Journal of Applied Geology
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LUSI MITIGATION IMPLICATIONS OF BPLS AND OTHER SUBSIDENCE MEASUREMENTS
Get PDFSince the beginning of LUSI eruption, extrusion of mud has been accompanied by deformation of the land surface extending out as much as three km from the main vent. Deformation generally consists of subsidence, however also includes uplift in certain areas and minor surface faulting and cracking as surface blocks of sediment move. BPLS monthly leveling since 12/2007 by laser surveying gives the most reliable measure of vertical movement around the perimeter of the mud ponds. This has been augmented by differential GPS measurements that extends farther out. Subsidence beneath the mud within the levees is difficult to be measured accurately. Rapid subsidence, rising mud, and continuous addition of dirt to maintain the internal dikes make it impossible to maintain a system of benchmarks in the inner area. Shape of the surface beneath the mud can be estimated by indicators such as early GPS measurements, tilting of partially buried buildings, and the rate at which tiers of sandbags have disappeared beneath the mud. We have synthesized all available data to produce a contour map of estimated total deformation for the first 35 months of eruption despite limitations of the data such as variable quality, contradictions, poor point distribution, and observations over variable time intervals.
Pre-eruption land surface near LUSI was a nearly level plain about 4 m above MSL sloping about 0.45 m/km NE toward the sea and away from the artificially high channel and levees of the Porong River. Land around the vent has subsided in the form of an asymmetrical shallow funnel where the gentle tilt of about 10 m/km around the margins increases dramatically near the vent. Early ITB continuous differential GPS measurements of horizontal movement indicated a point of maximum subsidence about 250 m northwest of the main vent. Our contours indicate 65 million m³ of mud is presently stored. About 60% occupies the subsidence depression, the rest is confined by the dikes. About 200 m south of the vent is a flexure zone trending generally east-west that separates fast subsidence from slower subsidence to the south. This flexure has caused difficulty in mitigation by blocking flow of mud southward towards disposal points along the Porong River.
On the west side of the subsidence cone, flexure toward the vent area has stretched the ground surface, breaking it with steep north-northeast trending fractures that localize methane gas venting. These resulting blocks settle unevenly, creating horsts and grabens with offset less than 15 cm. This fracturing probably extends east beneath the levees although it is not clearly expressed there. Transverse to this pattern near the former toll road bridge is a 100 m-wide zone characterized by the highest subsidence rates outside the levees. This subsidence of about 1.5 m in three years is much less than an estimated 40 m subsidence beneath the mud near the vent, but lies across natural drainage and causes local flooding. At present rates of subsidence, this area will be below sea level in four years and become a pond unless constantly pumped. Until the road realignment is completed, most of the commercial traffic of East Java must travel through this area, and the proposed realignment still lies perilously close to northwesterly expanding subsidence. Increased methane venting and ground cracking has made West Siring Village too hazardous for continued habitation.
Keywords: Subsidence, mitigation, LUSI, mud, eruptio
Evaluation of Engineering Geological Conditions for Slope Stability Analysis of Diversion Tunnel Portal of Jlantah Dam, Karanganyar, Central Java
Get PDFThis paper presents the research results carried out to analyze the slope stability of the diversion tunnel portal of Jlantah Dam based on the quality of the rock mass. The classification of the rock mass quality at the tunnel location refers to the Geological Strength Index (GSI) method while the analysis of portal slope stability is modelled numerically with the element method using Phase2 software. The modelling of the tunnel portal slope design with and without earthquake load was carried out to obtain the safety factor (SF) value. The results showed that the study area consists of residual soil, andesite breccia and lapilli tuff rocks with rock mass quality based on the GSI value ranging from poor to fair. The inlet portal slope is composed of rocks that have poor and fair mass quality while the inlet section is composed of rocks that have poor mass quality. The SF value>1.3 for conditions without earthquake effect was achieved on slope design 1V:1.5H and SF value>1.1 for conditions with earthquake effect was achieved on slope design 1V:2H. The SRF value at the portal outlet location is greater than the SRF value at the portal inlet location for the same slope design conditions indicating that the rock mass quality at the portal outlet location is better than the rock mass quality at the portal inlet location
Facies Analysis and Reservoir Characterization Using Petrophysical Methods in the Interest Zone in the 'FAN' Field, Kutai Basin, East Kalimantan
