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Methane hydrates (MHs) have been considered a promising future energy source due to their vast resource volume and high energy density. Understanding the behavior of MH formation and dissociation at the pore-scale and the effect of MH distribution on the gas–liquid two phase flow is of critical importance for designing effective production strategies from natural gas hydrate (NGH) reservoirs. In this study, we devised a novel high-pressure microfluidic chip apparatus that is capable of direct observation of MH formation and dissociation behavior at the pore-scale. MH nucleation and growth behavior at 10.0 MPa and dissociation via thermal stimulation with gas bubble generation and evolution were examined. Our experimental results reveal that two different MH formation mechanisms co-exist in pores: (a) porous-type MH with a rough surface formed from CH4 gas bubbles at the gas–liquid interface and (b) crystal-type MH formed from dissolved CH4 gas. The growth and movement of crystal-type MH can trigger the sudden nucleation of porous-type MH. Spatially, MHs preferentially grow along the gas–liquid interface in pores. MH dissociation under thermal stimulation practically generates gas bubbles with diameters of 20.0–200.0 μm. Based on a custom-designed image analysis technique, three distinct stages of gas bubble evolution were identified during MH dissociation via thermal stimulation: (a) single gas bubble growth with an expanding water layer at an initial slow dissociation rate, (b) rapid generation of clusters of gas bubbles at a fast dissociation rate, and (c) gas bubble coalescence with uniform distribution in the pore space. The novel apparatus designed and the image analysis technique developed in this study allow us to directly capture the dynamic evolution of the gas–liquid interface during MH formation and dissociation at the pore-scale. The results provide direct first-hand visual evidence of the growth of MHs in pores and valuable insights into gas–liquid two-phase flow behavior during fluid production from NGHs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reveals the inhibition effect of representative clays from South China Sea on CH 4 hydrate experimentally. • Thermodynamic inhibition is more significant for Na-montmorillonite than kaolinite and illite. • Develops a thermodynamic model accounting for the reduced water activity on clay surface. • Implications provided on the stability and fluid production from South China Sea clayey hydrate-bearing sediments. Clay minerals are widely distributed in hydrate-bearing sediments worldwide, especially in the clayey-silty sediments in the South China Sea. The debate on the influence of clay on the thermodynamics of natural gas hydrate (NGH) remains and impedes the fundamental understanding of hydrate-clay interactions and the design of effective production strategies for energy recovery. Specifically, the phase equilibria of MH in the presence of clay and how different types of water associated with clay particles affect NGH thermodynamics and stability are not fully elucidated and warrant investigation. In this study, the phase equilibria of methane hydrate (MH) were measured in the presence of typical clays from the South China Sea, i.e., montmorillonite, kaolinite, and illite. The shift of MH phase equilibria curve to a more stringent pressure was identified with Na-montmorillonite showing the most significant inhibition. The leftward shift (inhibition) of phase equilibrium temperature (T eq) is up to 3.9 K at a pressure of 10.40 MPa for Na-montmorillonite compared with pure water. Furthermore, we develop a thermodynamic model based on the classical Chen-Guo model first accounting for the change in water activity (a w) due to cation exchange of Na-montmorillonite. The developed model exhibits good predictability with the measured phase equilibira data. The inhibition on the phase equilibria of MH is linked to the reduction of a w due to the clay-bound water for clays with a swelling nature. The findings of this study offer direct evidence and explanations on how clay minerals thermodynamically inhibit CH 4 hydrate. It provides valuable insights into the resource estimation of clayey-silty NGH in nature and facilities the design of suitable production strategies targeting clay-rich hydrate-bearing sediments. [ABSTRACT FROM AUTHOR]

Clayey-silty hydrate-bearing sediments are widely distributed worldwide, presenting significant potential for natural gas hydrate (NGH) extraction. However, fundamental thermodynamic and kinetic properties of CH 4 hydrate (MH) within these sediments remain subjects of debate, necessitating further investigation. This study aimed to investigate the kinetics of MH formation and dissociation in clayey-silty sediments suspensions, alongside morphological examinations. Results demonstrated that SH-W02-B sediments (SS) effectively shorted the induction time (t ind), with even a minute mass fraction of 0.1 wt% SS reducing t ind by 14 min compared to pure water (41 min). Lower mass fractions (<5.0 wt%) exhibited slight promotion of MH growth kinetics, whereas higher mass fractions (>10.0 wt%) markedly promoted MH growth kinetics, peaking at 144 v/v (20.0 wt%), correspondingly, and facilitating the conversion of H 2 O to MH to ∼70%. Morphological observation unveiled the formation of a thin clay layer at the gas-liquid interface, retarding MH formation and inducing the development of an anti-seepage hydrate layer, leading to the initial slow growth phase. Subsequent upward water migration facilitated the transport of fine clay particles, while the progressive encasement of clay particles by hydrate disrupted the fine clay layer, triggering the rapid hydrate formation phase and ensuing stratification between fine and coarse sediments particles. During hydrate dissociation, a heterogeneous distribution of fine and coarse sediments particles manifested in the reservoir. Moreover, the results carrying profound implications on understanding NGH occurrence pattern and developing recovery strategies from clayey-silty hydrate-bearing sediments. [Display omitted] • Clayey-silty core sediments were recovered near the China second field production test well. • X-ray diffraction analysis reveals 31 wt% clay with primary illite/smectite mixed layer in core sediments. • The presence of core sediments expedite CH 4 hydrate nucleation and enhance the growth kinetics. • Transport of fine clay particles leads to two-stage growth with stratified hydrate-sediments layers. [ABSTRACT FROM AUTHOR]

[Display omitted] • The phase equilibria of 72CH 4 /28CO 2 hydrate with DIOX no more than 5.56 mol% were measured. • Kinetics and morphology were acquired for CH 4 /CO 2 + DIOX hydrate varying 1.00–5.56 mol% • DIOX below 5.56 mol% induces CH 4 /CO 2 + DIOX hydrate formation with heterogeneous compositions. • CH 4 /CO 2 + DIOX hydrate growth for DIOX below 5.56 mol% yields DIOX concentrated in hydrate phase with a lean DIOX solution. • Co-storage of CH 4 /CO 2 in hydrate was suggested based on GC measurement and Raman analysis. Hydrate technology could provide a novel approach to deliver convenient CO 2 -rich natural gas. The identification of a suitable and environmental-friendly promoter for enhancing CO 2 /CH 4 hydrate kinetics is critical. In this study, we evaluated the thermodynamics, kinetics, and morphology of CH 4 /CO 2 + DIOX mixed hydrates in the presence of a thermodynamic promoter 1,3-dioxolane (DIOX) at and below its stoichiometric concentration (SC, C DIOX = 5.56 mol%). Due to the thermodynamic preference of DIOX enclathration in mixed hydrates formation, a decrease in C DIOX in the unconverted solution was observed post nucleation below SC and the hydrates formed exhibit significant heterogeneity in cage occupancy. As C DIOX in the unconverted solution decreases, the DIOX concentration in hydrate (R DIOX) and the thermodynamic stability of the newly formed hydrates decreases. Based on the step-wise heating design, the thermodynamic stability of the hydrates formed below SC with high- R DIOX is close to that of hydrates formed at SC, while hydrates with low -R DIOX undergo dissociation at their P-T trajectories above the measured phase equilibria. Raman measurement indicates that the lower- R DIOX hydrates possess a higher CO 2 composition. This study provides new insights into the tuning effect of DIOX on mixed hydrates formation and the basis for using low thermodynamic promoter concentration in hydrate-based technologies. [ABSTRACT FROM AUTHOR]

Oceanic hydrate-based CO 2 sequestration (HBCS) holds great promise for achieving carbon neutrality. However, the presence of inorganic salts, particularly MgCl 2 besides NaCl, in seawater can significantly impact the formation rate and the stability of CO 2 hydrate. In this study, experimental investigations were conducted to examine the thermodynamics, kinetics, and the resulting morphological features of CO 2 hydrate in the presence of MgCl 2 , covering mass fractions ranging from 0 to 5.0 wt%. The experimental findings reveal that MgCl 2 exerts a thermodynamic inhibitory effect with its inhibitory capacity increasing with higher mass fractions. The solubility model of CO 2 in MgCl 2 solution was modified, demonstrating a gradual weakening of CO 2 solubility as MgCl 2 mass fraction increases. Additionally, the growth kinetics of CO 2 hydrate decreases with increasing MgCl 2 mass fraction. Regarding CO 2 hydrate morphology, it was observed that at low mass fractions of MgCl 2 (<1.0 wt%), a dense hydrate film rapidly formed at the gas-liquid interface after CO 2 hydrate nucleation, hindering the further conversion of CO 2 into hydrate. Conversely, at higher mass fractions (>3.0 wt%), CO 2 hydrate exhibits a more porous and slurry-like structure, facilitating more gas-liquid contact and mass transfer, thereby enhancing the conversion of CO 2 into hydrate. During hydrate dissociation, a salt-removal effect associated with CO 2 hydrate formation was observed, leading to the accumulation of concentrated electrolyte (MgCl 2) and facilitating CO 2 hydrate dissociation. These findings have implications for understanding the CO 2 hydrate formation and dissociation in the presence of MgCl 2 relevant in the subsea environment and can contribute to the development of effective hydrate-based CO 2 sequestration strategies. [Display omitted] • Measured phase equilibria of CO 2 hydrate in the presence of 0–5.0 wt% MgCl 2. • Increasing MgCl 2 reduced CO 2 solubility in H 2 O by 22 % for 5.0 wt% MgCl 2. • Increasing MgCl 2 yielded sluggish CO 2 formation kinetics but enhancement observed at 1.0 wt% MgCl 2. • CO 2 hydrate morphology transits from surface film growth to slurry with increasing MgCl 2. • CO 2 hydrate dissociation triggered by concentrated MgCl 2 after CO 2 hydrate formation. [ABSTRACT FROM AUTHOR]

