© IPA, 2006 - A Geological Trip to Cepu Area for Non-Geoscientist Personnel, 2003
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INTRODUCTION
THE GEOLOGY OF SANGIRAN AREA
THE GEOLOGY AND HYDROCARBON POTENTIALS OF NORTHEAST JAVA BASIN
3.1 Physiography
3.2 Tectonic Evolution and Structural Frame Work
3.3 General Stratigraphy.
3.4 Exploration and Production History
3.5 Oil and Gas Field
DESCRIPTION OF STOP LOCATIONS
4.1 Day - I(One)
Stop - I
Sangiran "Prehistoric Site" Museum - Sragen.
Stop - 2
"Bledug Kuwu" Mud Volcano - Wirosari.
Stop - 3
Foraminifera-rich sand reservoir of Selorejo Format~on- Gadu RiverNillage.
Stop - 3A
Massive mark of Mundu Formation - Ngawenan V~llage.
Stop - 38
Bedded sandy limestone of Ledok Formation - Modang River.
4.2 Day - 2 (Two)
Stop - 4
Pusdik Migas # 1 , Gas Producer Well - Balun Gas Field
Stop - 5
Loco Tour at Gubuk Payung Teak Forest. Lunch & Tayub Dance.
Stop - 6
Quastz sand Reservoir of Ngrayong Member of Tawun Formation - Braholo
River.
Stop - 7
:
The "Oldest" Oil Field in Java, - Ledok
4.3 Day - 3 (Three) :
Stop - 8
:
Traditional Oil Mine - Wonocolo Oil Field
Stop - 9
:
Teak Handy Craft - BatokanlBandar Village
Stop - 10
:
Deep Marine Sediments of Kalibeng Formation - Meduri Village.
Stop - II
:
Turbidite Sediments of Kerek Formation - Kedungkrambil Village.
4.4
Day - 4 (Four) :
Free Time and Batik Shopping at Pasar Klewer Solo City.
1. INTRODUCTION
NorthEast Java Basin, though it contributes only a small amount to the 1.3 million-barrel oil per day of
national production, has a significant means to the oil industry. It has the first well drilled in Indonesia
The well is located about 20 km west of Cepu and it was drilled in 1893. This well
(Ledok #I).
marked the beginning of oil industry in Indonesia. Since then, numbers of oil field have been
developed in the region (Kawengan, Ledok, Semanggi - Nglobo and other smaller fields). Some of
those fields are currently still in production. One of them, Wonocolo oil field, is still producing and it is
dedicated as a life monument. Currently, local peoples mine the oil using a traditional method.
North East Java Basin contains of thousands meters of tertiary sedimentary (rocks) sequences. The
sequences have a good potential of hydrocarbon source rock and reservoir rock, the two most
important elements of a petroleum system. Numbers of company have been discovered oil and gas
fields in the basin. One of them, JOB PertaminalSanta Fe (now Devon) produces approximately
10,000 bbl of oil per day from their Tuban oil field. The recent oil discovery was made by MobileExxon and can be categorised as a largest discovery over the decade.
Having considered those perfect setting, Pusdiklat Migas was established in Cepu years ago. It
provides a facility to train people to become professional workers in oil and gas industry.
The field trip is designed to introduce part of the upstream petroleum activities to the nongeoscientists. The participants will be introduced to the 'term' and 'jargon' use by geoscientists such
as: source rock, reservoir rock, formation, structural trap, oil seep, migration, fossil, oil fields etc. You
don't have to be bothered in remembering all of those, but by the end of the trip it is expected that
you will understand the big picture of petroleum exploration processess. This knowledge,
undoubtable, will help you in developing your career in petroleum bussiness in the future. Moreover,
you have chances also to be a 'fossil hunter' in some stop location, or you may prefer to be a dancer
in loco tour session. The choice is yours.
2. THE GEOLOGY OF SANGIRAN AREA
2.1 Introduction
Sangiran is located about 15 kilometers north from Solo, or about 30 kilometers from Adisumarmo
Airport, the airport of Surakarta.
A paved road connects Adisumarmo witli Surakarta and then to Kali Jambe. The remaining distance
of 5 kilometers will be traveled on a fairly good-asphalted road leading to the Sangiran museum. The
museum itself was built on a hilltop, sitting on the "Pleistocene Laharic Breccia of Pucangan
formation" and has a magnificent view of the surroundings.
From the geological point of view, Sangiran has been the subject of many studies since the half of
nineteenth century. The area has been studies intensively by Martin (1919), I-ovis Jean Crefien Van
Es (1031 - 1939), 1 Duyfies (1936), RW Van Bemmelen (1937 - 1949), and Van Koeningswald
(1934 - 1941). Very soon after the war, in the early 1960, Indonesian researchers in geology and
paleontology such as Sartono, T. Jacob and others resumed the study of physical anthropology of
the hominid fossil found in this area. One of the important discovery is the fossil of old java man or
known as Pithecanthropus erectus.
2.2 Physiography and Structure:
Physiographically, Sangiran lies on a board of depression called the Central Java depression zone or
the Solo zone (Van Bemmelen, 1949).
Structurally, the Sangiran area is an elongated dome in a North-Northeast to South South West
(NNE - SSW) direction and it is about 3 kilometers wide, while the North - South (N - S) diameter is
about 6 kilometers.
