triterpane chromatogram are depleted. However, it is unknown wheter the heavy oil is entirely produced by biodegration or there was also thermal influence (hidrotermal) which accelerated the degradation process. With regard to the fact that the oil seep location is near a hot spring associated with regional deep seated fault NW-SE from North Majenang to Karangbolong offshore, it was possible that during migration through the fault, the oil also contacted or was affected by hidrotermal which led to thermal degradation of the oil.

20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 75.00 80.00 85.000 5000

10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000

Time-->

Io n 1 9 1 .0 0 (1 9 0 .7 0 to 1 9 1 .7 0 ): 2 0 4 0 0 1 sa t.D \ d a ta .ms

50.00 52.00 54.00 56.00 58.00 60.00 62.00 64.00 66.00 68.00 70.00 72.00 74.00 5000

10000 15000 20000 25000

Time-->

Ion 217.00 (216.70 to 217.70): 204001sat.D\data.ms

50.00 52.00 54.00 56.00 58.00 60.00 62.00 64.00 66.00 68.00 70.00 72.00 74.00 1000

2000 3000 4000 5000

Time-->

Abundance

Ion 218.00 (217.70 to 218.70): 204001sat.D\data.ms

m/z 217

m/z 218

m/z 191

Ts Tm 29H 30H

31H 32H 33H Tricyclics

C27Ste C28Ste C29Ste C27Ste C28Ste C29Ste C27D C27D

Te 26T

OL

T W T

W T’ R

Hopane heavily biodegraded Into level 5 T

W T’ R

Abundance

Abundance Ion 217.00 (216.70 to 217.70) : 204001 sat.D\data.ms

Ion 287.00 (217.70 to 218.70) : 204001 sat.D\data.ms

Ion 191.00 (190.70 to 191.70) : 204001 sat.D\data.ms 25000

20000 15000 10000 5000

50.00 52.00 54.00 56.00 58.00 60.00 62.00 64.00 66.00 68.00 70.00 72.00 74.00

20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 75.00 80.00 85.00 50004000

30002000 1000

65000 60000 55000 50000 45000 40000 35000 30000 25000 20000 15000 10000 50000 Time-->

Time-->

Abundance Abundance

Abundance

Hopane heavily biodegraded into level 5

C. Discussion

Oil seepage in Cipari based on laboratory analysis can be classified as heavy oil (12° API gravity) and also severe biodegraded (level 5-6) based on the table conducted by Head, et al. (2013). The 5-6 levels biodegradation describes that all alkanes and isoprenoid pristane phytane are lost, while Hopane compounds from the triterpane chromatogram are depleted. However, it is unknown wheter the heavy oil is entirely produced by biodegration or there was also thermal influence (hidrothermal) which accelerated the degradation process. With regard to the fact that the oil seep location is near a hot spring associated with regional deep seated fault NW-SE from North Majenang to Karangbolong offshore, it was possible that during migration through the fault, the oil also contacted or was affected by hidrotermal which led to thermal degradation of the oil.

Biomarker finger printing results have also revealed that the Cipari oil seep probably originated

from higher plant organic matter which deposited in fluvio-deltaic/ transition sedimentary environment.

Unfortunately, this study did not cover collection of rock samples for oil to source correlation due to limited time during fieldwork. Previous correlation study of oil from DST of Jati-1 Well and several seepages in Banyumas Region also indicate fluvio- deltaic characteristic rather than marine characteristic.

The biomarkers distribution (tricyclic and pentacyclic triterpanes) of the equivalent Karangsambung sediment (from shallower marine) shows relatively identical with that of the crude oil indicating that they have a good correlation (Subroto, et al., 2008). The other source candidate, the Penosogan shale (Middle Miocene) is still in immature stage. Therefore, it is suggested that the crude oils found as seeps and a DST sample in the Banyumas Sub-basin might be derived from equivalent Eocene Karangsambung Formation (Paleogene) whose depositional environment was shallow marine. However, it is also possible that deltaic sediment of Nanggulan

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Figure 9

Ternary diagram based on the composition of C27 - C28 - C29 sterane, which indicates that the organic matter of Cipari oil sample possibly came from fluvio-deltaic environment.

Figure 10. Ternary diagram based on the composition of C

27

- C

28

- C

29

sterane, which indicates that the organic matter of Cipari oil sample possibly came from fluvio-deltaic environment.

Biomarker finger printing results have also revealed that the Cipari oil seep probably originated from higher plant organic matter which deposited in fluvio-deltaic/ transition sedimentary environment.

