Geologic reservoirs containing gas hydrate occur beneath permafrost environments and within marine continental slope sediments, representing a potentially vast natural gas source. Numerical ...simulators provide scientists and engineers with tools for understanding how production efficiency depends on the numerous, interdependent (coupled) processes associated with potential production strategies for these gas hydrate reservoirs. Confidence in the modeling and forecasting abilities of these gas hydrate reservoir simulators (GHRSs) grows with successful comparisons against laboratory and field test results, but such results are rare, particularly in natural settings. The hydrate community recognized another approach to building confidence in the GHRS: comparing simulation results between independently developed and executed computer codes on structured problems specifically tailored to the interdependent processes relevant for gas hydrate-bearing systems. The United States Department of Energy, National Energy Technology Laboratory, (DOE/NETL), sponsored the first international gas hydrate code comparison study, IGHCCS1, in the early 2000s. IGHCCS1 focused on coupled thermal and hydrologic processes associated with producing gas hydrates from geologic reservoirs via depressurization and thermal stimulation. Subsequently, GHRSs have advanced to model more complex production technologies and incorporate geomechanical processes into the existing framework of coupled thermal and hydrologic modeling.
This paper contributes to the validation of these recent GHRS developments by providing results from a second GHRS code comparison study, IGHCCS2, also sponsored by DOE/NETL. IGHCCS2 includes participants from an international collection of universities, research institutes, industry, national laboratories, and national geologic surveys. Study participants developed a series of five benchmark problems principally involving gas hydrate processes with geomechanical components. The five problems range from simple geometries with analytical solutions to a representation of the world's first offshore production test of methane hydrates, which was conducted with the depressurization method off the coast of Japan. To identify strengths and limitations in the various GHRSs, study participants submitted solutions for the benchmark problems and discussed differing results via teleconferences. The GHRSs evolved over the course of IGHCCS2 as researchers modified their simulators to reflect new insights, lessons learned, and suggested performance enhancements. The five benchmark problems, final sample solutions, and lessons learned that are presented here document the study outcomes and serve as a reference guide for developing and testing gas hydrate reservoir simulators.
•Code comparisons build confidence in simulators to model interdependent processes.•International hydrate reservoir simulators are compared over five complex problems.•Geomechanical processes significantly impact response of gas hydrate reservoirs.•Simulators yielded comparable results, however many differences are noted.•Equivalent constitutive models are required to achieve agreement across simulators.
•Tetra-n-butylammonium 2-ethylbutyrate (TBA-2 EB) semiclathrate hydrate was studied.•The highest equilibrium temperature of TBA-2 EB semiclathrate hydrate was 283.22 K.•Dissociation enthalpy of ...TBA-2 EB semiclathrate hydrate was 167 J/g.•Halogen-free latent heat storage material instead of TBA-Br semiclathrate hydrate.
The quaternary onium salt-based semiclathrate hydrates have been investigated in many kinds of fields such as latent heat storage materials and gas separation media. In the present study, equilibrium (temperature−composition) relations in the tetra-n-butylammonium 2-ethylbutyrate (TBA-2 EB) semiclathrate hydrate system have been measured. In addition, thermodynamic and spectroscopic properties of TBA-2 EB semiclathrate hydrate were analyzed. The maximal equilibrium temperature and stoichiometric concentration of TBA-2 EB semiclathrate hydrate was 283.22 ± 0.05 K and x1 = 0.0281 ± 0.0007, respectively. The crystal lattice of TBA-2 EB semiclathrate hydrate, determined by the single crystal X-ray diffraction, was tetragonal. Other properties, not only Raman spectrum but also the maximum allowable degree of supercooling, in the TBA-2 EB semiclathrate hydrate system were similar to those in the tetra-n-butylammonium bromide (TBAB) hydrate. The TBA-2 EB semiclathrate hydrate would be an alternative to TBAB hydrate as a halogen-free semiclathrate hydrate system.
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•Extensive literature survey on two-phase flow experiment using 12 m or longer vertical tube was conducted.•Experiments were conducted on two-phase flow regime observation, void fraction and ...frictional pressure drop measurement over a long channel length under high-pressure brine conditions.•The transition of flow regime took place at higher superficial gas velocity under brine conditions.•Through drift-flux model analysis, change in gas velocity under brine conditions was confirmed.•New frictional pressure drop model at high-pressure two-phase flow under brine conditions is proposed.
The offshore methane hydrate production test conducted in Japan has demonstrated a successful production of methane gas from marine gas hydrates using depressurization methods. The method produces methane gas by dissociating methane hydrate, which is stable at low temperature and high pressure conditions, by lowering the bottom-hole pressure in the wellbore. Under this method, stable control of bottom-hole pressure is necessary to ensure continuous methane gas production. Therefore, understanding the behavior of upward gas–liquid two-phase flow, involving gas-brine mixture, in a wellbore is essential for the proper pressure drop evaluation in the production line. In the present study, void fraction and frictional pressure drop behaviors under nitrogen-brine two-phase flow conditions is investigated using the high-pressure test facility of 52.7 mm inner diameter and 28 m height. The measured void fraction was assessed using drift-flux model, and the results showed that the decrease in bubble diameter under bubbly flow in gas-brine two-phase flow conditions resulted in decrease in bubble rise velocity and uniformity of bubble distribution. It was also found that, under bubbly flow in gas-brine mixture, the frictional pressure drop tends to further decrease with elevation. Based on these findings and obtained experimental dataset, the new frictional pressure model for gas-brine two-phase flow under high-pressure conditions is developed in the present study.