There are speculations about the origin of the dome; Van Bemmelen (1949) stated that its origin
corresponds with a compressive force related to volcano-tectonic collapse of the old Lawu volcano.
Van Gorsel (1987), on the other hand, speculated that it may be originated by diapiric shale flow, a
wrench related fold or even an incipent volcano.
Erosion following the formation of the dome has caused the exposure of rock formation in somewhat
concentric manner, in the form of circular hills and valleys.
2.3 Stratigraphy:
Kalibeng Formation
The oldest formation that croping out in the Sangiran area is the marine Kalibeng formation. Part of
the Kalibeng formation that exposed in Sangiran area, consists of dark grey to bluish grey marl clay
and callareous Sandstones. This part of formation is overlain by calcarenites and calcirudites, rich in
Balanus and Turitella fossils, indicates a shallow marine deposition.
Pucangan Formation
The lower part of the Pucangan formation called Lahar member: it consists of conglomeratic
sandstone and breccia with andesite fragments imbedded within the matrix. Fragment of ~marlsand
calcareous sandstones, originating from Kalibeng formation are also faund, indicating that Pucangan
is unconformably overlying the Kalibeng.
The rock of this lower member is resistant to erosion, and forms cicular hills surrounding the
Kalibeng formation. Numbers of vertebrate fossils like stegodon species of the Jetis fauna of Van
Koeningswald indicating of the early pleistocence age.
The upper part of the Pucangan Formation consists of blue-grey clay with brackish water mollusca,
ostracods and forams indicating a marine-fresh water transitional environment such as an estuary or
bay. This lower part terminated thick of laminated diatomites, composed of supposedly marine
diatoms Cyclothella and Thallasionema.
The upper part of black clay member consists mainly of fresh water black clay, probably of lacustrine
origin with mollusca, ostracods and some vertebrate bones. Thin tuff layers of only several
centimeters thick are also found on this upper member. The whole formation has been deposited
firstly on transitional environment and then eventually followed by fresh water deposition with
moderate volcanic influence.
Kabuh Formation
The lower part of the Kabuh formation consists of lenticular calcareous conglomeratic sandstone
layers, called the "Grenz Bank" or boundary layers overlying horizons are sequence of fining upward
fluvial deposits, consist of channel conglomerate graded into cross bedded sandstone. Several tuff
layers are found within this sandstone.
Vertebrate and Hominic fossils are found in the "Grenz Bank", in the rniddle part of the Kabuh
formation including the Homo erectus fossils. The exact location, where those fossils were originated
is very difficult to point out. The fossils were discovered as loose material scattered in blind valleys
after a heavy rain.
Notopuro Formation
This formation consists of mostly volcanic material such as volcanic sandstones, conglomerates and
breccias with cobble to boulder size andesite fragments, indicating a laharic deposit. This laharic
deposit is often called the upper lahar, just to differentiate it from the older or lower lahar of the
Pucangan formation.
This upper lahar forms the scarp face of the second or outer circular hill surrounding the Sangiran
area. The fossils are very rare in this formation, although some vertebrate fragments were found,
which may have been derived from the underlying Kabuh formation.
Notopuro formation is interpreted as has been deposited in a non-marine environment, influenced by
heavy volcanic activities during the upper Pleistocene.
2.4
Fossils
Different kinds of fossil that have been discovered in the Sangiran area include:
Pre Historic man:
-
lvlegantropus Paleojavanicus
-
Phitecanthropus Erectus
-
Phitecanthropus Mojokertoensis
Homo Soloensis
-
Homo Sapiens
Vertebrates:
-
Gading Gajah
Tanduk Kerbau
-
-
Tanduk Rusa
Gigi Buaya, Ikan Hiu
DII.
3. THE GEOLOGY AND HYDROCARBON POTENSIAL OF THE NORTH-EAST JAVA
BASIN
3.1, Physiography:
Base on the tectonic characteristic, stratigraphy, paleogeography and hydrocarbon potential, the
east Java area can be grouped into 5 (five) sedimentary regimes, (fig. 3.1) fro111the north to the
south:
1.
The stable Continental shelf of Rembang Zone.
2.
The Transitional of Randublatung Zone
3.
The labile deep sea basin of the Kendeng Zone
4.
The Volcanic Belt.
5.
The southern continental shelf ISouthern Mountains.
3.1.1 The Stable Continental Shelf of Rembang Zone:
The zone extends across the northern margin of east Java and separated from the Randublatung
zone by Lusi through in the west, Kening trough in the middle and the Solo trough in the east.
5
-
--
It IS a hllly zone wlth the tectonlc lntenslty IS hlgher than that of Randublatung zone, but lower than
that of the Kendeng zone
It formed the Rembang antrcl~nor~um,
or whlch marly anticlines are
superimposed
Sandstone and carbonate are the dominant lithologies of the area with marl and clay intercalation. It
is interpreted as having been deposited on a continental shelf. The rate of deposition is slower than
the rate of subsidence.
The zone has a very good reservoir and source rocks potential. More than 5 (five) oil fields have
been developed in the Rembang Zone
(Ledok, Kawengan, Nglobo, Semanygi, Banyubang,
Wonocolo), since 1800th.
3.1.2 The Randublatung Zone :
The Randublatung Zone includes Blora and Cepu hills, Ngimbang and Dander hill (van
Bemmelen,l949) or the transition zone ( Soeyono Martodjoyo, 1978), the zone is gently deformed
and structurally lower than the Kendeng Zone and Rembang Zone.
