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Periodic unsteady flow kinematics in a shrouded multistage low-speed axial compressor has been measured for the first time. Data have been acquired at the inlet and exit of a shrouded third-stage stator with a particular focus on the hub flows. The newly found features of the hub flow in a shrouded multistage compressor are different from those at the midspan or in unshrouded (i.e., cantilevered) compressors. First, the merging of the second-stage stator and third-stage rotor wakes causes positive radial migration near the rotor wake pressure surface at the hub of the third-stage stator inlet. Second, the low-momentum labyrinth seal leakage flow of the third-stage stator merges with the third-stage rotor wake to create streamwise vorticity at the third-stage stator inlet hub. Third, contrary to unshrouded stators, suction side hub corner separation in the shrouded third-stage stator reduces rotor wake stretching. Thus, velocity disturbances are attenuated less, and amplitudes of periodic fluctuations in flow angles are larger at the third-stage stator exit hub than at midspan. The positive radial migration of the rotor wake hub flow and wake stretching reduction are expected to decrease efficiency, whereas streamwise vorticity generation is expected to increase efficiency.

This study proposes a reliable evaluation method for three-phase saturation (water, gas hydrate (GH), and gas) evaluation during the GH dissociation core experiment using deep learning. A convolutional neural network (CNN) takes computed tomography (CT) images obtained during the GH core experiment as an input and provides three-phase saturation as an output. Although machine/deep learning methods have been applied to the saturation evaluation from CT images in previous research, they were not reliable due to the lack of adequate amount of training data where the model could not find appropriate parameters. Besides, non-zero gas hydrate saturation showed where it was supposed to be zero. This study improved the evaluation of three-phase saturation and solved the non-zero GH saturation problem by acquirement of extra data and application of data augmentation with CNN. The results of CNN and CNN with data augmentation presented 34% and 29% error compared to those of random forest. CNN with data augmentation brought 85% and 44% of error and its variance compared to those of CNN without data augmentation, respectively. Consequently, based on domain knowledge for GH, when it comes to the robustness of random data composition and consistency of performance, the evaluation of three-phase saturation can be boosted using CNN with data augmentation.

We experimentally examine the impingement of a fully turbulent round jet (with diameter Dj) on a long circular cylinder (with diameter D) in the crossflow plane coinciding with the jet axis for D/Dj = 2.5 and ReDj = 20,000. Particular focus is placed on the kinematics of boundary layer transition that occurs and subsequently leads to a second thermal peak on the cylinder surface downstream of the primary thermal peak near the stagnation point when placed inside the jet’s potential core. To this end, spectral analyses of wall shear stress data and time-resolved velocity data within both laminar and turbulent boundary layers have been performed. The present study demonstrates that the root mean square (rms) fluctuation of the stream-wise velocity component increases along both boundary layers due to the propagation of external perturbations from coherent structures that are shed from the jet exit, which incites the transition of the laminar boundary layer. The transition causes the local heat transfer elevation that interrupts the monotonic decrease from the primary thermal peak whereas it plays no direct part in forming the second thermal peak. Instead, the second thermal peak occurs at a delayed downstream azimuth angle from the transition where the rms velocity fluctuations of the boundary layer flow reach their peak at the dominant frequency, equivalent to that of the coherent structures of the jet.

