3 D P R O P E RTI E S M O D E L I N G T O S U P P O RT R E S E RV O I R
C H A R A C T E R I S T I C S O F W-I T B F IE L D I N M A D U R A S T R A I T A R E A
By :
P. Hadi Wijaya1 and D. Noeradi2
(Manuscript received 20-January-2010)
ABSTRACT
The gas field, initial named W-ITB Field, is located at the southwestern part of the East Java
sedimentary basin in Madura Strait area. W-ITB Field was discovered by W-ITB#1 well in 2006.
In W-ITB#1 well gas reservoir layer was just only found at Selorejo and Mundu Formation, on
the other hand, on W- ITB#2 the gas reservoir is not found in Mundu Formation.
Determination of reservoir characteristic including the distribution and quality at W-ITB
Field, was done by using 3D geological modelling both for structure and stratigraphy. This model
was executed based on integration of well data (petrophysics) and cross section seismic
interpretation.
The results, at Zone 2 and Zone 3 for vertical V-shale distribution shows as a good quality
reservoir (0-15%). Laterally distribution, area at southwest of W-ITB 1 well has low V-shale or
chatagorized as a good quality reservoir. While, porosity distribution, zone 1 and zone 2 have
better reservoir (29-35% V-shale value) than Zones 3 and 4. NTG distribution result indicates
that zone 2 and 3, with high value means a good reservoir. Due to only two exploration well, to
guide lateral distribution, so that acoustic from seismic data is used for porosity distribution.
Key words: modelling, reservoir, characteristic, V-shale, porosity, quality, Madura Strait
SARI
Lapangan gas dengan nama inisial W-ITB terletak di bagian barat daya cekungan sedimen
Jawa Timur yang termasuk di wilayah Selat Madura. Lapangan ini ditemukan dari Sumur W-
ITB#1 pada tahun 2006. Pada sumur W- ITB#1 Lapisan reservoir yang mengandung gas
hanya dijumpai pada Formasi Selorejo dan Mundu, namun dari hasil sumur W- ITB#2, lapisan
reservoir gas dalam Formasi Mundu tidak diperoleh.
Penentuan karakteristik reservoir termasuk distribusi dan kualitasnya di Lapangan W-ITB
dilakukan dengan pemodelan geologi 3-Dimensi baik secara struktur dan stratigrafi dengan
berdasarkan pada integrasi data sumur pemboran dan penampang seismik yaitu analisis
petrofisik dan interpretasi seismik.
Berdasarkan pemodelan 3-Dimensi, pada Zone-2 dan Zone-3 untuk distribusi V-shale secara
vertikal merupakan zone dengan kandungan reservoir yang baik dengan nilai V-sh 0 15%.
1. Marine Geological Institute of Indonesia
2. Institute Technology of Bandung
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Volume 25 No. 2, December 2010
Secara distribusi lateral, wilayah di bagian barat daya dari sumur W- ITB#1 memiliki
kandungan V-sh yang rendah atau dikategorikan reservoir dengan kualitas baik. Adapun pada
distribusi porositas, Zona-1 dan Zona-2 mengandung reservoir yang lebih baik dengan nilai 29-
35% daripada Zona-3 dan Zona-4. Hasil distribusi NTG mengindikasikan bahwa Zona-2 dan
Zona-3 dengan nilai tinggi mengandung reservoir yang baik. Karena hanya memilki dua sumur
eksplorasi, untuk memandu distribusi lateral maka hasil impedansi akustik dari data seismik
digunakan untuk distribusi porositas.
Kata kunci: pemodelan, reservoir, karakteristik, V-serpih, porositas, kualitas, Selat Madura
INTRODUCTION Objectives of research are firstly to built
The gas field, initial named W-ITB Field, 3D structural model from time and depth
is located eight kilometers to south of Madura structural maps, secondly to create 3D
island. It is situated in the southwestern part of properties model especially volume shale (V-
the East Java sedimentary basin. This field is shale), porosity and net to gross (NTG)
controlled by an inversion structure that has reservoir. The 3D properties model supported
been active since Early Pliocene times. The by 3D structural model, log analysis and
gas field is a part of the eastern inversion seismic attributes could support reservoir
structure which is one of a series of east-west characteristics.
trending anticlines that were created along the
inversion zone (Figure 1).