Methane hydrates are considered as the future energy due to its vast resource volume and high energy density. The fluid production and thermal response of two types hydrate-bearing sediments (i.e. , excess-gas and excess-water) under controlled depressurization are still unclear and warrant investigation. In this study, we devised two different hydrate-bearing sediments (HBS) synthesis methods and synthesized excess-water (S A = ∼27.2%) and excess-gas (S G = ∼26.5%) HBS with S H of 72.0%. The hydrate dissociation kinetics and fluid production behavior were examined under three bottom-hole pressures, i.e. , 3.0, 5.0, and 7.0 MPa. Gas production from the excess-gas HBS follows two-stage profile, while continuous gas production was observed after S G reaches 6.0% in the excess-water HBS. Water production from excess-gas HBS was significantly delayed compared with excess-water HBS and only started when S A reached above 22.5%. A logarithmic water production profile was observed in all cases. Rapid temperature drop due to hydrate dissociation is significantly delayed in excess-gas cases. Heat transfer from surroundings is relatively slow due to its low composite thermal conductivity. The findings on the contrast fluid production behavior between excess-gas and excess-water cases shed light on optimizing production strategies for future field production trials from these two different types reservoirs. • Excess-water (EW) and excess-gas (EG) HBS synthesized using novel method. • Controlled depressurization under BHP at 3.0 MPa, 5.0 MPa and 7.0 MPa. • Comparison of fluid production and heat transfer behavior of EW and EG HBS. • EG HBS is favored over EW HBS for production due to high R G , low R W and WGR. [ABSTRACT FROM AUTHOR]

• Four cooling regimes were employed to form CH 4 -hydrate bearing sediments. • All four multi-stage cooling regimes result in heterogeneous distribution of S H. • Heat inflow on the spatial distribution of S H (hydrate saturation) is significant. • Perfect insulation improves the uniformity of all phases in hydrate-bearing cores. Laboratory-created samples of methane hydrate (MH)-bearing media are a necessity because of the rarity and difficulty of obtaining naturally-occurring samples. The hypothesis that the inevitable heterogeneity in the phase saturations of the laboratory samples may lead to unreliable and non-repeatable results provided the impetus for this study, which aimed to determine the conditions under which maximum uniformity can be achieved. To that end, we designed four experiments involving different multi-stage cooling regimes (in terms of their duration and number of stages) to induce MH formation under excess-water conditions. In the absence of direct visualization capabilities, we analysed the experimental results by means of numerical simulation, which provided high-resolution predictions of the spatial distributions of the phase saturations in the cores and enabled the estimation of the parameters controlling the kinetic MH-formation behaviour through history-matching. Analysis of the numerical results indicated that, under the conditions of the experiments and with the design of the reactor, significant heterogeneities in phase saturation distributions were observed in all cases, leading to the conclusion that it is not possible to obtain cores with uniform phase saturation. Additionally, contrary to expectations, heterogeneities increased with the number of cooling stages and the duration of cooling, and this was attributed to imperfect insulation of the upper part of the reactor. A set of simulations involving perfect insulation of the reactor top confirmed the validity of this assumption: (a) predicting the formation of high-uniformity MH-bearing cores that became more homogeneous as the number of cooling stages and the length of the cooling period increased; and (b) providing important information for the improvement of the standard design of the experimental apparatus for the laboratory creation of MH-bearing cores using the excess water method. [ABSTRACT FROM AUTHOR]

Highlights • Numerical analysis of MH dissociation and fluids production by depressurization. • A function describing the change in MH surface area is incorporated in the T+H code. • Flow, thermal, kinetic parameters are optimized using a history-matching technique. • Simulation validated by experiment elucidates the issue of spatial heterogeneity. Abstract Methane Hydrates (MHs) are a promising energy source abundantly available in nature. Understanding the complex processes of MH formation and dissociation is critical for the development of safe and efficient technologies for energy recovery. Many laboratory and numerical studies have investigated these processes using synthesized MH-bearing sediments. A near-universal issue encountered in these studies is the spatial heterogeneous hydrate distribution in the testing apparatus. In the absence of direct observations (e.g. using X-ray computed tomography) coupled with real time production data, the common assumption made in almost all numerical studies is a homogeneous distribution of the various phases. In an earlier study (Yin et al., 2018) that involved the numerical description of a set of experiments on MH-formation in sandy medium using the excess water method, we showed that spatially heterogeneous phase distribution is inevitable and significant. In the present study, we use as a starting point the results and observations at the end of the MH formation and seek to numerically reproduce the laboratory experiments of depressurization-induced dissociation of the spatially-heterogeneous MH distribution. This numerical study faithfully reproduces the geometry of the laboratory apparatus, the initial and boundary conditions of the system, and the parameters of the dissociation stimulus, capturing accurately all stages of the experimental process. Using inverse modelling (history-matching) that minimized deviations between the experimental observations and numerical predictions, we determined the values of all the important flow, thermal, and kinetic parameters that control the system behaviour, which yielded simulation results that were in excellent agreement with the measurements of key monitored variables, i.e. pressure, temperature, cumulative production of gas and water over time. We determined that at the onset of depressurization (when the pressure drop – the driving force of dissociation – is at its maximum), the rate of MH dissociation approaches that of an equilibrium reaction and is limited by the heat transfer from the system surroundings. As the effect of depressurization declines over time, the dissociation reaction becomes kinetically limited despite significant heat inflows from the boundaries, which lead to localized temperature increases in the reactor. [ABSTRACT FROM AUTHOR]

Research on gas hydrates has progressed over the past several decades as a technology enabler for several innovative applications in the areas of water, energy, and environmental aspects. In this review, we present a systematic review of literature on the kinetic models describing the behaviour of gas hydrate growth. We reviewed a total of 27 classical and state-of-the-art models with their variations. These models were categorized into groups according to their controlling mechanism postulated (heat transfer, mass transfer, or intrinsic kinetic reaction), solution methods adopted (semi-empirical, analytical, or numerical) and reactor configurations (stirred-tank, packed-bed, flow reactor or hydrate film). We examined in-depth the main features of each kinetic model including its formulation, assumptions, governing equations, solution method, strengths and limitations. In addition, we have summarized the critical transport parameters of heat and mass transfer, and the intrinsic kinetic rate parameters associated with hydrate growth in these models. Knowledge gap still exists in understanding the controlling mechanism of gas hydrate growth, which is further augmented by the dynamic behaviour of multiphase fluids flow, the thermodynamics of hydrate-forming system, and the compounding interfacial phenomena. Future efforts need to be devoted to recognize the coupling effect of heat and mass transfer, fluids flow, and gas hydrate phase change behaviour (i.e. its intrinsic kinetics) from multiscale. [ABSTRACT FROM AUTHOR]

We analyse numerically an earlier experimental study that involved the formation of methane hydrates by the excess water method in a small reactor filled with a sandy porous medium, and seek to address questions about the type of the hydration reaction and the phase heterogeneity in the resulting hydrate-bearing sand. Using a fine discretization describing the reactor assembly, the experimental process is faithfully replicated numerically. The multi-stage process of hydrate formation is subdivided in 7 steps. The experimental data from the continuously-monitored pressure and temperature during each step are used for comparison against the numerical predictions, the identification of the dominant processes and the determination of the associated parameters through a history-matching process that minimizes deviations between observations and simulation results. The results of this first-ever study on this subject demonstrate unequivocally that the hydration reaction is a kinetic (as opposed to an equilibrium) process, and that the spatial distributions of the various phases (aqueous, gas and hydrate) at the end of the formation process are strongly heterogeneous. This has serious implications in simulation studies of hydrate dissociation that assume uniform initial phase saturation distributions. The history-matching process indicates that (a) the system behaviour is sensitive to some flow parameters (porosity and irreducible water saturation) only during the first water injection, (b) it is insensitive to the sand intrinsic permeability during all steps of the study, and (c) thermal processes dominate after the first water injection, yielding estimates of the thermal properties of the sand and of time-variable key parameters of the kinetic reaction. [ABSTRACT FROM AUTHOR]

A huge amount of natural gas hydrates remains untapped in permafrost and continental margin. While several short term field production tests have been carried out, the underlying challenges during hydrate dissociation in porous media, such as the interdependent production behavior of gas and water, is still not well understood. In this work, we employed depressurization technique to recover natural gas from a water saturated hydrate bearing sediment (40% S H , 50% S A and 10% S G ) at 281.5 K surrounding temperature. During depressurization, the bottom hole pressure (BHP) was maintained at constant pressures of 5.0, 4.0, 3.0 and 2.1 MPa respectively to evaluate its effect on gas and water production. As expected, a higher BHP (corresponding to a lower dissociation driving force) resulted in a slower gas and water production. At a BHP of 2.1 MPa, thermal buffering was observed below ice point (272.7 K), accompanied by enhanced gas production. By lowering BHP from 5.0 MPa to 2.1 MPa, the percentage methane produced increased from 45.5% to 83.0%; whereas the cumulative water production decreased from 217 mL to 157 mL. The difference in gas and water production was attributed to the preferential production of aqueous phase at higher BHPs (5.0 and 4.0 MPa) nearing the end of hydrate dissociation whereby less hydrates were present. [ABSTRACT FROM AUTHOR]

