IPA05-G-085
PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Thirtieth Annual Convention & Exhibition, August 2005 EXPLORATION IN WEST JAVA: PLAY CONCEPTS IN THE PAST, PRESENT AND FUTURE, EFFORTS TO MAINTAIN RESERVES GROWTH Suyono* Khozin Sahudi* Indra Prasetya*
ABSTRACT Hydrocarbon exploration activities in the West Java Province have been active since the period prior to Indonesian Independence. Play concepts both conventional and unconventional have been applied. It is considered that these concepts can be classified in to 5 stages. The first stage involved the play concept that was based on oil seepages and surface mapping. This concept has been applied since 1871 and early exploration drilling was conducted in areas which had oil seepages in the surrounding area. Futhermore this concept was supplemented by surface mapping to identify geologic structure. The second stage play concept was associated with the identification of the High Trend. This concept has been applied since about 1960 when Pertamina first started to operate in the West Java region. Exploration was focussed on the identification of prospect located on High Trends. This approach was successfully in discovering several fields i.e. Jatibarang, Cemara, Kandanghaur, Tugu, Cilamaya, Pamanukan and Gantar. The third stage was the development of the play concept of prospects created as a result of a Thrust Fault System. This concept has been applied since about 1980 and has been utilised to focus on identification of prospects generated by compressional. Fields discovered using this play concept included Pasirjadi, Subang, Jatirarangon and Cicauh.
The fourth stage involved the concept of the Basin Deep or Sub-Basin. Exploration was focussed on the identification of prospects on Sub-Basin. The concept is to identify clastic reservoirs whoch were deposited within a rift system in the basin deep or sub-basin. This concept have been applied since about 1995. Some wells discovered were Wanajaya-1, Melandong-1, Tb.Kelapa-1 and Karangbaru-1. The fifth stage is the play concept of the Present and the Future. For the future exploration e xploration play concept are adjusted to more fully understand the geologic features and petroleum systems are more comprehensive and detailed, and also use modern appropriate technologies. All of the above concepts are compiled, analyzed and combined, to search for opportunities for both conventional and unconventional exploration play concepts aimed at finding oil and gas reserves. Exploration targets are not only in new prospects but also in brown fields. Therefore, by application of these concepts it will be possible to maintain reserves growth in West Java. Java. INTRODUCTION General Setting
Geologically, the West Java area is located in the onshore part of the Northwest Java Basin which is one of a series of back-arch basins in the Western Indonesia (Figure 1). There are four main depocenters in the basin, from west to east i.e. Ciputat-Kepuh sub basin, Pasir Bungur sub-basin, Cipunegara sub-basin and Jatibarang sub-basin (Figure 2). Brief History
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P. T. Pertamina (Persero)
Exploration activities in West Java commenced during Indonesia’s pre Independence period. A 267
programme of exploration wells was drilled by Van Hoevel and Jan Reering in 1871 in Cibodas village located in the district of Majalengka, northern part of Mount Ciremai volcano (Pertamina, 1982). Drilling of these wells is considered to record the first drilling not only in West Java but in Indonesia. Two of the 4 drilled wells encountered sub-commercial hydrocarbon. Following this drilling, industry activities comprised geological field mapping during the period 1910-1942 and covered the Purwakarta, Cirebon, Karawang and Subang areas. During this time, West Java was held under a concession area by Dutch company NV de BPM (NV de Betaafsche Petroleum My). Arround 1928, a gravity survey was conducted in the Krawang, Bekasi, Indramayu, Purwakarta, Cirebon and Majalengka areas. During the period up to 1941 more than 30 exploration wells were drilled.