Get PDFOne of the most prospective oil and gas producing basins in Indonesia is Kutai Basin which is located in East Borneo. In Kutai Basin there is a natural resource potential in the form of gas which is quite abundant. This is due to the richness of the source rock aspect in the Kutai Basin which is dominated by coal. Besides coal, in the Kutai Basin there is also claystone with rich organic matter (organic shale) that has an important role as a prospective source rock. Therefore, a final project research was conducted in the Kutai Basin, East Kalimantan. The purpose of the research is to identifying the type and content of subsurface lithology and fluids, calculating petrophysical parameters, and making the facies distribution map at the research site in potential and prospective zone to produce hydrocarbons which is called the zones of interest. The research is focused on reservoir rocks at the research site because the hydrocarbons accumulated in the reservoir rocks itself. By focusing research on reservoir rocks, it will be able to describe the modelling and calculation results of petrophysical parameters using several analytical methods such as qualitative and quantitative analysis methods, electrofacies and parasequence analysis methods, stratigraphic correlation analysis methods, facies analysis methods and depositional environments, and facies map analysis methods. In addition, by focusing research on reservoir rocks, it can develop and increase the level of optimization of exploration and exploitation of drilling wells. Based on the analysis data, the research location is included in the transitional depositional environment, delta in particular with distributary channels and mouth bars facies and also it can be identified some lithology such as sandstone, claystone, coal, limestone, and organic claystone and there are fluids with gas and water types
Mineralogy and Ore Characteristics of the Kujang Pb-Zn Skarn Deposit, Sukabumi Regency, West Java
Get PDFThe Kujang Pb-Zn skarn deposit is known to be the newest skarn deposit found in the Sunda-Banda magmatic arc. The skarn orebodies are mostly hosted by limestone which might be the part of the Jampang Formation where dacite porphyry is interpreted to be the ore causative intrusion. Orebodies are mostly found at the contact between marbleized limestone and volcanic rocks and are controlled by NW-SE-trending strike-slip faults. Previous research on the mineralogy and ore characteristics of the Kujang Prospect remains limited on the preliminary studies. Using fieldwork data, petrography, ore microscopy, and assay data from core samples, this study is aimed to characterize the mineralogy of both alteration and ore of the deposit. The alteration of the Kujang Prospect skarn can be divided into 2 phases of alteration i.e. prograde and retrograde. The prograde alteration is characterized by the occurrence of clinopyroxene, wollastonite, and vesuvianite. Garnet is present in very rare amounts. the retrograde alteration is typified by epidote, chlorite, calcite and actinolite. Metalliferous minerals are represented by sphalerite, galena, pyrrhotite, chalcopyrite and pyrite. All ore minerals are formed at the early retrograde stage. the deposit’s average grade is 2.06% Pb, 6.45% Zn and 1.81% Cu
Volume Estimation of the Thickest Scoriaceous Tephra-Fall Deposits on the South-Southeastern Flank of Mt. Raung
Get PDFThick scoriaceous tephra-fall deposits are widely distributed in the south to the southeast flank of Mt. Raung, indicating the existence of past large explosive eruptions. The deposits are relatively young as the deposits are situated near the surface. Scoriaceous tephra-fall deposits can be divided into four layers from bottom to top, Scoria Fall 1, Scoria Fall 2, Scoria Fall 3, and Scoria Fall 4. There is no time gap between these layers, as evidenced by the deposits not being separated by any weathered layer or soil, suggesting that the deposits represent an eruptive product of a single active period. We estimated the volume of the deposits using isopach maps following Weibull method to identify the magnitude of the eruption. We limited the estimation only to Scoria Fall 2 and Scoria Fall 3 deposits which were consistently exposed on 13 and 9 observation points, respectively. The volume of Scoria Fall 2 is ~0.54 km3 and Scoria Fall 3 is ~0.26 km3 making the total volume of 0.8 km3 (VEI 4)
Identification of Permeable Structures and Heat Source in the Geothermal Working Area of Galunggung Volcano and the Heat Source Connectivity to the Karaha-Cakrabuana Area Using Gravity Data
Get PDFGalunggung volcano area is a geothermal concession area that adjacent with Karaha-Cakrabuana concession area with a distance around 1 km. Indonesian Government planning to build power plant in 2025 so additional research needed to support the plan. Gravity survey could help in identifying permeable structure (fault) as well as heat source to a certain depth. The results of data processing showed the presence of faults seen on the FHD, SVD, and ABL residual maps, while for heat sources it was shown from the closed contour patterns on the ABL, residual, and regional maps. Derivative analysis in strengthens the position and type of fault from the match between the maximum FHD value and zero SVD value. From these results, identified the existence of three faults in the study area and were all identified as normal faults. 3D modelling gave a picture of density contrast in research area. From the section profile that pass through Galunggung and Telaga Bodas crater, heat source was interpreted as density with value 2.8 – 3.0 gr/cm3 and marked by orange to red color that coincide below Galunggung crater and continoued to Talaga Bodas crater at depths below -3000 masl. This indicate that both concession area was connected
Initial Geochemical Assessment of Coaly Source Rocks in Sumatera, Java,and Kalimantan