Unfortunately, this study did not cover collection of rock samples for oil to source correlation due to limited time during fieldwork. Previous correlation study of oil from DST of Jati-1 Well and several seepages in Banyumas Region also indicate fluvio- deltaic characteristic rather than marine characteristic. The biomarkers distribution (tricyclic and pentacyclic triterpanes) of the equivalent Karangsambung sediment (from shallower marine) shows relatively identical with that of the crude oil indicating that they have a good correlation (Subroto, 2008). The other source candidate, the Penosogan shale (Middle Miocene) is still in immature stage. Therefore, it is suggested that the crude oils found as seeps and a DST sample in the Banyumas Sub-basin might be derived from equivalent Eocene Karangsambung Formation (Paleogene) whose depositional environment was shallow marine. However, it is also possible that

deltaic sediment of Nanggulan Formation (Eocene) could be source for oil in the basin (KIGAM &

Lemigas, 2011).

Purwasatriya, et. al. (2018), described that during Paleogen time, Banyumas sub-basin occurred as back-arc basin setting which more suitable paleogeography for petroleum potential. In the back-arc setting, fine grained sediments with high organic matter content can be deposited and well preserved. During burial history of the basin, the source rocks were thermally mature and the organic matter converted into hydrocarbon. The generated hydrocarbon was expelled and migrated through all available faults and fractures to the reservoirs and some even escaped to the surface as seepages. When the oil associated or contacted with fresh water, it would be biodegraded by micro-organism (bacteria) and resulted in losing of lighter fraction became heavy oil (Head, et.al, 2013; Pannekens, et. al., 2019).

C28(％)

C29(％) C27(％) 50

50 50

PeatSwamp MarineOpen Marginal

Marine Fluvial

(Modified after Huang & Meinchein, 1979)

Oilseep

(Modified after Huang & Meinchein, 1979)

Formation (Eocene) could be source for oil in the basin (KIGAM - LEMIGAS, 2011).

Purwasatriya, et al. (2018), described that during Paleogen time, Banyumas sub-basin occurred as back-arc basin setting which more suitable paleogeography for petroleum potential. In the back-arc setting, fine grained sediments with high organic matter content can be deposited and well preserved.

During burial history of the basin, the source rocks were thermally mature and the organic matter converted into hydrocarbon. The generated hydrocarbon was expelled and migrated through all available faults and fractures to the reservoirs and some even escaped to the surface as seepages. When the oil associated or contacted with fresh water, it would be biodegraded by micro-organism (bacteria) and resulted in losing of lighter fraction became heavy oil (Head, et al., 2003; Pannekens, et al., 2019).

It is unknown the typical microorganisms that responsible for biodegradation process of the Cipari oil seep. Since there are many microorganisms

are present in oil reservoirs around the world (Pannekens, et al., 2019), the microorganism should be isolated from the Cipari oil and then identified by molecular technique to determines the specific genus or species of microorganisms. Chaillan, et al.

(2004) based on their study on identification and biodegradation potential of tropical aerobic hydrocarbon-degrading microorganisms, have identified 33 distinct species of aerobic hydrocarbon (HC)- degrading microorganisms from Indonesia. The bacterial strains belonged to the genera Gordonia, Brevi-bacterium, Aeromicrobium, Dietzia, Burkholderia, and Mycobacterium. However, identification of typical bacteria responsible for biodegradation will led to estimation of possible biodegradation zone temperature and depth.

This example demonstrated by Lemigas (Hadimuljono & Firdaus, 2021) which isolated and identified Burkholderia multivorans ATCC BAA-247 from oil seep sample taken from Central Sumatera Basin to determine biodegradation

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Symbol Definition Unit

Bacteria

Bacteria are small single- celled organisms.

Bacteria are found almost everywhere on Earth and are vital to the planet's ecosystems. Some species can live under extreme conditions of temperature and pressure.

Biodegradation

Biodegradation is the breakdown of organic matterby

microorganisms, such as bacteria and fungi.

GC

The process of

separating compounds in a mixture by injecting a gaseous or liquid sample into a mobile phase, typically called the carrier gas, and passing the gas through a stationary phase. The mobile phase is usually an inert gas or an unreactive gas such as helium, argon, nitroge n or hydrogen

GC-MS

Combination of gas chromatography with mass spectrometry to enhanced its sensitivity.

The separated components can be analysed by a mass spectrometric detector (GC-MS) for maximum sensitivity and selectivity.