Dominant lithologies are mark
and clays with sand intercalation. Calcarenite and carbonates are
the most important reservoir that are thought to have been deposited upon on undulating continental
slope or transition zone. The Cepu Anticlinorium and other highs such as Pegat, Dander, Nginibang
and Gragis anticlines were elevated areas while the Lusi, Keriig and Solo troughs acted as deeper
regions.
It seems that the zone has the same capacity between the source and reservoir rocks, moderate rate
of deposition, which rate of deposition more or less equal to the rate of subsidence.
More than 20 (twenty) oil fields have been developed within the zone since the 1830, but most of
them were abandoned. Except the Kawengan, Wonocolo, Ledok and Nglobo oil fields and also the
Balun gas field, which still keep on production by Pertamina.
3.1.3 KENDENG ZONE:
It corresponds to the Kendeng hill (Van Bemmelen, 1949) or the labile deep basin (Sujono
Mortodjojo, 1978). lnstitut Teknologi Sepuluh Nopember Surabaya is sitting on a hilly zone, built from
very intensive tectonism that elevated the Kendeng anticlinoriunl.
Tectonic intensity in the Kendeng zone decreased from the west to the east.
There is no indication of hydrocarbon in the west. There are many oil seepages in the center
although no oil fields have been discovered. In the east, there are 3 (three) oil f~eldshave been
developed near Surabaya (Lidah, Metatu, Sekar Korong). The Kendeng zone is dominated by
volcanoclastics and mark. Minor intercalation of clays, sands and carbonates, which are interpreted
as originally deposited in a deep sea basin.
Source capacity (fine sediment) is bigger than the reservoirs (coarse sediment), the rate of
deposition is fast and possibly greater than the rate of subsidence.
3.2 Tectonic Evolution and Structural Frame Work
The tectonic evolution of East Java can be traced from late cretaceous (92 - 66 ma) to Recent,
during Paleogene (Pleocene - Eocene - Oligocene or 65.5 - 25 ma).
The tectonic tension regime
was active, and resulting of normal faulting, structure high and low on the basement, (see fig : 3.3).
During Neogen (Miocene - Pliocene or 25 - 1.6 ma), the tectonic conipresslon regime was active
and resulting of folding and faulting structure on the Paleogen and Neogen Sediment ( see fig : 3.8).
The recent geological frame work can be divided into two groups , first structural groups with SW -
NE direction parallel to the Meratus Structure as an old structure and the second structural
group ( young structure ) with E-W direction parallel to the Java Island, see fig. : 3.4.
3.3 General Stratigraphy
3.3.1 Stratigraphy of the Rembang Zone
Pre-Tertiary "Cretaceous" Basement
The Basement in the northeast Java basin consists of arcuate series of melanges of locally thrusted
metasediments separated by SW-NE trending micro continent highs. During the cretaceous, these
micro continents and associated sedimentary wedges were accreted to the southeast margin of the
Sunda Craton.
Wells data indicate that basement rock comprises accretion wedges of gabro, ophiolites,
metamorphic rock, and metavolcanic/volcanic, igneous, cretaceous sediments, which
IS
lithified
sequences of sandstonelshale with some chert.
The Eocene Nqimbann Formation
The Ngimbang formation is described base on Ngimbang-I well; there is no outcrop of the formation.
The middle Eocene sediment comprises of a sequence of sandstone, siltstones and shales
unconformably overlies the cretaceous basement.
This sequence is overlaid unconformably by the middle to late Eocene series of the alluviallfluvial,
deltaic, lacustrine and marginal marine deposits of the middle to late Eocene Ngimbang Formation.
This sequence can be divided into 2 (two) main sedimentary units, which are the Ngimbang clastic
and Ngimbang carbonate.
The Olinocene Kuiunn Formation
The Kujung sediments were deposited during the period of sea level high stand in the stable shallow
self-environment. The early Oligocene - Kujung sediment consists mainly of limestone, shale and
sandstone interbed, and conglomeratic sediments with coal intercalations.
The Late Oligocene Prupuh Formation
In the late Oligocene time, most of Northeast Java areas were covered by shallow marine
sedimentation, which typified by carbonate deposition with reefal carbonate on the paleo basement.
The reefal carbonate - Prupuh formation is an important reservoir target now, Santa Fe - Tuban,
Mobil Oil - Cepu and Pertamina.
The Lower Miocene Tuban and Tawun Formation
Tuban Formation:
The type locality of the formation is Drajat village, Tuban, East Java. The thickness of the formation
is more than 144 m (Ngesong village), -1- 533 m (Prupuh village) and 665 ni (Drajat village)
The lithology is mainly clay with intercalation of limestones and planktonic rich-foraminifera niarls.
Based on foraminifera1 content, the age of the formation is lower Meocene (N5 - NG), deposited in
shallow marine environment, between 50 - 150 m depth (outer neritic).
Tawun Formation:
The type locality of the formation is possibly Tawun village (near Cepu), the thickness is about 150
m. The lithology composed of interbedded between shale, shaly sand, and sandy shale with
intercalation of orbitoid limestone in specific brownis red color.
The Formation is Lower Meocene age (N7 - N8) and deposited in a shallow open marine
environment.