[Display omitted] • Depressurization followed CO 2 -N 2 injection for CH 4 recovery and CO 2 sequestration. • Effect of MH dissociation ratio on subsequently mixed hydrate formation. • CH 4 hydrate re-formation and dissociation occurred depending on CH 4 hydrate left. • CO 2 hydrate formation depended on the CH 4 left in both gas phase and hydrate phase. • Increasing CH 4 production decreased the CO 2 sequestration and hydrate restoration. Natural gas hydrates (NGHs) buried below the seafloor are globally abundant, energy-dense, and essential to the world's future energy mix. The combination of depressurization and CO 2 -N 2 injection processes for NGHs recovery has been identified as an environmental method to harvest energy, CO 2 sequestration, and to maintain the mechanical stability of sediment. In this regime, partial CH 4 was produced by depressurization followed by CO 2 -N 2 injection to form CH 4 -CO 2 -N 2 mixed hydrate (Mix-H). In this study, a series experiments were designed to examine the key factors in the depressurization process (i.e. bottom hole pressure BHP and CH 4 production ratio) on the subsequent processes of Mix-H formation, CO 2 sequestration and hydrate restoration. It was observed that Mix-H formation occurred in all cases, but the final amount of Mix-H were all lower than the initial amount of MH before depressurization. Particularly, the formation of CO 2 /N 2 hydrate in Mix-H is positively correlated with the amount of remaining CH 4 in the combined phases of gas and hydrate after depressurization. The formation of CH 4 hydrate in Mix-H during the reformation process occurred in five cases when MH dissociation ratio (D MH) reaches above 45.1 % during depressurization. MH was only observed to dissociate continuously after CO 2 /N 2 injection when D MH is low at 30.8 %, which indicates possible "CH 4 -CO 2 replacement reaction". Overall, increasing CH 4 production at the same BHP decreases the CO 2 sequestration and hydrate restoration. We first verified the feasibility of the combination method for synergistic CH 4 recovery and CO 2 sequestration in marine conditions. The experimental results provide possible guidance on the optimal design of the coupled processes and shed light on the relationship between CH 4 recovery and CO 2 sequestration that need to be wholistically balanced. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phase equilibria of CO 2 + DIOX hydrate for C DIOX between 0.05 mol% and 5.56 mol% • The kinetics of CO 2 + DIOX hydrate is quantified with morphology observation. • Phase separation of DIOX/H 2 O above 3.1 MPa weakens the promotion effect of DIOX. • A comprehensive evaluation of DIOX in the application of hydrate-based CO 2 storage. To reduce anthropogenic CO 2 emissions for the mitigation of climate change require novel CCUS solutions. Hydrate-based CO 2 sequestration (HCS) is a novel carbon-neutrality technology that aims to store CO 2 in solid hydrate form with long-term stability. However, imminent issues exist for the application of HCS in terms of demanding thermodynamic conditions, slow formation kinetics, and low CO 2 gas uptake. These challenges necessitate the quest for an efficient and eco-friendly CO 2 hydrate promoter. In this study, 1,3-dioxolane (DIOX) as a low-toxicity CO 2 hydrate promoter was systematically examined. The phase equilibria, cage occupancy, and the kinetics of binary CO 2 + DIOX hydrate were measured for DIOX concentrations (C DIOX) varying from 0.05 mol% to 5.56 mol%. It was confirmed that DIOX is a dual-function promoter for CO 2 hydrate, but its promotion effect is weakened for C DIOX between 0.60 mol% and 1.00 mol% and for all C DIOX at relatively high pressure. The CO 2 uptake in the hydrate phase increases with C DIOX above 2.00 mol% and is the highest for C DIOX = 5.56 mol% (57.08 ± 6.39 mmol/mol). Based on the morphology observation, hydrate transits from ice-like to slurry to mushy-like and finally to snow-like with increasing C DIOX. Interestingly, we observed that the aqueous phase separates into two phases (i.e., DIOX-rich and H 2 O-rich) at pressure above 3.09 MPa, which explains the gradual loss of the promotion effect. The results of our study provide a comprehensive evaluation on DIOX as a possible promoter for CO 2 hydrate in HCS application. [ABSTRACT FROM AUTHOR]

Buried depth, as an inherent occurrence feature of hydrate reservoir, plays a significant role in fluid production during hydrate dissociation. In this study, we experimentally investigate the production performance of hydrate reservoirs at various buried depths beneath the seafloor. The hydrate-bearing system is synthesized in quartz sand with grain size varying between 100 and 500 μm in a 0.98 L reactor. Similar hydrate saturation is obtained at different prevailing pressures between 5.6 and 8.8 MPa. Depressurization experiments are designed to investigate the effect of buried depths on fluid production behavior. The results show that gas and water production increase with elevated buried depths at the same production pressure. However, based on the gas to water ratio, a deep-buried reservoir has a higher production potential at the initial stage. In contrast, a shallow-buried reservoir is an ideal candidate for fluid production in the later stage. Depressurization to the equilibrium P - T condition could lead to potential hydrate dissociation, but the rate is less intensive with less than 46.0 vol% hydrates dissociated in a prolonged time. The experimental results also reveal that both the design of depressurization and the reservoir depths have a combined effect on the overall fluid production performance. • A series of hydrate-bearing sediments with different buried depths were synthesized. • An accurate calculation method quantifying multi-phase saturation was developed. • Stability of hydrate reservoir and fluid production performance were analyzed. • Different production pressures but with the same degree of pressure driving force were employed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrate-bearing sediments under excess-water condition were synthesized systematically. • Fluid production induced by depressurization below the quadruple point were examined. • Effect of pressure drawdown rate and hydrate phase saturation were investigated. • Both gas production rate and recovery ratio increased under ultra-deep depressurization. Driven by the large resource volume, extraction of CH 4 from hydrate reservoirs has received worldwide attention. Depressurization is a feasible method and has been widely used in past field tests. However, fluid production behavior from water-saturated hydrate-bearing sediments below the quadruple point of CH 4 + H 2 O has not been well understood and warrants investigation. In this study, we designed a series of experiments using ultra-deep depressurization with bottom hole pressure (BHP) of 1.0 MPa, 1.5 MPa and 2.1 MPa in water-saturated hydrate-bearing sediments to investigate the fluid production behavior, particularly in the region with potential ice or secondary hydrate formation. The effect of hydrate saturations and pressure drawdown rates on fluid production below the quadruple point were systematically examined. Our experimental results show that ice formation was likely based on the temperature response, however, the self-preservation effect by ice formation prevents a further drop in temperature to its equilibrium temperature at the corresponding BHP. The gas and water recovery ratios increased by 6.5% and 49.1%, respectively for BHP below the quadruple point. No significant benefit of water trapping due to ice formation was observed. Faster pressure drawdown rate results in a more substantial temperature drop, which could trigger ice formation. Still, interestingly gas production was continuous and not affected in the phase diagram of ice + CH 4. Higher hydrate phase saturation improves gas production rate and final gas recovery ratio, yielding a lower water-gas ratio for more economic-viable CH 4 recovery. Our results indicate that ultra-deep depressurization could be one technical feasible option for increasing both gas production rate and final recovery ratio. The findings provide valuable information for designing an ultra-deep depressurization scheme based on S H of interest in future production tests. [ABSTRACT FROM AUTHOR]

Implementing efficient measures to increase production is crucial for the commercial development of hydrate. Currently, several potential stimulation methods, including well type optimization, depressurization amendment and reservoir reconstruction, have been proposed. However, most studies tend to focus on a single measure, and there are few reports on the stimulation performance under multiple means. Therefore, our study concentrated on constructing production models for simplified layered hydrate reservoirs in the Nankai Trough using four different horizontal well systems. The production enhancement resulting from aggressive depressurization and various well patterns were explored. Additionally, the production performances under conditions of burden sealing and reservoir permeability enhancement were further evaluated respectively. Lastly, the common impact of employing both burden sealing and reservoir permeability enhancement was assessed. The prediction results show that: (i) Decreasing the bottomhole pressure effectively enhances gas recovery and can be combined with other techniques for better expectation; (ii) There exists an optimal burden sealing ratio that maximizes gas production while increasing the permeability enhancement ratio consistently stimulates gas recovery; (iii) Both single and dual well systems, assisted by aggressive depressurization, are expected to achieve commercialization whereas the triple well pattern is unfavorable for achieving a significant increase in yield. • Stimulation performance of multiple means for NGH was systematically evaluated. • The optimal sealing ratios under different situations were firstly obtained. • Effects of well type, production pressure and permeability increase were studied. • Some promising schemes reaching commercial standard were suggested. [ABSTRACT FROM AUTHOR]

