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Wireline Log Responses, Mudweight, Clay Mineralogy, and Implied Overpressure Condition: Insights from Aru Field, North Sumatra Basin Mohammad Syaiful; Lambok M. Hutasoit; Agus M. Ramdhan; Agus Haris Widayat
Indonesian Journal on Geoscience Vol 7, No 2 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.2.105-119

DOI:10.17014/ijog.7.2.105-119This paper comprehensively discusses overpressuring in the North Sumatra Basin by using wireline log, drilling events and parameters, and clay mineralogical data. It shows an interesting phenomenon related to overpressuring in this basin, i.e. strong log reversals indicating high overpressure, yet the mudweight used during drilling was relatively low, indicating low overpressure with no significant drilling events noted in the final well report.The result of the study shows that wireline log is the best parameter to imply overpressure magnitude. Regarding low mudweight in the strong log reversal zone, it would be elucidated that the drilling in that zone was in underbalance condition with respect to shale pressure, but not to sandstone pressure. The sandstone pressure is interpreted to be lower than shale pressure due to lateral drainage process. By applying the Eaton’s method, the estimated maximum overpressure magnitude in the Baong Formation is in the range of 1,594 - 3,185 psi. or equivalent to the mudweight of 1.61 - 192 g/cm3. The analysis of wireline log in combination with clay mineralogical data shows that there are two compaction lines in the studied area, i.e. smectitic and illitic compaction lines. The cross-plot of density and sonic logs in shale section suggest that the cause of overpressure was loading mechanism. The scanning electron microscope (SEM) image confirms that in overpressure zone, grain to grain contact is still able to be observed fairly well, inferring that loading mechanism is really the cause of overpressure in the studied area.

Density Normal Compaction Trend in the Peciko Field, Lower Kutai Basin, Indonesia Agus M. Ramdhan; Neil R. Goulty; Stuart J. Jones; Lambok M. Hutasoit
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 smectite–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 β. 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 β 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 Dwi Sarah; Lambok M Hutasoit; Robert M Delinom; Imam A Sadisun
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.

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

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

DOI:10.17014/ijog.9.1.1-13A 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.

Distribusi Vektor Aliran Air Tanah Dua Dimensi dalam Media Rekahan di Big Gossan, Tembagapura, Papua Lambok M. Hutasoit; Mudrik R. Daryono; Lilik Eko Widodo; Toddy Syaifullah
Jurnal Teknik Sipil Vol 17 No 2 (2010)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/jts.2010.17.2.2

Abstrak. PT. Freeport Indonesia (PTFI) berencana membuka tambang bawah tanah baru di Big Gossan dengan metode stope mine, yang menuntut daerah yang akan ditambang berada dalam kondisi kering. Di beberapa lokasi uji, air tanah keluar dari beberapa lubang stope dengan debit yang cukup mengganggu, tetapi di beberapa lokasi lainnya lubang berada dalam kondisi kering. Pemodelan hidrogeologi terdahulu, yang mengasumsikan bahwa akifer adalah media antar butir, tidak dapat menjawab variasi keberadaan air tanah tersebut. Akifer di daerah ini disusun oleh rekahan-rekahan. Dalam penelitian ini, dilakukan kembali pemodelan hidrogeologi dengan penekanan bahwa akifer adalah media rekahan dan pada titik-titik perpotongan antara sesar dan sungai terjadi peresapan. Dalam pemodelan ini, pertama-tama dilakukan analisis geometri dan orientasi rekahan. Hasil analisis digunakan untuk menghitung distribusi muka air tanah dengan Metode Gale dan konduktivitas hidrolik akifer dengan Metode Oda dkk. Kedua parameter tersebut digunakan untuk melakukan pemodelan hidrogeologi dalam dua dimensi, untuk mengetahui distribusi vektor aliran air tanah. Dari penelitian ini diperoleh bahwa konduktivitas hidrolik di daerah ini adalah heterogen, bukan homogen, seperti asumsi dalam pemodelan terdahulu. Hasil pemodelan hidrogeologi menunjukkan bahwa aliran air tanah terkonsentrasi disebelah barat laut dari Stope # 6.Abstract. PT. Freeport Indonesia (PTFI) is planning to open a new underground mine at Big Gossan by using stop mine method which requires dry mining area. In some pilot areas, groundwater flowed from some stope holes significantly, while in other areas, some holes were dry. Previous hydrogeologic modeling, assuming that aquifers were intergranular media, cannot answer the variation of the groundwater occurrence. The aquifers in the study area are composed of fractures. In this research, hydrogeology of the area is remodeled, stressing that the aquifers are fractured media and recharge takes place at the intersections of faults and rivers. In this modeling, fracture geometry and orientation are analysed first. The results are used to calculate groundwater table distribution by using Gale Method and hydraulic conductivity by using Oda et.al. Method. Both parameters are used to construct two dimensional hydrogeological modeling, to know distribution of groundwater flow vector in the research area. This research reveals that hydraulic conductivity in this area is heterogeneus, not homogeneous, as was assumed in the previous modeling. The hydrogeologic model shows that groundwater flow is concentrated to the northwest of Stope # 6.

