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Sawayama, Kazuki (Kyushu University) | Ishibashi, Takuya (National Institute of Advanced Industrial Science and Technology) | Jiang, Fei (Yamaguchi University / Kyushu University) | Tsuji, Takeshi (Kyushu University) | Fujimitsu, Ysuhiro (Kyushu University)
Hydraulic and mechanical behaviors of the geothermal reservoirs or the seismic faults are strongly controlled by the characteristics of rock fractures. To monitor and predict the hydraulic-mechanical coupling within the crust, geophysical explorations potentially are the powerful tools. However, there is few established rock physical model to link the hydraulic properties of fracture to the resistivity or elastic wave velocity. For our better interpretation of the exploration data, detailed investigation linking hydraulic properties to the mechanical/electric properties for the fractured rocks is required. Therefore, we explore the link by coupling the laboratory experiments and digital rock modeling on the fractures with different aperture distributions. We conduct the fluid-flow experiments and the numerical modeling on granite fractures. In our modeling, we first digitalized the real granite fractures by 0.1 mm grid system. Then, under the same condition with experiments, we calculate the fluid flow (Lattice Boltzmann Method) and resistivity/elastic wave velocity (finite-element method). Laboratory experiments show that fracture permeability decreases with increasing pressure, and this relationship could be reproduced in our modeling study. We further determine the aperture distributions based on the permeability matching approach. As a result, we successfully constrain the variation of permeability, resistivity and elastic wave velocity as well as fracture stiffness of the rock fracture against the pressure build-up; changes of permeability and resistivity are controlled by connection or disconnection of fluid-flow pathway whereas velocity and fracture stiffness are not. Our results suggest that the evolutions of permeability and flow area associated with aperture closure of fracture can be modeled by the changes of resistivity or fracture stiffness regardless of the roughness of the fracture.
Mechanical properties of fractured geological formations and fluid-flow in that are of interest in a number of contexts such as 1) developing and monitoring fractured reservoir (e.g., geothermal, shale and groundwater) and 2) elucidating the mechanism of earthquake (e.g., fault-valve model; Sibson, 1992). Although permeability is often discussed for evaluating the potential of reservoir exploration or reoccurrence of the earthquake triggered by pore pressure build-up, local behavior of fluid-flow (e.g., fluid-flow pathway) within fractures is also important because it controls preferential-flow and total thermal response in geothermal area (e.g., Hawkins et al., 2018). To monitor and predict these hydraulic properties and hydraulic-mechanical coupling within the crust, geophysical explorations potentially are the powerful tools. In geothermal fields, the change of resistivity or velocity associated with the hydraulic stimulation, earthquake and geothermal fluid production was detected (e.g., Peacock et al., 2012; Taira et al., 2018). Although these geophysical monitorings could detect the change of reservoir condition, quantitative interpretations about the injected water distribution, permeability enhancement associated with aperture changes of fracture have not been evaluated yet. To monitor these fluid-flow behaviors from the geophysical explorations, we should investigate the basic relationships between the hydraulic (permeability and fluid-flow pathway), electric (resistivity) and mechanical (elastic wave velocity and fracture stiffness) properties of rocks.
Yamaoka, Kyoko (National Institute of Advanced Industrial Science and Technology) | Suzuki, Atsushi (National Institute of Advanced Industrial Science and Technology) | Wang, Quan (The University of Tokyo) | Kawahata, Hodaka (The University of Tokyo)
In order to assess the potential effect of ocean acidification on deep-sea environment in the near future, the mobility of elements from ferromanganese (Fe-Mn) nodules and pelagic clays in weak acidic solutions was examined. In our experiments, two geochemical reference samples (JMn-1 and JMS-2) were reacted with phosphate buffer solutions or pH-controlled artificial seawater (ASW) using a CO2-induced pH regulation system. Our experiments demonstrated that deep-sea sediments have weak buffer capacities by acid-base dissociation of surface hydroxyl groups on metal oxides/oxyhydroxides and silicate minerals. Element concentrations in the leachate were mainly controlled by elemental speciation in the solid phase and sorption-desorption reaction between the charged solid surface and ion species in the solution. These results indicate that the release of heavy metals such as Mn, Cu, Zn and Cd should be taken into consideration when deep-sea sediments are exposed to pH-decreased seawater.