This study investigated a structural transition induced by cage-dependent guest exchange in the CH4 + C3H8 hydrate with CO2 injection for CH4 recovery and CO2 sequestration. The influence of the CO2 replacement on the crystalline structure of initial CH4 + C3H8 hydrates and the cage-dependent distribution of guest molecules were quantitatively investigated using powder X-ray diffraction, 13C nuclear magnetic resonance spectroscopy, and gas chromatography. The quantitative analyses demonstrated that the CO2 occupation caused the depletion of C3H8 molecules in the large 51264 cages of structure II hydrates, thereby resulting in the subsequent transformation into CO2-rich sI hydrates and the coexistence of structure I and structure II hydrates after the replacement. The guest-exchange behavior observed from time-dependent Raman spectra indicated that the replacement rate was increased with an increase in pressure of injected CO2 and that the extent of the replacement was enhanced at higher pressure of injected CO2. Overall experimental evidence of the partial structural-transition replacement suggests that CO2 molecules first occupied structure II hydrates predominantly with the rapid guest exchange at the surface and that the initial structure II hydrates were subsequently converted to the CO2-rich structure I hydrates from the surface to the inner side. Precise identification of the mechanism responsible for the partial structural transition occurring in the CH4 + C3H8 - CO2 replacement will be very helpful in developing a strategy for actual CO2 injection into structure II gas hydrate reservoirs for energy recovery and CO2 sequestration.

The purpose of this study was to determine the three-phase saturation (water; gas hydrate, GH; and gas) in real time to gain insights into the GH depressurization process. Although X-ray computed tomography (CT) can be used to investigate the density changes in the GH core during the depressurization experiment, it is hard to distinguish between water and GH due to their similar densities and the limited resolution of the CT image. To address this issue, random forest (RF) was applied to quantitatively predict the three-phase saturation: CT images were used as input data and the three-phase saturation was the output. In the previous research, a RF model was developed based on training data that only involved the five preliminary stages before the depressurization step. However, the previous RF model failed to estimate the saturation values of the CT images during the depressurization. It could not properly estimate general GH dissociation trend and the GH equilibrium pressure, neither. In this study, CT data obtained in the early and late depressurization stage were used for the training of the RF model. The proposed method can be used to reliably estimate the GH dissociation behavior. The trained RF in this study can identify the GH equilibrium at which the dissociation starts (~16 MPa), which is consistent with the theoretical dissociation at a temperature and salinity of 16 °C and 3 wt%, respectively. The reliability of the proposed method was tested by checking if the estimated results approached zero GH saturation at the end of the GH dissociation (6 and 0 MPa). Therefore, the originality of this study is to improve RF model to reliably predict the three-phase saturation in real time during the GH depressurization by properly utilizing CT images in the depressurization stage for training RF. Based on further improvement, the proposed method could be utilized in the future to help finding adequate depressurization velocity by reliable saturation modeling and analysis of GH experiment because GH productivity depends on depressurization gradient.

It is essential to understand the relative permeability of CO2 and brine when characterizing the flow of CO2 as it is injected into an aquifer. The relative permeability of CO2 and brine has a significant impact on CO2 migration and saturation distribution. This paper presents the results of experimental investigations into the effects of the viscosity ratio and interfacial tension (IFT) on steady-state relative permeability. A series of unsteady-state experiments were conducted with a wide range of flow rates. These enabled us to determine the low end-points of the relative permeability and high residual brine saturation of the two-phase CO2/brine system. The results clearly show that the steady-state relative permeability depends on the viscosity ratio and IFT of the CO2/brine system. Due to the low CO2 viscosity and flow rate, the residual saturation of brine is greater than 50%. The low end-point of the relative permeability of CO2 is associated with small viscous forces. In the CO2/brine system, these forces are normally smaller than the capillary force. The small viscous forces are caused by the injected CO2 having a much lower viscosity than brine. The viscous force increases with increasing flow rate, resulting in more efficient CO2 displacement.

In this study, three kinds of driving forces for the dissociation of CH4 hydrates were experimentally investigated to determine which was optimal for a consistent control of the depressurization process. A specially designed one-dimensional (1-D) reactor was used to examine the production behavior of CH4 from the hydrate-bearing sediment using depressurization at different temperatures. The saturation of CH4 hydrate based on the mass balance in the 1-D reactor was cross-checked with the saturation value obtained by powder X-ray diffraction. Under a constant pressure-based driving force (ΔP = 0.4 MPa), the dissociation rate of CH4 hydrate was slower at a higher temperature, whereas under a constant temperature-based driving force (ΔT = 1.0 K), an almost similar dissociation rate was observed at different temperatures. However, the dissociation behavior of CH4 hydrate with a constant modified chemical potential-based driving force (Δμ) demonstrated a remarkable consistency over the entire temperature range. Furthermore, it was found that the Δμ immediately reflected an abrupt temperature drop and subsequent recovery during depressurization. The experimental results clearly indicate that the Δμ can be adopted as a universal parameter to control the depressurization process consistently and will be useful for optimizing the production process of natural gas hydrates using depressurization.

