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Mizukami, Takuya (JX Nippon Oil & Gas Exploration Corporation) | Fukano, Tetsuo (JX Nippon Oil & Gas Exploration Corporation) | Aoyama, Takeo (JX Nippon Oil & Gas Exploration Corporation) | Maehara, Yuki (Schlumberger K. K.)
ABSTRACT The onshore Nakajo oil and gas field in Niigata Prefecture is composed of three different types of hydrocarbon accumulations: non-associated natural gas, black oil, and natural gas dissolved in water (GDW). The natural GDW is produced together with formation water as gas in solution under in-situ condition. While the formation water is lifting to surface, the dissolved gas is separated from the water. With this reason, well log response from GDW sandstone was believed to be almost the same as normal sandstone which does not contain any hydrocarbon. In the recent in-fill well drilling campaign for GDW reservoir, a full suite of wireline logging was carried out. With a success of good quality data acquisition, an advanced sonic and borehole image analysis was conducted. As a result, gas-effect-like sonic log response such as significant P-wave slowness slowing down and unchanged S-wave was newly observed in GDW sandstone formation, while other logs such as Neutron and Density did not show any hydrocarbon response. In addition, the sonic velocity radial-profiling analysis result indicated slow P-wave formation property radially continuing from near wellbore into the formation. Based on these observations and following desktop study, we successfully reached to the conclusion that gas-water 2 phase fluid model is a reasonable assumption rather than a single-phase fluid model for GDW formation. These new findings on sonic log response will bring new aspect to the formation evaluation of GDW reservoir in Nakajo oil and gas field.
ABSTRACT Response in a porous seabed under dynamic environmental loading is a vital engineering issue in marine geotechnics. Lots of investigations for seabed response under dynamic loading have been developed through mathematical, numerical and experimental approaches. Most previous numerical models for seabed response in marine environments were based on finite element models. In this paper, based on local radial basis function collection method (LRBFCM), a meshfree model is proposed for the seabed response in the marine environments. In the present model, partial dynamic approximation (u-p approximation) will be used, and three different types of natural loading will be considered, i.e., wave, current and earthquake loading. INTRODUCTION In the last twenty years, more and more marine structures are constructed with the deeper exploration and study for the offshore area. The most important aspect to be considered in engineering practice is the stability after putting in use of those marine structures under the complicated environment loading. In general, three types of the environmental loading needs to be taken into account for the design of marine structures, which are ocean waves, currents, and probable earthquake respectively. The dynamic response under these loading has attracted great attention among coastal and geotechnical engineers due to the growth of activities in marine environments. As the conventional loading, how ocean wave and current affect the marine structure stability is a vital problem for coastal engineers. In general, the propagating ocean wave will generate the dynamic pressure in the sea floor, which may trigger soil liquefaction of the seabed as reported in the laboratory test (Sassa and Sekiguchi, 1999). Meanwhile, the effect of earthquake is also important for engineering design. Although the probability of earthquake occurred nearby the marine structures is not so high, once the earthquake happened, the damage would be devastating. As one of the major natural disasters need to be considered in structure design, earthquake is also able to liquefy the saturated soil through seismic shaking effect. The liquefaction phenomena induced by seismic wave was fully aware by the public from the Niigata earthquake in 1964 in Japan, which caused unprecedented damage. The problem of earthquake-induced liquefaction attracted a great deal of attention of geotechnical researcher and great achievements have been made in the past (Seed et al., 2003). However, as pointed by Ye and Wang (2015), most of the studies for earthquake loading are concerned with onshore structures, while only a few studies considered offshore structures whatever by experiment or numerical simulation. For the earthquake loading, Chen et al. (2018) has developed the analytical solution for layered porous seabed under vertical seismic motion.
