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Petrophysical Study and Rock Type Determination of Siliciclastic Reservoir: Case Study Sand of Bekasap Formation, AF Field, Central Sumatra Basin, Indonesia Dwi Charisah Andriyani; Sarju Winardi; Sugeng Sapto Surjono
Journal of Applied Geology Vol 7, No 2 (2022)
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/jag.83471

An integrated subsurface study has been performed for a large and mature field at the Bekasap Formation in Central Sumatra Basin. The Bekasap Formation sand represents an undeveloped reservoir because of its heterogeneity. There are five sand reservoirs (BK1, BK2, BK3, BK4, and BK5) from Bekasap Formation, which each zone or layer bounded by a flooding surface. Each sand reservoir has particular characterization based on petrophysical properties that represent geological process. The petrophysical properties consist of shale volume, porosity, and water saturation obtained by wireline log calculation. This study uses conventional core data to validate the log calculation to achieve an accurate interpretation. Bekasap reservoir is a sandstone reservoir deposited in an estuarine with tide-dominated. Formation evaluation was done to determine the interest zone by petrophysical properties. The result well-log calculation and reservoir cut-offs showed the thickest reservoir in the BK 3 with the best average values of petrophysical properties with an average shale volume 0.32; porosity of 0.245. Otherwise, in rock type determination, four lithofacies are divided in the reservoir based on flow units. The sample RT 1 and RT2 provided the best reservoir zones with HFU1 and HFU2. The RT 3 and RT 4 dominated in HFU3 and HFU4 had the lowest potential zones of reservoir. The final findings showed a good correlation between sedimentologic analysis and petrophysical properties in the rock type determination. As a result, the best reservoir quality development is controlled by the depositional environment (texture and structure) rather than the diagenetic process in this reservoir. It is proven by petrophysical properties in BK1, and BK2 is coastal barrier sand (tidal sand bar) has more clean sand rather than in BK3 and BK4 deposited in the offshore bar.

Source Rock Quality and 1D Maturity Model in Pendalian Sub-basin, Central Sumatra Basin Putri Dwi Afifah; Hendra Amijaya; Sarju Winardi; Widi Atmoko
Journal of Applied Geology Vol 8, No 1 (2023)
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/jag.78104

Pematang Formation is well known as the main source rock in the Central Sumatra Basin (Mazied et al., 2008). The formation which acts as source rock has been studied thoroughly in the central and eastern parts of the basin, but research regarding source rock in the western part of the basin, which is the study area, is very limited. This paper aims to define the quality of source rock from a geochemical view through the determination of organic content quantity based on the Total Organic Carbon (TOC) data, determining the type of kerogen, and thermal maturity of the source rock according to the values of Tmax and Vitrinite Reflectance (%Ro). Burial history and thermal maturity models (1D basin modeling) were also constructed to understand the timing of hydrocarbon generation. The results show that Pematang Formation among Sihapas and Telisa Formation has good organic content with TOC ranging from 0.2 to 42.48 wt%, and the maturity parameters indicate that the Pematang Formation has reached the mature stage. Both formations are dominated by Type II kerogen. 1D modeling of the SHT-1 Well indicates that the Pematang Formation is currently in the oil maturity window starting from early oil to main oil at 20.61 Ma, but the model of the SMB-1 Well has not reached the oil maturity window. Tectonic activity is estimated to have a significant effect on this difference when the uplift activity of Bukit Barisan in the Middle Miocene increased the maturity in the northwest, but the inversion that occurred in the Late Miocene resulted in uplift and erosion of young sediments, thus lowering the temperature in some area.