Ferromanganese (Fe-Mn) nodules have been explored as potential targets of deep-sea mining due to their enrichment in valuable metals, such as Ni, Cu, Co, Mo, Zr, Li, Y, and rare-earth elements (REEs) (Hein et al., 2013). They occur on the surface of sediment-covered abyssal plains at any water depth, but the highest-grade nodules form near or below the calcite compensation depth (CCD) (Verlaan et al., 2004; Glasby, 2006). The area of greatest economic interest is the Clarion-Clipperton Zone (CCZ) in the northeast Pacific Ocean. The International Seabed Authority (ISA) estimates that the total amount of nodules in the CCZ is 21,100 million tons in dry weight (ISA, 2010). Based on the United Nations Convention on the Law of the Sea, the ISA has entered into contracts with 16 contractors for exploration of Fe-Mn nodules in the area as of 2018.
It is no doubt that deep-sea mining will impact the surrounding environment and biological communities. However, it is currently difficult to assess the risks due to our limited knowledge about deep-sea. For the first step to reduce the impacts on deep-sea ecosystems, environmental baseline studies are essentially needed. Based on the ISA environmental guidelines (ISBA-19LTC-8), the contractors have conducted several environmental baseline surveys under current ocean condition. On the other hand, numerous studies predict that increasing anthropogenic CO2 will cause serious ocean acidification in the near future. Although uptake of atmospheric CO2 initially decreases pH of shallow waters, ocean general circulation will slowly spread the acidification to deep waters. According to the simulation by Caldeira and Wickett (2003), the pH of surface waters will decline from 8.1 to 7.4, while the pH reduction of the deep waters will be about 0.4 units, from 7.6 to 7.2 by the end of this century. The pH decrease of seawater may release previously bound metals from sediments and hence cause toxicity in deep-sea environment (Millero, et al. 2009; De Orte, et al. 2014).
Yoneda, Jun (National Institute of Advanced Industrial Science and Technology)
3D printers allow us to create geo-structural materials, jigs for laboratory experiments, and geometry of geomaterials itself. In this study, the performance of 3D printers and the mechanical properties of the output materials are reviewed to encourage their use for laboratory soil tests. In addition, 3D printing was performed by fused deposition modeling and stereolithography desktop printers. The applicability of various jigs used for soil testing was studied. The products using acrylonitrile butadiene styrene, polylactic acid, and resin were shown to be effective substitutes. X-ray CT based printed sand and hydratebearing sand showed reasonable permeability reduction due to hydrate existence.
Three-dimensional (3D) printing technology has been in use since the 1980s. This technology has been particularly useful where there is need for fast design and fabrication, such as prototyping. However, industrial 3D printers have few users because they are quite expensive. When the basic patent expired in 2009, 3D printers for individual users were introduced in the market. In 3D printing technology, various methods are used for product development: fused deposition modeling (FDM), stereolithography (SLA), selective laser sintering (SLS), and the material jetting or binder jetting method. FDM is one of the most popular technologies for desktop 3D printers that extrude semi-liquid polymers for printing (Crump, 1991). SLA is used for photocuring a liquid resin (Lee et al., 2017), and SLS is a type of powder bed fusion in which a bed of powder materials, such as a polymer, a resin, or a metal hardened with a laser (Frazier, 2014; Wang et al., 2017), is used. The material jetting or binder jetting method prints the liquid resin or polymers by using inkjet printers and photocures (Moore and Williams, 2016). Currently, the market size of 3D printers and their materials is dramatically growing.
There are three reasons why 3D printers have become popular in recent years. First, many innovators, inventors, and others have improved the accuracy of printers, and it is becoming possible to create the final products directly rather than the prototypes. First, user-friendly free software is also available, and everyone can easily do 3D modeling. Also, it is necessary to have trouble shooting at the community on the internet. Third, a wide variety of materials are being developed based on the product requirements.
