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Density Normal Compaction Trend in the Peciko Field, Lower Kutai Basin, Indonesia Ramdhan, Agus M.; Goulty, Neil R.; Jones, Stuart J.; Hutasoit, Lambok M.
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.253-265

DOI:10.17014/ijog.7.3.253-265The density normal compaction trend is the mandatory parameter in order to calculate contribution of disequilibrium compaction to overpressure, in the presence of unloading to total overpressure. In this paper, mudrock compaction behaviour is studied in the Peciko Field. The density normal compaction trend was constructed in a normally pressured section, where the temperature is <1200C, within the transformation of smectiteâ€“illite zone. The compaction trend includes not only vertical effective stress, but also diagenesis, especially smectite-illite transformation, as dependant factor for compaction, both termed as Î². This compaction trend is also known as Skempton-Duta compaction model. Quardros-Linares fifth-order kinetic reaction was found that could model smectite-illite transformation in the studied area fairly well. The plot between Î² and smectite content shows a very good match, confirming that Skempton-Dutta compaction model is valid for the entire range of smectite-illite transformation. In the area where the density log is unavailable, the density normal compaction can be constructed from temperature history acting as a proxy for smectite-illite transformation, with some local calibration.

Natural Compaction of Semarang-Demak Alluvial Plain and Its Relationship to the Present Land Subsidence Sarah, Dwi; Hutasoit, Lambok M; Delinom, Robert M; Sadisun, Imam A
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.273-289

DOI:10.17014/ijog.7.3.273-289Land subsidence is the lowering of ground surface due to natural and/or anthropogenic processes. Land subsidence in the Semarang-Demak plain has been going on for more than thirty years, however the contribution of natural and anthropogenic causes is relatively unknown. The Semarang-Demak plain has only been formed recently, as a result of rapid sedimentation during the Holocene. The basin mainly consists of underconsolidated thick clay, vulnerable to excessive settlement due to its own weight and additional pressures. The rate of natural subsidence is quantified by modelling the delayed dissipation of measured overpressure and the resulting vertical deformation, resulting in natural compaction rate of less than 0.8 cm/year in Semarang City and more than 0.8 cm/year in Demak Regency. The subsidence computed for parts of the Semarang-Demak plain were compared to the measured geodetic rate, and the relative contributions of natural and anthropogenic causes are derived. Modelling results show that natural subsidence is more significant at the eastern part of the plain (Demak region) with compaction rate reaching 0.9 - 2.2 cm/year that counts for 48 - 92% of the total land subsidence.

Natural Compaction of Semarang-Demak Alluvial Plain and Its Relationship to the Present Land Subsidence Sarah, Dwi; Hutasoit, Lambok M; Delinom, Robert M; Sadisun, Imam A
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

DOI:10.17014/ijog.7.3.273-289Land subsidence is the lowering of ground surface due to natural and/or anthropogenic processes. Land subsidence in the Semarang-Demak plain has been going on for more than thirty years, however the contribution of natural and anthropogenic causes is relatively unknown. The Semarang-Demak plain has only been formed recently, as a result of rapid sedimentation during the Holocene. The basin mainly consists of underconsolidated thick clay, vulnerable to excessive settlement due to its own weight and additional pressures. The rate of natural subsidence is quantified by modelling the delayed dissipation of measured overpressure and the resulting vertical deformation, resulting in natural compaction rate of less than 0.8 cm/year in Semarang City and more than 0.8 cm/year in Demak Regency. The subsidence computed for parts of the Semarang-Demak plain were compared to the measured geodetic rate, and the relative contributions of natural and anthropogenic causes are derived. Modelling results show that natural subsidence is more significant at the eastern part of the plain (Demak region) with compaction rate reaching 0.9 - 2.2 cm/year that counts for 48 - 92% of the total land subsidence.

Contributions of Loading and Unloading to Overpressure: Analytical Results from The Shelfal Area of The Lower Kutai Basin, Indonesia Ramdhan, Agus M.; Hutasoit, Lambok M.
Indonesian Journal on Geoscience Vol 9, No 1 (2022): in-press
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.9.1.1-13

A modified Bowers Method is applied to analyze the contribution of loading and unloading to total overpressure magnitude in the shelfal area of the Lower Kutai Basin. The method combines Bowers Method with density-sonic cross plots to differentiate contributors to overpressure. This method has a strong physical background, and has proven to give satisfactory overpressure estimation in the studied area. Several processes related to overpressure and compaction in the studied area have also been deduced: 1) top of overpressure is caused by unloading due to gas generation, 2) gas generation on its own can produce overburden-scale overpressure magnitude, 3) loading starts to contribute to overpressure at depth, where the lithology is dominated by mudrocks, 4) effective stress history experienced by mudrocks before unloading, and 5) the presence of two compaction lines and therefore two associated velocity-effective stress relations.