The CH 4 -flue gas replacement that occurs in structure H (sH) hydrates was investigated, with a primary focus on thermodynamic phase behavior, structure identification, heat flow monitoring, and dissociation enthalpy, for its dual function of CH 4 recovery and CO 2 sequestration. The significant shift in the equilibrium line of the CH 4 + neohexane (2,2-dimethylbutane, NH) hydrates replaced with CO 2 (10%) + N 2 (90%) and CO 2 (20%) + N 2 (80%) indicates that CH 4 molecules in the sH hydrates were significantly exchanged with flue gas mixtures. Furthermore, 13 C NMR spectroscopy revealed that replacement using flue gas occurs without a structural transition, and that CO 2 molecules preferentially attack CH 4 molecules occupied in the medium 4 3 5 6 6 3 cages of sH hydrates. The extent of the CH 4 + NH – flue gas replacement was approximately 74%. During CH 4 – flue gas replacement in sH hydrates, there was no significant change in heat flow associated with the dissociation and subsequent reformation of gas hydrates. Dissociation enthalpies of gas hydrates before and after replacement, measured using a high-pressure micro-differential scanning calorimeter (HP μ -DSC), also supported isostructural replacement with the high extent of reaction. This study reports the first experimental evidence of isostructural CH 4 – flue gas replacement occurring in sH hydrates, and thus, might contribute to extending the potential fields of CH 4 exploitation using a flue gas replacement, into sH natural gas hydrate reservoirs.

Natural gas hydrates, known to exist in both continental margins and permafrost regions, have received tremendous attention, owing to their potential use as an unconventional natural gas resource. Among the options to develop natural gas hydrates, a gas exchange method using an external CO2 or N2/CO2 mixture is considered one of the most promising technologies because (i) the process can prevent structural destruction of the gas hydrate deposits by swapping CO2 or N2/CO2 for CH4 molecules and (ii) injected CO2, a global warming gas, can be sequestered and locked away through the formation of thermodynamically stable CO2 or N2/CO2 hydrate. During and after N2/CO2 injection, however, the progress of gas exchange and the stability of the mixed CH4/N2/CO2 hydrate must be monitored. In this study, the electrical resistivity of CH4 hydrate before, during, and after N2/CO2 swapping was investigated using a lab-constructed tube-type reactor system for in situ electrical resistance measurement. The natural environ...

A replacement technique has been regarded as a promising strategy for both CH4 exploitation from gas hydrates and CO2 sequestration into deep-ocean reservoirs. Most research has been focused on replacement reactions that occur in sI hydrates due to their prevalence in natural gas hydrates. However, sII hydrates in nature have been also discovered in some regions, and the replacement mechanism in sII hydrates significantly differs from that in sI hydrates. In this study, we have intensively investigated the replacement reaction of sII (C3H8 + CH4) hydrate by externally injecting CO2/N2 (50:50) gas mixture with a primary focus on powder X-ray diffraction, Raman spectroscopy, NMR spectroscopy, and gas chromatography analyses. In particular, it was firstly confirmed that there was no structural transformation during the replacement of C3H8 + CH4 hydrate with CO2/N2 gas injection, indicating that sII hydrate decomposition followed by sI hydrate formation did not occur. Furthermore, the cage-specific replacement pattern of the C3H8 + CH4 hydrate revealed that CH4 replacement with N2 in the small cages of sII was more significant than C3H8 replacement with CO2 in the large cages of sII. The total extent of the replacement for the C3H8 + CH4 hydrate was cross-checked by NMR and GC analyses and found to be approximately 54%. Compared to the replacement for CH4 hydrate with CO2/N2 gas, the lower extent of the replacement for the C3H8 + CH4 hydrate with CO2/N2 gas was attributable to the persistent presence of C3H8 in the large cages and the lower content of N2 in the feed gas. The structural sustainability and cage-specific replacement observed in the C3H8 + CH4 hydrate with external CO2/N2 gas will have significant implications for suggesting target gas hydrate reservoirs and understanding the precise nature of guest exchange in gas hydrates for both safe natural gas production and long-term CO2 sequestration.

