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Ono, Y. (Tottori University) | Noguchi, T. (Tottori University) | Kiyono, J. (Kyoto University) | Suzuki, T. (Toyo University) | Aydan, Ö. (University of the Ryukyus) | Rusnardi, R. P. (Padang State University) | Hakam, A. (Andalas University)
Abstract: Padang is the capital city of West Sumatra Province located on the west coast of Sumatra Island, Indonesia. The seismicity around Padang is quite active, and more than 1000 casualties occurred due to the M 7.6 earthquake of 30th October 2009. Besides, the existence of a seismic gap in the off-shore of Padang, where the plate boundary between the Eurasian and the Indo-Australian plates, has been pointed out and occurrence of an M 8.0 class earthquake is expected. In 2008, Engineers Without Borders Japan (EWB-JAPAN), a nonprofit organization (NPO) set up three earthquake ground motion observation sites in Padang and one in Bukittinggi approximately 80 km northward from Padang. Subsequently, one more site was set up in the campus of Padang State University. Currently, two sites in Padang are non-operational. So far, 86 earthquake ground motions have been recorded in total. In the present paper, 36 records whose horizontal PGA exceed 5 cm/s/s were selected, and Fourier analyses of them were conducted. The dominant frequencies of analyzed earthquake ground motion records coincided approximately the peak frequencies of the microtremor horizontal-to-vertical spectrum ratio (HVSR) obtained by the past study. Furthermore, the time-frequency analysis of two records obtained at two sites on the deep sedimentary ground was carried out. The results showed that surface waves of 2 Hz were dominant in the fat area along the coast of Padang. For more than ten years have elapsed since the installation of the observation sites, urgent maintenance works for the observation equipment are strongly required. 1 Introduction Padang, the capital city of Western Sumatra Province, Republic of Indonesia, is located on the west coast of the Sumatra islands where the seismic activity is very high (Figure 1). The earthquake of M 7.5 occurred at the offshore Padang on 30th September 2009 and resulted in more than 1,000 casualties. It is expected that an M8 class earthquake will take place at the plate boundary of the offshore Padang shortly and will cause severe damage in Padang (Natawidjaja et al., 2006).
Abstract Iran is located in a seismic prone region along Alpine-Himalaya Orogenic belt. Along two main mountain ranges of Alborz and Zagros in the country (in north and west parts of Iran, respectively) several active faults exist, that are the roots of many destructive earthquakes occurred during the recent decades such as Manjil (1990), Awaj (2002), Firouz Abad-Koujour (2004), Silakhor (2006) and recentlyVarzaghan (2012) Earthquakes. Most of these events were associated with some types of landslides and rock-falls, due to topography of the affected regions. In this paper, having a look on the causes and impacts of these earthquakes, different types of the slope instabilities observed or reported after each event will be introduced and discussed. In addition, the impacts of landslides on post-earthquake activities such as emergency response and reconstruction of the damaged areas will be presented. Finally having a look on socio-economic impacts of these geological instabilities, some recommendation will be presented to be applied for reducing the impacts of those hazards that can be applied in Iran and other countries facing similar challenges. Introduction Many destructive earthquakes have been occurred in Iran during its history, due to its geological condition and existing numerous active faults extended at different parts of the country; the major ones are shown in Figure 1. Seismicity studies show that the country will undoubtedly experience large earthquakes in the future; averagely in each year one seismic event with magnitude higher than 6.0 and every ten years an event with magnitude of about 7.0 (Amini Hosseini et al., 2009). In most of the recent seismic events in Iran and all around the world, some types of geological hazards were also triggered by ground shaking that caused further damages and casualties. As example, the Tohoku, Japan Earthquake (2011) triggered many landslides that caused further destruction of buildings and infrastructure (Higaki et al., 2011). Landslides triggered by Padang, Indonesia Earthquake (2009) are another example that caused about 600 deaths in hillside of the Padand Pariman district in West Sumatra. This is almost equal to the number of casualties of collapsed buildings by ground shaking (Vigny, 2009). Similar impacts of landslides and rock-falls can be also found in Port au Prince, Haiti (2010), Sichuan, China (2008) some types of landslide or rock-fall. In some seismic events in Iran, the damages of such instabilities were much higher than the ground shaking. Therefore, during the recent years the impacts of such ground failures were also studied and some guidelines and plans have been developed to reduce their impacts. In this paper, having a look on the damages of slope instabilities associated with recent earthquakes in Iran, the existing conditions on geo-hazards risk mitigation and management activities in Iran will be reviewed and discussed.