The Ngravonn Member or Formation :
The type locality is possible in the Ngrayong village, closed to Kawengan oil field; the thickness of
the member or formation reached 300 m thick. The lithology is dominated by quartz sands,
intercalated by sandy shale and limestone and sometimes lignite or coals with parallel laminations,
crossbeddes structures.
The depositional environment of the unit is fluvial or estuarine (Jatirogo), marine shallowing upward
shore face to beaches (Ngampel) and becomes more marine to the south.
The quartz and of the Ngrayong formation is the main reservoir in Cepu areas, The thickness range
from 30m to 60 m, the porosity ranges from 16 - 21 %, permeability 31 - 1G5 milli darcy and with the
depth varies from 400 - 600 m in Kawengan - Wonocolo oil fields.
Bulu Formation
This unit was formerly called "Platen - Complex" by Trooster (1973, and consists of platy, sandy
limestone with intercalation of sandy marl. Extremely large foraminifera (Cycloclypeous annulatus)
are abundant locally. Harsono (1983) formally describes this unit as a formation by establishing a
type - locality near Bulu village, district of Rembang. Age of this formation is Middle Ivliocene, zone
N13. In the Rembang quadrangle, this formation is widely distributed especially in the northern
Rembang anticlinorium. The unit thickens to the west, and at the Larangan River it reaches a
thickness of about 360 m. In the east, the Besek River (type - locally area) it is about 80 m thick.
Lithology and fauna indicate deposition in a shallow open - marine.
Wonocolo Formation
The Wonocolo marl was classified as the lower member of the Globigerina Formation by Trooster
(1937).
It consists of generally unstratified mark and clay. Sandylimestone and calcareous
sandstone are present in the lower part, which represents a deepening - upward transgressive
sequence. According to Marks (1957) and Harsono (1983), its age is middle to late Miocene, zone
N14 - N16. Thickness of the unit is variable, and increases to the south (up to 500 m?). To the north
it may grade into a limestone facies. Lithology and fauna indicate deposition in a deeper marine,
outer sublitoral environment.
Ledok Formation
Trooster (1937) first described this unit as a member of the Globigerina Formation. Many authors
have later been using this name as its original status; Marks (1957) and Harsono (1983) raised this
member to a formation level and described it as (glauconitic) sandstone with intercalations of platy
10
calcarenite and claystone. Its age is late Miocene. In the Ledok anticline, it is 230 m thick, about 160
m at the Panowan River and about 50 m at the Cegrok River section of Ngampel. In some places the
sandstone is mainly compossed of planktonic foraminifera1 shells and minor quartz. The formation
locally contains abundant glauconites. Cross beddings are observed in several localities. Overall, the
lower part of the formation is finer grained than the upper part, suggesting a marine shallowingupward sequence. To the north, the formation probably grades into limestone facies (Paciran
Formation).
Mundu Formation
This unit was called Mundu stage by Trooster (1937) and was named Globigerine Mark by van
Bemmelen (1949). Marks (1957) placed this marl in a formation level. It consists of white-grey,
massive marl with abundant planktonic foraminifera and comformably overlies the Ledok Formation.
The formation is very widely distributed. It is thickening to the South (up to 700 m). The age ranges
from Miocene to Pliocene (zones N17-N21), environment of deposition is deep marine (bathyal).
Seloreio Formation
Formerly called as Selorejo beds by Trooster (1937), then was classified as a member of the Lidah
Formation by Udin Adinegoro (1972) and Koesoemadinata (1978). Since Harsono (1983) did not
observe any unconformity between the Lidah and Mundu Formation, he included the Selorejo
member in the Mundu formation. The type locality is in the Selorejo village near Cepu and consists of
harder and softer interbeds, and the remainder is being mostly glauconite. The forams suggest a
deep marine environment, but the facies is unusual in that all the fines usually found in such an
environment are winnowed out.
This member is narrowly distributed in the areas west and east of Blora as well as south Pati. Its
thickness varies from 0 to 100 m. The age of this unit is late Pliocene, zone N21, based on the
relatively high occurrence of calcarenites and produced gas from the same, or very similar unit in the
Surabaya Area.
Lidah Formation
This unit was called Margelton by Trooster (1937), which he divided into two stages, Tambakromo
and Turi - Domes. Harsono (1983) formalized this unit and placed it in a formation level. This
formation consists of bluish claystone and bedded marl with intercalations of sandstone and lenses
of coquina. The lower part of this formation is supposed to have been deposited in middle to outer
sublittoral environment, as indicated by faunal associations: abundant on planktonics, Pseudorotalia
sp, and Asterorotalia sp. Shallowing upward sequence occurred in the upper part of this unit, where
a shallow water environment prevailed, indicated by the presence of molluscan bearing layers.
Paciran Formation
This unit was called "Karren Limestone" by Van Bemmelen (1949). It is massive limestone typically
weathering to a Karren-surface where it is exposed. Harsono (1983) formally used the name Paciran
and placed it in a formation level by establishing type locality at pyramid hill, Pacarian, Tuban, Area.
It is present mainly in the northern part of the Rembang zone and its age is still debatable. Harsono
(1983) placed in the Pliocene - Early Pleistocene, being lateral equivalent of Mundu and the Lidah
Formations. However, in places it maybe older -equivalent of the Ledok and Wonocolo formations.
