Entity

Time filter

Source Type

South Melbourne, Australia

Suzuki K.,Japan Oil, Gas and Metals National Corporation | Schultheiss P.,Geotek Ltd. | Nakatsuka Y.,Japan Oil, Gas and Metals National Corporation | Ito T.,Japan National Institute of Advanced Industrial Science and Technology | And 5 more authors.
Marine and Petroleum Geology | Year: 2015

Before producing gas from gas hydrate, it is important to clarify the physical properties of the methane hydrate reservoir and its sediments. During the 2012 pressure coring campaign, pressure core samples were retrieved from the northwest slope of Daini-Atsumi Knoll, one of the outer ridges of fore-arc basins along the northeast the Nankai-Trough. The pressure cores were sampled continuously throughout the turbidite sequences in the Methane Hydrate Concentrated Zone (MHCZ); the cores were subjected to onboard nondestructive property analyses, and X-ray Computed Tomography (X-ray CT) images of the cores were collected. Internal structures of the cores were observed in the X-ray images, which were used to judge core quality. Results for P-wave velocities and bulk densities, which were also measured on the pressure cores aboard the ship were compared with data from logging-while-drilling (LWD).P-wave velocities of cores that were retrieved by pressure corer were compared with methane-hydrate saturations calculated from several methods. In general, P-wave velocities from logging while drilling (LWD) measurements corresponded to gas hydrate saturation calculated from LWD. After compensating for the different vertical resolutions of LWD tools and pressure core analysis, P-wave velocities from the pressure cores corresponded well to methane hydrate saturation calculated from logging. A unique interval at 290-300 m below seafloor was identified where methane hydrate saturations computed from LWD data did not correspond to P-wave anomalies measured in cores from the same interval. This difference could be due to lateral inhomogeneity in lithology between the logging and coring wells, with distinct local hydrate crystallization/precipitation environments. © 2015 Elsevier Ltd. Source


Konno Y.,Japan National Institute of Advanced Industrial Science and Technology | Jin Y.,Japan National Institute of Advanced Industrial Science and Technology | Yoneda J.,Japan National Institute of Advanced Industrial Science and Technology | Kida M.,Japan National Institute of Advanced Industrial Science and Technology | And 6 more authors.
Marine and Petroleum Geology | Year: 2015

Sediment cores containing methane hydrate were obtained under pressure from the Eastern Nankai Trough offshore Japan, and they have been analyzed to investigate the relationship between compressional wave velocity (P-wave velocity), methane hydrate saturation, and pore space hydrate morphology. P-wave velocities of pressure cores were measured at near in-situ pressures, thus preventing hydrate dissociation. After the measurement of P-wave velocity, the cores were cut, under pressure, into separate P-wave velocity intervals. Each core interval was depressurized while measuring the evolved gas volume to quantify methane hydrate saturation. The results show that P-wave velocity correlates well with hydrate saturation; the P-wave velocity varied from less than 1700 m/s in the hydrate-free section to greater than 2300 m/s in the section with the highest hydrate saturation of 72%. The measured P-wave velocities were correctly reproduced by the sediment frame component model by adjusting model parameters such as sand-clay ratio and effective stress. It was found that all core data plotted within the model predictions assuming zero effective stress and assuming in situ effective stress. This may indicate that the cores were in the process of relaxing from their in situ effective stress at the time of measurement. By using pressure cores and pressure core analysis technology, the relationship between P-wave velocity and methane hydrate saturation has been directly obtained nondestructively. The observed relationship in high-resolution core-scale specimens enables estimation of the hydrate morphology and is expected to be more accurate than cross-plot data in well logging. © 2015 Elsevier Ltd. Source


Egawa K.,Japan National Institute of Advanced Industrial Science and Technology | Nishimura O.,Japan National Institute of Advanced Industrial Science and Technology | Izumi S.,Japan National Institute of Advanced Industrial Science and Technology | Fukami E.,Japan National Institute of Advanced Industrial Science and Technology | And 9 more authors.
Marine and Petroleum Geology | Year: 2015