Kinetic hydrate inhibitor laboratory testing before field application is one of the key priorities in the oil and gas industry. The common induction-time-based technique is often used to evaluate and screen for kinetic hydrate inhibitors (KHIs). However, the main challenge relates to the stochastic nature of hydrate nucleation observed in fresh systems, which often results in scattered data on hydrate formation with unacceptable uncertainties. A much more precise KHI evaluation method, called crystal growth inhibition (CGI), provides comprehensive insights into the inhibitory behavior of a kinetic hydrate inhibitor, including both hydrate formation and decomposition. Given that industry does not require this much information, it is not feasible to expend either much time or cash on this strategy. This study aims to provide a cost-effective technique that presents maximum data accuracy and precision with relatively little time and cost expenditure. Hence, the impact of water-hydrate memory on improving the accuracy and repeatability of the results of the induction-time-based technique (IT method) was examined. First, the concept of water-hydrate memory, which contains information about how it is created, was reviewed, and then, the factors influencing it were identified and experimentally investigated, like the heating rate of hydrate dissociation and the water-hydrate memory target temperature during heating. Finally, a procedure was developed based on the background information in the earlier sections to compare the consistency of the results, originating from the conjunction of water-hydrate memory with the IT technique. The results of replications at KHI evaluation target temperatures of 12.3-12.4°C and 11.5-11.7°C showed that more repeatable data were obtained by applying water-hydrate memory, and a more conclusive decision was made in evaluating KHI performance than with an IT method. It seems that combining the IT method with water-hydrate memory, introduced as the "HME method", can lead to more definitive evaluations of KHIs. This approach is expected to gain in popularity, even surpassing the accurate but complex and time-consuming CGI method. [ABSTRACT FROM AUTHOR]

• Hydrate dissociation induced by multi-stage depressurization (MDP) were conducted. • Fluid production behaviour and heat transfer characteristics were analysed. • MDP improves the energy efficiency and increases the minimum temperature approached. Natural gas hydrates (NGH) are globally abundant, high in energy density, and are a clean energy source with great potential. The efficient and safe production of CH 4 from NGH has attracted widespread attention in the scientific and industrial fields. Depressurization (DP) has been assessed to be a technically feasible method of producing CH 4 from hydrate-bearing sediments (HBS). However, technical challenges (e.g. sand production and flow assurance issues) remain when using direct fast single-stage DP. Multi-stage depressurization (MDP) has been proposed to be an effective solution but less understood. In this study, we designed a series of experiments employing MDP processes (2-stage, 3-stage, 6-stage, and up to 10-stage DP) to dissociate water-saturated HBS with high S H > 56 vol%. We examined the fluid production behaviour, the evolution of temperature, and evaluated the energy efficiency ratio of the MDP processes with a comparison with single-stage DP process. Increasing the number of DP stages with finer steps controlled the rate of hydrate dissociation and significantly reduced the cumulative fluid produced in each stage. However, the overall recovery was not altered and largely depends on the initial and final thermodynamic states. Fluid production was driven by different mechanisms: gas production driven by heat transfer yielded the highest recovery at final P = 3.0 MPa, whereas water production driven by pressure drawdown resulted in the highest recovery when P first dropped below P eq = 4.6 MPa. Moreover, increasing the number of DP stages leads to an increase in the minimum temperature by 2.2 °C and an overall energy efficiency ratio improvement by 36.6%. The findings of this study could be significant in tuning the water–gas production performance and in designing the optimal MDP strategies in future field production tests. [ABSTRACT FROM AUTHOR]

• Integrated history-matching workflow coupling PSO with T + H v1.5 was developed. • Composite thermal conductivity of hydrate-bearing sands was estimated. • Bejan model shows superiority than Somerton model in depicting temperature response. • Optimal composite thermal conductivity yielded is 2.16 W/mK with S H = 0.40. • Particle size over 20 and maximum velocity coefficient 0.5 in PSO is recommended. Knowledge of the thermophysical properties of methane hydrate-bearing sediments (MHBS) plays a critical role in the evaluation of fluid production potential from gas hydrate accumulations in geologic media. The process of estimating the values of key flow and transport parameters related to MHBS is of great importance. In this paper, we developed an integrated optimization workflow by integrating a global optimization algorithm, specifically particle swarm optimization (PSO) with the TOUGH+Hydrate v1.5 hydrate simulator. The optimization technique was employed to estimate the composite thermal conductivity of MHBS (λ MHBS) through history-matching the simulated results with the experimental observation over time automatically in a process of stepwise heating an aqueous-rich heterogeneous MH-bearing core sample (S H = 0.40 and S A = 0.57) at P = 7.0 MPa. Two different composite models were tested and compared for their performance in predicting the temperature response. A sensitivity study was conducted to provide guidance on the selection of PSO parameters to accelerate the convergence speed. The optimal λ MHBS obtained from the Bejan linear model is 2.16 W/mK with an absolute average deviation (AAD) of 2.66%, which is superior than the Somerton nonlinear model. Based on the results from the sensitivity study, the coupling of PSO algorithm with T+H v1.5 was proved to be robust and reliable. It is found that a particle size over 20, a maximum velocity coefficient around 0.5 and a well-defined parameter range guided by literature improves the efficiency in searching the optimal solution, achieving a global best cost with fewer iterations. The optimization procedure developed in this paper can be adopted in estimation of other groups of parameters related to MH-bearing systems (i.e. thermal, flow, geomechanical properties and the kinetic rate parameters of MH reactions) and in the optimization of production strategies from MH reservoirs (e.g. well positioning, pressure drawdown level and rate, etc.) to improve the energy efficiency of the production process. [ABSTRACT FROM AUTHOR]

• Hydrate-bearing sediments with saturation above 0.40 was synthesized consistently. • Three drawdown rates were employed to induce hydrate dissociation and fluid production. • Two-stage water production and continuous gas production profiles were observed. • Cumulative water production rate increases linearly with drawdown rate. • Gas recovery of 0.83 and water recovery of 0.26 were attained at BHP = 3.0 MPa. Methane hydrates have been considered as the future source of energy due to its vast resource volume and high energy density. Depressurization has been demonstrated to be a technical feasible method in producing gas from hydrate reservoirs in the past field production tests. However, major technical challenges, i.e. low gas production rate, excessive water production, and uncontrollable sand production remain. Such undesirable production behaviour is directly linked to one key process variable, the rate of pressure drawdown. It controls the rate of hydrate dissociation and governs the multiphase fluid flow in sandy media. However, precise control of bottom hole pressure in large-scale production tests is difficult and it remains unclear how different drawdown rates affect the fluid production behaviour. Herein, we performed a series of hydrate formation experiments synthesizing aqueous-rich methane hydrate-bearing sediments with hydrate saturation above 40% and subsequently a series of depressurization experiments employing different controlled drawdown rates to dissociate the hydrate-bearing samples. Cumulative production of gas and water were monitored during the depressurization. The goals of the experiments were to examine the fluid production rate, the recovery ratio, and the temperature response in the hydrate-bearing system under different drawdown strategies. Cumulative water production rate increases linearly with drawdown rate, while cumulative gas production rate is directly linked to the hydrate dissociation rate, which is controlled by heat transfer at the early stage and dissociation kinetics toward the final stage. Water gas ratio can be regulated within a threshold by employing a slow drawdown rate. In addition, the final recovery of fluid is not controlled by the drawdown rates but is related to the final stable conditions of pressure and temperature. Our findings expand the understanding of fluid production behaviour from hydrate-bearing sediments and provide guidance in optimizing production strategies and in assessing the fluid production potential for future experiments and field production tests from hydrate reservoirs. [ABSTRACT FROM AUTHOR]

The field production test of gas hydrate conducted in South China Sea has been proven to be successful, but the production still cannot satisfy the requirement for commercial production. In order to achieve a higher production efficiency, the numerical simulation code Tough + Hydrate was employed to estimate the detailed production potential of four typical coring sites XX01∼XX04 in Shenhu area, which have distinct reservoir conditions and are considered as the focus for production tests. Our simulation results show that the hydrate deposit at Site XX03 featured with the highest permeability has the most promising gas production, despite the least thickness 11.56 m of the hydrate-bearing layer. In addition, we have also investigated the impact of the controllable engineering facts on the production, which suggests that the lower depressurization pressure and longer perforated interval would contribute to a higher gas production. And when the lower water production is considered, the bottom half perforated interval would be a relatively more promising design for the production. This research gives a forward sight for production prediction and our findings may provide a theoretical guideline in selection and design of the production targets. • Characteristics of four typical hydrate deposits are depicted by a schematic diagram. • Production potentials are evaluated just based on the analysis of geologic conditions. • The largest gas production is obtained though it has the thinnest hydrate layer. • Desirable production design is identified and can be directed in the field production. [ABSTRACT FROM AUTHOR]

• Fluid production from uniform and non-uniform hydrate-bearing samples is compared. • Assumption of uniformity results in slower rate of cumulative production of water. • Sensitivity analysis on controlling mechanisms of fluid production is conducted. • Gas production is dominated by thermal conductivity and kinetic rate parameters. • Water production is sensitive to absolute permeability and kinetic rate parameters. Methane hydrates (MHs) have been considered as the future source of energy because of its vast resource volume and high energy density. Energy recovery from MH-bearing sediments has attracted intensifying research activities. Fundamentally, heat transfer, fluid flow through porous media, and the kinetics of hydrate reaction are the three key processes controlling the behavior of MH dissociation and the associated fluid production. Earlier studies have suggested that heterogeneous spatial distribution of S H is inevitable in MH-bearing samples synthesized in laboratory. In this paper, we extend our study to analyze numerically the simulation results from the two realizations of the samples (homogeneous and heterogeneous) to identify differences in the fluid production and to determine if they are sufficiently different. Additionally, we conduct a sensitivity analysis and a statistical analysis on the key transport and kinetic rate parameters that could affect hydrate dissociation and fluid production in the context of a heterogeneous hydrate-bearing sample, in an effort to provide insights that could lead to improved designs for laboratory experiments and (possibly) field applications. Our results suggest that the approximation of an artificial hydrate-bearing core with heterogeneous phase saturations by an assumption of uniform phase saturation distributions results in practically similar fluid production profile except for the very early stage with maximum 20.0% deviation in the water production. From the sensitivity and statistical analysis, we determine that gas production depends strongly on the kinetic rate constant, K d 0 and the composite thermal conductivity of the hydrate-bearing sediments, λ θ ; while, water production is very sensitive to K d 0 and the absolute permeability of the sandy medium, k. Understanding the effect of phase heterogeneity and the relative importance of key parameters on the production behavior of hydrate-bearing sediments could provide basis for novel production technologies that lead to enhanced gas production and energy efficiency in the energy recovery process. [ABSTRACT FROM AUTHOR]