Abstract Kenali Asam field, Pertamina EP working area, is located in West Sumatra of Indonesia. The field was discovered by NIAM in 1929. There are 285 wells were drilled which consist of 99 producing wells, 20 injector wells, and 8 dry well wells, and the rest are suspended wells. The reservoirs are layered reservoirs from shallow to deep zone, and 16 production zones. The oil was produced from primary stage to secondary stage. The secondary stage has been started by injecting water since March 1993. The water was injected to specific layer such as B/650, F/730, N/990, and S/1170. The peak production of primary recovery was 13,643 BOPD with water cut 14.4% in September 1954. Peak production of secondary recovery was 2105 BOPD with water cut 50% in October 1994. Pertamina’s EOR department and Business Unit of Jambi field conducted pilot project to the zone of P/1050 with line drive pattern flood. The line drive pattern consist of 4 injection wells and 4 production wells. The pilot plan purposes are to evaluate the effect injection in that area to increase the energy of the reservoir, to sweep the oil to enhance the oil production. Before the water flood was commencing, chemical tracer was conducted to check the connectivity among the producers and injectors. The chemical tracer IWT-2000 was injected to the KAS 63 (east area) for amount of 26 liters on November 17, 2007. The chemical tracer will be expected to flow to the monitor wells (KAS 227, KAS-028, KAS-164, KAS-39). Monitor wells are also considered as producer wells. The chemical tracers was detected in the monitor well (KA 39) after four months of injection from KAS 63. The rest of the monitor wells were not detected at all after 284 days of injections. But the connectivity analysis of injection and production showed that gross production, fluid level and bottom hole pressure increased in production wells. In the west area, the chemical tracer IWT-1700 was injected to the injector KAS-73 in the mouth of 61 liter. The monitors wells, as well production wells, are KAS 35, KAS 38, KAS 243. The chemical tracer was detected in 3 months after injections in KAS 35. But there is no chemical detection in well KAS 38 and KAS 243 after 283 days. But, from the production analysis shows similar phenomena as in the east area. KAS 38 and KAS 243 showed the increment of gross production, pressure, and fluid level in the wellbore. The waterflood pilot of layer P/1050 in Jambi area already conducted for couple years and the cumulative oil produced is more than 22 MBBO. This paper will described and evaluate the difference respond of fluid injection using chemical tracers and water. In the chemical tracer, it was detected the chemical concentration to evaluate the connectivity. Based on the water injection, it was evaluated the production performance to see the incremental of gross production, pressure and fluid level in the production performance.
Abstract The underground shelter was built by Japanese Imperial Army in 1943 in pyroclastic flow deposits resulting from nearby Singgalang and Merapiti Volcanoes. The Singkarak Lake earthquake, took place as two large shocks on March 6, 2007 and caused extensive damage to slopes in Sianok Valley, in which the underground shelter is situated. This article is concerned with the seismic effects on the underground shelter and its seismic response during the earthquake. A brief outline of geography, geology, the layout of the underground shelter and the shape and size of underground openings are fırst described. Then the characteristics of the earthquake are briefly presented. And then the seismic effects on the underground shelter is described. In the fınal part, the results of some preliminary dynamic numerical simulations for the response of the underground shelter during the earthquake are explained and discussed. 1. Introduction The West Sumatra Province of Indonesia was struck by an earthquake on March 6, 2007, killing 73 people and caused heavy damage in the cities of Solok, Payah Kumbuh, Batusangkar and Simabur. Two large events with a moment magnitude of 6.4 and 6.3 occurred at an interval two hours on March 6, 2007[2,3]. The first author visited the epicentral area between Bukit Tinggi and Solok in July, 2007. This earthquake induced many slope failures in sceneric Sianok Valley in Bukit Tinggi. This valley was created by Sumatra fault cutting through pyroclastic flow deposits from nearby Volcanoes. In Sianok Valley Japanese Imperial Army built an underground shelter in the same geological formation in 1943. While there were many extensive slope failures along the valley, the damage to the underground shelter was almost none, which may be of great value for understanding the behaviour of underground openings during earhquakes. This article is written with a sole purpose of pointing out the importance of underground shelter as a rock engineering structure in weak rock and to discuss the long-term behaviour and dynamic response during the earthquake. There is no doubt that the evaluation of the long-tem stability and dynamic response of this underground shelter from a rock engineering perspective would provide an important data set. The geography, geology, the layout of the underground shelter, the shape and size of underground openings and underground climate and ventilation are briefly described. Then the rock classifications and static stability of assessments of the underground shelter are presented. And then, the characteristics of the earthquake, the seismic effects on the underground shelter and the results of some preliminary dynamic numerical simulations are explained and discussed. 2. Geography and Geology This area is called the Padang Highland. A geologica1 sketch map of the area is shown in Figure 1, which was compiled by Sato  from the 1250000 quadrangle geologic maps published by the Geological Survey of Indonesia.