After Indonesian Independence Proclaimation in 1945, the concession areas were taken over by PTMN (Perusahaan Tambang Minyak Nasional, National Petroleum Company) which had its head-office in Cepu, Central Java. In 1948, PTMN changed its name to PTMRI (Perusahaan Tambang Minyak Nasional Republik Indonesia) and was taken over again by Dutch Company until 1960. In 1961, the Government of Indonesia formed PN Permigan in order to manage the business of petroleum activities in Java, and for further expansion, the Cirebon Administration Area Office in Bongas Majalengka was built. In 1966, Permigan was terminated and the government then formed PN Pertamin for the Marketing Business and PN Permina for the Production Business. PN Permina had the Exploration and Production Unit which included Java and Madura Island. Since 1966, PN Permina conducted seismic surveys and followed up with the drilling of exploration wells in Jatibarang. Jatibarang (JTB)-42 was noted as the first well of Pertamina in West Java.
Until the present-day, Pertamina has continued to conduct seismic surveys and to drill wells. Sewismic data totals about 20,000 kms of 2-D data and 700 km 2 of 3-D data. More than 90 exploration wells have been drilled. Gravity, magnetic and field geological surveys acquired cover almost all of the northern part of West Java.
GEOLOGY Tectonic Setting
Many papers have been written which discussed the Northwest Java Basin (Eksplorasi, 2003) . During the Late Cretaceous - Early Tertiary, the Northwest Java Basin was situated in a tectonic setting classified as a fore-arc basin which was controlled by the Meratus Trend. During the early phase of its evolution in the Paleogene (Eocene-Oligocene), the basin evolved as a wrench-induced pull-apart basin which resulted in the creation of faulted highs and a half graben system. Deposition of lacustrine deposits and volcanics (Jatibarang Formation) were overlain by deposition of transitional deposits of the Talang Akar Formation. This was then overlain by limestone deposits of the Batu Raja Formation. The structural trend of normal faulting is south to north and is known as the Sunda Fault Trend. The later phase of basin evolution occured in the Early Neogene (Oligo-Miocene) and resulted from the creation of a new subduction zone along the southern part of Java Island. The resulting East-West structural trend is different from the earlier phase and is known as Java Trend. The Upper Cibulakan Formation was deposited in shallow-marine environment during the Early Miocene and overlain by the Parigi Formation. A recent compressional phase occured during the Plio-Plistocene as evidenced by the presence of a thrust- fault in the southern part of Northwest Java Basin. During this time the Cisubuh Formation was deposited. General Stratigraphy
Tertiary sediments cover Pre-Tertiary basement with the sedimentary stratigraphic succession ranging in age from Late Paleocene (?)-Mid Eocene to Holocene. Pre-Tertiary basement consists of igneous, metamorphic and metasedimentary rocks and it is considered to be older than Eocene. The general stratigraphy is illustrated in Figure 3. The oldest sequence, the Jatibarang Formation, uncomformably overlies the pre-Tertiary. The Jatibarang Formation is considered to be of Eocene268
middle Oligocene age. The Jatibarang Formation consists of interbedded volcanics ie. tuffs, amalgamated tuffs and andesitic/basaltic tuffs and volcaniclastic sands. This formation was unconformably overlain by the Talang Akar Formation.
EXPLORATION CONCEPTS
The Talang Akar Formation was deposited during the early to late Oligocene and is divided into the Lower Talang Akar and Upper Talang Akar formations. The Lower Talang Akar, consist dominantly of siliciclastic rocks deposited in a fluvial depositional environment while in the Upper Talang Akar Formation, the influence of volcanic activity is reduced and the depositional setting became more of a marine-deltaic environment.
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The Batu Raja Formation of early Miocene age, consists of bioclastic carbonates and reefal carbonates and comformably overlies the Talang Akar Formation. The Batu Raja carbonates were deposited in an open-marine environment.
Several of these stimuli appear to have been responsible for generating five exploration concepts.
The Cibulakan Formation is characterized by a mixture of clastic and carbonate rocks. Reefal carbonates are developed in the middle of this formation and are refered to as the Mean Carbonate. The age of the Cibulakan Formation is considered to be Early-Middle Miocene. Thre are some marker horizons in this formation such as Zone-14 and Zone-15.