Figure 1. Study area of W-ITB Field as a gas field in Sampang PSC of Madura Strait (courtesy Santos Pty.
Ltd.)
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Figure 2. Deposition model of the Middle Miocene Ngrayong sediments from the North Madura Platform
to the Madura Strait including depositional environments/facies from nearshore to bathyal.
Wells Camplong-1 and Pakaan-1 are now located on the uplifted Madura Island.
Sedimentologic succession of each facies is indicated (Satyana and Armandita, 2004)
Depositional Setting of South Madura Sub- associated with hemipelagic muds and
Basin contourites of Unit II and III.
In the South Madura Sub-Basin, recently An important aspect of the Selorejo/
acquired seismic data show good reflectors at Mundu play is the influence of tectonics. On a
the Ngrayong equivalent level, which may regional scale the position of the shelf-edge
relate to direct hydrocarbon indicators. break and other constraints, such as the timing
Ngrayong deposition in this area is considered of the areas various inversion structures, will
to be storm generated shelf turbidites and affect the distribution of the reservoir.
deepwater fans in slope to bathyal Significant deposition did not take place over
environments (Satyana and Armandita, 2004). the structural highs. The shelfal depositional
The Camplong-1 well drilled on Madura processes focussed the accumulation of the
Island by Shell in the 1980s penetrated feeder reservoir into the lows between the highs. To
channel facies in the Ngrayong. Southward be able to predict where the best quality
into the Madura Strait, Ngrayong sands were reservoir is likely to be, an understanding the
deposited as deepwater fans in the slope area distribution of accommodation space on the
(Figure 2). The Ngrayong sandstones in this shelf is needed. Good quality reservoir will be
fan are considered to be composed of in those areas where accommodation space
quartzose sands and channelized sand bodies was available during the Early Mid Pliocene.
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The key sequence boundary is top of Lower and seismic attributes, as well as considering
Mundu. regional geology to be input of geological
Top of Lower Mundu had a significant concept in petroleum system. For a reservoir
impact on the evolution of the Mundu-Selorejo with limited information it is clearly
depositional system. In the Early Pliocene the impossible to construct a model that fulfils this
volume of clastic input was minimal, a condition. But, it is possible to build models
carbonate platform (Karren) established itself that are designed with different specifications.
to the immediate north and water circulation So we can build models which would respond
patterns on the shelf changed. The period the same as the real reservoir for a very narrow
following top of Lower Mundu represents a subset of possible interrogations (Tyson and
time when conditions were optimal for the Math, 2009)
accumulation of foraminiferal grainstones and Building 3D static geological models for
packstones. W-ITB Field incorporating 2D interpretation
According to Triyana et.al., 2007, Santos both horizons and faults, petrophysical
geoscientists have developed a interpretation of well W1 and stratigraphic
chronostratigraphic scheme for the East Java subdivision of W- ITB#1 to W- ITB#2 Wells.
Basin based on commonly used sequence A new geological model will be built based on
stratigraphic principles (Van Wagoner et al, interpretations and analyses of all the available
1988). This paper uses nomenclature for geological, geophysical and 2D Seismic data
several chronostratigraphic units (notably the in around of W-ITB Field.
Mundu and Paciran Sequences) that are In determining reservoir properties, the
defined in that work. The geologic time scale integrated process between well logs and core
of Gradstein et al., (2004) has been used to test interpretation include Repeat Formation
build the chronostratigraphic chart (Figure 3). Test (RFT), Drill Steam Test (DST) cutting, X-
On the basis of geological outcrops Ray Diffraction (XRD) and the core routine
supported by core description and laboratory should be done to calibrate the validity of log
evaluations it was envisaged that the Pliocene derived reservoir properties is carried out by
productive Globigerinid-sand has been means of Geoscience Software and
deposited on the shelf, slope and deep floor Petrophysics Petrel. Using standard
settings of the NE-Java Basin (Sutadiwiria and formulas, reservoir properties i.e. V-shale and
Prasetyo, 2006). David M. Schiller et.al (1994) net porosity were obtained from gamma ray
noted that at least two distinct types of log, density velocity combined logs
Globigerinid sand deposits are documented respectively. Then, the analysis using cut-off
i.e.: planktonic foraminifera sand drift values of V-sh and net porosity logs will
deposited by bottom currents and less produce net to gross reservoir (NTG).