Bulk sediment mineralogy was measured from a gas hydrate-bearing Middle Pleistocene deepwater turbidite interval at the offshore production test site of the Eastern Nankai Trough area. We used core samples recovered from a 60-m-long section of the borehole for semi-quantitative analysis of mineral and organic contents of the gas hydrate reservoir. Powder X-ray diffraction analysis, ignition loss test, and field-emission scanning electronic microscopy revealed the followings: (i) ten bulk minerals vary in concentration and most of them have a good exponential correlation with median grain size; (ii) the upper muddy section is dominated by coccolith-rich hemipelagites, whereas the middle and lower sections are characterized by relatively coccolith-poor, probably humic substance-rich turbiditic sediments; and (iii) the common occurrence of authigenic gypsum, siderite, and framboidal pyrite indicates early diagenesis in anoxic and relatively high salinity conditions probably associated with gas hydrate formation in some degree. Such mineralogical data can provide useful information on evaluation of thermal properties, geomechanical characteristics, effective permeability, and early diagenetic mechanism of the sediments to characterize and exploit gas hydrate reservoirs. © 2015 Elsevier Ltd. Source


Yoneda J.,Japan National Institute of Advanced Industrial Science and Technology | Masui A.,Japan National Institute of Advanced Industrial Science and Technology | Konno Y.,Japan National Institute of Advanced Industrial Science and Technology | Jin Y.,Japan National Institute of Advanced Industrial Science and Technology | And 7 more authors.
Marine and Petroleum Geology | Year: 2015

Geomechanical and geotechnical properties are essential for evaluating the stability of deep seabed and subsea production systems for gas hydrate extraction from marine sediments. In this study, natural gas hydrate-bearing sediment was subjected to triaxial compression tests (shearing) using a newly developed triaxial testing system (TACTT) to investigate the geomechanical behavior of sediments recovered from below the seafloor in the eastern Nankai Trough, where the first Japanese offshore production test was conducted in 2013. The sediments were recovered using a hybrid pressure coring system, with pressure cores cut using onboard pressure core analysis tools. The pressure cores were subsequently transferred to our shore-based laboratory and subsampled using pressure core non-destructive analysis tools (PNATS) for the TACTT system. Pressure and temperature conditions were maintained within the hydrate stability boundary during coring and laboratory testing. An image processing technique was used to capture deformation of the sediment sample within the transparent acrylic test cell, and digital photographs were obtained for each 0.1% strain level experienced by the sample during the triaxial compression test. Analysis of the digitized images showed that sediments with 63% hydrate saturation exhibited brittle failure, whereas hydrate-free sediments exhibited ductile failure. The increase in shear strength with increasing hydrate saturation in natural gas hydrates is in agreement with previous data from sediments containing synthetic gas hydrates. © 2015 Elsevier Ltd. Source


Yoneda J.,Japan National Institute of Advanced Industrial Science and Technology | Masui A.,Japan National Institute of Advanced Industrial Science and Technology | Konno Y.,Japan National Institute of Advanced Industrial Science and Technology | Jin Y.,Japan National Institute of Advanced Industrial Science and Technology | And 7 more authors.
Marine and Petroleum Geology | Year: 2015

The study of mechanical properties of marine sediments is essential for the prediction of the occurrence of geohazards (e.g., subsea landslides and seafloor subsidence) and the design of submarine structures for offshore industry. In this study, triaxial compression tests of gas-hydrate-bearing sandy sediments and clayey-silty sediments were conducted. The sediments were recovered by pressure coring in the Eastern Nankai Trough, the area of the first Japanese offshore production test. Soil index properties were measured and revealed porosity of 40%-50%, with porosity decreasing gradually with greater depth below the seafloor. The mean particle size was less than 10 μm for clayey-silty sediments and approximately 100 μm for sandy sediments. Permeability, estimated by a consolidation process of triaxial testing and with X-ray diffraction analysis, depended on the content of fines, which consisted chiefly of mica, kaolinite, and smectite. The results of undrained compression tests for clayey-silty sediments showed positive excess pore pressure under all test conditions. This mechanical behavior indicates that the core samples are normally consolidated sediments. Drained compression tests showed that the strength and stiffness of sandy sediments increase with hydrate saturation. Furthermore, the volumetric strain of hydrate-bearing sediments changed from compression to dilative. This result was obtained for hydrate saturation values (Sh) of more than 70%. The shear strength of hydrate-bearing turbidite sediments of the Eastern Nankai Trough is shown to be a function of the confining pressure. © 2015 Elsevier Ltd. Source

Discover hidden collaborations