The commercial production process of methane gas from methane hydrate has been developed by the MH21-S R&D consortium (MH21-S) in recent years. In order to establish the gas production method, an ...accurate gas-liquid two-phase flow regime identification under high-pressure conditions is indispensable. In the present study, a 28 m long test section with an inner diameter of 52.7 mm was newly constructed, and a nitrogen-water two-phase flow experiment was conducted at 3.0 MPa G. Two-phase flow images were successfully acquired using the high-speed camera from the visualization port. The sequential image of upward gas-liquid two-phase flow was merged into a single image by the time strip method. Then, flow regime identification using the convolutional neural network (CNN) trained under sequential images was carried out. The proposed method has shown an excellent capability to identify flow regime images obtained at the current high-pressure conditions. In addition, for the slug flow regime, it was found that the Taylor bubble length highly influences the identification performance, and the model proposed by Street and Tek showed good agreement for the present dataset. Furthermore, the bubbly-slug transition region was successfully evaluated and quantified through the present model. The current methods have shown a good correlation with the existing model. These results indicate that the gas void fraction at the transition region to be larger than the theoretical value for the elevated pressure system.
•Supervised learning was applied to merged images of gas-liquid two-phase flow.•Conducted 28 m long upward gas-liquid two-phase flow experiments under high pressure conditions.•Current method exhibits excellent identification of flow regime.•Taylor bubble length in slug flow regime was measured from the experiment.•Quantified the bubbly-slug flow regime transition with supervised learning.
The use of low-temperature geothermal resources is important from the viewpoint of global warming. In order to evaluate various underground projects that use low-temperature geothermal resources, we ...have estimated the parameters of a typical underground system using the two-well model. By changing the parameters of the system, six different heat extraction scenarios have been studied. One of these six scenarios is recommended because of its small energy loss.
Since 1985, the New Energy and Industrial Technology Development Organization (NEDO) has conducted a Hot Dry Rock project at the Hijiori test site, Yamagata prefecture. The objective of this project ...is to develop and test technologies such as borehole logging, hydraulic fracturing, fracture mapping and reservoir evaluation, which are essential for the development of a Hot Dry Rock power generation system. In 1991, heat was successfully extracted from a shallow reservoir at a depth of 1800 m for three months using one injection well (SKG-2) and three production wells (HDR-1, HDR-2 and HDR-3). About 80% of the injected water was recovered from these production wells. The thermal output of hot water and steam reached about 8 MW. Since 1992, a deep reservoir at a depth of 2200 m has been developed. In 1995 and 1996, heat extraction tests were conducted using one injection well (HDR-1) and two production wells (HDR-2 and HDR-3). A long-term circulation test, lasting about two years, is planned to evaluate the reservoir, starting in 2000.
Methane Hydrate (MH) is one of the potential new-generation energy resources. The depressurization method has been proposed for extracting methane gas from MH sediment in marine sediments. During the ...depressurization operation, sediment deformation may occur due to MH dissociation and increase of effective stress. Thus, "Development of evaluation technologies for sedimentary characteristics" was studied by the Re-search Group for Production Method and Modeling, MH21 Research Consortium. A geo-mechanical simulation code, 'Coupled thermo-hydro-mechanical analysis with dissociation and formation of methane hydrate in deformation of multiphase porous media' (COTHMA) was developed to predict the sediment deformation during methane gas production from MH sediments. To grasp the influence of the depressurization rate, we conducted a sensitivity analysis for the stresses and deformation near MH production wells and the deep sea-bed using COTHMA. The analysis was performed assuming an elastic axi-symmetry problem.
In this paper, electrical field distributions in a tire and radiation levels from a tire are clarified through electromagnetic simulations. Moreover, measured radiated levels are compared with ...calculated results and received level probabilities are shown
At the Hijiori Hot Dry Rock (HDR) field in Yamagata prefecture, the Long-Term Circulation Test (LTCT, Term 2 and Term 3) was conducted from December 23, 2001 to August 31, 2002. The test used two ...injection wells SKG-2 and HDR-1, and two production wells HDR-2a and HDR-3. At the beginning of this test, water was injected at a constant flow rate of 8.35 kg/s into SKG-2 and HDR-1. The ratio of injection flow rate at wells, HDR-1: SKG-2 was changed from 1:1 to 3:1 during the test, and production flow rate of HDR-2a decreased from 8 kg/s to 6kg/s. Production rate in HDR-3 remained almost constant during the test. Because of difficulties in obtaining a match between the simulated and measured pressure of HDR-1 in the Term 1 of LTCT, the Bed-of-Nails model for fracture flow was modified. We re-developed a simple multi-reservoir model and simulated the test data using the FEHM (Finite Element Heat and Mass transfer) code developed at Los Alamos National Laboratory. In addition, to estimate the productivity and the heat extraction of the multi-reservoir system during the long-term circulation, we studied four different injection scenarios by changing the ratio of injection rate or wells. The two most important conclusions of the calculation are: 1) Production flow rate of HDR-2a decreased under the influence of decrease the injection rate of SKG-2, and 2) one of these four scenarios is recommended because of its high recovery and thermal output.
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