Get PDFIn Western Indonesia’s petroleum system, one of the hydrocarbon source rocks was deposited in parallic-deltaic environment with high organic content, categorizing it as coaly source rock. This study focused on geochemical characteristics of 25 coal and coaly shale samples from rock outcrops and well representing the Central Sumatra, South Sumatra, South Central Java, Barito, and Kutai Basin, with additional data from previous studies. TOC analysis and Rock-eval Pyrolysis were carried out to reveal the geochemical characteristics and maturation pathway of the source rock. The TOC analysis results showed a value of 0.5-67.73 wt%, indicating poor-excellent source rock potential. Further rock-eval pirolysis exhibits kerogen type II/II-III (excluding samples from Ngimbang Fm.), with gas-dominated hydrocarbon. Hydrocarbon Index ranging from 4-308 mg/gC indicates possible low-moderate quantity of hydrocarbon that can be generated by the source rocks. Despite the overall fair-good source rock potential, Tmax of the samples indicates a very poor maturity level, with only Upper Talang Akar as the mature candidate. Thus, it can be concluded that young source rock candidates in Western Indonesia (limited to the basins studied in this research) initially possess potential in generating hydrocarbons, if it is not for the immature level of most coaly source rock formations
Susceptibility Zoning of Soil Movement in Tawangmangu District, Karanganyar Regency with Bivariate Statistic Method - Weight of Evidence
No full textTawangmangu district which is located in Karanganyar Regency, Central Java is a crowded area which is susceptible to disaster. Therefore, susceptibility zoning analysis is needed to support the planning and development of the area. The method used is bivariate statistics - weight of evidence which has never been implemented in its location. There are two types of data, data of potential and soil movement case (divided into train data as 61 points and test data as 40 points); and parameter data of soil movement causes. Parameter data of soil movement is processed to be a WoE (Weight of Evidence) parameter map through the use of train data to know the weight. Later on, it will be validated based on the AUC value. If it’s > 0,60, then the process will proceed. Parameter which has AUC value > 0,60 is type of lithology, slope, hill, elevation, slope direction, distance from the fault, and index of vegetation density. All of those parameters are attached and being final validated by test data. Further, the zonation consists of four; zone of very low soil movement susceptibility, low, medium, and high. The area of the very low soil movement susceptibility zone is 19,68%. Zone of low susceptibility is mostly 24,57%. Zone of medium susceptibility is 25,88%. Meanwhile, the zone of high susceptibility is 29,86%. The result of final validation shows that AUC value from the zoning model made belongs to a good category, which is 0,757
Nickel as A Strategic Mineral and Its Potential Resources in X-Field, North Konawe, Southeast Sulawesi, Indonesia
Get PDFIndonesia is the world's largest producer of Nickel laterite deposits. By the regulation of UU No. 3 2020, due to its utility as the main component of batteries on electric vehicles (EV), nickel is one of the metal minerals that play important role in energy transition issues. It will drive the increasing demand for Nickel and Indonesia needs a massive exploration and specific regulation, especially for this deposit. The focus of this research is to discuss how important Ni is as a strategic mineral and its potential resources in North Konawe, Southeast Sulawesi. The methods are based on field data analysis and references study.X-Field is located in Lasolo Island, North Konawe, Southeast Sulawesi. This area has potential resources of Ni-laterite deposit. The lithological condition consists of a massive ultramafic igneous rock complex. The host rock has already been enriched by the serpentinization process. The geochemical analysis shows various ranges of 0.87-2.43% Ni content from different soil zone. To this day, the government regulation of Ni in a specific way as a critical mineral is still not present. The lack of data transparency (supply chain) and policy synchronization urgently need to be solved.
Stability Analysis of Saka DAM Diversion Tunnel Portal
Get PDFThe Saka Dam has a channel in the form of a diversion tunnel. This paper presents the results of rock mass characterization using the Geological Strength Index (GSI) classification and evaluation of the stability of the tunnel portal slope with earthquake loads using numerical methods. Based on the GSI classification, the Saka Dam tunnel portal slope is composed of rock masses that are poor quality, fair, and good. The calculation results show the Saka Dam can experience earthquake loads with an acceleration value of 0.4g. Earthquake loads can cause a decrease in the safety value (SRF) of the tunnel portal slope based on the results of numerical analysis. SRF value of natural portal slope without earthquake effect is 10.23 (inlet) and 1.5 (outlet). SRF value of the design slope portal without earthquake effect is 6.64 (inlet) and 1.76 (outlet), whereas if the earthquake effect is taken into account the SRF value obtained is 20.31 (inlet) and 0.99 (outlet). This shows that the condition of the natural portal slope and the portal slope design planner section of the Saka Dam inlet diversion tunnel is in the safe category. Meanwhile, for the portal slope excavated from the outlet section, modification is needed to obtain a safe slope condition. The results of the modified geometry of the slopes at the outlet section resulted in an SRF value of 1.47 which indicates the slope is stable