Heavy Oil

Heavy oil is a crude oil that has a viscosity typically greater than 0.01 Pa. s [10 cP] and a high specific gravity. The World Petroleum Congress classifies heavy oils as crude oils that have a gravity below 22.3 degree API

Oil seepage a natural leak of crude oil that migrates up through the surface or seafloor

Bacteria

Biodegradation

GC

The process of

GC-MS

Heavy Oil

Bacteria

Biodegradation

GC

The process of

GC-MS

Heavy Oil

Bacteria

Biodegradation

GC

The process of

GC-MS

Heavy Oil

Bacteria

Biodegradation

GC

The process of

GC-MS

Heavy Oil

zone in Central Sumatera Basin. Knowing the sub-surface biodegration zone will help to identify reservoir or hydrocarbon traps that possibly preserve from biodegradation of microorganisms.

Oil seeps prove that the sedimentary rocks within a basin have generated oil and that a mature source rock is present (Link, 1952). As discussed above, the source rock of Cipari oil seep is inferred from Paleogen mature source rock that deposited in fluvio-deltaic environment. In exploration history, oil and gas seeps gave the first clues to most oil producing region. Many oilfields are drilled near or direct to the seepages. Unfortunately, seeps are not always located directly above accumulations. If the seeping hydrocarbons encounter a fault or permeable conduit, their vertical movement may develop a significant lateral component (Waples, 1985). The Cipari oil seep that associated with faults possibly migrated from subsurface reservoirs/ traps or kitchen area somewhere from the seep location. Therefore, it is need more geological and geophysical method to identify sub-surface oil accumulations/ traps within Banyumas sub-basin area.

CONCLUSIONS

Integrated works of field geology and laboratory analysis of Cipari oil seepage led to several main points that can be concluded:

The Cipari oil seep has 12° API Gravity, that can be classified as heavy oil. GC-GCMS analysis revealed losing of lighter fraction of oil, which indicated biodegradation. It is observed that the oil seep associated with fresh water, which led to biodegration by bacteria during migration and accumulation in surface or shallow reservoir. It is also possible that degradation process accelerated by hydrothermal system near the oil seep location which led to severe biodegradation level.

Finger printing analysis interpretated that the Cipari oil seep probably derived from higher plant organic matter which deposited in fluvio-deltaic/

transition sedimentary environments. It is inferred that the source rock was Paleogen sediment since it has good source potential and enough maturity to generate hydrocarbon.

Oil seep Cipari give the clue for petroleum exploration that sedimentary rocks within Banyumas- subbasin have generated hydrocarbon. It is need more geological and geophysical method to identify

sub-surface oil accumulations/traps within the Banyumas sub-basin area.

ACKNOWLEDGEMENt

We would like to acknowledge the management of PPPTMGB “LEMIGAS” for supporting and permission to publish this work.

GLOSSARY OF tERMS

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170

Scientific Contributions Oil & Gas, Vol. 44. No. 3, December 2021: 161 - 171

Bacteria

Biodegradation

GC

The process of

GC-MS

Heavy Oil

Oil seepage a natural leak of crude oil that migrates up through the surface or seafloor Microorganism

an organism of microscopic size, which may exist in its single- celled form or as a colony of cells.

Migration

Movement of bitumen, oil, and gas in the

subsurface. Migration includes expulsion (primary migration), secondary migration, accumulation, and leakage.

Source rock

a rock rich in organic matter which, if heated sufficiently, will generate oil or gas

Bacteria

Biodegradation

GC

The process of

GC-MS

Heavy Oil

Oil seepage a natural leak of crude oil that migrates up through the surface or seafloor Bacteria

Biodegradation

GC

The process of

GC-MS

Heavy Oil

REFERRENCES

Armandita, C., Mukti, M. M. & Satyana, A. H., 2009.

Intra-arc trans-tension duplex of Majalengka to Banyumas area : Prolific Petroleum Seeps And Opportunities In West-Central Java Border. Jakarta, Indonesian Petroleum Association (IPA).

Bolliger, W. & De Ruiter, P. A. C., 1975. Geology of The South Central Java Offshore Area. Jakarta, Indonesian Petroleum Association (IPA), pp. 67-81.

Chaillan, F., Le Fleche, A., Burry, E., Phantavong, Y-h., Grimont, P., Sailot, A., & Oudot, J., 2004. Identification and biodegradation potential of tropical aerobic hydrocarbon-degrading microorganisms. Research in Microbiology, 155(7), pp. 587-595.

Hadimuljono, J. S. & Firdaus, N., 2021. Determination of Biodegradation Zone in Central Sumatra Basin.

Scientific Contributions Oil and Gas (SCOG), 44(1), pp. 55-63.

Head, I. M., Jones, D. M. & Larter, S. R., 2003. Biological activity in the deep subsurface and the origin of heavy oil. Nature, Volume 426, pp. 344-352.

