IPA08-SG-080
PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Thirty-Second
Annual Convention & Exhibition, May 2008
PERMIAN-CRETACEOUS HYDROCARBON PROSPECTIVITY AT BERAU PAPUA
Yanto Kambu*
Wahyu Permana*
ABSTRACT Berau area is located in the south of Salawati Basin,
Birds head, Irian Jaya Barat Province. Interaction eustatic sea
level with tectonic in bird head to result transgression and
regression phase that deposited potential sediment that useful in
petroleum system element that identified in well and seismic.
Perkins & Livsey R. A, (1993) to show Vitrinite reflectance
coal and claystone Permian Jurassic sediment from Gunung-1 well
have value above 1 ( v >>1), indicated over mature. Modern
well data, indicated in well JY-2 that the Berau area has
hydrocarbon potential. The result of this research, have been
interpreted with the following conclusion : Permian and Jurassic
sediment in Berau area have complete petroleum system element such
as Permian Jurassic Source rock(Coal, shale and interbedded black
carbonaceous mudstones), Jurassic and Cretaceous sediment as a
reservoir(Limestone, sandstone Jurassic Cretaceous shale as seal
rock and trap. So, we could conclude that this area has a good
hydrocarbon potential. Prospect area in Berau is located in south
area, precisely, at inverted fault anticline. INTRODUCTION Berau
area had been discussed by many researchers, such as: PigramJ. C.
& Panggabean.H, 1981; W.T ., and Livsey R. A, 1993.
Tectonically, the Berau area could be divided into two phases of
tectonic: rift phase and syn-orogenetic phase. The complexity of
tectonic activity caused the changing of depositional environment
from fluvial to shallow marine, this changing caused the sediment
that had been deposited have capability to generate hydrocarbon. *
University of Padjadjaran
This paper explains about petroleum system of the Berau area
using seismic, well log, and biostratigraphy data in order to
identify prospect area for hydrocarbon. METHODOLOGY Data collection
was done firstly. It was included seismic, well log, and
biostratigraphy. Depositional environment for each geological time
were generated by integrating biostratigraphy and log data that had
been interpreted. Stratigraphic cross-section was generated by
using seismic and log interpretation in order to know the lateral
continuity of sediment in detail and structure. Sediment thickness
of Permian to Cretaceous was interpreted by using seismic data.
Petroleum system and its relationship to depositional environment
were evaluated based on all interpretation. Finally, hydrocarbon
prospectivity of the Berau area was evaluated. RESULT Petroleum
System 1. Source Rock Potential
Source rock potential was determined by doing analog to the
source rock identified in the KBSA area (Paul J. Dolan, Hermany,
1988). Identified source rocks in the Berau area are Jurassic shale
and coal, and Permian carbonaceous mudstones and coal. Jurassic
Source rock Jurassic shale is characterized by induction log (ILD)
of 2-5 ohm, GR log of 112-131API and thickness about 265ft in well
JY-5, its lateral continuity spreads in all research area and were
found in all wells.
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Jurassic coal is characterized by low induction log of 2-10 ohm,
GR log of 57 API, and thin. It presences at well JY-2, JY-3 and
JY-6. The depositional environment of the Jurassic source rock were
inner to outer neritic. Its kerogen type is Type II (marine algae,
polen and spora, and fosil resin). This kerogen has capacity to
generate liquid hydrocarbon and gas (Figure 3).
Permian Source rock Permian source rock is composed of
interbeded
black carbonaceous mudstone and coal (Figure 2): Black
carbonaceous mudstoneS is a characteristic by Induction Log(ILD) of
2-15ohm, and thickness abouth 410ft, it presences in all well. The
Permian Interval was not penetrated in well JY-1. The Permian
source rock was deposited in shore to shallow marine
environment/inner-outer neritic (Figure 3), so it is possibly type
II of source rock kerogen (Marine algae, pollen and spora, and
fosil resin) and type III (shore organic material).
2. Reservoir Potential Some reservoir potential were identified
based
on log data (figure 2), they are: Cretaceous sediment
(limestone, sandstone) and Jurassic sediment (limestone,
sandstone).
Cretaceous Reservoir sediment is compoced of limestone which has
GR value between 17-19API, Induction log(ILD) of 9-20 ohm(figure 2)
and thickness about 1105ft in well JY-1, and thinner in the other
well and sandstone which has GR value between 70-75API, Induction
Log (ILD) of 2-9ohm(Figure 2) and thickness about 245 ft in well
JY-2. This sandstone presences in every well of research area
(Figure 4,5,6).
Jurassic reservoir consist of limestone that
characteristic by GR value of 35-50 API, Induction log (ILD) of
5-10 ohm and thickness about 50ft. this limestone presences in all
wells(Figure 4,5,6).
3. Seal Potential
Potential seal in the research area are Jurassic ands Cretaceous
shale (figure 2). Cretaceous shale has significant thickness of
1463 ft in well JY-2 and thinner in well JY-3, but it is very wide
spread. Jurassic shale has thickness about 98 -243 ft in well JY-6.
(figures 4,5,6).
4. Migration and Maturity The Roabiba and Ofaweri Jurassic gas
samples were generated at extremely high maturities greater than Ro
equivalence to 2.0%. The roabiba condensate was generated at a
middle mature Ro equivalence to 0.85%. This result indicates that
the Roabiba condensate was not generated as a thermal condensate
from the same source rock area as the highly mature Roabiba gas
(Perkins & Livsey , 1993). Base on that information, it can be
assumed that oil show in Roabiba and Ofaweri well is one package of
sediment. It can be estimated that migration were occurred through
Permian rifting (vertical migration) and accumulated in top of
anticline. We interpreted that hydrocarbon come from south of
research area or from north of Seram island and moved toward
anticline and fold that had been faulted (in seismic, it is marker
by symbol F1,F2, dan F3).
5. Trap From seismic data, hydrocarbon trap in research area are
stratigraphic and structural trap.
CONCLUSION Permian and Jurassic sediment in Berau area have
complete petroleum system element such as Permian Jurassic Source
rock(Coal, shale and interbedded black carbonaceous mudstones),
Jurassic and Cretaceous sediment as a reservoir(Limestone,
sandstone Jurassic Cretaceous shale as seal rock and trap. So, we
could conclude that this area has a good hydrocarbon potential.
Prospect area in Berau is located in south area, precisely, at
inverted fault anticline. REFERENCES Perkins. W.T and Livsey.R. A.,
Geology of theJurassic Discoveries in Bintuni bay, Western Irian
Jaya., proceedings Indonesian Petroleum Association, 1993
Froidevaux .M.C., Geology Of The Misool Island(Irian Jaya).,
Proceedings Indonesian Petroleum Association, 1974. Gumvan.R and
Martodjojo S., The Pretertiary System Of Misool Area., Proceedings
Indonesian Petroleum Association, 1984 Pigram J. C. and
Panggabean.H., Pretertiary Geology Of Western Irian Jaya and Misool
Island :