The overlying Parigi Formation developed as a relatively low-energy sequence comprising finegrained, shaly, lime-muds but also including packstone and wackestone facies. The bottom of this formation is characterized by a gradual change from the mixed facies of clastics and carbonates of the Cibulakan Formation. The Parigi Formation of Late Miocene age, is overlain by the Cisubuh Formation, which is Pliocene in age and the youngest formation in the basin. The Cisubuh Formation is dominated by carbonaceous shales and thin sandstones. The shales of this formation form the main seal for underlying hydrocarbons in the Parigi Formation carbonate reservoirs. The sands in this formation become more thickly developed higher in the sequence. Glauconite and thin coal seams are often found in this formation.
Exploration activities are initiated as a result of numerous stimuli. These include :
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The working area and its exploration status, ie ranging from frontier to mature The presence of a major discovery in a previously unproductive or unknown reservoir A favorable situation in the political or investment climate An improvement in key exploration tools (e.g : seismic acquisition, processing, geological modelling etc). The development of new exploration play concepts
Oil Seepages and Surface Mapping Concept
Early oil searching in Indonesia was initiated only 12 years after the milestone in the USA when Colonel Drake drilled the first well in Pennsylvania. Early exploration wells in the onshore West Java area were drilled by Jan Reering & Van Hoevel. They visited the USA, collected drilling equipment and skills, and began drilling at Cibodas in 1871 with the financial backing of Nederlandsche Handel Maatschappij (the predessor of Royal Dutch Shell). Drilling locations were selected on numerous oil seepages. Subcommercial oil was found in two of the first four wells which were drilled using buffalo for power (Bishop, 2000). Drilling resumed in 1874 with steam-powered drilling equipment, but the next 5 wells were unsuccessful, which discouraged the investors. Refering to the chronology of the exploration concepts, the first play concept involved looking for anticlinal structures with shallow objectives, localized oil seepages, by using surface geological mapping and where necessary digging pits to be able to measure in detail the dip and strike of the beds. Based on the application of these methods, geological mapping was carried out in the areas of Purwakarta, Cirebon, Karawang and Subang in between 1910 and 1942. However, exploration activities were systematically were started in 1928 (Koch,1942 vide Sembodo 1967). Around 1928, gravity surveys were 269
conducted in the areas of Karawang, Bekasi, Indramayu, Purwakarta, Cirebon and Majalengka. During 1932 – 1934, approximately 1000 surface holes were dug to obtain samples for confirming geological structure. More than 32 exploration wells were then drilled in the period between 1932 and 1941 (Figure 4). In 1939, the drilling of RDG-33 in Randegan to a depth of 1532,5 m resulted in the discovery of commercial oil and gas. The folllow-up wells were RDG-34 and RDG -35 confirmed Randegan as an oil field. Other drilling operations were conducted in the Jatibarang area during the period 1932-1939 and there were several wells (Djatibarang-18, 38 and 41) drilled to 300-712 m depth with encouraging gas shows. Bangaudua-30 only indicated oil. In the Subang-Purwakarta area, drilling the Pasirdjadi-18, 19, 21 and 22 wells discovered gas however, Tjitjadas-75 and 75A wells failed to discover hydrocarbons. Most of the wells were drilled in the KarawangBekasi area, with additional gas discoveries were at Tjitjauh-1 and 2, Bolang-56, 113, 130 and 140 (Figure 5). From all the wells drilled during this periode only the Randegan wells were successful in discovering commercial oil. The productive reservoirs are sandstone of Upper Cibulakan. No report can be explained about reserves and production rates. During the War World II period(1942-1945), exploration activities in West Java were largely iddle and following that, only rehabilitation of fields destroyed during the war was conducted until 1965. High Trend Concept