Purpose: This study aimed to compare the possible standard-setting methods for the Korean Radiological Technologist Licensing Examination, which has a fixed cut score, and to suggest the most appropriate method. Methods: Six radiological technology professors set standards for 250 items on the Korean Radiological Technologist Licensing Examination administered in December 2016 using the Angoff, Ebel, bookmark, and Hofstee methods. Results: With a maximum percentile score of 100, the cut score for the examination was 71.27 using the Angoff method, 62.2 using the Ebel method, 64.49 using the bookmark method, and 62 using the Hofstee method. Based on the Hofstee method, an acceptable cut score for the examination would be between 52.83 and 70, but the cut score was 71.27 using the Angoff method. Conclusion: The above results suggest that the best standard-setting method to determine the cut score would be a panel discussion with the modified Angoff or Ebel method, with verification of the rated results by the Hofstee method. Since no standard-setting method has yet been adopted for the Korean Radiological Technologist Licensing Examination, this study will be able to provide practical guidance for introducing a standard-setting process.

Breaking the bounds of classical natural gas hydrate (NGH) production processes, a newborn concept based on the gas exchange mechanism provides an opportunity to catch two birds with one stone: simultaneously achieving the sequestration of CO 2 for climate change mitigation and the enhanced recovery of CH 4 for energy production. As a ‘new paradigm’ in NGH production schemes, the non-destructive gas exchange as one of the most stable and promising NGH recovery approaches has received much attention in the fields of physics, chemistry, chemical engineering, civil engineering, petroleum engineering and geology. In this review, we assess the state-of-the-art gas exchange concept for NGH production by understanding its principles and developments, with emphasis on another technical breakthrough using the CO 2 + N 2 gas mixture injection. After establishing the fundamentals of the gas exchange process, we make a general survey of the NGH field production in the North Slope of Alaska in 2012, which practically adopted the gas exchange as a key technology. Several recent international NGH field production tests that basically use depressurization are also briefly analyzed for comparison. We suggest that the gas exchange method is ready to be tested in the NGH deposits with the valuable lessons learned from past pioneering tests.

Replacement technique is known as a promising method for potential energy extraction from gas hydrate deposits and greenhouse gas sequestration into deep ocean sediments. When it comes to the utilization of the replacement method in field applications, the soaking duration or the frequency of CO2/N2 gas injection becomes an important process variable. In this study, the influence of soaking duration and frequency on the CH4 replacement efficiency was quantitatively investigated for the first time by imitating the gas hydrate-bearing sediments. The CH4 replacement process with CO2/N2 was performed through two consecutive stages: dynamic replacement and soaking process. While any additional soaking process after the dynamic process enhanced the CH4 replacement efficiency from 35–36 to 52–60%, several replenishments of a fresh CO2/N2 gas mixture into the vapor phase were considered more effective than solely increasing the soaking time. The present study will help in establishing the basic process variables ...