ABSTRACT The big wave suddenly invaded to the beach, and three children were carried off to the sea by the wave though they played on the beach. The beach characteristic topography has the cusp topography and steep slope. This study tried to comprehend the reason why this accident occurred. Firstly, this study comprehended the wave condition when the accident occurred. Secondary, this study made the survey about the geographic feature of the beach. And this study obtained the geographic data for the numerical simulation from the aerial photograph which were taken by Drone. Finally, this study comprehended the wave dynamics on the beach by the numerical simulation. This study simulated the wave dynamics by the horizontal two dimensional numerical model and the vertical two dimensional numerical model. INTRODUCTION The accident that three children and two adult males who tried to rescue the children died occurred at Jogehama beach Japan in 2014 (see Fig.1). The wave run up to 28m from the shoreline when the accident occurred. The beach was known in the around area for the small cusp topography and steep slope. Therefore, the beach was the swimming prohibited area, and they played on the beach when the accident occurred. However, the big wave suddenly run up to the beach, and the children were swept out to sea. Our group reproduced the wave run up condition by the numerical simulation, and compre-hended about the wave run up speed and the water level. This time, we tried to know whether the same phenomenon occurs or not at other coast area in Niigata prefecture. Firstly, we comprehended the wave condition when the accident occurred. In this case, we used vertical two dimensional model, CADMAS-SURF2D. After comprehending the accident ouucred condition, the wave run up condition was comprehended by changing the wave height and the period. According to the result, when the wave height will be about 1m, adults will fall down in the wave run up area. Secondary, we tried to extract the same beach with Jogehama. As the result, some beachs were extracted. According to the result, we went to the extracted beachs, and comfirmed that the wave run up conditions were same with Jogehama beach.
ABSTRACT The mechanical properties of soil samples are directly determined by their behavior when the material is subjected to changes in pore-water pressure and by the rearrangement of soil particles caused by the penetration of the tube during sampling. Shogaki (2017) examined how samples were disturbed by tube penetration during a single tube sampling based on pore-water pressure, void ratio, and the movement of clean sand particles. However, the model tests were conducted in the laboratory under atmospheric condition, i.e., not under confining stress. In this paper, the effect of the confining pressure on the deformation behavior of Toyoura sand and Kawasaki clay caused by tube and cone penetration is examined under confining stress. INTRODUCTION The mechanical properties of soil samples are directly determined by their behavior when the material is subjected to changes in pore-water pressure and by the rearrangement of soil particles caused by the penetration of the sampling tube during sampling. Shogaki (2017) examined how samples were disturbed by tube penetration during a single tube sampling based on pore-water pressure, void ratio, and the movement of clean sand particles. Samplers with tubes having inner diameters of 35, 45, and 75 mm, and cutting-edge angles of 6° and 90° were used for the model tests on Toyoura sand. The speed of penetration was 0.6–5.8 cm/s while the relative density ranged from 6% to 83%. Horng et al (2010) also discussed the effect of the sampling-tube geometry on reconstituted Kasaoka clay samples prepared in the laboratory under atmospheric conditions, i.e., not under confining stress. The height of the tank used in their 1-g physical model test was about 30 cm. Shogaki (2016) demonstrated that the semicircular tube penetration of Toyoura sand was similar to circular cylinder tube penetration of sands from Niigata Meike, Niigata Airport, Niigata East Port, the port of Kansai, and the third Meiji fortress (Shogaki, 2016). However, these model tests were conducted in the laboratory under atmospheric conditions, i.e., not under a confining stress.
Marc, Odin (Deutsches GeoForschungsZentrum GFZ-Potsdam and University of Strasbourg/EOST) | Hovius, Niels (Deutsches GeoForschungsZentrum GFZ-Potsdam) | Schönfelder, Christoph Sens (Deutsches GeoForschungsZentrum GFZ-Potsdam) | Meunier, Patrick (Ecole Normale Superieure, Paris) | Illien, Luc (Deutsches GeoForschungsZentrum GFZ-Potsdam) | Hobiger, Manuel (ETH Zurich) | Hsu, Ya-Ju (Academia Sinica, Taipei) | Ohzono, Mako (ETH Zurich) | Sawazaki, Kaoru (National Research Institute for Earth Science and Disaster Resilience, Tsukuba) | Rault, Claire (Ecole Normale Superieure, Paris)
Some studies have suggested that the shaking and deformation associated with earthquakes would result in a temporary increase in hillslope erodibility. However very few data have been able to clarify what causes this transient state and what controls its temporal evolution. We present integrated geomorphic data constraining an elevated landslide susceptibility to rainfall following 5 continental shallow earthquakes, the Mw 6.9 Finisterre (1993), the Mw 7.6 ChiChi (1999), the Mw 6.6 Niigata (2004), the Mw 6.8 Iwate-Miyagi (2008) and the Mw 7.9 Gorkha (2015) earthquakes. We constrained the magnitude (5 to 20 fold) and the recovery time (1 to 4 years) of this susceptibility change and associated it with subsurface damage caused by the strong shaking (Marc et al. 2015). The landslide data suggest that this ground strength weakening is not limited to the soil cover but also affects the shallow bedrock. Coseismic rock damage is supported by observations of shallow (0 to ~100m) seismic velocity drops constrained with ambient noise waveform correlations within the epicentral area of four of those earthquakes (e.g., Takagi etal. 2012, Hobiger et al. 2015). For most stations we observe a subsequent exponential velocity recovery (i.e. proportional to e) with a τ value in fair agreement with the one estimated based on landslide observation. This recovery dynamic is also consistent with post-seismic processes, namely GPS post-seismic displacement and aftershocks decay (Fig. 1, Marc et al., in review). We analyzed strain time series in Japan and Taiwan and it appears inconsistent with the recovery of landslide susceptibility and shallow seismic velocities. In contrast, surface dynamic strain associated with ground shaking caused by aftershocks display similar relaxation time and may control the subsurface property recovery.
