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Repeated multibeam echosounder (MBES) surveys conducted using autonomous underwater vehicles (AUVs) have the potential to document the magnitude and areal extent of seafloor changes associated with both human and natural causes, including seafloor subsidence, fault or slope movements, fluid expulsion, volcanism, and biological activity. If AUV survey design does not consider the practical limits to change detection and include best practices to minimize noise, however, the results may be ambiguous or even useless. Using a series of simulations combining real bathymetric digital elevation models (DEMs) with idealized perturbations representing seafloor subsidence and faulting, this paper examines limits to seafloor change detection using repeat MBES surveys in terms of the standard deviation of the noise in the surveys. In general, the magnitude of vertical change between surveys should be greater than the standard deviation of the noise (also known as uncertainty or error) in each of the surveys compared in order reliably recognize seafloor change. Filtering can suppress noise and recover the real seafloor change, possibly even if the magnitude of the change is less than the standard deviation of the noise. Based upon the simulations in this paper, filtering is more effective for broad features like subsidence bowls than localized features like faults even if the amount of vertical change is identical. A probabilistic threshold based upon the standard deviation of the noise appears to be less useful than filtering in the simulations undertaken for this paper.
Keber, M. (Fincantieri Oil & Gas S.p.A.) | Ambrosio, L. (Fincantieri Oil & Gas S.p.A.) | Camerlenghi, A. (OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) | Donda, F. (OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) | Tinivella, U. (OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) | Volpi, V. (OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale)
Mining in the deep sea is the next frontier for the offshore industry, which will be challenged to move farther from shore to reach resource deposits at water depths often exceeding those of oil and gas operations. The three types of resources that can be found on or just below the seabed at depths between 800 and 6,000m, are considered by several countries as an alternative source of critical minerals that could reduce the reliance on a single producer and thus unfavourable dynamics in raw material supply. A comparison of value chains of both deep sea mining and oil & gas revealed a substantial overlap in the exploration and production phases. This suggests that there exist possible business opportunities for Italian companies working in the oil & gas supply chain to provide their products and services also in this new industry. Furthermore, the Italian maritime research community has in the past years gained valuable experience and could therefore actively contribute to further development of very important aspects of the nascent industry, such as resource assessment, environmental monitoring and mining risk assessment. On the other hand, research equipment and vessels could be usefully employed throughout the entire mining campaign to not only monitor, but also support resource exploitation. A combination of advanced research capabilities in the maritime field and a strong, well established oil & gas supply chain could form a basis for providing technological solutions also in deep sea mining. To this end, it is proposed that a cluster of select companies and research institutes is formed around Key Public Institutions such as MISE and Assomineraria with the objective of creating an Italian mining contractor.
Seafloor massive sulfides (SMS) which contain Au, Ag, Cu, Zn, and Pb have been interested in as a target of commercial mining these 15 years. Japan has large potential of SMS and a national R&D project for the mining has been active these 5 years. However, the economy of SMS mining is very bad, because the waste tailing disposal cost is very expensive in Japan. A slurry flushing method is experimentally examined in this study for the improvement of the economy. During the flushing, because of density difference between the metal-rich ore and the waste rock, a kind of gravity separation is possible. The results suggest a possibility of the actual application.
The evaluation of fault sealing is an important step in the calculation of fault trap reserve. When it comes to the issue of complex 3-D fault trap structures and thin reservoirs, how to appraise and calculate the reserve properly and effectively is still a subject that needs further researching. In this respect, a certain rift basin that has experienced multi-periods rift movement and evolved in a fluvial faces and braided deltaic depositional environment has been chosen as the object of our research on fault trap evaluation and calculation of reserves. The method has been preformed in the following steps. 1) The tectonic evolution and the structural characteristics of the studying area are accomplished through 3-D seismic interpretation; 2) Based on the results of the well to seismic combination, the provenance direction sedimentary system interpretation and sedimentary evolution are completed; 3) On the basis of achievements of the tectonic evolution and sedimentary evolution interpretation, the 3-D fault trap geologic model is established by spatial interpolation. A certain method invented by Li Qingzhong is employed to forecast the fault trap reserves quantitatively. Moreover, this method can be described as follows. Constrained by the seismic horizons, fault data and sedimentary isochronous interfaces, the connected sand body units in every depth slice of the 3-D fault trap geologic model can be identified automatically. Meanwhile, their sealing degree and connectivity is appraised quantitively from the top slice to the bottom slice. Finally, through quantitative calculation of reserves for fault trap, the effective forecasting of reserves has been achieved. The results of our work have testified that this appraisal method can be applied to improve the prospecting accuracy and reserve forecasting precision of fault trap reservoirs.
AUV vs. ROV survey efficiency Comparing AUV vs. ROV survey efficiencies using historical data from Nautilus Mineral exploration programmes, over an equivalent cruise duration, shows an improvement of nearly double in square km coverage using AUV technology (average of 4.8 km 2 covered in an ROV dive compared to an average of 9.39 km 2 per AUV dive). However, it must be noted that this is a comparison of an AUV traverse line spacing of 120 m vs. an ROV traverse line spacing which varied between 200-300 m. Future survey efficiency improvements could realistically enable AUV traverse line spacing to be opened up to 200-300 m to gain greater areal coverage efficiencies over and above ROV survey, as geological targeting confidence is increased with ongoing dataset familiarity from mapping sensors onboard the AUV. Comparing line km coverage between AUV and ROV methods over a 21 day cruise duration shows that AUV's are at least 5-6 times more efficient (an accumulative total of 212.54 line km for ROV compared to 1199 line km for AUV's, or 1007 line km if considering data loss due to a faulty payload sensor experienced during the R/V Kilo Moana cruise). The platform stability and payload flexibility afforded by AUV's enables 100% coverage of the seafloor with high resolution MBES or Side Scan Sonar, to a resolution of 50 or 5 cm respectively, which enables much higher confidence in geological mapping than afforded through the limited field-of-view offered by ROV camera footage at wider traverse spacings.