The CH 4 –flue gas replacement in naturally occurring gas hydrates has attracted significant attention due to its potential as a method of exploitation of clean energy and sequestration of CO 2 . In the replacement process, the thermodynamic and structural properties of the mixed gas hydrates are critical factors to predict the heat flow in the hydrate-bearing sediments and the heat required for hydrate dissociation, and to evaluate the CO 2 storage capacity of hydrate reservoirs. In this study, the 13 C NMR and gas composition analyses confirmed that the preferential enclathration of N 2 molecules in small 5 12 cages of structure I hydrates improved the extent of the CH 4 recovery. A high pressure micro-differential scanning calorimeter (HP μ -DSC) provided reliable hydrate stability conditions and heat of dissociation values in the porous silica gels after the replacement, which confirmed that CH 4 in the hydrates was successfully replaced with flue gas. A heat flow change associated with the dissociation and formation of hydrates was not noticeable during the CH 4 –flue gas replacement. Therefore, this study reveals that CH 4 –flue gas swapping occurs without structural transitions and significant hydrate dissociations.

In this study, the mixed gas hydrates formed from the flue gas mixtures of CO 2 + N 2 have been investigated with a primary focus on the structure identification and the dissociation enthalpy measurements. The stability conditions of the CO 2 + N 2 gas hydrates are determined using an isochoric (PVT) method and a differential scanning calorimeter (DSC). It is found from the comparison of the hydrate phase equilibrium data measured using two methods that the DSC can be effectively used as an alternative method for measuring the stability conditions of the CO 2 + N 2 gas hydrates. The microscopic analyses, such as powder X-ray diffraction and Raman spectroscopy, demonstrated that the gas mixtures of CO 2 + N 2 form a structure I hydrate and that the structural transition does not occur in the range of the flue gas composition. To reveal the dissociation behavior of the mixed gas hydrates, the dissociation enthalpies of the CO 2 + N 2 gas hydrates have been measured using a micro-differential scanning calorimeter (μ-DSC). The dissociation heats of the CO 2 + N 2 gas hydrates increased with an increase of the CO 2 composition in the hydrate phase. The experimental results obtained in this study provide the thermodynamic and physical background required to estimate the heat liberated or absorbed during hydrate formation and dissociation and to predict the operation conditions for the gas hydrate-based CO 2 capture and storage process.

Investigations on the intrinsic properties of gas hydrates with multiple guests are essential to scientific and technological fields. In particular, even though evaluating and designing a hydrate phase process require isothermal phase equilibria, it is difficult to obtain extensive data with various components and compositions in a short period of time due to the static-analytic method. The present study introduces a new experimental determination on hydrate phase equilibria using continuous dissociation induced by extremely slow vapor volume expansion at a constant temperature. When a syringe pump is automatically operated at the microliter level during the dissociation process, the endothermic dissociation can be traced from the temperature readings. The validity and stability of the proposed technique were evaluated using pure CH4 hydrates, and repeated measurements of three-phase (LW–H–V) equilibrium conditions are used to optimize the volumetric expansion rates. Then, an experimental approach is appl...