Hirobayashi, Satoshi (School of Marine Science & Technology / Tokai Univercity) | Kiyono, Fumio (National Institute of Advanced Industrial Science and Technology) | Morita, Hiromitsu (Former AIST) | Shimizu, Yoshiyuki (Tokai Univercity / School of Marine Science & Technology)
Taking part in the Japanese National hydrate research program (MH21, funded by METI), we have conducted examinations about flow assurance in a production well of the methane hydrate (hereinafter called the MH). In this study, we clarified distribution of the gas bubble diameter by an experiment after passing through a sand exclusion screen when dissociated gas flows from the MH reservoir to the production well. The gas-liquid separation ratio in the production system was evaluated from the experimental results. Further, numerical analysis was conducted to examine the methane gas and water two-phase flow in the production system using the estimated gas-liquid separation ratio.
The MH has gained international attention as an alternative energy resource to conventional fossil fuels. In Japan, research on required production technology is carried out with the goal that private enterprises commercialize gas production from the MH. To promote MH resource development, the Ministry of Economy, Trade and Industry formulated “Methane Hydrate Development Program in Japan” in 2001, and the Methane Hydrate Resource Development Research Consortium (MH21) was organized within the same year. The initial offshore production test in 2013 and the second in 2017 have succeeded in producing gas from the MH under the seafloor by decomposing the MH into methane gas and water. In offshore production tests, the system based on the depressurizing method was used. The depressurization method lowers the bottom pressure in the production well and reduces the pressure applied to the MH reservoir, promoting the dissociation of MH into a methane gas and water. Methane gas production by the depressurization method have some obstacles. For example, the problems of sand trouble and gas-liquid separation. The MH reservoir and the production well are separated by the sand exclusion screen. The screen prevents the inflow of sand into the well. If the filtering size is reduced to prevent sand particles from flowing into the production well, the bubble diameter of the methane gas that passes through the filter also becomes finer, resulting in lower gas-liquid separation ratio. When gas flows into the water line, efficiency of the pump reduces. Furthermore, the MH may be regenerated, causing flow disruption, then leading to a blockage at downstream of the pump in the water line.
Yoneda, Jun (National Institute of Advanced Industrial Science and Technology) | Takiguchi, Akira (West Japan Engineering Consultants) | Ishibashi, Toshimasa (West Japan Engineering Consultants) | Yasui, Aya (West Japan Engineering Consultants) | Mori, Jiro (West Japan Engineering Consultants) | Kakumoto, Masayo (National Institute of Advanced Industrial Science and Technology) | Aoki, Kazuo (National Institute of Advanced Industrial Science and Technology) | Tenma, Norio (National Institute of Advanced Industrial Science and Technology)
During gas production from offshore gas-HBS, there are concerns regarding the settlement of the seabed and the possibility that frictional stress will develop along the production casing. This frictional stress is caused by a change in the effective stress induced by water movement caused by depressurization and dissociation of hydrate as well as gas generation and thermal changes, all of which are interconnected. The authors have developed a multiphase-coupled simulator by use of a finite-element method named COTHMA. Stresses and deformation caused by gas-hydrate production near the production well and deep seabed were predicted using a multiphase simulator coupled with geomechanics for the offshore gas-hydrate-production test in the eastern Nankai Trough. Distributions of hydrate saturation, gas saturation, water pressure, gas pressure, temperature, and stresses were predicted by the simulator. As a result, the dissociation of gas hydrate was predicted within a range of approximately 10 m, but mechanical deformation occurred in a much wider area. The stress localization initially occurred in a sand layer with low hydrate saturation, and compression behavior appeared. Tensile stress was generated in and around the casing shoe as it was pulled vertically downward caused by compaction of the formation. As a result, the possibility of extensive failure of the gravel pack of the well completion was demonstrated. In addition, in a specific layer, where a pressure reduction progressed in the production interval, the compressive force related to frictional stress from the formation increased, and the gravel layer became thin. Settlement of the seafloor caused by depressurization for 6 days was within a few centimeters and an approximate 30 cm for 1 year of continued production.