3.3.2 Stratigraphy of the Kendeng Zone
Pelann Formation :
The oldest formation in outcrop is the early Miocene Pelang Formation. The type locality for this
formation is in Pelang village, near Juwangi - Central Java. It consists of alternating massive to
bedded foraminifera rich mark; with some hard calcarenites bed containing displaced shallow marine
larger foraminifera.
Maximum measured thickness is 125 m but the base of the formation is not exposed. The formation
was accumulated in neritic environment.
Kerek Formation
The overlying Kerek Formation can be subdivided into the Banyu -Urip Sentul and Kerek Formation,
with the type locality is in Kerek village - Ngawi, East Java.
The formation is composed of a turbiditic series of clays and marls, alternating with callareous,
tuffaceous sandstone. At several localities, such as in Ngawi along Solo River, a coarse
conglomeratic zone with fragment of limestone and volcanics is present at the top of formation
(Kerek Limestone).
The thickness of the formation is more than 800 m thick. Based on the planktonic foraminifera1
content, the age of the Kerek Formation is middle to late Meocene (N10 - N17), deposited in the
deep marine environment.
Kalibenn Formation :
The late meocene to pleocene (N17 - N21) are mainly represented by globigerina marl, with few
intercalations of limestones. The thickness of the Kalibeng Formation is 500 - 700 m. The type
locality is in Kalibeng River, North of Jombang - East Java.
The formation was distributed in the deep marine environment, since is has no indication of
sedimentary structures and massive.
Klitik Limestone - Sonde Formation :
Klitik Limestone is the lower part of the Sonde formation, it is about 50 - 150 m thick, with the type
locality is in Ngawi - East Java.
Sonde member is the upper part of the Sonde Formation. The thickness of the formation is about
260 m. The type locality is at Sonde village - West of Ngawi - East Java. It is consists of orgilaceous
carbonate rocks or marls and Balanus wackstone or grainstone.
Pulangan Formation :
The type locality of the formation is in the Gunung Pucangan - North of Jombang East Java. The
thickness of the formation is about 323 m.
The formation is mainly composed of conglomeratic coarse sandstone, tuffaceous sandstone, and
volcanic breccia with shallow marine fossils.
It becomes more terrestrial toward the west, as black clay, which contain fresh water mollusk,
fragments of terrestrial aquatic animals such as alligators, hippos and even fragments of the early
hominoids, the Homo erectus in the Sangiran area.
Those features indicate that paralic to lamnic environment was preailed during the early Pleistocene.
Kabuh Formation :
The type locality of the Kabuh Formation is in the Kabuh village North of Jombang - East Java, and
the thickness reached more or less 150 m.
The formation consists of interbedded of crossbedded sandstones, lenses of conglomerates and
yellow tuff. Vertebrate fragments are frequently found within the coarser part of this formation.
Overall grain size is decreasing from very coarse to medium grained sandstones in central java
(Sangiran area) into medium to fined grained sandstone in east java (Kabuh area).
The formation is interpreted as having deposited in the continental, fluvial and limnic environment
during late Pleistocene or 0.75 my.
Notopuro Formation :
The type locality is in Gunung Notopuro, East of Ngawi East Java. It is about 50 meter thick.
The formation consists of mostly volcanic lahars and fluvio volcanic products such as breccia with
boulder size fragments imbedded within tuffaceous materials, conglomerates with volcanic fragments
and volcanic sandstones. This formation indicated the late Pleistocene volcanic activities, which are
direct predecessors of the present volcanoes in Java.
3.4 Hydrocarbon Exploration & Production History
Hydrocarbon exploration in the Northeast Java Basin has been started since 1871, based on surface
geology and oil or gas seepages in the area, exploration drilling were conducted and finally resulted
the discovery of the Kuti Gunug Anyar Oil Field (1888), Lidah Oil Field (1889) in the Surabaya area,
and the Ledok Oil Field (1893) and Kawengan Oil Field (1894) in Cepu area.
14
Following these discoveries, during the same delade, more than 25 oil fileds have been discovered
and developed in the Cepu - Surabaya area, but most of them were now abandoned.
In the 19701s, Pertamina conducted modern and intensive exploration in Cepu and surrounding
areas, several exploration wells such as Kujung-I, Dermawu-I, Purwodadi-I, Dander-I and Jatirogo1 have been drilled but failed to discover oil or gas in commercial quantities.
In the 19801s,Pertamina in Cepu area, JOB-Stanvac in Gundih area and JOB-Trend in Tuban area,
run geological and geophysical surveys and drilled several exploration wells but again they failed to
discover oil or gas.
In the 19901s, modern sequence stratigraphy concept was world widely applied in the petroleum
industries. Based on this modern concept, Pertamina, Humpuss, JOB-Santa Fe and JOB-Huffco
Brantas, started again to explore the onshore area of the Northeast Java Basin. Finally, JOB-Santa
Fe discovered oil in Tuban area, Pertamina found gas in Rembang area and JOB Huffco Brantas
found gas in Porong area, while Humpuss is still continuing exploration in Cepu and surrounding
areas.
In the 20001s, Humpuss and Mobil-Oil, finally discovered the oil reserve in commercial quantities
within "the reservoir of the Prupuh reefal limestone formation" in the Kalitidu area, south of
Bojonegoro - East Java.