가스 하이드레이트는 고압 및 저온의 조건에서 주체 분자인 물의 수소 결합에 의해 형성된 격자 내로 저분자량의 기체 분자가 포집되어 있는 고체의 함유 화합물이다. 심해저 퇴적층과 영구 동토지역에 매장되어 있는 막대한 양의 천연가스 하이드레이트는 미래 청정 에너지원으로 주목받고 있다. 우리나라의 경우에도 동해안 울릉분지 부근 심해저에 천연가스 하이드레이트의 부존 가능성을 확인하였다. 이러한 심해저 천연가스 하이드레이트의 개발/생산을 위해서는 천연가스 하이드레이트의 상평형, 생성/해리 속도 등의 물리적 특성 뿐만 아니라 해리와 관련된 열물성에 대한 정보가 매우 중요하다. 따라서, 이 논문에서는 고압 마이크로 시차 주사 열량계를 이용하여 천연가스 하이드레이트의 주성분인 메탄, 에탄, 프로판 하이드레이트의 해리 엔탈피를 측정하였다. 메탄 하이드레이트의 경우 92.3 bar의 압력 조건에서 502.1 J/g-water, 437.3 J/g-hydrate, 54.2 kJ/mol-gas의 해리 엔탈피 값을 가졌으며, 해리 온도는 285.66 K이었다. 에탄 하이드레이트의 경우 18.7 bar에서 해리 엔탈피는 534.5 J/g-water, 438.8 J/g-hydrate, 73.8 kJ/mol-gas이었으며, 이때 해리 온도는 283.85 K이었다. 마지막으로 프로판 하이드레이트의 경우 압력이 3.2 bar일 때 해리 엔탈피는 417.2 J/g-water, 363.8 J/g-hydrate, 127.7 kJ/mol-gas 임을 알 수 있었고, 276.30 K에서 해리되는 것을 확인하였다. 또한, 해당 압력에서 각 기체의 가스 하이드레이트의 해리 엔탈피 측정과정에서 얻은 해리 온도를 문헌상의 가스 하이드레이트 3상(하이드레이트상(H)-물상(Lw)-기상(V)) 평형 데이터와 비교해 보면 거의 유사함을 알 수 있었다. 따라서, 고압 마이크로 시차 주사 열량계를 이용하여 가스 하이드레이트의 정확한 해리 엔탈피 측정 뿐만 아니라 가스 하이드레이트의 3상 평형도 함께 측정 가능함을 확인하였다. 【Gas hydrates are inclusion compounds formed when small-sized guest molecules are incorporated into the well defined cages made up of hydrogen bonded water molecules. Since large masses of natural gas hydrates exist in permafrost regions or beneath deep oceans, these naturally occurring gas hydrates in the earth containing mostly $CH_4$ are regarded as future energy resources. The heat of dissociation is one of the most important thermal properties in exploiting natural gas hydrates. The accurate and direct method to measure the dissociation enthalpies of gas hydrates is to use a calorimeter. In this study, the high pressure micro DSC (Differential Scanning Calorimeter) was used to measure the dissociation enthalpies of methane, ethane, and propane hydrates. The accuracy and repeatability of the data obtained from the DSC was confirmed by measuring the dissociation enthalpy of ice. The dissociation enthalpies of methane, ethane, and propane hydrates were found to be 54.2, 73.8, and 127.7 kJ/mol-gas, respectively. For each gas hydrate, at given pressures the dissociation temperatures which were obtained in the process of enthalpy measurement were compared with three-phase (hydrate (H) - liquid water (Lw) - vapor (V)) equilibrium data in the literature and found to be in good agreement with literature values.】

Summary This paper experimentally analyzes the production characteristics of hot-brine stimulation accompanying hydrate reformation in the presence of methane hydrate. Many attempts have been made to recover methane hydrate commercially, such as depressurization, thermal stimulation, and inhibitor injection. Hot-brine injection coupled with thermal recovery with inhibitor injection has been investigated as an efficient production scheme, but the hydrate reformation during the dissociation is problematic, and it negatively influences the recovery rate. An experimental apparatus divided the sediment sample into 12 blocks not only to describe 1D dissociation effectively but also to control the temperature accurately. The specified amount of methane hydrate was formed artificially in unconsolidated and packed sediments where the average particle size, absolute permeability, and porosity were 260 µm, 4.4 darcies, and 42%, respectively. The production trends were observed in the temperature range of approximately 283.85 - 303.15 K and with injection rates of 10 and 15 cm3/min. Methane hydrate reformed in all the tests; the reason for this may be the recombination of water and the dissociated methane in the downstream zones. In the early time, the production rate was low, but it increased significantly in later time. The former was why most of gas that dissociated in the upstream zones was consumed to reform hydrate in the downstream areas, while the latter came from the dissociation of initial and reformed hydrate. The dissociation front moved fast at the higher temperature and injection rate. The production efficiency of the test at 15 cm3/min and 294.55 K was similar to that of the test at 10 cm3/min and 303.15 K. The results confirmed the production behaviour of methane hydrate under the reformation phenomenon and could provide the fundamentals to develop an efficient production scheme based on hot-brine stimulation.