• Five different wellbore designs are employed in production from hydrate-bearing sediments. • Continuous gas production and step-wise water production are observed at all pressures. • Slotted-liner design offers better control of water production than bore-hole design. • Partial perforation and perforation location affect water production more than gas production. Methane hydrates have been considered as the future clean energy resource. To recover energy from hydrate-bearing sediments safely and effectively requires a fundamental understanding of the dynamic behaviour of hydrates in sandy media. Past field production tests have proved the technical feasibility of gas production from hydrate reservoirs. However, technical challenges (e.g. sand production and excessive water production) remain in realizing long-term economic-viable production. In this study, we investigate the effect of various wellbore designs (specifically the shape and the location of perforations) on the fluid production behaviour in aqueous-rich hydrate-bearing sediments. Slotted-liner design was first-time incorporated in depressurization under different bottom-hole pressures (2.5 MPa, 3.0 MPa and 4.0 MPa). Continuous gas production and step-wise water production during the early stage of depressurization were observed at all pressures because of the change of fluid flow path from reservoir to wellbore. Compared with traditional borehole design, slotted-liner design showed advantage in controlling water production under low BHP (2.5 MPa). Using wellbores with different perforation locations, it was observed that perforation location does not pose a significant impact on the behaviour of gas production; whereas, middle perforation away from the aqueous-rich and hydrate-rich region yielded the least water production. The experimental results from this study demonstrated the possibility of employing slotted-liner well and varying the perforation location in reducing water production from methane hydrate-bearing sediments. Our findings can pave way for the testing of novel wellbore designs to further enhance gas recovery and reduce water production from hydrate reservoirs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The amount of dissociation of natural gas hydrates below the quadruple point is non-linearly correlated with the depressurization rate. • The existence of a metastable state could be beneficial for increasing the gas production rate of methane hydrates and for improving the recovery rate of reservoir temperatures. • When hydrates disengagement the metastable region, the gas production rate of hydrates is improved. • The time that the hydrate is in the metastable region needs to be kept at the right time interval. The depressurization method has been proven to be an energy-efficient and relatively feasible production technique for natural gas hydrates. However, during the depressurization process, especially when the hydrates reservoir approaches the quadruple point, it is inevitable to experience phenomena such as freezing and hydrates secondary formation. Therefore, most researchers think that the P-T near the quadruple point may not be suitable for the dissociation of hydrates and a series of depressurization control methods were adopted to avoid this. However, according to other researchers, the effect of depressurization near the quadruple point on the dissociation behavior of hydrates is not inhibitory, but even a promoting effect to a certain extent. In addition, A special region called metastable state appears with the decrease of pressure near the quadruple point, which makes the dissociation behavior of hydrate below the quadruple point different from that above it. Therefore, in this paper, to reveal more clearly the dissociation behavior of natural gas hydrates near the quadruple point and the influence of the existence of metastable state on the depressurization dissociation of hydrate, the dissociation experiment of natural gas hydrates in the porous medium peri -freezing point is investigated in different depressurization rates and amplitudes, peri -freezing point and pressure stabilization times quadruple point. Experimental studies have shown that the amount of dissociation of natural gas hydrates below the quadruple point is non-linearly correlated with the depressurization rate. This correlation is synergistically regulated by the depressurization magnitude per unit of time and the environmental heating efficiency. Compared with the dissociation of hydrates above the freezing point, the metastable region does not show an obvious inhibitory effect on the dissociation of hydrates, and it even effectively shortens the dissociation time of hydrates and improves the heat transfer efficiency of the reservoir. Under the dissociation pressure of 2.5 MPa (metastable state), the reservoir temperature rose from 0 °C to 1 °C in 2.9 h, 3.6 h less than that under 2.6 MPa (above the quadruple point), and 0.7 h more than that under 1.0 MPa (below the metastable state). In addition, the gas production rate of hydrates is improved when hydrates disengagement the metastable region, increasing by 65.12 % compared with those above the quadruple point. However, pressure stabilization times when hydrates are in a metastable state need to be kept within a certain interval, too long or short pressure stabilization time will inhibit the dissociation of hydrates, and reduce the promotion effect on the dissociation of hydrates. [ABSTRACT FROM AUTHOR]

• Depressurization followed by CO 2 -N 2 injection for CH 4 recovery and CO 2 sequestration. • A pilot-scale investigation on the combined processes at South China Sea NGH condition. • Spatio-temporal evolution of mixed CH 4 /CO 2 /N 2 hydrate formation was investigated. • Hydrate saturation reverts back to 50%-70% of its original after mixed hydrate formation. • Employment of horizontal well enhanced the storage of CO 2 after CO 2 /N 2 injection. To ensure sustainable energy supply while mitigating climate change, combining CH 4 recovery with CO 2 storage in marine natural gas hydrate (NGH) reservoirs is a promising carbon–neutral technology. In this study, a pilot-scale reactor (V = 22 L) was used to study the combined processes of CH 4 recovery from the methane hydrate-bearing sediment by using depressurization followed by in-situ CO 2 /N 2 injection to form mixed CH 4 /CO 2 /N 2 hydrate (Mix-H) at marine NGH reservoir conditions (T = 283.8 K and P = 11.0 MPa). The bottom hole pressure (BHP = 3.2 MPa, 5.3 MPa, and 6.8 MPa) during depressurization and the setting of horizontal wellbore (HW), were systematically investigated to optimize the synergistic CH 4 recovery and CO 2 storage. The CH 4 recovery ratio (55.4–80.6%) and the CH 4 production rate (5.15–134.98 mol/d) increased as BHP decreased. After CO 2 /N 2 injection, Mix-H formed first in the CH 4 -rich region in the upper section of the reactor and propagated downward to the lower. The Mix-H formation kinetics were significantly enhanced with an increase in BHP, leading to a decrease in CO 2 composition in the Mix-H. The use of a horizontal wellbore (HW) facilitates a more even distribution of the CO 2 /N 2 within sediments, resulting in a 13.5% increase in CO 2 composition of Mix-H compared with no HW setting. The CO 2 conversion ratio and hydrate restoration ratio reaches 52.8% and 69.4% at BHP = 5.3 MPa with HW, respectively. The technical feasibility of CO 2 storage in exploited marine NGH reservoirs was first proved at pilot-scale. The results provided insights into the synergistic method of NGH exploitation and CO 2 storage at the marine NGH reservoirs. [ABSTRACT FROM AUTHOR]

Being a promising potential source for natural gas, methane hydrate (MH) is attracting increasing interest due to its great amount and diverse geographic distribution. The formation of MH is significantly influenced by the properties of sediment media such as porosity and permeability. In this study, in order to have a better understanding on the relationship between MH formation behavior and sediment properties, as well as to synthesize representative hydrate samples, MH was formed in six different sets of mixed-size porous media composed of clay, silt and fine sand, with saline water and circulating methane gas to reflect MH formation with free methane flux in marine sediment. The sediment composition, experimental pressure (15 MPa) and temperature (286.2 K) were chosen based on the SH2 drilling site in the Shenhu area in South China Sea. A two-stage growing behavior was observed for all systems. The gas consumption and hydrate formation rate exhibited positive relations with the permeability and porosity of the sediments. Furthermore, hydrates were found to be preferably formed in the bottom layer of the sediment, which could be attributed to the drastic drop of permeability at the early stage of hydrate formation. Lastly, the hydrate formation rate constant was calculated based on the intrinsic kinetic model and found to be a good reflection of the mass transfer properties of different porous media. [ABSTRACT FROM AUTHOR]

