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GEOMORPHOLOGY OF SMALL ISLANDS AND ITS SEAFLOOR PROFILES IN THE EASTERN AND WESTERN HALMAHERA WATERS
Get PDFThe geomorphology of small islands in the eastern and western parts of Halmahera Island encompasses diversities of geological processes, island forms and types, and topography. The typology of the small islands to the west of Halmahera Island is volcanic and are categorized as hilly islands. To the east, there are coral islands classified as flat islands with smaller area contrast to volcanic ones. This study aims to analyze the land mass elevation of the small islands and the sub-bottom profiles in the eastern and western Halmahera waters. Island elevation data was obtained from Sentinel-2B imagery, whereas seafloor topographic data was acquired from direct field measurements using a GPS sounder. First, the image data underwent atmospheric, radiometric, and sunlight corrections, while the actual depth was estimated through bathymetry correction using tidal data. Then, QGIS version 3.16.6 and ArcGIS version 10.8 were used to analyze the data. The results show that the slope degree of volcanic islands is higher and their seafloor topography is steeper than that of coral islands. The slope degree of Ternate, Maitara, Tidore, and Hiri Islands, abbreviated as Termadoreh, is more than 30o with elevation of more than 100 meters, characterizing hilly islands. While there is only Pakal Island in Buli Bay that has a slope of 33o and the highest elevation of only 100 meters, it is nevertheless considered a flat island. Significantly, the different typologies indicate different morphogenesis and sub-bottom topography; i.e., volcanic islands have higher slope degrees and steeper seafloor profiles compared to coral islands
DISTRIBUTION OF BENTHIC FORAMINIFERA IN THE WATERS FROM OFF PUTRI ISLAND, NORTHERN BATAM, RIAU ARCHIPELAGO
Get PDFPutri Island is the outermost island bordering Singapore, located north of Batam City, Riau Archipelago Province. A total of 29 sediment samples were collected from the seafloor off Putri Island for foraminiferal study. The purpose of this study is to determine their abundance and distribution related to previous data of environmental conditions. For this study, we analysed quantitative analysis of benthic foraminifera including its abundance, diversity, dominance, and evenness indices. The results denoted that benthic foraminifera was composed of 62 species that belonged to 31 genera. The diversity index was categorized as a moderate to high diversity index (1.85-3.12), with a low to high evenness index (0.37 – 0.78), and a low dominance index (0.05-0.24). This indicates that in general the waters of Putri Island are considered to have a fairly good environment and are quite stable for foraminiferal growth. A slight environmental stability degradation occurred in the north eastern part of the study area which demonstrates high levels of pollutants in the waters. This situation influent the benthic assemblages which are indicated by lowering index diversity at that location
LOW RESISTIVITY PAY DEVELOPMENT: CASE STUDY OF TALANGAKAR FORMATION ASRI BASIN, OFFSHORE SOUTHEAST SUMATRA, INDONESIA
Get PDFSoutheast Sumatra is a prolific oil and gas block located offshore in the Java Sea, 90 km north of Jakarta Bay. This area covers two major basins, namely Sunda Basin and Asri Basin. The initial development of the area focused on faulted and high closures and high-resistivity reservoirs. Further analysis shows that there are special low-resistivity reservoirs in Widuri Area, especially in the Aryani field. This paper will discuss the low resistivity pay zone reservoirs and fluid containment of the intervals. The paper will also include further assesment this undeveloped interval to increase oil production, considering the upside potential of the reservoirs using current geological, geophysical, and reservoir engineering approaches. Additionally, it will describe the operational challenges faced during the production period. The low-resistivity pay zone, a hydrocarbon-bearing reservoir in the Aryani field of the Widuri area, was identified using gas readings in the daily drilling reports, complemented with mud logging data. The Basal Sand interval, which drapes above the basement, was the site of the first producing well of Basal Sand, Aryani AC-X, preceded by a hydraulic fracturing job. Lambda-mu-rho inversion was implemented to delineate this reservoir. To recognize the potency in those wells, data reconfirmation was conducted between the elan summary, sidewall core, and cutting data. Aryani AC-X has successfully drained oil using a submersible pump, with an initial production of 408 bopd and cumulative production of 240 MBO
KARBON ORGANIK TOTAL PADA AIR PORI DI SEDIMEN PULAU PAYUNG, SUMATERA SELATAN
Get PDFAir pori sedimen merupakan air laut yang terjebak dalam sedimen dan merupakan salah satu komponen penting bagi kehidupan biota laut khususnya mikroorganisme. Kandungan karbon organik dalam air pori berperan dalam menyumbang kesuburan dan mempengaruhi kualitas perairan. Penelitian ini bertujuan untuk menganalisis kandungan karbon organik total pada air pori, tekstur sedimen, dan hubungan parameter perairan (suhu, salinitas, pH, dan kandungan oksigen terlarut) terhadap kandungan karbon organik pada air pori di sedimen Pulau Payung. Berdasarkan 5 (lima) sampel air pori yang diambil dengan menggunakan pore water profiler, selanjutnya kandungan karbon organik total dalam air pori dianalisis dengan menggunakan metode titrasi permanganometri. Analisis hubungan parameter perairan dengan karbon organik pada air pori dengan menggunakan Analisis Komponen Utama (Principal Component Analysis). Hasil penelitian menunjukkan bahwa karbon organik total dalam air pori sedimen Pulau Payung berkisar antara 15,8 - 142,2 mg/L dengan nilai tertinggi pada stasiun 5 dan terendah pada stasiun 2 dengan nilai rata-rata 72,68 mg/L. Perairan Pulau Payung memiliki jenis substrat lempung pada seluruh stasiun pengamatan