Tritium: Implies Young Groundwater Age? Insight from the Isotope and Hydrochemical Data of Mud Volcano and Hydrocarbon Well in East Java Lambok M. Hutasoit, Ph.D.; Agus M. Ramdhan; Irwan Iskandar; Arifin Arifin
Jurnal Lingkungan dan Bencana Geologi Vol 12, No 3 (2021)
Publisher : Badan Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.34126/jlbg.v12i3.388

ABSTRACT The use of tritium isotope is one of the methods for determining groundwater age. It can be used to determine the age of groundwater classified as young. However, if it is the only method used, the results may not be valid. In this study, tritium application in determining groundwater age was evaluated based on deuterium and oxygen-18 isotopes and hydrochemical data from seven mud volcanoes and one hydrocarbon production well in East Java Basin. The tritium analysis shows that the age of groundwater samples is young, 1.75 to 9 years. However, deuterium, oxygen-18, and hydrochemical analysis indicate that the groundwater age is relatively old. It shows that the results of groundwater age analysis using tritium are not valid in this study. It is because tritium is not only from the atmosphere but also from tritium enrichment below the surface through water and rock interaction. The shifting of oxygen-18 isotope, which becomes heavier, indicates that isotope enrichment occurred in the subsurface. Based on the composition of the major cations and anions, the groundwater samples in this study have Na-Cl type with high TDS values as saline water. The shifting of oxygen-18 isotope, the water type, and the high TDS value also indicate that water and rock interaction occurs beneath the surface and can increase the tritium content in groundwater.Keywords: deuterium, groundwater age, hydrochemical data, mud volcano, oxygen-18, tritiumABSTRAK Salah satu metode untuk menentukan umur airtanah adalah dengan menggunakan isotop tritium. Tritium dapat digunakan untuk menentukan umur airtanah yang tergolong muda. Namun, jika hanya menggunakan metode ini, maka hasil yang diperoleh mungkin tidak valid. Dalam studi ini, penggunaan tritium untuk menentukan umur airtanah dievaluasi berdasarkan data isotop deuterium dan oksigen-18, serta data hidrokimia dari tujuh gunung lumpur dan satu sumur produksi hidrokarbon di Cekungan Jawa Timur. Analisis tritium menunjukkan umur sampel airtanah yang tergolong muda, yaitu 1,75 hingga 9 tahun. Namun, analisis deuterium, oksigen-18, dan analisis hidrokimia menunjukkan bahwa umur airtanah tergolong tua. Hal tersebut memperlihatkan bahwa hasil analisis umur airtanah berdasarkan tritium pada studi ini tidak valid. Hal ini disebabkan karena tritium tidak hanya berasal dari atmosfer, tetapi dapat juga berasal dari pengayaan tritium di bawah permukaan melalui reaksi air dan batuan. Pergeseran nilai oksigen-18 yang menjadi semakin berat mengindikasikan bahwa terjadi pengayaan isotop tersebut di bawah permukaan. Berdasarkan komposisi kation dan anion utama, sampel airtanah dalam studi ini memiliki tipe Na-Cl dengan nilai TDS yang tinggi dan air yang tergolong asin. Pergeseran oksigen-18, tipe air dan nilai TDS yang tinggi tersebut juga menunjukkan bahwa terjadi interaksi air dan batuan di bawah permukaan yang dapat meningkatkan nilai tritium pada airtanah.Kata kunci: deuterium, umur airtanah, data hidrokimia, mud volcano, oksigen-18, tritium

ANALISIS PENGARUH NILAI KONDUKTIVITAS HIDRAULIK DAN DISPERSIVITAS DINAMIK TERHADAP REMEDIASI AIR TANAH MENGGUNAKAN SIMULASI NUMERIK Agus Mochamad Ramdhan; Arifin Arifin; Erik Hermawan; Lambok M. Hutasoit
JURNAL TEKNIK HIDRAULIK Vol 12, No 2 (2021): JURNAL TEKNIK HIDRAULIK
Publisher : Pusat Litbang Sumber Daya Air, Kementerian Pekerjaan Umum dan Perumahan Rakyat

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.32679/jth.v12i2.658

Groundwater remediation is one of the solutions to restore the contaminated groundwater. This study was conducted to determine the effect of hydraulic conductivity and dynamic dispersivity on the groundwater remediation effectiveness. As a case study, in 2020, in an area located in Balikpapan, groundwater remediation will be carried out by injecting water containing NaOH through five wells and pumping it back through five wells to form a cycle. The method used is a numerical simulation consisting of groundwater flow simulation, mass transport, and sensitivity analysis. The results show that it takes 124 to 300 days for the injected NaOH to arrive at the pumping wells. The sensitivity analysis results show that when the hydraulic conductivity value is ten times greater, the time required is reduced to 84 to 172 days. Meanwhile, when the dynamic dispersivity is twice larger, the time required is reduced to 75 to 189 days. These results indicate that the groundwater remediation method will be effective for aquifers with high hydraulic conductivity and dynamic dispersivity values. For the study area, the groundwater remediation is suggested to be carried out by increasing the number of injection and pumping wells with a relatively close distance, i.e., around 10 meters, so that NaOH arrives at the pumping wells more quickly.Keywords: groundwater, remediation, hydraulic conductivity, dynamic dispersivity, numerical simulation