Park, Se-Hun (Korea Ocean Research & Development Institute) | Yang, Hee-Cheol (Korea Ocean Research & Development Institute) | Lee, Kyeong-Yong (Korea Ocean Research & Development Institute) | Moon, Jai-Woon (Korea Ocean Research & Development Institute)
Yamazaki, Tetsuo (Osaka Prefecture University Sakai, Japan) | Ikemoto, Masahito (Osaka Prefecture University Sakai, Japan) | Nakatani, Naoki (Osaka Prefecture University Sakai, Japan) | Arai, Rei (Osaka Prefecture University Sakai, Japan)
The distribution characteristics of chemosynthetic communities around seafloor massive sulfide deposits provide important quantitative background information for the understanding of these sensitive ecosystems. Using visual seafloor observation data obtained by a towed camera system, a preliminary quantification approach of the distribution of chemosynthetic communities around seafloor massive sulfide deposits is presented. A manual visual definition and a semi-automatic color intensity analysis of the seafloor video images are the methods tested for quantifying the distribution. Some requirements for improving the approach are discussed.
Kuroko-type seafloor massive sulfides (SMS) in the western Pacific have received much attention as resources for gold, silver, copper, zinc, and lead for the commercial mining by private companies (http://www.nautilusminerals.com; http://www.neptuneminerals.com). Since the end of the 1980s, SMS have been found in the back-arc basin and on oceanic island-arc areas at 1 to 2 km of water depths. The typical representatives found are in the Okinawa Trough and on the Izu- Ogasawara Arc near Japan (Halbach et al, 1989; Iizasa et al. 1999), in the Lau Basin and the North Fiji Basin near Fiji (Fouquet et al., 1991; Bendel et al, 1993), and in the East Manus Basin near Papua New Guinea (Kia and Lasark, 1999). The high gold, silver, and copper contents in one of the areas have increased the likelihood that mining would be profitable, and a pioneer commercial mining venture is scheduled to start in a few years (http://www.nautilusminerals.com). However, no quantitative data is available for the environmental assessment of the mining, though many scientific observations have been conducted by ROVs and manned submersibles. A preliminary quantification approach of the distribution characteristics of chemosynthetic communities around the SMS deposits are introduced in this study.
High temperature hydrothermal activity was first observed 30 years ago in the modern oceans where hot springs are precipitating sulfide-sulfate-silica mounds and columnar edifices ("chimneys??) of calcium, barium, iron, copper, zinc, lead, silver and gold with other minor elements. Hydrothermal fields are now known in several major geodynamic settings (slow and fast spreading ridges, back-arc basins, arcs, and fore arcs) and associated with various types of basement rocks (basalt, andesite and dacite volcanic; sediment; and ultramafic intrusions from the mantle). According to their geodynamic setting and the composition of the basement rocks, hydrothermal sulfide deposits can be divided in five major types: 1) Mid ocean ridges + basalt = oceanic crust type; 2) Slow spreading ridges + ultramafic rocks = mantle type; 3) Arc or immature back-arc + felsic lava = Back-arc type); 4) Mid-ocean ridge + sediments + basalt = sedimented ridge type; and 5) Back-arc + continental sediments + felsic lava = sedimented back arc type. Active sites are known at water depths from a few hundreds of meters to 4100 m. The mineral and chemical compositions of sulfides are strongly dependent on the basement rock composition, the degree of maturation of the deposit, the geodynamic setting and, in some cases, on the input of magmatic fluids. At another scale, the composition of fluids and sulfide mineralization is controlled by various physical and chemical processes. One important process, related to pressure and water depth, is phase separation. Modern hydrothermal fields provide insight into geological controls, as well as the mode of formation of Submarine Massive Sulfide (SMS) deposits. On fast spreading ridges, the discharge is unstable and the style of activity varies according to the relative importance of tectonic and volcanic activities. Axial hydrothermal fields are small; however, large sulfide deposits can be formed on off-axial volcanoes. On slow spreading ridges, the hydrothermal activity is more stable and better focused. Hydrothermal fields are much larger than on fast spreading ridges but the spacing between fields is greater. Geological controls are variable: the top of the axial volcanoes where the control is volcanic is one control, but also the base and the top of the rift valley walls, as well as non-transform discontinuities where the control is tectonic and basement rocks often dominated by ultramafic rocks. Back-arc hydrothermal fields also vary depending on the importance of tectonic versus volcanic activity. The style of the discharge and the morphology of mineralization are influenced by the strong permeability of the felsic, vesicular and brecciated lava. Discharge occurs often as extensive (>1km) low temperature deposits at the top of the volcaniclastic ridges. The first observations of black smokers led to the understanding that the SMS deposits were formed primarily by accumulations of chimneys on the oceanic floor. The most recent investigations, and in particular operations of the Ocean Drilling Program showed that they are formed by three principal processes: 1) Accumulations of chimneys on the seafloor; 2) sulfate and sulfide precipitates within the mound; and 3) Replacement of basement rocks (volcanic, ultramafic rocks or sediments). The morphology of mineralization is controlled by the permeability of basement rocks. In the more mature mounds, zone refining processes produces a mineral and chemical zonation of the sulfide mounds.