THE APPLICATION OF SEM-EDS FOR THE SURFACE TEXTURE OF FORAMINIFERA: IDENTIFICATION OF EARLY DIAGENESIS OF REWORKED L. DIMIDIATUS WITHIN MODERN COASTAL DEPOSITS Rahmadi Hidayat; Sarju Winardi; Akmaluddin Akmaluddin
BULLETIN OF THE MARINE GEOLOGY Vol 38, No 2 (2023)
Publisher : Marine Geological Institute of Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.32693/bomg.38.2.2023.831

Sediment recycling has been known to occur within Quaternary coastal barriers of the greater Coorong Coastal Plain, southern Australia. A high degree of reworking of skeletal carbonates from Late Pleistocene deposits (Robe Range) is evident based on the novel application of amino acid dating of the single-foraminifera species Lamellodiscorbis dimidiatus. More importantly, some apparently transparent, well-preserved tests indicate anomalously high extents of amino acid racemization, implying that reworked fossils could not be easily distinguished based on taphonomic signatures such as corrosion. Here, we examine the surface microtexture of this species, constrained with well-preserved specimens, on a modern beach of Canunda, southern Australia, using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The aim is to identify surface features of foraminifera in more detail, capturing signs of early diagenesis associated with weakly consolidated Late Pleistocene coastal barriers. The results reveal that some well-preserved tests show localized blocky calcite cementation, most notably within intraseptal spaces or impact sites. The EDS spectra of cement indicate lower Mg content than unaltered foraminifera surface. This suggests low-Mg calcite precipitation due to meteoric diagenesis experienced by the onshore Late Pleistocene coastal barrier. It implies that these foraminifera shells are reworked fossils originated from older successions and were subsequently redeposited within the present-day beach. SEM-EDS used in this study demonstrates its capability in examining small-scale carbonate diagenesis products beyond the traditional binocular microscope. Thus, this tool is recommended to aid amino acid dating in detecting reworked fossils.

Lithofacies, Facies Association, and Depositional Environment of 34-1, 33-6, and 33-4 Sandstone, Wida Field, Gita Member, Talang Akar Formation, Asri Basin, Offshore Southeast Sumatra Saputra, Adi Danu; Surjono, Sugeng Sapto; Winardi, Sarju; Setyadi, Abdul Latif; Ralanarko, Dwandari
Jurnal Ilmiah Geologi PANGEA Vol 11, No 1 (2024): Jurnal Ilmiah Geologi Pangea
Publisher : PROGRAM STUDI TEKNIK GEOLOGI FAKULTAS TEKNOLOGI MINERAL UPN VETERAN YOGYAKARTA

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.31315/jigp.v11i1.12011

Three Gita Member reservoirs 34-1, 33-6, and 33-4 produce from solution gas drive with rapid pressure decline and low recovery factor. After successful oil production enhancements through waterflooding injections prompt the need for a reservoir model in further field development. Before such models were built reservoir characterization was carried out to determine facies and depositional environment for facies modeling. The study integrated core, wireline log, petrophysical logs, seismic attribute, petrography, etc. Next, well correlation was carried out to distribute stratigraphic markers. Finally, seismic attribute and well correlation were integrated to construct pie chart and depositional environment map. External geometry from seismic attribute revealed distributary channel with point bars which act as reservoir and consist of medium-fine grained planar tabular cross bedding sandstone, mud drapes sandstone, and ripple-wavy lamination sandstone. The wireline log showed fining-upward pattern and core displayed abundant channel rip up clasts, sharp or erosional contact with underlying lithology. Frequent mud drapes found within channel sandstone indicate tidal influence in proximity to marine environment probably in lower delta plain. Channels are trending west-east (34-1) and north-south (33-6 and 33-4). Other facies associations are shallow marine, swamp, interdistributary bay, and tidally influenced interdistributary bay. Shallow marine FA consists of skeletal limestone (Lm), calcareous mudstone, and calcareous sandstone (Sc). Rootlet mudstone (Fb) and interlamination of carbonaceous mudstone with very fine-grain sandstone (Fl) formed interdistributary bay FA. Swamp FA consists of coal and coaly mudstone. Tidally influenced interdistributary bay FA consists of carbonaceous laminated mudstone high in carbon (Flb), intensely bioturbated carbonaceous mudstone (Flb), very finely laminated mudstone-very fine grain sandstone (Fl) and black fissile shale (Fm).