Highlights • Vertical wellbore was incorporated within water saturated hydrate sediment. • Hydrate accumulation around wellbore reduced gas production and dissociation rate. • Cumulative gas production enhanced by up to 8% through vertical wellbore. • Simultaneously, water production was reduced by up to 43% at 4.5 MPa. Abstract Natural gas hydrates, an abundant source of natural gas in nature, have the potential of supplying energy for the future. However, due to the complexity of physical processes that occur simultaneously during the dissociation of hydrates within porous media, further understanding on the dynamic behavior of hydrates dissociation (e.g. heat transfer associated with phase transition, permeability changes, and simultaneous gas/water production) is required to elucidate the process of gas recovery from hydrates. In this work, we investigate the effect of a single vertical wellbore incorporation on the production behavior from hydrates formed in sandy sediments (0.1–0.5 mm). Depressurization approach (3.5, 4.0 and 4.5 MPa) was applied to dissociate the hydrate-bearing sand at a constant surrounding temperature of 281.5 K. Through the incorporation of a vertical wellbore, the gas production rate decreased with increasing bottom hole pressure, and continuous production of gas was observed at 4.5 MPa even after 10 h of dissociation. For water production, a majority of water was produced within the first 2 h, beyond which only a small amount of water was recovered. It was also observed that the incorporation of a vertical wellbore in the current design and apparatus impeded hydrate dissociation, which was attributed to a stronger flow resistance for fluids to exit through the vertical wellbore. Cumulatively, the incorporation of vertical wellbore enhanced gas production by up to 8% and reduced water production by up to 42%. In the future, innovative production schemes, such as heated wellbore and hydraulic fracturing can be applied to further optimize gas production from hydrate-bearing sediments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coupling L -Val with THF enhanced the kinetics of H 2 -THF hydrate formation. • The optimal concentration of L -Val is 0.3 wt% to achieve a maximum H 2 uptake of 29.83 v/v (0.26 wt%) • The reusability of L-Val as a kinetic promoter was demonstrated by five consecutive cycles. • Lower cooling rate promotes H 2 gas uptake with an optimal cooling rate at 0.05 K/min. • A H 2 -THF hydrate growth mechanism is proposed explaining the enhanced H 2 gas uptake using slow cooling. Hydrogen (H 2) emerges as a promising future clean energy for the low-carbon and sustainable future due to its high energy density and no pollutant or greenhouse gas emissions after combustion. The advantage of H 2 storage in solid-hydrate form is the requirement of only moderate pressure and temperature compared to compressed H 2 storage and the relatively lower energy consumption compared to liquid H 2 storage. However, the slow kinetics of H 2 hydrate formation is one major challenge to breakthrough for the large-scale development of hydrate-based H 2 storage. In this study, we introduced an environmental-benign kinetic promoter (L -valine, L -Val) and coupled it with a thermodynamic promoter tetrahydrofuran (THF) using stoichiometric concentration (5.56 mol%) to enhance H 2 hydrate formation kinetics. 0.3 wt% L -Val coupled with 5.56 mol% THF yields the optimal kinetic enhancement, and the maximum volumetric H 2 uptake (V H2) is 29.83 ± 1.22 volume of H 2 /volume of H 2 -THF hydrate (v /v). The reusability of L -Val is proved in five consecutive cycles of H 2 -THF hydrate formation and dissociation with consistently superior H 2 uptake. Furthermore, it was identified that cooling rate (R c) was an important factor determining the H 2 -THF hydrate formation kinetics. Lower R c (0.05 K/min) shows an optimal promoting effect of V H2 , which was 105.29% higher than that at higher R c (0.3 K/min). A mechanism is proposed to explain the effect of R c on H 2 -THF hydrate formation kinetics. The maximum gravimetric H 2 (G H2) reported in our study reaches 0.26 ± 0.01 wt%, which was superior in current literature below 15.0 MPa. The results provide insights into speeding up H 2 uptake in solid-hydrate form and have potential applications in hydrate-based hydrogen storage. [ABSTRACT FROM AUTHOR]

Tetra- n -butylammonium bromide (TBAB) semi-clathrate hydrate is an attractive phase change material for cold energy storage and transport. The high viscosity of hydrate slurry is a major challenge for process design and causes large pumping power consumption, not to mention the significant discrepancy of viscosity data observed in the literature. In this study, the discrepancy was clarified by studying the rheology of TBAB semi-clathrate hydrate slurry (SHS) using a rheometer with seed-induced in-situ formation of hydrate up to a high hydrate fraction (∼0.51). TBAB SHS exhibited a non-Newtonian shear-thinning behavior. Its apparent viscosity increased exponentially with the increase of hydrate fraction. Type B TBAB SHS was recommended due to its lower apparent viscosity than type A TBAB SHS. Energy analysis revealed that TBAB SHS with appropriate hydrate fractions could outperform chilled water to provide the same cooling capacity but consume less pumping power. Furthermore, to reduce the viscosity, an environmentally benign additive l -tryptophan was identified and employed for the first time. Addition of l -tryptophan up to 1.0 wt% in TBAB SHS significantly decreased the apparent viscosity and lead to a 68.7% reduction of pumping power consumption compared with chilled water. This work demonstrated the potential of TBAB SHS as a more efficient next-generation secondary refrigerant and the addition of a small dosage of l -tryptophan would considerably enhance its economic strength in cooling applications. [Display omitted] • Rheological study of TBAB hydrate slurry up to 0.51 hydrate fraction. • Apparent viscosity for type A TBAB hydrate slurry was greater than type B. • Energy analysis of TBAB hydrate slurry flow and benchmarked with chilled water. • Viscosity-reducing agent l -tryptophan (1 wt%) reduces energy consumption by 68.7%. [ABSTRACT FROM AUTHOR]

Hydrate-based desalination is a promising technology that offers low energy consumption. However, the low hydrate conversion rate and sluggish hydrate formation still hinder its applicability and therefore has not been commercialized yet, as it is necessary to enhance hydrate formation kinetics and obtain more freshwater. Hence, this study introduces a dual function (thermodynamic and kinetic) promoter cyclopentane and hydrophobic graphite and investigates the effect of cyclopentane/water volume ratio from 0.05 to 0.325, graphite size (75 μ m − 1. 6 μ m), and graphite/water volume ratio (ranging from 0.625 mg/mL to 3.25 mg/mL) on the CO 2 + C 3 H 8 hydrate formation kinetics at 275.6 K and 2.0–3.0 MPa. The results indicated that cyclopentane could shift the hydrate phase equilibrium condition to low pressure and high temperature and accelerate CO 2 + C 3 H 8 hydrate formation. Additionally, the experimental findings highlighted that the cyclopentane/water volume ratio of 0.175 afforded a faster hydrate formation rate and water conversion to hydrate. Moreover, we demonstrated that hydrophobic graphite with a smaller size provided more sites for hydrate nucleation and growth, and the synergy of graphite and cyclopentane reduced the hydrate induction time from 8.25 (±4.42) mins to 1.95 (±1.7) mins and increased the hydrate conversion rate from 35.62 (±1.76) % to 43.25 (±0.14) %. Overall, this study provides a guide for selecting the appropriate experimental condition, promoter, and porous media and lays a foundation for the hydrate-based desalination technology's feasibility and sustainable development. [Display omitted] • Cyclopentane combined with graphite to enhance hydrate formation rate was studied. • Synergy of cyclopentane and graphite shortens the hydrate induction time. • Cyclopentane/water volume ratio of 0.175 shows the fastest hydrate formation rate. • Graphite size of 6. 5 μ m indicates the highest gas uptake and hydrate conversion rate. [ABSTRACT FROM AUTHOR]

The prediction of gas productivity and reservoir stability of natural gas hydrate (NGH) reservoirs plays a vital role in the exploitation of NGH. In this study, we developed a THMC (thermal-hydrodynamic-mechanical-chemical) numerical model for the simulation of gas production behavior and the reservoir response. The model can describe the phase change, multiphase flow in porous media, heat transfer, and deformation behavior during the exploitation of NGH reservoirs. Two different production scenarios were employed for the simulation: depressurization and depressurization coupled with CO2 exchange. The simulation results suggested that the injection of CO2 promotes the dissociation of NGH between the injection well and the production well compared with depressurization only. The cumulative production of gas and water increased by 27.88% and 2.90%, respectively, based on 2000 days of production simulation. In addition, the subsidence of the NGH reservoir was lower in the CO2 exchange case compared with the single depressurization case for the same amount of cumulative gas production. The simulation results suggested that CO2 exchange in NGH reservoirs alleviates the issue of reservoir subsidence during production and maintains good reservoir stability. The results of this study can be used to provide guidance on field production from marine NGH reservoirs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phase equilibrium for CH 4 -DIOX hydrates in DIOX concentrations 0.15 mol%–5.56 mol%. • Low dosage DIOX induces more CH 4 in sII hydrate large cage but with inferior gas uptake. • The kinetics and morphology of mixed CH 4 + DIOX hydrate formation were observed. • An evaluation of DIOX promoting effect based on thermodynamics and kinetics. Hydrate-based CH 4 storage is a promising technology for safe and economically-viable natural gas storage and transportation. Solid CH 4 hydrate possesses advantages in both energy density and storage stability. The quest for an effective and economic-friendly thermodynamic promoter for CH 4 hydrate formation is imminent with the aim of (a) reducing CH 4 hydrate formation P - T condition and (b) increasing both the CH 4 gas uptake rate and final CH 4 storage capacity. In this study, a non-carcinogenic thermodynamic promoter 1,3-dioxolane (DIOX) was systematically investigated to quantify the effect of DIOX concentrations (0.15–5.56 mol%) on the process of mixed CH 4 + DIOX hydrate formation. A series of thermodynamic, kinetic, Raman spectroscopy measurement, and morphology observation experiments were conducted to elucidate the mechanism of the promotion effect of DIOX at concentrations below the stoichiometric concentration (5.56 mol%). DIOX with various concentrations shifts the thermodynamic phase equilibrium of binary hydrate to the region of moderate temperature and pressure. Raman spectra provided evidence of more CH 4 molecules filling in the large cages of sII hydrate with the decrease of DIOX concentration. The ratio of CH 4 in large cages to CH 4 in small cages of sII hydrate increases from 0.05 to 0.38 with the decrease in DIOX concentration. The gas uptake rate of CH 4 declined with the decrease in DIOX concentration. We also observed that DIOX concentration is an important factor affecting the morphologies during hydrate formation. These findings provide fundamental evidence for improving the CH 4 storage capacity and environmental friendliness in the application of DIOX in hydrate-based CH 4 storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrical resistivity can quantify the real-time TBAB hydrate fraction in slurry. • Sequential phase transition from type A to type B TBAB hydrate was observed. • From 278.2 K to 274.2 K, the hydrate growth rate was enhanced by 2.5 times. • L-tryptophan enhanced TBAB hydrate formation at 500 ppm but inhibited at 1000 ppm. Tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate has a large latent heat and suitable phase transition temperatures to be used as a phase change material for cold energy storage and transport. The mass fraction of hydrates in the semi-clathrate hydrate slurry is a key parameter determining the cold carrying capacity and flow properties. We developed a new experimental methodology based on electrical resistivity to quantify the hydrate fraction in semi-clathrate hydrate slurry during hydrate formation. Relationship between electrical resistivity and hydrate fraction of semi-clathrate hydrate slurry was established based on Bruggeman's effective-medium approximation. After validation, this method was employed to quantitatively investigate the effect of temperature on TBAB hydrate formation from 20 wt% TBAB/water system. As the temperature was lowered from 278.2 K to 274.2 K, the induction time was reduced by 97.8% and the hydrate growth rate was enhanced by over 2.5 times. At 274.2 K and 276.2 K, type A hydrates were preferentially formed followed by a structural transition to type B. At 278.2 K, only type A hydrates were observed. Furthermore, given an appropriate concentration, amino acid L-tryptophan was identified to be a good kinetic promoter for TBAB hydrate formation. The presence of 500 ppm L-tryptophan reduced the induction time by 60% and boost the hydrate growth rate by more than 32%. The electrical resistivity-based method developed in this work has shown simplicity, low cost, high accuracy, and repeatability. It would enable precise investigation of semi-clathrate hydrate kinetics in the future for cold energy applications and beyond. [ABSTRACT FROM AUTHOR]