SALINITAS AIRTANAH AKIFER TERTEKAN KEDALAMAN 0 – 20 M DAERAH KALIDERES – CENGKARENG, JAKARTA BARAT Abdurrachman Asseggaf; Hendarmawan Hendarmawan; Lambok M. Hutasoit; Johannes Hutabarat
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 27, No 1 (2017)
Publisher : Indonesian Institute of Sciences

The presence of salt water in the West Jakarta is still disputed by the groundwater experts. This research is aimed to clarify the cause of saline groundwater in the confined aquifer at the depth of 0 – 40 m by litostratigraphic correlation of Kalideres-Cengkareng section. Observation of the groundwater physical properties was carried out for 8 wells, consisting of 3 dug wells and 5 bored wells. The groundwater salinity classification was derived based on the total suspended solids and chloride content. Those data were compared to the groundwater flow pattern, aquifer system, groundwater facies and stable isotope 2H and 18O. Research results showed that the salinity is determined by the aquifer rock type and the change of groundwater facies to the flow pattern. Salinity is higher at the north east due to mixing of fossil water (connate water) or leaching of the rock salt. Stable isotope results also indicate that all samples have groundwater characteristics and none of seawater characters was present. AbstrakHingga saat ini keberadaan air asin di wilayah Jakarta Barat masih diperdebatkan oleh para ahli airtanah. Tujuan penelitian ini adalah untuk menjelaskan penyebab tingginya nilai salinitas airtanah pada akifer tertekan kedalaman 0 – 40 m dengan cara mengkorelasi aliran airtanah, sistem akifer, fasies ion airtanah, dan isotop stabil di daerah Kalideres – Cengkareng. Pengamatan sifat fisik airtanah dilakukan pada 8 titik sumur yang terdiri dari 3 sumur gali, dan 5 sumur pantek. Data sifat fisik airtanah diintepretasikan dengan mengacu pada klasifikasi salinitas berdasarkan nilai jumlah padatan terlarut dan kadar Khlorida. Data tersebut dibandingkan dengan pola aliran airtanah, sistem akifer, fasies airtanah dan isotop stabil 2H dan 18O. Hasil penelitian memperlihatkan bahwa kadar salinitas ditentukan oleh jenis batuan akifer dan perubahan fasies airtanah terhadap pola aliran. Perubahan nilai salinitas yang semakin tinggi ke arah Timur laut disebabkan oleh adanya pencampuran dengan air fosil atau proses pencucian garam batuan. Hal inipun didukung oleh data isotop stabil yang menunjukkan bahwa seluruh sampel masih mencerminkan karakteristik air meteorik dan tidak mencirikan air laut.

PENERAPAN MODEL NRECA PADA DAERAH RESAPAN LAPANGAN PANASBUMI WAYANG WINDU, JAWA BARAT Fajar Hendrasto; Lambok Hutasoit; Syahril Badri Kusuma; Benyamin Sapiie
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 28, No 1 (2018)
Publisher : Indonesian Institute of Sciences