3.5 Oil and Gas Fields
For the time being, only 5 (five) oil fields and l(one) gas field in the onshore area of the Northeast
Java Basin are still being kept in production:
1.
Kawengan oil field (Pertamina).
2.
Ledok oil field (Pertamina).
3.
Nglobo - Semanggi oil fields (Pertamina).
4.
Traditional Wonocolo oil field (Pertamina).
5. Soko-Tuban oil field (JOB-Santa Fe).
6.
Balun gas field (Pertamina).
The other oil fields, which have been developed and produced since 1888 until 1900's, have already
abandoned.
Kawengan is the biggest oil field in the Northeast Java Basin, the cumulative production reached 150
million cubicmeter in the 1990's. The production layers are the upper part of the Tawun Formation
(I),
the Ngrayong sand formation (2) and the lower part of the Wonocolo formation (3-9).
The quartz sand of the Ngrayong formation is the main reservoir, it is porosity range from 16 - 21%
permeability 31 - 165 milidarcy, with water saturation (Sw) more than 90% with the depth varies
from 400 - 600 meter in Kawengan-Wonocolo area.
Structurally, Kawengan is an asymmetric anticline with NW - SE direction. The south flank is
bounded by the reserve fault with the same direction. Several normal faults with NE -SW directions
devided Kawengan anticline into several blocks or culminations and become the boundaries of
production system. They are Kidangan (east), Ngudal, Wonosari, Kawengan and Wonocolo (west).
Balun is the only gas field in the Northeast Java Basin (onshore) structurally is a simple symmetric
anticline, east-west direction the reservoir is the globigerenid sand of the Selorejo Formation in a
depth around 400 - 500 meter. The Selorejo formation composed almost entirely of sand size
planktonic foraminifera and has major type of interparticle primary porosity, with porosity range from
APPENDICES
Geological Trip to Cepu Area for Non-Geoscientist personnel
October 10- 13, 2003
IPA - PUSDIKLAT MIGAS CEPU
Trip Leaders: 1. Nachrowi T Y.
2. Yohanes P. Koesoemo
Fridav, October 10.2003
04.30 - 05.00
06.40 - 07.40
08.00 - 09.00
09.00 - 10.30
10.30 - 13.00
13.00 - 14.30
14:30 - 15130
15.30 - 17.00
17.00 - 17.30
17.30 - 19.00
19.00 - 22.00
-
Assemble at Soekarno Hatta Airport Terminal I1 F
Soekarno Hatta Airport - Solo GA-220.
Solo - Sangiran (land transportation).
Sangiran Dome & Fossil Museum observation.
Sangiran - Kedungombo; Lunch break at Kedungombo Dam Site
Kedungombo - Bledug Kuwu / Mud Volcano.
Observation and explanation of Mud Volcano Eruptions.
Kuwu - Cepu (3 km west of Cepu) via Randublatung.
Observation of Cepu Gas Field
Check in at Widya Patra-I1 (Mentul Complex) and free time.
Dinner at Sate Ayu (Padangan - East Java)
Saturdav, October 11,2003
06.30 - 07.30
07.30 - 09.00
09.00 - 10.00
10.00 - 11.00
11.00- 12.00
12.00 - 13.00
13.00 - 14.00
14.00 - 16.00
16.00 - 17.00
17.00 - 18.30
18.30 - 19.00
19.00 - 22.00
Breakfast at Widya Patra-11.
PUSDIKLAT'S MINIATURE FIELD
Cepu - Wonocolo, 20 km NE of Cepu.
Traditional Oil Mine in Wonocolo.
PERTAMINA's Oil Wells and block station.
Lunch in PERTAMINA OFFICE.
Cepu - Blora, 30 km west of Cepu.
Geological Observation ; reservoir and source rock of oil.
Kalimodang outcrop & Gadu gas reservoir.
Back to Cepu.
Free time.
Dinner and Karaoke.
I
Sundav, October 12,2003
06.30 - 08.00 Breakfast at Widya Patra-I1 and check-out.
08.00 - 10.00 BatokanIKasiman Village (Jati Wood Home Industry).
10.00 - 13.30 Loco Tour and Lunch at Gubug Payung (Jati Alam Musseum).
13.30 - 15.00 Deep Marine Sediment Observation at Meduri.
15.00 - 17.30 Meduri - Ngawi - Solo (Novotel Hotel).
17.30 - 19.00 Check in and Dinner at Novotel Hotel. Free Time.
Mondav. October 13.2003
06.00 - 07.30 Breakfast at Novotel.
07.30 - 11.00 Free time and shopping.
13.00
Fly back to Jakarta GA-223.
1
Safetv
Safetv awareness is the number one ~rioritvon this fieldtri~,and is an integral art of each locality
Of particular note is the fact that a lot of outcrops are road cuttings, and consequently extreme
caution must be exercised at all these localities with regard to the traffic.
Health
It is advisable that all participants bring their own personal medical requirements with them on the
'
trip.
1 Emergency Contact Details
In the event of a medical emergency, it is advisable that all participants check on their insurance
cover, includmg insurance for medical evacuation to Jakarta or Singapore (e.g. AEA)
I
Transw rt
We will travel around Cepu area on a tourist coach. However, your main luggage bag will be sent on
directly to the following night's hotel accommodation, so it is recommended that a small rucksack or
bag is also taken for personal effects required during the day.