The growth kinetics and macroscopic morphology evolution of CO 2 hydrate promoted by l -Methionine (L -Met) in NaCl aqueous solutions in a wide range of mass fractions were systematically investigated. 0.05 wt% was the threshold mass fraction of L -Met to have prominent promotion effects in a batch mode. The addition of NaCl could suppress its promotion performance, while it could be regained by further addition of L -Met to 1.0 wt%. Porous feature and wall-climbing phenomena of CO 2 hydrate were obvious in the presence of L -Met while it could be suppressed by NaCl. The tangential (lateral) growth rate of the hydrate film on planar pure water surface was the highest while both L -Met and NaCl could decrease it. For L -Met, it was the highest at 0.05 wt%. Special ball-like, mosaic-like and sword-like appearances of CO 2 hydrates were found. Both the adsorption-capillary effects of L -Met and the hydration effects of L -Met and NaCl were thought to account for all the phenomena and a detailed scenario was proposed and discussed. A macroscopic growth model based on the tangential growth rates of hydrate films was proposed and evaluated. • Excellent kinetic promotion effects of l -Methionine at 0.05 wt% were found. • NaCl suppressed the promotion effects by competing for water molecules. • CO 2 hydrate films first formed with different tangential growth rates. • Both the adsorption-capillary effects and hydration effects played a role. • Growth model was proposed and the control factor was evaluated. [ABSTRACT FROM AUTHOR]

Abstract: Polymeric composite microspheres consisting of a poly(d,l-lactic-co-glycolic acid) (PLGA) core surrounded by a poly(d,l-lactic acid) (PDLLA) shell layer were successfully fabricated by coaxial electrohydrodynamic atomization (CEHDA) process. Process conditions, including nozzle voltage and polymer solution flow rates, as well as solution parameters, such as polymer concentrations, were investigated to ensure the formation of composite microspheres with a doxorubicin-loaded PLGA core surrounded by a relatively drug-free PDLLA shell layer. Various microsphere formulations were fabricated and characterized in terms of their drug distribution, encapsulation efficiency and in vitro release. Numerical simulation of CEHDA process was performed based on a computational fluid dynamics (CFD) model in Fluent by employing the process conditions and fluid properties used in the experiments. The simulation results were compared with the experimental work to illustrate the capability of the CFD model to predict the production of consistent compound droplets, and hence, the expected core–shell structured microspheres. [Copyright &y& Elsevier]

The transition to a low-carbon economy requires the implementation of effective carbon capture and sequestration (CCS) strategies. One of the potential CCS strategies is to capture industrial CO 2 emissions and inject them into the oceanic sediments to be stored as CO 2 hydrates. However, the success of this technique depends on a few key factors such as the type of sediments where CO 2 is injected, the kinetics of CO 2 hydrate formation and dissociation, the accuracy of the models for prediction of formation kinetics, and the CO 2 hydrates morphology. So, in this first-gen work, a highly complex set of experiments was carried out to examine the CO 2 hydrate formation and dissociation processes by injecting CO 2 via injection tube into different size wet sediments, i.e., coarse (diameter: 0.5–1.5 mm), granules (diameter:1.5–3.0 mm) and dual-layered sand (coarse + granules), embedded inside high-pressure reactor as the artificial seabed. The experiments were carried out at 3.5 MPa at T = 1.5–2.0 °C with 500 ppm of the eco-friendly hydrate promotor (l -tryptophan). The images of morphological changes during hydrate formation/dissociation, the Scanning Electron Microscope analysis of the sediments, and the estimated water-to-hydrate conversations have been reported in this work. A novel mathematical four-parameter-based CO 2 hydrate kinetics model was also developed. A set of 32,843 experimental data points was used to train a supervised machine learning algorithm using two parameters with the other two taken from published literature. The water-to-hydrate conversion was estimated and follows the order of dual-layered sand [88.26 (±4.62) %] > coarse [77.77 (±5.72) %] > granules [65.36 (±2.3) %]. The proposed ML-based model predicted the water-to-hydrate conversion with an Average Absolute Relative Deviation [%AARD] of 4.23–13.29 %. This work serves as a step forward in developing a sustainable hydrate-based oceanic carbon storage technology. [Display omitted] • CO 2 hydrate kinetics and morphology in dual-layered sediments. • Effect of injecting CO 2 inside the sediments directly via vertical injection tube. • Developed and trained CO 2 hydrate formation kinetics model in sediments via a supervised machine learning (ML) algorithm. • ML model can predict CO 2 hydrate formation kinetics in sediments with accuracy in terms of AARD of 4.23–13.29 %. [ABSTRACT FROM AUTHOR]

[Display omitted] • Feasibility of CH 4 recovery and CO 2 storage by gas injection at marine condition. • CH 4 hydrate co-growth and dissociation occurred depending on the gas composition. • High CO 2 composition is beneficial for co-growth of mixed hydrate. • Continuous CH 4 hydrate dissociation was observed with high N 2 composition. CH 4 hydrate have been considered as the future clean energy resource. Recovery of CH 4 from natural gas hydrates by CO 2 replacement is a promising method for energy harvest and CO 2 sequestration. Field production tests have proved the feasibility of gas production by CO 2 replacement in the permafrost region. However, most of the hydrate reservoirs are located at marine conditions where pressure and temperature conditions are not favorable for the replacement process. In this work, we identified a possible marine condition, where mixed hydrates could potentially form. We investigated the technical feasibility of CH 4 recovery by a depressurization process followed by the injection of CO 2 -N 2 gas. To quantify the dynamic behavior of mixed hydrates formation and dissociation, we developed a numerical method to estimate the phase partitioning during the replacement process. The effects of mixed gas compositions in the reactor on the replacement efficiency were investigated. Our experimental results showed that rapid co-growth of mixed hydrates occurs when the injected gas composed of a lower N 2 concentration (<25.2%). On the other hand, continuous CH 4 hydrate dissociation was observed when the injected gas was composed of a higher N 2 concentration (28.5%). During the prolonged replacement stage, the amount of CH 4 hydrate decreased and the amount of CO 2 -N 2 hydrates increased only slightly, which indicated that possible replacement occurred but at a very localized level. The results proved the technical feasibility of CH 4 production by gas injection at marine conditions, but the compositions of the mixture gas injected need to be well controlled. [ABSTRACT FROM AUTHOR]

[Display omitted] • Delamination and the electric field induced by clay particle shortens induction time. • Delayed growth kinetics observed in clay suspension with increasing mass fraction. • Water migration and clay agglomeration yielded the stratification of CO 2 hydrate and clay layer. • Heterogeneous spatial distribution of CO 2 hydrate observed in formation and dissociation. Hydrate-based CO 2 sequestration in marine sediments has emerged as a novel sustainable technology for long-term and stable CO 2 sequestration. However, the role of clay minerals in CO 2 hydrate formation and dissociation in clay-rich sediments, which are widely distributed in the South China Sea, remains controversial due to a lack of experimental evidence. This study investigates the effect of a representative clay mineral, sodium montmorillonite (Na-MMT), on the nucleation and growth kinetics of CO 2 hydrate in suspensions with a msass fraction below 20.0 wt%. The kinetic experiments reveal that Na-MMT significantly reduces the induction time due to the additional nucleation sites provided by the delamination of clay particles and the induced surface electric field. While the average growth rate of CO 2 hydrate is reduced by ∼72 % for Na-MMT mass fraction above 5.0 wt%. Morphologically, hydrate-clay stratification and gas-tunneling behaviors were observed, providing explanations for the retarded kinetics. The mass transfer of CO 2 from the gas phase to the liquid phase is impeded by the high viscosity of the suspension and the clay-induced strongly-polarized water layer, which retards the overall kinetics of CO 2 hydrate formation. Upon thermal stimulation, partial CO 2 hydrate dissociation was observed within the pure CO 2 hydrate stability region for 10.0 wt% Na-MMT suspension, indicating a possible impact of Na-MMT on CO 2 hydrate thermodynamics. Moreover, the addition of Na-MMT clay promotes CO 2 hydrate dissociation kinetics significantly. This study provides fundamental insights into the interaction between Na-MMT clay and CO 2 hydrate, offering new perspectives for designing effective strategies for CO 2 sequestration in abundant clay-rich marine sediments. [ABSTRACT FROM AUTHOR]