In 1968 PERTAMIN and PERMINA were integrated as one entity known as PERTAMINA, who then intensively conducted seismic surveys. The drilling of the Jatibarang (JTB)-42 well in 1967 was noted as Pertamina’s first well in West Java; the next well was Jatibarang-44 which discovered the major oil field. The play concept during this phase involved exploration activities aimed at searching for anticlinal structures on a High Trend. Subsequently, with the improvement of resolution of digital seismic data, Pertamina conducted a seismic survey around the Jatibarang and surrounding areas. The Jatibarang oil
discovery marked the start-up of the excistence of the modern Petroleum Industry in West Java. Reserves at Jatibarang were estimated at more than 200 MMBO and the early production rate was approximately 27,000 BOPD. The productive reservoirs are volcanics of the Jatibarang Formation. Since that time, exploration well drilling has continued until the end of 1980’s. Some discovered oil fields were Jatibarang, Sindang, Gantar, Tugu and Cemara (Figure 6). Seismic acquistion technology has improved continously, from 6-folds coverage to 12-fold, recording channels 14 to 48, etc. As the High Trend concept was applied, exploration efforts expanded to include areas away from the Jatibarang area. Some additional oil fields discovered include Cilamaya, Pegaden, Pamanukan and Rengasdengklok. Seismic section in figure 7 & 8 showing fields on High. The next discovery, Tambun-1 that was drilled in 1991, and discovered oil in limestone of the Batu Raja Formation, flowing at a rate of 1337 BOPD. The field was abandoned due to small reserves (< 5 MMBO). In 2000, the Tambun sytructure was reevaluated by geological modelling and a successful appraisal well was drilled, such that Tambun became a significant field. The latest discovery well was Pondoktengah-1. It was drilled in 2004. That is similar to Tambun-1, the productive reservoirs are limestones of Batu Raja Formation, flowing at rate of 1428 BOPD and also sandstone of Talang Akar Formation, flowing at rate of 1042 BOPD . Thrust Fault System Concept
Begining in the 1980’s the thrust-induced fold concept was applied. This concept also still focussed in the search for anticlinal structures however the origin of the structures is related to the presence of thrust-faulting. In Early Neogen a new subduction zone to the south resulted in series of east-west structures in the southern part changes of West Java. The compressional stresses peaked during the PlioPleistocene. Thrust faults were formed with associated anticlines and provide suitable structures for the trapping of hydrocarbons. Seismic acquisition technology has greatly improved to 24-fold coverage, 2 msec sampling rate, 48 channels etc and the seismic processing and resolution quality has also improved. 270
The main play concept was to identify anticlinal structures having the Parigi Limestone as the primary objective as a result of the strong amplitude associated with the Top Parigi reflector. The drilling of the Pasirjadi (PSJ)-P.1 well in 1984 resulted in a blow-out and the rig caught on fire. In 1985 the next well, Pasirjadi (PSJ)-P.2 resulted in the successful discovery of the Parigi gas-field with a flow-rate of 8.7 MMCFGPD. Additional successes were made at Cicauh (CCH)-P.1 in 1988 and Subang (SBG)-1 in 1995 (see Figures 9 & 10). Deep or Sub-Basin Concept
This play concept involves the identification of clastic reservoirs deposited within rift-systems of the basin deep or sub-basin. This concept has been applied since about 1995 (Figure 11). Wanajaya(WNJ)-1 was the first well to have been drilled in the Cipunegara Low and resulted in subcommercial hydrocarbons. The next well was Tambun Kalapa (TKP)-1, located in the Ciputat Deep also resulted in uneconomic hydrocarbons. Subsequently, the Melandong (MLD)-1 well in the Cipunegara Low discovered commercial hydrocarbons at various levels. On test two sandstones reservoir in the Talang Akar Formation flowed at 872 BOPD + 5 MMCFGPD and 854 BOPD + 6.7 MMCFGPD, and a test of Batu Raja Formation limestone resulted 652 BOPD + 5.2 MMCFGPD. Due to the success of Melandong (MLD)-1 in 2000, Pertamina then carried out a 3-D seismic survey which covered approximately 560 km 2. The survey resulted in the generation of several drillable prospects. The drilling of Karangbaru (KRB)-1 in 2004 was a significant event and hydrocarbon were present at various levels. On test a conglomeratic reservoir in the Jatibarang Formation flowed at 447 BOPD + 5.3 MMCFGPD. A sandstone unit in the Talang Akar Formation flowed at 225 BCPD + 1.5 MMCFGPD and a test of the Batu Raja Formation limestone resulted in 1510 BOPD+ 5.6 MMCFGPD. Several other prospective zones were present but not tested. Present and Future Concept