GEOLOGICAL INTERPRETATION OF 2D GRAVITY MODELING IN TULUNG SELAPAN AREA AND SURROUNDINGS, SOUTH SUMATRA BASIN
Get PDFThe South Sumatra Basin is a prolific oil and gas basin. The Tulung Selapan area, which is to the east and part of the South Sumatra Basin, is considered to have hydrocarbon potential. Several sub-basins, including the South Palembang and the North Palembang sub-basins, exist in the region. One of the geophysical methods for determining the presence of sedimentary sub-basins, structural patterns, and bedrock is the gravity method. The purpose of this study is to determine the structural pattern and interpret the subsurface geological model of the Tulung Selapan area using 2D modeling. The complete Bouguer anomaly (CBA) reveals circular and relatively northwest-southeast trending patterns, ranging from +33 mGal to +62 mGal. 2D gravity forward modeling results in eight successive rock layers. From top to bottom, the uppermost layer is swamp sediment with a mass density of 2.1 g/cm3, followed successively by the sedimentary rocks of the Kasai Formation (2.28 g/cm3), the Muara Enim Formation (2.32 g/cm3), the Air Benakat Formation (2.39 g/cm3), the Gumai Formation (2.3 g/cm3), the Baturaja Formation (2.48 g/cm3), and lastly a layer with a density of 2.7 g/cm3, which represents the bedrock. Due to the limited depth of 2800 m in 2D forward modeling, it is unable to identify the source and reservoir rocks. The seal rock (caprock) is interpreted to be shale from the Gumai Formation at an average depth of 1.53 km. Based on Second Vertical Derivative (SVD) analysis, 2D modeling identifies the presence of geological structures with normal faults
EXPLORING MARINE GEOLOGY AND OCEANOGRAPHY IN MANGGAR WATERS: A PRELUDE TO THE BURGEONING BELITONG GEOPARK
Get PDFA survey on marine geology and oceanography was conducted in Manggar Waters, East Belitung, in order to protect the geological heritage of the newly inaugurated Belitong UNESCO Global Geopark (UGGp) in 2021. This study is aimed at understanding the characteristics of the seabed, marine sediments, currents, and coastal features in the area. A bathymetrical survey was done using an Echotrac echosounder to measure water depths, and current measurements were taken with an Infinity device. Forty sediment samples were collected and analyzed for their characteristics. The coastal features were examined through direct observation, and an unmanned aerial vehicle (UAV) drone was used to investigate the morphology of small islands. The results showed that the seabed was mainly composed of coarse sediments, such as sand and clayey sand, with some areas containing gravel near Buku Limau Island. The microfauna foraminifera analysis indicated a relatively low diversity, with Operculina and Amphistegina being the dominant species. Two types of beaches were recognized: the northern part, consisting of rocky beaches made of igneous rocks, and the southern part, which has flat beaches made of beach alluvium deposits. Abrasion was found to be dominant in the southern part, particularly at Tambak Beach. The study provides valuable information for the planning and management of marine areas in the Belitong Geopark. It also highlights the importance of preserving and protecting the geological heritage of the region. With this newfound knowledge, stakeholders can make cognizant decisions to ensure the conservation of the Belitong Geopark and its unique geological features
GEOLOGICAL INTERPRETATION OF THE OFFSHORE SEDIMENTARY BASIN OF NORTH CENTRAL JAVA BASED ON SPECTRAL ANALYSIS AND 2D GRAVITY MODELING
Get PDFThe offshore sedimentary basin of North Central Java is a marine basin located in the northern part of North Serayu Basin. This basin was formed through the uplift of the southern part of Central Java (Bumiayu) caused by the movement of a pair of horizontal faults. Studies of sub-basin delineation and basement configuration are rarely carried out in this basin. Therefore, the gravity method referring to subsurface-density variations was carried out to obtain this information. This research aims to delineate sedimentary basins and interpret the geological subsurface based on gravity data using spectral analysis, highpass and lowpass filters, also 2D gravity modeling. An average estimation depth to the basement in the study area of about 2.22 km was determined using spectral analysis. Qualitative analysis shows the basement-high pattern, sub-basin, and structure lineament patterns. The 2D model shows three layers consisting of the upper sedimentary layer of Tertiary-Neogene and the middle layer of Tertiary-Paleogene sediment with a density value of 2.3 gr/cc and 2.5 gr/cc, respectively. The lower layer has the highest density of 2.67 gr/cc, assumed as a granitic basement. The results of the Second Vertical Derivative (SVD) analysis on the residual anomaly cross-sectional paths indicate the presence of thrust and normal faults which can be used to assist the interpretation of fault structures in subsurface geological models. Gravity analysis of the offshore North Central Java sedimentary basin indicates the occurrence of sub-basins and geological structure patterns that considered as a potential zone for the development of the petroleum system in this area