pervasive planktonic turbidite deposited as The upscaling process imports the well
submarine channel-fills and fans. data into those cells of the model penetrated by
the wells. Each cell has a single value for each
METHODS property and it is derived from averaging the
To determine reservoir characteristics both log values within each cell. The well data are
distribution and quality of W-ITB field, 3D the key input data for the property modelling,
geological modeling include structural and i.e. for defining the range of property values
stratigraphic model are carried out based on for each of the electrofacies within the model.
integrated wells and seismics data through The following well data are upscaled i.e: V-
petrophysical analysis, seismic interpretations Shale and net-porosity. Upscaling to an
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Figure 3. Stratigraphic column of East Java Basin from Late Miocene to Pleistocene (Triyana, et.al., 2007)
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81
Figure 4. Upscalling W-1 well log data of V-shale and porosity
average layer thickness of 2 m has effectively content of Globigerina tests (a type of
captured the logs heterogeneity. The upscaled foraminifera) include a foraminiferal
log values corresponding well with input log limestone and deposited in an outer shelf to
curves can be seen in histogram (Figure 4). upper bathyal setting. Based on
biostratigraphic correlation and analysis of W-
RESULT AND DISCUSSION ITB#1 and W- ITB#2 wells, there is missing
In W-ITB Field the reservoir facies is zone in W- ITB#2 represented as an
equivalent to Oyong field to the east i.e. Unconformity/Hiatus.
Globigerina rich packstones and grainstones.
Lateral Facies Variations and Erosional
This reservoir is currently producing gas from
Surfaces
the Maleo field in the Madura Offshore PSC
and oil from Oyong Field. This reservoir facies The section above dealt with the
represents one of the primary exploration depositional processes associated with the
targets in the area. The Mundu and Selorejo reservoir. However it is very important to
reservoirs are unique due to the very high understand the sequence of events that led to
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Figure 5. W-1 and W-2 wells correlation indicate Lidah Fm. Channel incising into the
Selorejo and Upper Mundu Fm.
the present day structural/stratigraphic accumulated in the W- ITB#1 area, thinning to
configuration in the W-ITB Field area. For the east. One could speculate that lithological
instance, the Upper Mundu in W-ITB#1 changes accompany the easterly thinning, but
contains foraminiferal grainstones whilst the this cannot be confirmed at present. Note the
time equivalent a kilometre away at W- ITB#2 intra Lidah channel has completely eroded the
is calcareous clay. Selorejo and part of the Upper Mundu
The Selorejo/Mundu interval in W- ITB#1 formation in the area between W- ITB#1 and
is dominated by foraminiferal limestone with W- ITB#2 (Figure 5).
the only variation represented by calcareous
claystone in the bottom most of 15 m. In 3D Properties Modelling of W-ITB Field
contrast the W- ITB#2 has a complete absence The petrophysical modelling populates the
of Selorejo aged limestone and the Mundu is static model with petrophysical properties,
described as a claystone throughout the well. using the upscaled well data as calibration.
A correlatable equivalent is not present in W- Sequential Gaussian Simulation (SGS) is a
ITB#1. Lateral facies changes in the Selorejo stochastic simulation using an algorithm and
are hard to predict with only one well co-kriging of Acoustic Impedance (AI) that
penetration. ensures the modelled property having a normal
The depositional model suggests the distribution that honours the input data. This is
greatest thickness of Selorejo sediments often applied in areas with sparse well control.