Pore Pressure Prediction Using Velocity-Mean Effective Stress Relationship in Madura Sub-basin, East Java Basin - Indonesia Sena W Reksalegora; Lambok M. Hutasoit; Agus H. Harsolumakso; Agus M. Ramdhan
Indonesian Journal on Geoscience Vol 9, No 2 (2022)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.9.2.247-262

DOI:10.17014/ijog.9.2.247-262Pore pressure prediction using velocity-mean effective stress relationship is introduced in Madura Subbasin which is located in a compressional tectonic setting. The new workflow accommodates the three principal stresses, those are vertical stress, maximum horizontal stress, and minimum horizontal stress in a form of mean stress as the compaction main inducing agent. The application of this new workflow has resulted in a more accurate pore pressure prediction where the normally used pore pressure prediction method tends to underestimate the actual data. In Dukuh-1 well, as an example, the pore pressure prediction from the new work flow is able to explain the continuous hole problems such as well flows and well kicks that were recorded during drilling. In MDA-2 well, the new pore pressure prediction closely matches the well data in comparison to the normally used prediction. As a result, a more accurate regional pore pressure prediction map using mean stress is generated to aid both hydrocarbon exploration and development activities in the study area

The Study of Wind Field ERA-20C in Monsoon Domains for Rainfall Predictor in Indonesia (Java, Sumatra, and Borneo) Trinah Wati; Tri Wahyu Hadi; Ardhasena Sopaheluwakan; Lambok M Hutasoit
Agromet Vol. 37 No. 1 (2023): JUNE 2023
Publisher : PERHIMPI (Indonesian Association of Agricultural Meteorology)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.29244/j.agromet.37.1.34-43

In recent years, various research institutions have developed diverse global data reanalysis projects. This provides an opportunity to gain long-term of meteorological data for local scale. This study aims to select the potential predictor of wind fields u and v of the ERA-20C dataset, a reanalysis dataset, at 850 mb from seven domains or windows of Asian, Maritime Continent, Australian, and Western North Pacific monsoon related physically to rainfall anomaly patterns in Indonesia. The vector wind velocity scalar was obtained by using a Helmholtz decomposition to separate the total circulation v = (u,v) into the divergent component/velocity potential (Ï‡) or Phi and rotational component/stream function (Ïˆ) or Psi for obtaining the scalar variable of vector wind velocity. The method applied Singular value decomposition (SVD) to identify pairs of spatial patterns (expansion coefficients) between the predictors of Phi and Psi in seven domains, with rainfall data from 48 stations in Java, Sumatra, and Borneo Islands from 1981 to 2010. The results revealed that spatial patterns correlations of Java Islands were the highest in the Maritime Continent monsoon domain (80oâˆ’150o E and 15oSâˆ’15o N), while Sumatra and Borneo Island were in the Western North Pacific monsoon domain (100oâ€“130o E and 5oâ€“15o N) with predictor Psi. The lowest correlation for Java, Sumatra, and Borneo was the Australian monsoon domain (110o Eâ€“130o E and 5o Sâ€“15o S) with predictor Phi. In general, spatial pattern correl-ations of Java Island were higher than others, agreeing with monsoonal rainfall type dominantly in the region.

The TESTS OF pH, CONDUCTIVITY, TOTAL DISSOLVED SOLIDS, SALINITY AND TURBIDITY IN THE BATANG ARAU RIVER SURROUNDING, PADANG CITY-WEST SUMATRA Rusli HAR; Aprisal; Isril Berd; Lambok M. Hutasoit; Denny Akbar Tanjung
BIOLINK (Jurnal Biologi Lingkungan Industri Kesehatan) Vol. 10 No. 1 (2023): August
Publisher : Universitas Medan Area

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.31289/biolink.v10i1.9642

Humans need fresh water for many functions, including cleaning, irrigating plants, drinking, cooking, industrial uses, and more. It cannot be denied that the excessive exploitation of the environment by humans is the cause of the current decline in water quality. This study aims to test water quality such as pH, conductivity, total dissolved solids, salinity, and turbidity. The research method uses quantitative methods. The research area was taken from 10 subdistricts around the Arau River Basin. The sample is measured using a predetermined measuring instrument. Based on the test results from all research areas, several parameters for testing water quality meet the standards of the 2010 Ministry of Health Regulations, such as the pH test except for the Indarung and Lubuk Begalung sub-districts. and East Padang. The Total Dissolved Solids test in all areas is in good water standard except for Koto Tangah. The salinity test for all areas met the requirements for water quality standards except for the West Padang sub-district and the Turbidity test showed that all areas had turbidity values > 5 NTUs..

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

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.5.1.65-80

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.

Pore Pressure Prediction Using Velocity-Mean Effective Stress Relationship in Madura Sub-basin, East Java Basin - Indonesia Sena W Reksalegora; Lambok M. Hutasoit; Agus H. Harsolumakso; Agus M. Ramdhan
Indonesian Journal on Geoscience Vol. 9 No. 2 (2022)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.9.2.247-262

DOI:10.17014/ijog.9.2.247-262Pore pressure prediction using velocity-mean effective stress relationship is introduced in Madura Subbasin which is located in a compressional tectonic setting. The new workflow accommodates the three principal stresses, those are vertical stress, maximum horizontal stress, and minimum horizontal stress in a form of mean stress as the compaction main inducing agent. The application of this new workflow has resulted in a more accurate pore pressure prediction where the normally used pore pressure prediction method tends to underestimate the actual data. In Dukuh-1 well, as an example, the pore pressure prediction from the new work flow is able to explain the continuous hole problems such as well flows and well kicks that were recorded during drilling. In MDA-2 well, the new pore pressure prediction closely matches the well data in comparison to the normally used prediction. As a result, a more accurate regional pore pressure prediction map using mean stress is generated to aid both hydrocarbon exploration and development activities in the study area

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