Natural gas hydrate is a potentially vast energy resource for the future. However, the fundamental behavior of hydrate dissociation during energy recovery is not fully understood due to the complex interplay of phase change and multiphase flow within porous media. In this study, the effect of horizontal wellbore incorporation on the simultaneous gas and water production during the dissociation of methane hydrates in sandy sediment (0.1–0.5 mm) was investigated. A horizontal perforated wellbore was incorporated within water saturated hydrate bearing sediments of 40% hydrate, 55% aqueous and 5% gaseous phase saturation to mimic marine hydrate sediments, and the gas and water production behavior from horizontal wellbore (HW) was compared with the base case (without well) at 3 bottom hole pressures (BHPs) of 3.5, 4.0, and 4.5 MPa under a constant surrounding temperature of 281.5 K. The evolution of temperature across 12 measured locations within the 1 L sediment demonstrated the significant effect of horizontal wellbore incorporation on heat transfer within sediment. Through the incorporation of horizontal wellbore, a continuous production of gas was observed for an extended period of time as compared to the base cases without a well. The resulting cumulative gas production was enhanced by 5.5–10% at various BHPs; whereas the cumulative water production was significantly reduced by 30.8–36.9% at different BHPs from the base cases. By estimating the percentage of hydrate dissociated, it was found that the incorporation of horizontal wellbore in the current apparatus caused a slower hydrate dissociation, as reflected by a longer time to dissociate 50% ( t 50, h ) and 90% ( t 90, h ) of the hydrates. This study demonstrates the potential of horizontal wellbore incorporation to simultaneously enhance gas production and reduce water production, unveiling a future direction in optimizing gas recovery from hydrate reservoirs through innovative wellbore design, configurations and well placement strategies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Revealed the completion behavior between CO 2 hydrate and ice by experiments carried out at both micrometer-scale and mesoscale. • The morphological characteristics of the co-formation of ice and CO 2 hydrate were observed in-situ in optical cells. • Hydrate forms preferably and replaces ice at small subcoolings; while, at large subcoolings, ice forms first and hydrate emerges subsequently as a fibrous envelope around ice crystals. • Experimental results shed new light on hydrate stability cycle in permafrost caused by temperature fluctuations. As climate change and industrial requirements intensify, the potential of CO 2 hydrates for carbon storage has attracted increasing attention. However, despite continuous progress, the subzero phase behavior of the CO 2 -H 2 O system is not well understood and merits further research. To investigate the competing and coexisting growth mechanisms of CO 2 gas hydrate and ice below the quadruple point, we conducted experiments at both the micrometer-scale and mesoscale scales. The growth morphology of hydrate and ice at large and small subcooling temperatures was observed in situ in a high-pressure optical cell, and the thermodynamic behavior of the competitive process after hydrate formation was investigated in a high-pressure reactor with sands. When hydrates and ice are formed together at small subcooling temperatures, preferential hydrate formation leads to ice dissolution or even disappearance. At large subcooling temperatures, ice forms first, and the hydrate mainly forms a fibrous envelope. A small decrease in the subzero temperature after hydrate formation partially decomposes the hydrates owing to ice formation, followed by more rapid hydrate production. This study provides a thorough and expanded understanding of the competition between ice and hydrates by connecting the evolution of crystal frameworks with the thermodynamic features of the process. [ABSTRACT FROM AUTHOR]

• Effect of hydrate saturation, morphology and particle size on HBS permeability. • Analysis of pore-scale flow behavior at pore throat on HBS permeability. • Abrupt permeability reduction identified at S H = 33.9% for pore-filling HBS. • A new model proposed for HBS permeability calculation considering tortuosity. • HBS permeability comparison between uniform and non-uniform settings. The distribution pattern of CH 4 hydrate in hydrate-bearing sediments (HBS) significantly impacts the permeability, which is one of the critical flow properties controlling the fluid production in the exploitation of natural gas hydrate (NGH) reservoirs. Thus, it warrants investigation on the key influencing factors, i.e., (a) hydrate saturation; (b) hydrate distribution patterns; (c) sediment particle size on the associated permeability of HBS especially at pore-scale. In this study, a series of two-dimensional geometric models were constructed that best represent the commonly-observed hydrate distribution patterns. The pore-scale flow behavior of the resulting models was simulated through computational fluid dynamics. The simulation results suggest that the reduction of permeability is dependent on the distribution pattern of hydrate. The permeability of grain-coating HBS decreases by a maximum of five orders of magnitude at S H = 0.3. Additionally, increasing S H results in new pore throats and induces clogging in fluid flow that controls permeability reduction. A strong log-log linear relationship was identified between sediment particle size and the simulated permeability. A modified empirical model for the estimation of HBS permeability was proposed considering both tortuosity and effective porosity. Moreover, a heterogeneous sediment particle distribution model was constructed for the first time that accurately described the particle size distribution of a hydrate-bearing core sample recovered from Japan Nankai Trough. Compared to the homogeneous model, a heterogeneous model results in a more substantial reduction of permeability with S H and better represents the permeability of the HBS core sample. The finding of this study can be significant in understanding the pore-scale flow behavior in HBS and are meaningful for the design of safe and effective production methods in the exploitation of NGH reservoirs. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A comparison of the promoting effect of SDS and L -Met on CO 2 hydrate formation. • Morphology of CO 2 hydrate in the presence of SDS and L -Met with stirring. • A calculation method quantifying CO 2 distribution in gas, liquid and hydrate phase. • Verification of L -Met promoting effect in repeated tests and at various G-L ratios. The continuously increasing CO 2 emissions since industrialization has sparked widespread concerns on environmental and climate change issues. Carbon sequestration and storage technologies (e.g., hydrate-based CO 2 sequestration) present promising potential for the disposing of excessive CO 2 in geological media. High gas uptake capacity and rapid CO 2 hydrate formation kinetics are required for the application of such a technology. In this study, we compared the kinetic promotion effects of sodium dodecyl sulfate (SDS) and L -methionine (L -Met) on CO 2 hydrate with the objective of identification of an effective and eco-friendly CO 2 hydrate kinetic promoter. The experimental results suggested that L -Met (0.1 wt%) promotes CO 2 hydrates formation significantly with a gas uptake in CO 2 hydrate five times more than SDS at the same concentration. The hydrate morphology observations indicated that the wall-climbing hydrates associated with the addition of L -Met induced by the capillary driving force offer a possible explanation for the difference in the observed kinetics. A novel calculation method was developed to quantify the partition of CO 2 in gas, liquid and hydrate phases. Increasing the initial gas–liquid ratio promotes CO 2 stored in the hydrate phase as solid rather than in the liquid phase as dissolution. We further demonstrated the reusability of L -Met in five consecutive cycles of CO 2 hydrate formation and dissociation. It was assessed that L -Met as a CO 2 hydrate kinetic promoter is superior to SDS and can be employed as an efficient, reliable and eco-friendly kinetic promoter for the hydrate-based CO 2 sequestration technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Shorter nucleation time but slower growth kinetics observed for MH in clay suspension. • Clay-bound water induced by diffuse double layer results in slow MH formation kinetics. • Migration of water and the agglomeration of clay resulted in gas hydrate-clay stratification. • Implications for hydrate occurrence and energy recovery in clay-rich geological sediments. Silty-clayey host sediments have been widely identified in naturally-occurring hydrate-bearing sediments in the South China Sea. However, the effect of clay minerals on the kinetics of CH 4 hydrate (MH) formation and dissociation remains unknown and warrants further investigation. The objective of this paper is to elucidate the effect of montmorillonite (MMT) clay particles on the formation and dissociation kinetics of MH. A series of experiments involving kinetics and morphological observations were designed to investigate the kinetics of MH in MMT suspensions with mass fractions ranging from 0.1 wt% to 9.0 wt%. The experimental results reveal that MMT promotes nucleation but delays the growth kinetics of MH. The diffuse double layer (DDL) on clay minerals is quantified to explain the observed kinetic behavior. The electric field induced on the clay surface resulted in a shorter induction time. The morphology observed indicated that MH initially forms at the gas–liquid interface and develops upward along the reactor surface, resulting in the hydrate-clay stratification behavior. The upward migration of water due to hydrate growth promotes the agglomeration of MMT clay and reduces the conversion of free water to hydrate. The findings of this study are essential in understanding the mechanisms of the naturally occurring negatively-charged clay particles on the kinetics of MH. Moreover, the results have implications for the occurrence of MH in clay-rich sediments in nature and the development of energy-efficient recovery strategies from silty-clayey hydrate-bearing sediments. [ABSTRACT FROM AUTHOR]