The Comparation of Water Saturation Approaches to Reveal a Low Resistivity Reservoir Potential Case in Gumai Formation, South Sumatra Basin Dhea Adisty Pratami; Sarju Winardi; Sugeng Sapto Surjono; Widi Atmoko
Scientific Contributions Oil and Gas Vol. 46 No. 2 (2023): SCOG
Publisher : Testing Center for Oil and Gas LEMIGAS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.29017/scog.46.2.322

The LRLC reservoir zone has been identified in SN-3 well, at the DAP-1 interval on Gumai Formation. This interval has a low resistivity value from 3-5 ohm.m and the drill stem test (DST) results show oil with gas without water. This study is objected to identify the causes of LRLC reservoir in gumai formation and finding a suitable sw calculation method. Some data such as well logs, reports, cores, and XRD are used to calculate petrophysical parameters such as Vsh, Phie, and Sw, and would be validated by DST data. Water saturation (Sw) calculations from Archie and the CEC method (Waxman Smits, Dual Water, Juhasz) were performed and the results were compared. The results showed that the main cause of the DAP-1 interval LRLC zone was the presence of clay minerals consisting of mixed layers (Illite/smectite). These clay minerals will be associated with high cation exchange capacity (CEC) values, with the value 70 (meq/100g), which can increase conductivity and reduce resistivity values. Based on lumping the more optimistic results of sw calculation from Waxman Smits Sw method (Sw based on CEC method). The DST data on the SN-3 well does not have water test data, so the calculation of the Sw value that is close to the Swirr value is considered the most suitable Sw for the low resistivity reservoir conditions of the Gumai Formation in the study area. The best practice for low resistivity reservoir for suitable petrophysical calculation is necessary to pay attention to the rock lithology conditions, the presence of mineral clay, and determining suitable Sw appropriate to the reservoir conditions

Quantifying the Impact of Siderite Composition and Reservoir Resistivity (Rt) on Water Saturation Estimation in Low-Resistivity Sideritic Sandstone Reservoirs Using the Graphic Plot Method Sarju Winardi; Sugeng Sapto Surjono; Donatus Hendra Amijaya; Wiwit Suryanto
Scientific Contributions Oil and Gas Vol. 47 No. 2 (2024): SCOG
Publisher : Testing Center for Oil and Gas LEMIGAS

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The case studies on low-resistivity-low-contrast (LRLC) reservoirs have started using a conductive matrix model approach based on the assumption that the rock matrix is composed of conductive minerals. The previous studies on reservoir resistivity (Rt) against conductive-minerals-rich sandstone were limited to pyritic types without developing the others such as the sideritic which was found in Indonesia. Therefore, there is a need to determine the relationship between siderite volume within the sandstone reservoir and the reduction number of Rt. Relation profiles were applied to accurately estimate the actual water saturation (Sw) while the resistance of the sandstone samples was determined through the voltage (V, volt) and current (I, ampere). The samples were designed as pseudo-core in the laboratory and simulated to have siderite composition in the range of 0-30% followed by the injection of brine at different saturation conditions. The Rt was calculated through the modification of Wenner and Ohm’s Law and later compared graphically with siderite volume of each Sw line. It was observed from the results that siderite led to an exponential reduction in Rt value. Moreover, the threshold volume of siderite required to reduce Rt significantly to 50% of the original value was found to be 6%. The actual Sw was later estimated simply through the application of the Graphic Plot Method from the curves. Keywords: low resistivity, reservoir, LRLC, siderite, sandstone, water saturation

Rock Typing Pada Reservoar Gas Upper Eastern View Coal-Measures (EVCM), Cekungan Bass, Australia Dinar Hananto Kurniawan; Sarju Winardi; Ferian Anggara
Lembaran Publikasi Minyak dan Gas Bumi Vol. 56 No. 3 (2022): LPMGB
Publisher : BBPMGB LEMIGAS