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Figure 6. V-Shale distribution after upscalling well
V-shale, porosity and permeability properties throughout good to excellent with the range
were created for the whole model. between 30 35%. The reservoir in the Zone-
2, southwestern to the northeastern part of the
V-Shale Distribution Modeling area is better than other areas with the ranges
The V-Sh distribution using scale up V-sh porosity 28 34% (Figure 8).
log of W-ITB#1 and Sequential Gaussian
Simulation with Co-Kriging of AI secondary Net to Gross (NTG) Modeling
variable. The result indicates that zone-2 and NTG Distribution used Boolean Logic in
zone-3 are good quality reservoirs with V-sh calculator with Cut-off V-Sh 37%, Porosity
value ranges 0 15% (figure 6). These zones with three categories (High:16.2%, Mid: 18%,
have low values of v-shale indicating good to Low: 22%) and cut-off Sw 70% (Figure 7).
excellent reservoirs. According to laterally The result indicates that zone-2 and zone-3 are
distribution, V-sh value of south-western area good quality reservoirs but Zone-1 and 4 are
of W-ITB#1 well is lower than others. It poor quality reservoirs. The Red colour area is
indicates that this area has a better reservoir reservoir zone but the purple area is non-
quality (Figure 7). reservoir zone (Figure 9).
Porosity Distribution Modeling CONCLUSION
Porosity distribution used scale up Phi-log Gas bearing formation in W-ITB Field
of W-ITB#1 and Sequential Gaussian belongs to Selorejo and Mundu formations of
Simulation with Co-Kriging of AI secondary Late Miocene to Late Pliocene ages. The
variable. The result indicates that zone-1 and Mundu and Selorejo formations both consist
zone-2 are good quality reservoirs with of planktonic foraminifera of wackestone to
porosity ranges between 29 35% but Zone-1 grainstone facies deposited in outer neritic to
and 4 are poor quality reservoirs. Related to upper-bathyal setting. Based on petrophysical
laterally distribution, porosity value of the analysis, the reservoir interval can be devided
western area of W-ITB#1 well in Zone-1 has
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Figure 7. 3D Modeling of V-sh distribution
Figure 8. Porosity distribution of four zones showing Zone-1 is the best reservoir
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Figure 9. Porosity distribution of four zones showing Zone-1 is the best reservoir
into four zones respectively top to bottom; well in Zone-1 has throughout good to
Zone-1, Zone-2, Zone-3 and Zone-4 excellent ranging between 30 35%. The
Based on 3D properties modeling, the best NTG result indicates that Zone-2 and Zone-3
reservoir quality of W-ITB Field is correspond are good quality reservoirs.
to Zone-2 and Zone-3 while Zone-1 and Zone- Since the reservoir properties are derived
4 have relatively poor reservoir quality. The only from W-ITB#1 well, there is some
Gas trap in the W-ITB Field is related to uncertainty in the lateral distribution of the
combination of anticlinal and faults structure properties away from the well control.
combine with stratigraphic traps related to Seismic Acoustic Impedance (AI) data have
deep-channeling of the Lidah shaly formation. therefore been used to help constrain the
For V-sh vertically distribution, Zone-2 porosity distribution.
and Zone-3 are good quality reservoirs
ranging from 0 15%. As laterally ACKNOWLEDGMENTS
distribution, south-western area is better We would like to thanks for our colleagues
reservoir. As for porosity distribution, zone-1 in MGI especially Lili Sarmili, M.Sc., Ir. Dida
and zone-2 are good quality reservoirs range Kusnida, M.Sc., Dr. Susilohadi, Ir. Agus
29 35% but Zone-1 and 4 are poor quality Setiya Budhi, M.Sc. and Mustaba Ari
reservoir. Related to laterally distribution, Suryoko, ST. who give continuously support,
porosity value of western area of W-ITB#1
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Volume 25 No. 2, December 2010
discussion and correction to publish the paper. Conference and Exhibition, Adelaide,
Also, we wish to thanks LAPI-ITB and the Australia, SPE 100957.
Santos Project Team that have fully supported Tyson, Stephen., Math, C.,2009, Regulatory
to this research particularly to Dr. Tutuka Aspects of Geological Modeling,
Ariadji, Dr. Sonny Winardhi and Saifatur Proceedings, Indonesian Petroleum
Rusli, MT. Association, Thirty-Third Annual
Convention & Exhibition, May 2009
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