Panasbumi dikenal sebagai sumber energi yang dapat diperbaharui dan proses pembaruan terjadi di daerah resapan. Makalah ini membahas tentang daerah resapan air meteorik untuk reservoir panasbumi dan rasio debit aliran dasar terhadap debit limpasan permukaan berdasarkan neraca air, yaitu dengan melakukan simulasi hujan-limpasan model NRECA pada Daerah Aliran Sungai (DAS) yang terletak pada kisaran elevasi daerah resapan. Interpretasi berdasarkan peta densitas sesar dan rekahan (FFD) dan peta daerah resapan hasil analisis isotop stabil menunjukkan terdapat tiga zona dengan nilai FFD tinggi yang diperkirakan sebagai daerah resapan untuk reservoir panasbumi Wayang Windu. Untuk mengetahui besarnya debit aliran dasar dan debit limpasan permukaan pada daerah resapan tersebut, maka dilakukan perhitungan berdasarkan neraca air dan pembuatan data debit sintetis untuk zona FFD tinggi. Hasil simulasi hujan-limpasan dengan model NRECA adalah untuk mendapatkan nilai koefisien resapan untuk setiap DAS. Hasil perhitungan rasio antara debit aliran dasar terhadap debit limpasan permukaan pada zona FFD tinggi yang terletak pada DAS Cisangkuy terlihat lebih tinggi (98%) jika dibandingkan dengan dua DAS lainnya, yaitu DAS Cilaki (66%) dan DAS Citarum (43%). Hal ini menunjukkan bahwa zona FFD tinggi yang terletak pada DAS Cisangkuy memiliki debit aliran dasar yang lebih besar dibandingkan pada DAS Cilaki dan DAS Citarum.Geothermal is known as a renewable energy resource and the renewing process occurs in the recharge area. This paper discusses about the meteoric water recharge area for geothermal reservoir and the ratio of baseflow discharge compared with surface runoff discharge based on water balance, i.e. conducting rainfall-runoff of NRECA model simulation in the Drainage River Area (DRA) which is located in the elevation range of recharge area. The interpretation of FFD map and recharge area map resulting from stable isotope analysis shows that there are three high FFD zones interpreted as recharge areas for Wayang Windu geothermal reservoir. To know the ratio of baseflow discharge and surface runoff discharge in that recharge area, infiltration analysis has been carried out based on water balance and synthetic discharge data for high FFD zone. The result of rainfall-runoff simulation by using NRECA model is used to get infiltration coefficient for each DRA. The ratio between baseflow discharge to surface runoff discharge in high FFD zone located in Cisangkuy DRA is higher (98%) than Cilaki DRA (66%) and Citarum DRA (43%).It shows that high FFD zone located in Cisangkuy DRA has higher baseflow discharge than Cilaki DRA and Citarum DRA.

Kondisi Permukaan Air Tanah dengan dan tanpa peresapan buatan di daerah Bandung: Hasil Simulasi Numerik Lambok M. Hutasoit
Indonesian Journal on Geoscience Vol 4, No 3 (2009)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol4no3.20093Significant groundwater level drawdown caused by groundwater abstractions has been reported to occur in Bandung and its surrounding area. One potential method to recover the groundwater condi- tion is artifical recharge, considering high quantity of rainfall in this area. In this research, numerical simulation has been performed in order to predict groundwater condition in the next five years, if: 1) no recovery action is taken (do-nothing) (Scenario 1), and 2) artificial recharge is performed (Scenario 2). Hydrogeological condition reconstruction required for physical model development reveals that the main aquifer in the researched area is Cibeureum Formation, which comprises volcanic fans; the main aquitard is Kosambi Formation, crasisting of lake deposit, whilst the hydrogeologic basement in the research area is the Cikapundung Formation, other Quaternary volcanic rocks, except the Cibeureum Formation, and Tertiary rock units. The recharge area is the areas where the Cibeureum Formation crops out. The result of numerical simulation of Scenario 1 shows that if there is no recovery action taken on the groundwater condition, then in year 2013 the Critical Zone will increase about 116 % and the Damage Zone will increase about 570 %. The result of this scenario also shows that there will be groundwater mining in several areas in the Damage Zone with the total area of 244 km2 or 41 % of the total confined aquifer area. Result of the numerical simulation of Scenario 2 shows that the artificial recharge in the above Critical and Damage Zones will effectively recover groundwater condition in year 2013 which means is, the whole area becomes Safe Zone. The amount of the artificial recharge is about 164 million m3/year and it started from year 2009. The artificial recharge means recharge well, surface reservoir, or recharge ditch where the Cibeureum Formation crops out, or injection well where this formation does not crop out.

Lateral Reservoir Drainage in some Indonesia’s Sedimentary Basins and Its Implication to Hydrodynamic Trapping Agus Mochamad Ramdhan; Lambok Maringan Hutasoit; Edy Slameto
Indonesian Journal on Geoscience Vol 5, No 1 (2018)
Publisher : Geological Agency

DOI: 10.17014/ijog.5.1.65-80Lateral reservoir drainage is a hydrodynamic flow type driven by the difference in overpressure. It can lead to hydrodynamically tilted hydrocarbon water contact, and open an opportunity of finding oil and gas in places where previously are not considered as potential traps. In this paper, some examples of the presence of hydrodynamic traps in Indonesia’s sedimentary basin are discussed. Tilted hydrocarbon water contacts are present in some fields in the Lower Kutai Basin, and our interpretation is that regional lateral reservoir drainage is present in this basin and is responsible for the tilted contacts. It is also interpreted that lateral reservoir drainage leading to tilted hydrocarbon water contacts may be present at the Arun Field - North Sumatra Basin, Vorwata Field - Bintuni Basin, and BD Field - offshore East Java Basin. As most Indonesia’s sedimentary basins are overpressured, the presence of lateral reservoir drainage driven by overpressure difference in the same stratigraphic unit is very plausible to occur, opening the opportunity for hydrodynamically tilted hydrocarbon water contact to be present.

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