Abstract There are many kinds of methods to improve oil production such as production optimization, implementing of enhanced oil recovery, horizontal drilling, etc. It's depending on the reservoir characteristics. For example, changing pump size with the big one is not always to get a good result particularly in the reservoir that has sand problem. Acidizing treatment is also sometimes successful and failed. In order to get the best solution, a hydraulic fracturing is one of many alternatives to handle sand problem and also could improve the production at the Kenali Asam field. Kenali Asam field is located approximately 7 Km South of Jambi City, South Sumatra, Indonesia. Since the field was found in 1931, has drilled 260 wells with 19 layers in Air Benakat Formation group. Hydraulic fracturing has implemented since 4 years ago in this field, particularly in layers d/320, b/400, P/1050, and S/1170. The best result is obtained from sand b/400 (shallow sands). The most problem in these layers one of them were tight (the permeability is less than 20 md) and another layer has a good permeability (more than 200 md), but unfortunately has sand problem. Using hydraulic fracturing the production could be increased significantly and some of them also could solve the sand problem. For instance, from sand d/400 has been giving the gain around 1.170 barrel per day. And, from economical side this job still attractive due to the total cost of hyfract job (including rig cost) is still less than US $ 100,000 per well. Due to sand b/400 is very potential and attractive, in this paper, the focus discussion about sand b/400 and also will discuss about the kind of suitable proppant for this reservoir. Introduction Hydraulic fracturing is kinds of stimulation using pressure fluid to get the fractured. Continuing press the fluid will increase wide of the fracture from borehole to formation. In order to get a good permeability it will be supported by proppant. Recently, there are three kinds of reasons the oil company doing hydraulic fracturing. First, increasing PI (Productivity Index) especially in the low permeability. Second, to minimize formation damage, and the last, fracpac to handle sand problem. Beside that, sometimes hydraulic fracturing also is used to improve ultimate recovery, to assist in the secondary recovery operation, and injecting water or sludge disposal. The long-term productivity in low permeability reservoirs usually depends on fracture penetration and fracture conductivity. Fracture conductivity is a function of the proppant properties (i.e., strength, roundness, and fines content), closure stress, drawdown rate, formation properties, and resultant propped fracture width. Four factors control improvements in productivity (PI) provided by hydraulic fracturing such as: propped fracture area, conductivity of the propped fractured, reservoir permeability, and drainage radius. In this paper will be showed the implementation of hydraulic fracturing to improve oil production and to handle sand problem in the layer b/400 sand. Sand b/400 is the best of producer sand in the shallow layer group in the Kenali Asam Field. b/400 sand has been developing since 1955 and recently produces 1900 BOPD or 60% production contribution of Kenali Asam Field.
Summary Conoco successfully has used four different radioactive tracers simultaneously to determine the direction of fluid movement in a sequence of Pennsylvanian-age sandstone benches within the northern half of the West Sumatra Unit. Radioactive tracer material introduced at the injection well and identified at the producing well provides the flow direction and rate of movement of injected fluids. This information will be used to maximize sweep efficiencies and optimize depletion plans in this multipay, discontinuous reservoir. Introduction Production in the West Sumatra Unit, Rosebud County, MT, originates from one or more of four stratified and lenticular sandstone benches within the Lower Tyler formation of Pennsylvanian age. The sandstone benches, which are the result of stream channel deposits, alternate with shale and/or limestone and are bound on top and bottom by unconformities (Fig. 1). Thus, the correlation of individual sandstone benches and the continuity between wells becomes a matter of interpretive judgement. Moreover, the heterogeneous nature of the Lower Tyler sand poses considerable difficulty in matching producing responses to offset injection. Therefore, it was decided to implement an interwell radioactive tracer program and use results of the program to maximize sweep efficiencies and optimize depletion plans in the unit.This paper describes the implementation and initial results of an interwell radioactive tracer program conducted in the northern half of the West Sumatra Unit. The basic design of the tracer program, injection of the tracer, sampling and rate measurements, and analyses of the produced water are described. The results of the program clearly demonstrate that radioactive tracers can be used effectively and economically to diagnose reservoir pay continuity and fluid movement. The test further confirms the advantage of radioactive tracers over chemical tracers.Conoco used four radioactive tracers - carbon- 14, cobalt-57, cobalt-60, and tritiated water - to resolve the relationship of injectors to offset producers in the field. Results of the program have identified both reservoir continuities and discontinuities as well as probable areas of poor sweep efficiency. In several instances, geologic interpretations were changed as a result of the tracer study. Further monitoring of tracer concentrations will allow the calculation of the optimal secondary input volumes that should be directed toward the respective offset producers. Theory The primary objective of an interwell tracer program is to define the direction of fluid movement from a particular injection well to an offset producer. Assessment of channeling effects, volumetric sweep efficiencies, fluid transmissibility, reservoir permeabilities, and permeability distribution are all secondary goals. Before the program can be initiated, an estimate of the fluid response time between injector and producer is required to decide whether the project is feasible time-wise. A method for determining the time required for tracer-tagged fluid to flow from injector to producer was used for this purpose. According to this method, the time required is mainly a function of the effective permeability to the injected fluid and the total pressure drop from injector to producer, assuming the most permeable continuous layer between producer and injector will give the fastest response. JPT P. 779^