The dissociation behavior in methane hydrate-bearing sediments was experimentally analyzed by changing temperature of hot-brine ranged from 16.3 to 42.0 Celsius. The experimental apparatus was designed to demonstrate an idealized one-dimensional dissociation phenomenon. The movement of dissociation front was directly measured from the temperature distribution during dissociation. The dissociation front advanced faster with increasing injection temperature. The normalized speed of dissociation front could imply the probable zone to be dissociated by injecting unit pore volume of hot-brine in hydrate reservoir, and was linearly correlated with the temperature-driving force.

Anomalous chloride concentration enrichment has been detected in marine sediments comprising methane hydrates (MHs). In this study, we designed an electric circuit system linked to the high-pressure resistance cell in which the chloride ion concentration can be directly measured within reliable accuracy under in situ conditions of the deep-sea floor pressure and temperature. Chloride concentration increased under a fast MH formation rate, but no noticeable concentration change was detected under a relatively low-rate. Furthermore, we suggested that the MH formation rate must be maintained at least ∼102 mol m−2 yr−1 so as to efficiently enrich chlorides and retain the acquired chlorinity. The present experimental system dose not fully reflect the relatively minor effective variables such as vertical advections in real system, but the results seem to be sufficient for revealing chloride enrichment phenomena induced by fast MH formation rate with free methane gas. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Natural gas hydrates were recovered from near-seafloor sediments and analysed to compare two distinctive methane inclusion phenomena. We document the first observation of abnormal methane occupancy in sediment-rich NGH deposits.

Structure-H hydrate has been highlighted due to its higher gas storage capacity and favorable thermal stability. Here, we introduce a new structure-H hydrate former, tert-butyl nitrite, and identify it through spectroscopic analysis. The hydrate structure and guest distribution were examined by using powder X-ray diffraction, Raman spectroscopy, and solid-state high-power decoupling 13C NMR spectroscopy. The phase equilibria (Lw + H + Lg + V) of tert-butyl nitrite + CH4 hydrate were measured at pressures from (3 to 4.5) MPa and at temperatures from (277 to 282) K. We also investigated the kinetic behavior of this new high-polarity hydrate former.

The competitive inclusion behavior of multiguests in the cages of clathrate hydrates is not yet well understood in spite of its significant importance in both scientific and technological fields. Here, we derive simple and generalized expressions related to cage occupancy ratios of binary clathrate hydrates, measure the cage occupancy ratios, and finally compare the proposed expressions with the experimental results. The present approaches cover three independent categories: the binary guests competitively occupy (1) both small and large cages, (2) only small cages, and (3) only large cages. In addition, we demonstrate that cage occupancy ratio is a simple but powerful variable that indicates the guest behaviors. More importantly, the present approaches only need to have the precise composition measurements to reveal the general nature of guest popularity in cages, while the original van der Waals−Platteeuw model requires several complex variables such as Langmuir constants and fugacities as indispensable...

Smectite clays are widely dispersed in deep ocean sediments and can be subdivided into two representative clay types, Cheto- and Wyoming-montmorillonites. In this study, we measured the thermodynamic phase behavior of methane hydrates intercalated at various concentrations of these clays and found the relatively weak promotion tendency when compared to that of pure methane hydrate stability. The structure and morphology of intercalated methane hydrate (IMH) samples were analyzed using the MAS NMR, RAMAN, LT-XRD, and Cryo-FE-SEM. The 27Al and 29Si solid-state MAS NMR spectra of IMH Cheto and Otay clays represent that the structural stability is preserved during the IMH formation, which is also indicated with the XRD pattern showing no structural transformation but different d-spacing values due to clay−water suspension and IMH. In addition, Cryo-SEM images of IMH samples show that IMH Otay clays provide well-developed methane hydrate (MH) morphology, compared to the IMH Cheto clay.