Abstract Effects of the tube diameter, the cutting edge angle and the penetration speed influencing Toyoura sand movement caused by tube penetration during sampling is examined based on the movement of the soil particles caused by the tube penetration. Samplers with tubes having inner diameters of 35 mm, 45 mm and 75 mm, and cutting edge angles of 6%#176 or 90%#176, are used for model tests on Toyoura sand. Physical characteristics and grain size properties of Toyoura sand are similar to those for the Niigata sand samples. Therefore, for the model tests on Toyoura sand, the ground is assumed to be like that of naturally occurring Niigata sand with few alluvial grains. The tube penetration speed (Sp) is in the range of 0.6 cm/sec to 5.8 cm/sec, while the relative density (Dr) is in the range of 30 % to 70 %. The disturbed area was easily formed by the tube cutting edge angle of 90%#176, since the vertical displacement (Dv) of the targets of the tube cutting edge angle of 90%#176 obtained from all Dv, Sp and tube diameter conditions in this test were smaller than those of the tube cutting edge angle of 6%#176. Introduction Sample quality is directly controlled by the pore water pressure/effective stress behavior and the rearrangement of soil particles caused by the tube penetration during sampling. Up to now, no sufficiently demonstrative research has been conducted on this issue despite the information that elucidates the nature of sample disturbance. Baligh, et al. (1987) and Clayton, et al. (1998) studied the effect of sample disturbance on the sample quality due to the tube cutting edge angle and the tube diameter through numerical analyses. They pointed out that the sample quality decreases with a decreasing tube diameter. However, these results cannot explain the quality of the samples obtained by the 45-mm and 75-mm samplers, since the quality of the samples obtained with the 45-mm sampler is similar to or higher than that of the samples obtained with the 75-mm sampler (Shogaki and Sakamoto, 2004; Shogaki, et al. 2006; Shogaki and Nakano, 2010). One reason given for the higher quality of the samples obtained with the 45-mm sampler is the higher penetration speed (Shogaki and Nakano, 2010). However, this opinion is inadequate, since it is based on field sampling and has not been examined by means of a quantitative evaluation for each factor. Horng et al. (2010) also discussed the effect of sampling tube geometry on reconstituted Kasaoka clay prepared in the laboratory under atmospheric conditions, i.e., not under confining stress. The tank used in their 1 g physical model test was also about 30 cm tall.
Abstract The big wave suddenly invaded to the beach, and three children were carried off to the sea by the wave though they played on the beach. The beach characteristic topography has the cusp topography and steep slope. This study tried to comprehend the reason why this accident occurred. Firstly, this study comprehended the wave condition when the accident occurred. Secondary, this study made the survey about the geographic feature of the beach. And this study obtained the geographic data for the numerical simulation from the aerial photograph which were taken by Drone. Finally, this study comprehended the wave dynamics on the beach by the numerical simulation. This study simulated the wave dynamics by the horizontal two dimensional numerical model and the vertical two dimensional numerical model. Introduction The big wave suddenly invaded to the beach, and three children were carried off to the sea by the wave though they played on the beach. The beach characteristic topography (Uchiyama) has two lines of the small cusp topography. And two lines of cusp have the different phases. The beach slope is about one-tenth, therefore, the wave breaks at the beach line however the comparatively high wave height, and run up to the beach with few kinetic energy attenuated. Furthermore this slope condition can make the beach cusp easily. If the beach slope condition is one-tenth, the median diameter of the beach sand becomes to be about 1mm, and if one-eighty, the diameter becomes to be about 2mm (BEACH EROSION BOARD). The slope of the large beach in Niigata prefecture is about one-eighty (Inukai), therefore the diameter of beach sand in Jogehama beach is bigger than other large beach. This study tried to comprehend the reason why this accident occurred. Firstly, this study comprehended the wave condition by using the weather chart and wave data when the accident occurred. Secondary, this study made the survey about the geographic feature of the beach. And this study made the geographic data for the numerical simulation from the aerial photograph which were taken by Drone (UAV).