Miyazaki, Kuniyuki (National Institute of Advanced Industrial Science and Technology) | Ohno, Tetsuji (National Institute of Advanced Industrial Science and Technology) | Karasawa, Hirokazu (National Institute of Advanced Industrial Science and Technology)
Percussion drilling is frequently adopted in advancing boring performed for forward exploration and drainage in the construction of road and railway tunnels. It is also used to make blastholes for mine development and mountain tunnel construction. Drilling efficiency declines with progressing wear of drill bit. In the present study, the effect of rock abrasiveness of granite on the tip wear on percussion bit is examined through laboratory drilling tests. Percussion drill bits equipped with cemented tungsten carbide (WC-Co) and polycrystalline diamond compact (PDC) tips were used in the test. Three types of Japanese granite (Sori granite, Inada granite and Takine granite) were employed as the drilling medium. The height loss of gage tips were measured every drilled length of about 6 m. The effects of some mechanical properties, e.g., unconfined compressive strength and indirect tensile strength, and some abrasivity indexes, e.g., CAI (CERCHAR Abrasivity Index) and Schimazek F value, on the increasing ratio of the height loss of tips to drilled length are discussed.
Percussion drilling is frequently adopted in advancing boring performed for forward exploration and drainage in the construction of road and railway tunnels and also used in making blastholes for mine development. The maximum rate of penetration (ROP) reaches 50-100 cm/min or higher in the percussion drilling of hard rock such as granite (Okubo et al., 1992), indicating that percussion drilling is a very efficient drilling technique.
Percussion bits are conventionally equipped with cobalt (Co)-containing cemented tungsten carbide (WC-Co) tips. Recently, percussion bits with polycrystalline diamond compact (PDC) tips have been put to practical use. Hereafter, these bits are respectively called WC-Co and PDC percussion bits. PDC is superior to WC-Co in terms of wear resistance. Therefore, PDC percussion bits are considered to exhibit better drilling performance (long bit life) than WC-Co percussion bits.
The wear of tips on a percussion bit is thought to be affected by the mechanical properties or abrasivity indexes of drilled rock. In this study, percussion drilling tests on hard and highly abrasive granite were performed in a laboratory using PDC and WC-Co percussion bits to evaluate the influence of the mechanical properties and abrasivity indexes of drilled rock on the tip wear. The test result contains some published data (Miyazaki et al., 2016).
Sawata, Masaru (Waseda University) | Iwata, Shigeki (Japan Oil, Gas and Metals National Corporation) | Tenma, Norio (National Institute of Advanced Industrial Science and Technology) | Kurihara, Masanori (Waseda University)
In general, conventional oil and gas reservoirs are not deformed significantly. However, some unconventional reservoirs including those of methane hydrate and heavy oil/bitumen are soft and deformable. Therefore, it is important to introduce the geomechanical effects such as the changes in porosity/permeability associated with the deformation of a reservoir for accurately predicting production performances for these unconventional reservoirs.
Recently, the reservoir fluid flow behavior has been simulated in conjunction with geomechanics simulation, using various coupling methods such as fully implicit method, explicit method, iterative method, etc. All of these methods have both advantages and disadvantages. For example, the fully implicit method, which solves flow and geomechanical behavior simultaneously, is accurate, but requires a huge computer time. In addition, it is difficult to utilize existing flow simulators and geomechanics simulators in this method. Meanwhile, the explicit method does not require much computational time, but is not accurate since the geomechanical behavior is predicted without being reflected enough in flow simulation. The iterative method is accurate because geomechanical information and flow information is transferred to each other until the flow performances become consistent with geomechanical behavior. This method, however, requires considerable computer time. Therefore, we conducted this research seeking for a new method coupling fluid flow with geomechanics that enables the accurate prediction in a reasonably short computer time.