Hydrocarbon accumulations associated with a particular petroleum system have key elements i.e. reservoir, trap, seal, source rock, maturity and charge. As a result, exploration play concepts have to be
adjusted to better understand geological features. Petroleum systems, therefore become more comprehensive and refine and also incorporate appropriate technologies as required. All of the above concepts are compiled, analyzed, combined and modified in order to search for opportunities for either conventional or unconventional exploration play concepts for finding oil and gas. Exploration targets should be concentrated not only outside of and among fields but also in brown fields areas. Therefore, subsequent improvement of key exploration tools in conjunction with application of these concepts will be able to maintain hydrocarbon reserves growth in West Java. In deep areas, exploration targets could be focussed by searching for objectives in the Jatibarang (Pre Talang Akar), Talang Akar and Batu Raja Formations. In High Trend areas the targets could be focussed on remaining structures in the Batu Raja limestone or Parigi limestone(Figure 13, 14&15). In the Thrust Fault belt system there still remaining areas offering potential for exploration with the Parigi limestone as the objective. Proven low-resistivity Upper Cibulakan Formation sandstones in the offshore Java area provide an exploration objective in the Pertamina onshore area, for example the Upper Cibulakan Formation sandstone was proven in Tegaltaman (TTM)-1, there is oil in string when it was swabbed tested. Figure 16 illustrate exploration reserves in period between 1968 and 2004.
CONCLUSIONS
It can be considered that the development of exploration play concepts in the West Java region can be classified in to 5 (five) stages. The first stage was the concept that was based on exploration near to oil seepages in conjuction with surface mapping. This concept has been applied since 1871 and early exploration drilling was done close to oil seepages areas. The second stage involved the concept of exploration on the ‘High Trend’. This concept has been applied since about 1960. Exploration drilling was focussed on prospects located on a particular High Trend. This play concept was successfull in the discovery of several fields i.e. Jatibarang, Cemara, Kandanghaur, Tugu, Cilamaya, Pamanukan and Gantar. 271
The third stage in the development of the play concept in West Java was that of the Thrust Fault System. This concept has been applied since about 1980 and guided the identification of anticlinal structures that developed as a result of compressional force. Several fields were discovered including Pasirjadi, Subang, Jatirarangon and Cicauh.
permission to publish this paper. We wish to thank also the members of Pertamina’s Exploration staff in Cirebon and Jakarta, especially Mr Waluyo for correcting the text language.
The fourth stage involves the concept of a basin Deep or Sub-Basin. The concept is to identify clastic reservoirs which were deposited within a rift system in the basin-deep or sub-basin. This concept has been applied since about 1995. Discoveries associated with this concept include Wanajaya-1, Melandong-1, Tambun Kelapa-1 and Karangbaru-1.
Bishop,G.M., 2000. Petroleum System of the Northwest Java Province, Java and Offshore Southeast Sumatera, Indonesia, US Dept. of the Interior , Geological Survey.
The fifth stage is the concept of Present and Future. Better understanding of geologic features and refinement of the petroleum system to be more comprehensive and detailed, and use of appropriate technologies are required. All of the above concepts can be combined to search for opportunities for either conventional or unconventional exploration play concepts for finding oil and gas. Exploration targets are not only outside and among fields but also in brown fields. ACKNOWLEDGEMENTS
The writers wish to thank the Management of PT Pertamina (Persero) for their support and kind
REFERENCES
Eksplorasi DOH JBB, 2003. Buku Data Eksplorasi DOH Jawa Bagian Barat, Pertamina DOH JBB, Cirebon (Pertamina Internal Report). Pertamina , 1982. Buku 25 Tahun Pertamina, 19571982, Jakarta. Sembodo,1967., Laporan Tentang Hasil Survey Sumur-sumur di Djawa Barat, Bagian Eksploitasi PN Permina, Djakarta (Pertamina Internal Report).
Zeliff, C.W.,Trollope, S.W., and Maulana, E., 1985. Exploration Cycles In The Corridor Block South Sumatera, Proceedings Indonesian Petroleum th Association, 14 Annual Convention, v. 2, p. 379400.