Hotel Accommodation
All hotel rooms are on twin sharing basis. IPA will cover room accommodation and group meals
only (breakfast, lunch and dinner). Minibar, phone and laundry will not be covered.
CEPU (October 10-11,2003)
Widya Patra I1
Jln. Sorogo No.1
Cepu
Ph. :(0296) 421-888 ext 202
Fax :(0296) 421 -891
SOLO (October 12-13,2003)
Novotel
Jln. Slamet Riyadi No. 272
Solo
Ph. :(0271) 724-555
Fax :(0271) 724-666
Surat Jalan
As per the letter from the IPA, it is your responsibility to obtain a travel permit prior to departure, if
required.
Thinps to bring
Please bring along your rain coat to anticipate rainy season, sun block cream, sun glasses and your
own personal medecine. Please also bring formal dress for 2ndday dinner.
Post~onement
The committee has the right to postpone the trip due to the political situation.
Fig. 2.1 : Geological of Sangiran Area (Stop Side -1)
Fig. 2.2 :Stratigraphy of Sangiran Area
MAGMATIC
BACK ARC BASIN
(NE. JAVA BASIN)
I
PALEOGENE TECTONIC REGIME
BACK ARC BASIN
NEOGENE TECTONIC REGIME
Fig. 3.3 : Tectonic Evolution Of East Java
FIG. 3.5
A G. MERAPI
A G . MERBABU
A G . LAWU
Tectono - Physio Stratigraphic zones of the North East Java Basin )
SURAKARTA
SEA LEVEL
CHANGES
t-""'I
IN
HYDROCARBON
SEQUENCE STRATIGRAPHY
OF CEPU AREA
I
OCCUR
I
OIL
FELD
BALUN
KAWENGAN
LEDOK
NGLOBO
S = Source Rock
LITHOL. UNIT
MAT.
MEMBER
DESCRIPTION
COLUMN
Lahar. dep. tufa. ss
Vluvlatile
Volc. Agl.
Marty
Volcanic fuff
Coraline 1st.
Unbedded Globigerina mari
Intercalation of cgl. ss. tuffa
Tuff. 1st. calcaren
Tuffa. and clay
Hard, sd
Marly and, clay
Intercalation of hard calcarenit
Harsono Pringgoprwiro, 1979
Fig. 3.7 : Stratigraphy of Kendeng Zone
W
0
AGWILIS
AG.ARJUN.4
Dataran Aluvial
Jalur Gunung Api
Lapangan Minyak I Ditiiggal
Lapangan Minyak I Produksi
tampak zone Kendeng, Randublatung dan Rembang serta lapanganlapangan minyak ( ditinggalkan atau masih diproduksi )
FIG. 3
.8 Zone Tectono - Physio - Stratigraphy Cekungan Jawa Timur Utara,
SCALE 1: L000.bDO
A G. L A W
0
0
Depresi Randublatung
Perbukitan Kendeng
KETERANGAN :
Bledug Kuwu Mud Volcano
Fig. 4.1 : The Mud Volcano of "Bledug Kuwu"
Location : South of Wirosari or east of Purwodadi. (Stop Side - 2)
A shale diapir generated by a combination of Neogene tectonic
compression and hydrocarbon gas pressure in the subsurface. The gas
from Ngarayong sandstone of Tawun formation which laid under the
plastic shale layer, push the shale layer formed a diapiric structure.
The explosion of diapiric shale occurred when the pressure is high
enough and exceeding the strain of the shale layer. The explosion
occurs periodically.
The shale layer thickness is 300 meters. This is the youngest formation
in the northeast Java basin.
Gadu River at Gadu village
Fig. 4.2 : An outcrop of Foraminifera1 sand
of Selorejo Formation
Location : Western Cepu city (Stop Side - 3)
An outcrop of foraminifera rich sand of Selorejo formation in Gadu
river. This marine sand was deposited during sea level drop 2.9 million
years ago. This sand act as a gas reservoir rock in Cepu.
Ngawenan village.
Location :8 km western side of Cepu city (Stop Side 3A)
An outcrop of massive marl of Mundu Formation containing more
than 98 % planktonic foraminifera indicating clays marine
sedimentation. The marl has low porosity and permeability and
deposited 5 - 2.9 ma (Pliocene)
Kalimondang river
Fig. 4.4.1 :~n outcrop of series sandy limestone,
of Ledok Formation
Location :8.5 km western side of Cepu city. (Stop Side - 3B)
An interbedded of sandy limestone and calcareous sands of Ledok
Formation cropping out along Kalimodang river, southern flank of
Ledok anticline. These sands were deposited during the late Miocene
(N.16 - 17) Bedding planes, mega cross beds, bioturbation, are all
indicating shallow marine depositional environment.
35
Fig. 4.4.2
Location : Kalimodang River (Stop Side - 3B)
An outcrop of Ledok Formation, Interbedded of Sandy limestones
Hard calcareous sands (soft), with bioturbation / burrows, mega
cross bedding, age of late Miocene (N. 16 - 17), 6.3 ma.
36
Balun Field, Gas well
Fig. 4.5 Balun Gas Field I Pra # 1 Gas Well
Location : Cepu city (Stop Side - 4)
Balun field reservoir is formed by foraminifera rich sandstones (N.21)
overlain by shales of Lidah Formation which acted as a caprock. The
hydrocarbon source is interpreted coming from Ngimbang Formation
shale and migrated through the fault zone.