Nagao, Masayuki (National Institute of Advanced Industrial Science and Technology) | Takasugi, Yoshio (National Institute of Advanced Industrial Science and Technology) | Suzuki, Atsushi (National Institute of Advanced Industrial Science and Technology) | Tanaka, Yuichiro (National Institute of Advanced Industrial Science and Technology) | Sugishima, Hideki (Japan Oil, Gas and Metals National Corporation) | Matsui, Takaaki (Japan Oil, Gas and Metals National Corporation) | Okamoto, Nobuyuki (Japan Oil, Gas and Metals National Corporation)
Current velocity in deep-sea areas must be measured during physical environmental assessments of exploration areas for cobalt-rich ferromanganese crusts. However, the use of an acoustic Doppler current profiler (ADCP) for velocity measurement in the abyssal zone has technical disadvantages: (1) Insufficient acoustic backscatter due to the low density of suspended matter; and (2) difficulty in detecting low abyssal velocity. Therefore, an appropriate method for confirming the validity of velocity measurement results is needed. We examined physical aspects of the reliability of ADCP velocity measurements made during 1 year, by verifying the Coriolis effect, validating the velocity power spectrum, and comparing the ADCP results with second version of Japan Coastal Ocean Predictability Experiment (JCOPE2) reanalysis velocity data.
Cobalt-rich ferromanganese crusts, composed of manganese, cobalt, nickel, platinum, and rare earth elements (REEs) occur on the tops and slopes of seamounts. Their thickness varies from a few centimeters to ten centimeters in the depth range from 1000 to 5000 m. In the 21st century, cobalt-rich ferromanganese crusts have attracted attention as an important resource for metals presently in short supply or whose terrestrial sources have become depleted (Narita et al., 2015).
The International Seabed Authority (ISA) regulates mining areas in the high seas in accordance with the “Mining Code” under the 1982 United Nations Convention on the Law of the Sea. To avoid or reduce as much as possible the environmental impacts from the point of view of biodiversity conservation during prospecting and exploration for marine minerals, ISA recommends that contractors conduct environmental impact assessments and environmental monitoring surveys (ISA, 2013a). Additionally, contracts between ISA and contractors for mineral exploration in the license area require the contractor to collect oceanographic and environmental baseline data and to establish baselines against which to assess the likely effects of its programme of activities under the plan of work for exploration on the marine environment and a programme to monitor and report on such effects. The ISA Legal and Technical Commission issued these recommendations as document ISBA/19/LTC/A (ISA, 2013a). In this document ISA emphasizes the importance of environmental baseline studies as follows: “It is important to obtain sufficient information from the exploration area to document the natural conditions that exist prior to test mining, to gain insight into natural processes such as dispersion and settling of particles and benthic faunal succession, and to collect other data that may make it possible to acquire the capability necessary to make accurate environmental impact predictions. The impact of naturally occurring periodic processes on the marine environment may be significant but is not well quantified. It is therefore important to acquire as long a history as possible of the natural responses of seasurface, mid-water and seabed communities to natural environmental variability.” Additionally, ISA (2013a) lists seven classes of baseline data requirements: (a) physical oceanography, (b) geology, (c) chemical oceanography, (d) sediment properties, (e) biological communities, (f) bioturbation, and (g) sedimentation. Baseline physical oceanography data collection should include the following activities (ISA, 2013a):
“(i) Collect information on the oceanographic conditions, including the current, temperature and turbidity regimes, along the entire water column and, in particular, near the sea floor;
(ii) Adapt the measurement programme to the geomorphology of the seabed;
(iii) Adapt the measurement programme to the regional hydrodynamic activity at the sea surface, in the upper water column and at the seabed;
(iv) Measure the physical parameters at the depths likely to be impacted by the discharge plumes during the testing of collecting systems and equipment;
(v) Measure particle concentrations and composition to record distribution along the water column”.