Natural methane hydrates occurring in marine clay sediments exhibit heterogeneous phase behavior with high complexity, particularly in the negatively charged interlayer region. To date, the real clay interlayer effect on natural methane hydrate formation and stability remains still much unanswered, even though a few computer simulation and model studies are reported. We first examined the chemical shift difference of 27Al, 29Si, and 23Na between dry clay and clay containing intercalated methane hydrates (MH) in the interlayer. We also measured the solid-state 13C MAS NMR spectra of MH in Na-montmorillonite (MMT) and Ca-montmorillonite (MMT) to reveal abnormal methane popularity established in the course of intercalation and further performed cryo-TEM and XRD analyses to identify the morphology and layered structure of the intercalated methane hydrate. The present findings strongly suggest that the real methane amount contained in natural MH deposits should be reevaluated under consideration of the compositional, structural, and physical characteristics of clay-rich sediments. Furthermore, the intercalated methane hydrate structure should be seriously considered for developing the in situ production technologies of the deep-ocean methane hydrate.

On the basis of crystallographic analysis results, a recent study reported that structure H (sH) hydrate exists in the natural environment, providing direct evidence from hydrate samples recovered ...

Streamline simulations have been extensively used due to their computational speed and invulnerability to numerical dispersion. However, many works have been applied to transport modeling without considering dispersive transport. A new term, advection-dispersion ratio, is introduced, which is defined as a relative extent of advection to dispersion along a streamline. By using the advection-dispersion ratio, analytical solution to the advection-dispersion equation is mapped onto streamlines so that dispersive transport can be effectively modeled by streamline simulation. With the advection-dispersion ratio incorporated, streamline simulation was applied to model transport in an artificially fractured sample, and validated by comparing with an experiment. It is observed that the tracer breakthrough curve from the simulation matches well with that from the experiment. By allocating variable advection-dispersion ratios to streamlines, streamline simulations were performed on various fields generated by sequen...

Large amounts of CH4 are stored as hydrates on continental margins and permafrost regions. If the CH4 hydrates could be converted into CO2 hydrate, they would serve double duty as CH4 sources and CO2 storage sites in the deep ocean sediments. As preliminary investigations, both the phase behavior of CH4 hydrates and kinetic behavior of CO2 hydrate were measured at versatile conditions that can simulate actual marine sediments. When measuring three-phase equilibria (H-LW-V) containing CH4 hydrate, we also closely examined pore and electrolyte effects of clay and NaCl on hydrate formation. These two effects inhibited hydrate nucleation and thus made the hydrate equilibrium line shift to a higher pressure region. In addition, the kinetic data of CO2 hydrate in the mixtures containing clay and NaCl were determined at 2.0 MPa and 274.15 K. Clay mineral accelerated an initial formation rate of CO2 hydrate by inducing nucleation as initiator, but total amount of formed CO2, of course, decreased due to the capillary effect of clay pores. Also, the addition of NaCl in sample mixtures made both initial formation rate and total amount of CO2 consumption decrease.

The permeability and resistance of 4 artificial sediments samples were measured with saturation of gashydrate changed. It is observed that the reduction patterns of permeability of the samples in this study are similar with increasing gas-hydrate saturation, which shows the possibility of existence of correlation with permeability and gas-hydrate saturation. In the measurements of resistance, the resistance of the gas hydrate sediments shows totally different value depending on saturated fluid.

A styrene monomer t BQSt, having a tert -butyloxycarbonyloxy ( t -BOC)-protected quinizarin dye precursor as a pendent, has been copolymerized with N -(tosyloxy)maleimide (TsOMI) to obtain a dual functional polymer P( t BQSt/TsOMI). The polymer P( t BQSt/TsOMI), as a single component photoimaging system without using an external photoacid generator (PAG), was applied for fluorescent photopatterning by dry process based on the chemical amplification (CA) process. The TsOMI units in the polymer chains were responsible for photochemical generation of p -toluenesulfonic acid by UV exposure and the acid generated in the solution cast polymer film induced the catalytic deprotection of acid labile t -BOC groups of the quinizarin dye precursors. Accordingly, the quinizarin moieties were regenerated in the polymer chains by the CA process, thereby recovering the original color and fluorescence of the quinizarin dye. Fluorescent patterns were readily delineated on the thin polymer films by imagewise UV exposure even without a wet development process.