Abstract The reason why the applicability of the economically feasible (EF) method, utilizing changes in density, for estimating in situ dynamic strength and deformation properties of sand samples is unrelated to the sediment sites and the grain size distribution properties of sands is discussed through the grain size distribution properties and the angle of repose of sands. The shape and the surface condition of the sand particles were almost similar from observation using the scanning electron microscope. Therefore, it was considered that the reason for the high applicability of the EF method at different sediment sites and for different sands is the smaller effects of the shear strength and the dilatancy properties caused by sample disturbance during the tube sampling. These samples are generally deposited in coastal areas in Japan as high liquefaction potential sands.
Summary Source repeatability is one of the most important problems in time-lapse seismic and reservoir monitoring. We introduce a new time-lapse approach using a permanent seismic source ACROSS (Accurately Controlled and Routinely Operated Signal System) and elastic full waveform inversion. The ACROSS source, fixed in cement at surface, can produce repeatable, extremely precise two-component seismic signal. We first performed field data observation at a Kashiwazaki test field, Niigata, Japan using two ACROSS sources with sweep frequency ranging between 5-50 Hz. Signals from each ACROSS source are clearly separated owing to an accurate source control, and transfer functions (or shot gathers) corresponding to each ACROSS are generated. The waveforms arriving before surface waves, mostly P-wave related, show little waveform changes over time and confirm excellent source repeatability. With the assumption that two ACROSS sources are installed at a CCS (carbon capture and storage) field, we performed 2D simulation study using time-lapse elastic full waveform inversion (FWI) for differential P-wave velocity. Since ACROSS precisely controls the sweep source signature, it is more suitable to apply elastic algorithm than conventional acoustic method. To simplify the multi-component and multi-parameter problems on elastic FWI, we invert only for P-wave velocity residual using so-called scalar potential of the elastic wavefields to prevent from crosstalks caused by P- and S-wave interference. The synthetic FWI result shows sharp delineation of P-wave velocity residual associated with fluid replacement. The superior repeatability of ACROSS and the proposed time-lapse FWI approach may bring a breakthrough towards hydrocarbon reservoir or CO2 monitoring.
Abstract The purpose of this study is to detect the locations of Slope failure caused by earthquakes and heavy rains in mountainous regions by using Satellite remote sensing technique. Remote sensing is basically an effective method to capture the disaster situation due to a Large-scale disaster because it can safely observe wide damaged areas. We could not analyze small-scale slope failures by using conventional medium resolution satellite images in the past, however, we have now been able to analyze them by using recent high resolution satellite remote sensing technique. In the future, moreover, it is scheduled that new satellite with more high resolution will be launched and it is expect that we will be able to analyze damaged areas more in detail. From this point of view, as a first step, we tried to detect the locations of slope failure by using images of AVNIR-2(Advanced Visible and Near Infrared Radiometer type 2)sensor loaded on ALOS (Advanced Land Observing Satellite)for four natural disasters i.e., the 2007 off Niigata-chuetsu earthquake, the 2008 Iwate-Miyagi inland earthquake, the 2009 Chugoku- Kyushu-hokubu heavy rain and the 2010 Shobara in Hiroshima prefecture heavy rain. In detecting the locations, from the satellite images taken after the events, we first obtained two indices, i.e., INDVI(Inverse Normalized Difference Vegetation Index)which is newly proposed in this study and NDSI (Normalized Difference Soil Index). For each index, we determined three categories, i.e., soil, vegetation and water areas based on the range of pixel numbers which belong to these areas. From the results, it was found that the proposed INDVI is the most suitable parameter to detect the locations of slope failure.