Sugiyama, Shumpei (Kyoto University) | Liang, Yunfeng (University of Tokyo) | Murata, Sumihiko (Kyoto University) | Matsuoka, Toshifumi (Fukada Geological Institute) | Morimoto, Masato (National Institute of Advanced Industrial Science and Technology) | Ohata, Tomoya (Japan Petroleum Exploration Company Limited) | Nakano, Masanori (Japan Petroleum Exploration Company Limited) | Boek, Edo S. (University of Cambridge)
Digital oil, a realistic molecular model of crude oil for a target reservoir, opens a new door to understand properties of crude oil under a wide range of thermodynamic conditions. In this study, we constructed a digital oil to model a light crude oil using analytical experiments after separating the light crude oil into gas, light and heavy fractions, and asphaltenes. The gas and light fractions were analyzed by gas chromatography (GC), and 105 kinds of molecules, including normal alkanes, isoalkanes, naphthenes, alkylbenzenes, and polyaromatics (with a maximum of three aromatic rings), were directly identified. The heavy fraction and asphaltenes were analyzed by elemental analysis, molecular-weight (MW) measurement with gel-permeation chromatography (GPC), and hydrogen and carbon nuclear-magnetic-resonance (NMR) spectroscopy, and represented by the quantitative molecular-representation method, which provides a mixture model imitating distributions of the crude-oil sample. Because of the low weight concentration of asphaltenes in the light crude oil (approximately 0.1 wt%), the digital oil model was constructed by mixing the gas, light-, and heavy-fraction models. To confirm the validity of the digital oil, density and viscosity were calculated over a wide range of pressures at the reservoir temperature by molecular-dynamics (MD) simulations. Because only experimental data for the liquid phase were available, we predicted the liquid components of the digital oil at pressures lower than 16.3 MPa (i.e., the bubblepoint pressure) by flash calculation, and calculated the liquid density by MD simulation. The calculated densities coincided with the experimental values at all pressures in the range from 0.1 to 29.5 MPa. We calculated the viscosity of the liquid phase at the same pressures by two independent methods. The calculated viscosities were in good agreement with each other. Moreover, the viscosity change with pressure was consistent with the experimental data. As a step for application of digital oil to predict asphaltene-precipitation risk, we calculated dimerization free energy of asphaltenes (which we regarded as asphaltene self-association energy) in the digital oil at the reservoir condition, using MD simulation with the umbrella sampling method. The calculated value is consistent with reported values used in phase-equilibrium calculation. Digital oil is a powerful tool to help us understand mechanisms of molecular-scale phenomena in oil reservoirs and solve problems in the upstream and downstream petroleum industry.
Shimizu, Tsutomu (National Institute of Advanced Industrial Science and Technology) | Yamamoto, Yoshitaka (National Institute of Advanced Industrial Science and Technology) | Tenma, Norio (National Institute of Advanced Industrial Science and Technology)
The local two-phase gas/liquid flow behavior at a high velocity gradient is essential for managing gassy wells. In this study, the methane/water bubbly flows passing through a perforated pipe were characterized in a 10.4-m flow loop in which the pressure was varied up to 5.5 MPa at 291 K. To characterize the two-phase flow behavior at the bore, we obtained the bubble sizes from high-speed photographs and digital image analysis. As the flow velocity and/or pressure increased, the flow patterns shifted from bubbling to jetting, suggesting that the local two-phase flow pattern can control the bubble size in flowlines.
Multiphase flow control in wells and pipelines is crucial in the oil and gas industries. The most important components affecting the production efficiency, cost, and safety of gassy wells are the gas/liquid separators and multiphase flow pumps. For instance, the gas/liquid separators reduce the void fraction at the pump intake, thereby minimizing the pump surging (Hua et al., 2012; Gamboa and Prado, 2011). Phase separation reduces the risk of pipe plugging through the formation of gas hydrates (Shimizu et al., 2017; Joshi et al., 2013; Sakurai et al., 2014). In gas production from offshore natural gas hydrate reservoirs, these devices must handle two-phase flows under variable pressure and void fraction in a natural-gas/seawater mixture, while stably maintaining the bottom-hole pressure below the three-phase equilibrium pressure (Cyranoski, 2013). Optimizing the performance of these devices in such situations is a necessary yet challenging task.
Bubbles formed by breakup and coalescence are of paramount importance in industrial heat and mass transport processes and are typically generated by a gas distributor (Idogawa et al., 1987; Quinn and Finch, 2012; Tsuge and Hibino, 1983) or a rotating impeller (Kracht and Finch, 2009; Minemura et al., 1998; Masui et al., 2011). Hence, bubble formation has been studied extensively for decades. However, few studies have focused on the bubble behavior under a high velocity gradient in pipelines, where bubbles assist the transmission of the gas/liquid flow mixture in practical production fields.