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Kesulitan terkadang muncul ketka menentukan permeabilitas, terutama pada interval yang tidak memiliki data batuan inti (core). Pada penelitian ini, digunakan teknik sedimentary rock type (SRT) dan petrophysical rock type (PRT) dengan tujuan untuk mengurai permasalahan tersebut. SRT terdapat 4 rock type, yaitu thoroughly bioturbated sandstone and mudstone, fl aser bedded sandstone, laminated sandstone and mudstone, dan thoroughly bioturbated mudstone. Teknik PRT dilakukan dengan mengkomparasikan metode Hydraulic Flow Unit, Global Hydraulic Element, Winland R35, dan Pore Geometry Structure untuk mendapatkan metode yang paling cocok. Hasilnya, metode GHE yang menghasilkan nilai permeabilitas prediksi paling mendekati nilai permabilitas dari data core (koefi sien korelasi 0,9139). Aplikasi metode GHE pada interval yang tidak memiliki data core dilakukan dengan menggunakan data wireline log menghasilkan 4 RT (RT 1, RT 2, RT 3, dan RT 4). Setiap rock type tersebut digunakan rumusan poro-perm transform-nya untuk mementukan nilai permeabilitas. Dipadukan dengan data DST, dapat diambil nilai cut-off , yaitu porositas 0,183, permeabilitas 0,55 mD, volume shale 0,6, dan saturasi air 0,99. Dengan nilai cut-off tersebut menghasilkan satu zona potensial pada kedalaman 2216 mRT - 2234 mRT. Dengan demikian maka manfaat yang didapatkan dari penelitian ini antara lain: mengetahui metode PRT yang cocok diaplikasikan di reservoir ini, jumlah rock type beserta karakteristiknya, serta zona yang potensial.

Lithofacies, Facies Association, and Depositional Environment of 34-1, 33-6, and 33-4 Sandstone, Wida Field, Gita Member, Talang Akar Formation, Asri Basin, Offshore Southeast Sumatra Saputra, Adi Danu; Surjono, Sugeng Sapto; Winardi, Sarju; Setyadi, Abdul Latif; Ralanarko, Dwandari
Jurnal Ilmiah Geologi PANGEA Vol. 11 No. 1 (2024): Jurnal Ilmiah Geologi Pangea
Publisher : PROGRAM STUDI TEKNIK GEOLOGI FAKULTAS TEKNOLOGI MINERAL UPN VETERAN YOGYAKARTA

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.31315/jigp.v11i1.12011

Three Gita Member reservoirs 34-1, 33-6, and 33-4 produce from solution gas drive with rapid pressure decline and low recovery factor. After successful oil production enhancements through waterflooding injections prompt the need for a reservoir model in further field development. Before such models were built reservoir characterization was carried out to determine facies and depositional environment for facies modeling. The study integrated core, wireline log, petrophysical logs, seismic attribute, petrography, etc. Next, well correlation was carried out to distribute stratigraphic markers. Finally, seismic attribute and well correlation were integrated to construct pie chart and depositional environment map. External geometry from seismic attribute revealed distributary channel with point bars which act as reservoir and consist of medium-fine grained planar tabular cross bedding sandstone, mud drapes sandstone, and ripple-wavy lamination sandstone. The wireline log showed fining-upward pattern and core displayed abundant channel rip up clasts, sharp or erosional contact with underlying lithology. Frequent mud drapes found within channel sandstone indicate tidal influence in proximity to marine environment probably in lower delta plain. Channels are trending west-east (34-1) and north-south (33-6 and 33-4). Other facies associations are shallow marine, swamp, interdistributary bay, and tidally influenced interdistributary bay. Shallow marine FA consists of skeletal limestone (Lm), calcareous mudstone, and calcareous sandstone (Sc). Rootlet mudstone (Fb) and interlamination of carbonaceous mudstone with very fine-grain sandstone (Fl) formed interdistributary bay FA. Swamp FA consists of coal and coaly mudstone. Tidally influenced interdistributary bay FA consists of carbonaceous laminated mudstone high in carbon (Flb), intensely bioturbated carbonaceous mudstone (Flb), very finely laminated mudstone-very fine grain sandstone (Fl) and black fissile shale (Fm).

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