Huang, W.-Y. & Meinschein, W. G., 1979. Sterols as ecological indicators. Geochimica et Cosmochimica Acta, 43(5), pp. 739-745.

KIGAM-LEMIGAS, 2011. Hydrocarbon Potential Review of South Central Java Basin, Indonesia (unpublished), Jakarta: KIGAM-Lemigas.

LEMIGAS, 2010. Kajian Pengembangan Sumber Daya Migas Di Cekungan Indonesia Barat (Unpublished), Jakarta: Lemigas.

LEMIGAS, 2020. Kajian Potensi Minyak Berat (Oil Sands) dan Bitumen di Cekungan Sumatera Tengah (Study on Heavy Oil Potential of Central Sumatra Basin) - Final Report (Unpublished), Jakarta: Lemigas.

Link, W. K., 1952. Significance of Oil and Gas Seeps In World Oil Exploration. AAPG Bulletin, 36(8), pp.

1505-1540.

Lunt, P., Burgon, G. & Baky, A., 2009. The Pemali Formation of Central Java and equivalents: Indicators of sedimentation on an active plate margin. Journal of Asian Earth Sciences, 34(1), pp. 100-113.

Meyer, R. F., Attanasi, E. D. & Freeman, P. A., 2007. Heavy Oil and Natural Bitumen Resources in Geological Basins of the World, Reston, Virginia:

USGS Open File- Report.

Mulhadiyono, 1973. Petroleum Possibilities of The Banyumas Area. Jakarta, Indonesian Petroleum Association (IPA).

Pannekens, M., Kroll, L., Muller, H., Mbow,F.t., &

Meckenstock, R.U., 2019. Oil reservoirs an exceptional habitat for microorganisms. New Biotechnology, Volume 49, pp. 1-9.

Peters, K. E. & Moldowan, J. M., 2005. The Biomarker Guide, Interpreting Molecular Fossils in Petroleum and Ancient Sediments. United States: Prentice-Hall.

Purwasatriya, E. B., Surjono, S. S. & Amijaya, D. H., 2018. Oligocene-Pleistocene Paleogeography Within Banyumas Basin and Implication to Petroleum Potential.

Yogyakarta, UGM.

Purwasatriya, E. B. & Waluyo, G., 2012. Studi Potensi Minyak Dangkal dengan Pendekatan Metode Statistik Berdasar Data Geologi Permukaan Di Cekungan Banyumas. Jurnal Ilmiah Dinamika Rekayasa, 8(2), pp. 48-52.

Rizal, Y., Santoso, W.D., Rudyawan, A., tampubolon, R.A., & Nurfarhan, A.A., 2018. Sedimentary Facies and Hydrocarbon Reservoir Potential of Sand Flat In The Upper Part of Tapak Formation in Banyumas Area, Central Java. Jurnal RISET Geologi dan Pertambangan, 28(2), pp. 251-263.

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Said, S., Jatmiko, t. & Widada, S., 2020. Potensi Batuan Induk Hidrokarbon Satuan Batulempung Formasi Rambatan Daerah Wangon Sub-Cekungan Banyumas.

Jurnal Offshore, 4(1), pp. 9-16.

Santoso, B., Zeiza, A. D. & Nugroho, F. P., 2007.

Neogene Tectonic And Sedimentary Control To Hydrocarbon Generation In Banyumas Sub-Basin, South of Central Java. Jakarta, Indonesian Petroleum Association (IPA).

Satyana, A. H., 2005. Oligo-Miocene Carbonates of Java, Indonesia: Tectonic-Volcanic Setting And Petroleum Implications. Jakarta, Indonesian Petroleum Association (IPA).

Satyana, A. H., 2007. Central Java, Indonesia - A

“Terra Incognita” In Petroleum Exploration: New

Considerations On The Tectonic Evolution And Petroleum Implications. Jakarta, Indonesian Petroleum Association (IPA).

Seubert, B. W. & Sulistianingsih, F., 2008. A Proposed New Model For The Tectonic Evolution Of South Java, Indonesia. Jakarta, Indonesian Petroleum Association (IPA).

Subroto, E. A., Ibrahim, A., Hermanto, E. &

Noeradi, D., 2008. Contribution of Paleogene and Neogene sediments to the Petroleum System in the Banyumas Sub-Basin, Southern Central Java. Cape- town-South Africa, AAPG International.

Waples, W. D., 1985. Geochemistry in Petroleum Exploration. 1^st ed. Denver, Colorado: D. Reidel Publishing Company.