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Figure 1 - Location Map of Exploration Working Area in the Northwest Java Basin.
Figure 2 - Regional Tectonic Map and Schematic West-East Structural Cross-Section.
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Figure 3 - Generalized Stratigraphy of the Northwest Java Basin.
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Wells (Location)
Year
Terminal Depth ?
Tested Interval /Formation
1871
4 wells in Cibodas
1932
Tjitjau-1
677 m
590 m
Blow-out, 50 m3/day Gas
1932/33
Djatibarang-18
502.5 m
313 – 316 m
Gas 53 mm3
1932/33
Bolang-56
710.5 m
505 m
1000 m3/day Gas
1933
Djatibarang-38
712 m
?
Blow out, abandoned
1933
Anjatan-65
723 m
?
dry
1933
Tjiasem-48
906.7 m
1933
Tjitjadas-75
650 m
?
dry
1933
Tjitjadas-75A
300 m
?
dry
1933
Tjitjende-19
1933
Bolang-130
1933
2 wells with oil indication
906.7 m
Gas 200 m3/day
832-850 m
75 m3/day gas
1181 m
566-598 m
70 m3/day, crush fondation
Bolang-113
535 m
490-496, 522-534 m
620 m3/day gas
1933
Binong-185
545 m
477 - 479 m
gas indication
1933/34
Bolang-140
562 m
450 m
1500 m3/day gas Gas
1933/34
Pagelaran-40
1144 m
?
1934
Pasirdjadi-19
2700 m
584 - 598 m, Parigi
Gas 149 m3/day
1934
Tegalwaru-1
2046 m
679,5 m
dry
1938
Tjitjau-2
3157 m ?
575 – 610 m
70 m3/day gas
!938/39
Bangadua-30
3100 m ?
1938/39
Pasirdjadi-18
1160 m
669-671 m
Oil odour
1939
Randegan-33
1532.5 m
Upper Cibulakan
Oil & gas
1939
Djatibarang-41
300.4 m
Rengasdengklok-1
2507 m
1940/41
?
?
Result
?
?
100 m3/day gas
gas indication
Gas indication
1678 – 1683 m
0.9 m3/day oil +
1645 -1670 m
9.6 m3/day gas
566 – 569 m
Gas
1941
Pasirdjadi-21
569 m
1941
Pasirputih-1
2031 m
?
dry
1941/42
Kandanghaur-28
451 m
?
dry
1941/42
Karokrok-1
2095 m
1942
Pamanukan-1
1327 m
1469 – 1488 m,
oil & gas indication
2014-2031 m
oil & gas indication
?
dry
Resumed from : Sembodo, 1967, Laporan hasil survey sumur-sumur di Jawa Barat Author assume that number of wells more than above table
Figure 4 - Drilling Activities during the Period of Indonesian Pre-Independence.
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Figure 5 - Oil Seepage and Anticline Play Concept – location of wells and fields in West Java.
Figure 6 - High Trend Exploration Play Concept-location of fields and discoveries.
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Figure 7 - North-South Seismic Section across Jatibarang field between Babadan and Jatibarang Lows.
Figure 8 - Seismic Section showing High Trend Play Concept.
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Figure 9 - Thrust Fault Anticline Play Concept-location of fields and discoveries.
Figure 10 - North-South Seismic Section illustrating Thrust Fault Play Concept.
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Figure 11 - Deep Exploration Play Concept-location of fields and discoveries.
Figure 12 - Exploration concept in Cipunegara Low with objectives limestone of Batu Raja, sandstones of Talang Akar and volcanic sandstone & conglomeratic of Pre-Talang Akar Formations.
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Figure 13 - Integrated Exploration Play Concept in Present and Future.
Figure 14 - Seismic Section showing Exploration Concept on High Trend with Baturaja limestone objective.
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Figure 15 - Seismic Section showing High Trend Exploration Concept on High with Baturaja limestone and Parigi limestone objective.
Figure 16 - Diagram of Exploration Reserves discoveries in West Java.
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