The reservoir was penetrated at a depth of about 100 m the crest of
Balun anticline structure. Reservoir thickness is 20 meters in average.
Balun reservoir showed a good reservoir quality. Produced gas is used
for PPT MIGAS internally such as housing complex, refinery,
laboratory and student dormitory.
Braholo River
Fig. 4.7 : An Outcrop of Quartz Sand of Ngrayong member
Location : 10 km northern side of Blora. ( Stop Side - 6 )
Quartz sandstones, sandy clay and orbitoidal limestones croppe out at
Braholo river side cliff. The outcrop is part of Ngrayong Member of
Tawun Fonnation. In Cepu area the quartz sandstone is a reservoir
rock. The orbitoidal limestones contain fragmens and well preserved
molluscas and larger foraminifera (Lepidocyclina and cycloclypera).
The latests indicate Middle Miocene Age (Age (N.9 - 10).
Fault zone
A Fault zone as indicated by a water fall, fault breccia, slickenside on the fault
plane, striations joints, and H,S seepage in the bearing formation water.
Possible as a hydrocarbon migration pathway.
E - W Fault zone direction
Southern flank of Ngampel Anticline
39
Fig. 4.9 : An outcrop of hydrocarbon source rock
(carbonaceous shale, Middle Miocene Age)
Stop Side - 6
Fig. 4.10 : An outcrop of fault breccia in the Middle
of Braholo river (Ngampel Village)
Ston Side - 6
Y
Ledok Old Oil Field (7 km NW Side of Cepu)
Stop Side - 7
Fig. 4.11 : Well Ledok # 1 @ Ledok oil field, Stop Side - 7
Well Ledok - 1 (drilled in 1893 by BPM), is the first well of Ledok oil field
The discovery of the accumulation of hydrocarbon in this field is based on the
existence of oil seepage located at about 20 m west of Well Ledok - 1.
The hydrocarbons seepage on the surface is the product of migration, probaby
Coming from quartz sands of Ngrayong reservoirs below. The fault zones of
this area may act as migration pathway.
Ledok anticline with E-W fold axis direction, 4 km long and 1,5 krn wide, acts
as structural trap, shale of lower Wonocolo Formation behave as caprock, and
shale of Ngimbang Formation (more than 2500 m depth) Possible as source rock.
As a whale, BPM geologist have significant contributions to the beginning of oil
Industry in Jawa.
Stoo Side - 7
1
r
Fig. 4.13 :Pumping unit at Well Ledok # 152, Ledok oil field
(Stop Side - 7)
Ledok oil field, oil produced through pumping well unit
(Modern method)
I
* Government officials visiting traditional oil mine (above)
* A man transporting oils using traditional equipment (below)
Explanation :
A. Petroleum System at Wonocolo oil Field
1 . Source rock : Possible nature shale of Ngiiubang Formation
at over than 2500 111 depth, age Eocene
(P15-17) 138 - 37 ma.
2. Migration pathway : Fault zone.
Kawengan Tiust f a d t, a cross Southein
flank of Wonocolo anticline
3. Reservoir rock : Two horizons of HC bearing quartz sand of
Ngrayong member of Tawon FOI-mation,
12 111 thick,
age : Middle Miocene (N9 - 12) / 15 - 12 ma
Reservoir Data :
Porosity = 20.5 96,Permeability 52 md (~nilidal-cy),
Recovery factor = 65,5 %
4. Traps : WOIIOCO~O
Anticline I Structural Traps
5. Cap rocks : Intercalatioi~shale of power Wonocolo FOI-mation
B. Cuini~~ulative
Production = 2.035.000 in7(198 1)
S.G. of oil = 0.86 - 0.88
Oil Composition : - Bensene = 4 - 18 %
- Keresine = 37 - 49 %
- Residu = 32 - 58 %
- Paratine = 1 - 10 %
C. Traditional oil mine started fro111 : 1929
Meduri village
Fig. 4.19 An outcrop of massive marls of Kalibeng Formation
at Meduri Village, Stop Side 10
-
Location : 16 km southern part of Cepu (Stop Side - 10)
An outcrop of massive mads of Kalibeng Formation which is equivalent with Mundu
Formation. The outcrop is a deep marine facies. Age Pliocene (N.18-20)
Kedungkrambil village
Fig. 4.20 :An outcrop of Turbidite Sediment of Kerek
Formation at Kedungkrambil Villalge
-
Location : 10 km north of Ngawi. (Stop Side 11)
A turbidite outcrop of kerek Formation. Indicated by Bouma sequence
(Ta - Te). Age Middle - Late Miocene (N9 - N17)
Kerek Formation consist of 3 members : Banyuurip, Sentul and Kerek
limestone member (See Stratigraphy of Kendeng Zone, Fig. 8A)
.Teak forest plantation sight seeing with other natural beauties
.Using a three wagon train driven by an antique steam locomotive made by
Berliner Maschinenbau in 1928
.Taking approximately 4 hours to cover 60 km route ( not including several stops
for break, sight seeing and refreshment )
.Stop for lunch in Gubug Payung ( Natural Teak Forest Monument ) entertained by
local dance
.Teak trees with up to 50 meters high and of 125 centimetres diameters can be
seen. The use of teak wood : construction, bridges, shipdecks, furniture and
various kind of souvenirs