Hydrate Grains Research Articles

Simultaneous inversion of four physical parameters of hydrate reservoir for high accuracy porosity estimation

AbstractEstimation of the porosity of a hydrate reservoir is essential for its exploration and development. However, the estimation accuracy was usually less certain in most previous studies that simply assumed that there is a linear relationship between the porosity and single‐elastic wave velocities or other rock physical parameters, thus affecting the evaluation of the reserves. In the three‐phase Biot‐type equations that are fundamental to model a hydrate‐bearing reservoir, porosity, alongside hydrate saturation, mineral constituent proportions and hydrate–grain contact factor, is non‐linearly responded by density, compressional and shear wave velocities. To improve porosity estimation, we propose to invert simultaneously four‐parameter (porosity, hydrate saturation, mineral constituent proportions and hydrate–grain contact factor) using an iteratively nonlinear interior‐point optimization algorithm to solve a nonlinear objective function that is a summation of the squared misfits between the well log and three‐phase Biot‐type equation–modelled density, compressional and shear wave velocities. A test in Mount Elbert gas hydrate research well was conducted for the case of a gas hydrate stratigraphic test well where elastic wave velocities, density, porosity and mineral composition analysis data are available. The four‐parameter inversion yielded a lower root mean square error for porosity (0.0245) across the entire well‐logging section compared to previous estimations from the linear relationship, post‐stacked and pre‐stacked seismic traces as well as the pore‐filling effective medium theory model applied to other well cases. Additionally, the other three parameters demonstrated good agreement with well logs. Inversion tests conducted at three additional hydrate sites also produced accurate results. Consequently, the new method surpasses previous approaches in porosity estimation accuracy.

HTR+: a novel algorithm for identifying type and polycrystal of gas hydrates

In this work, the hierarchical topology ring (HTR+) algorithm, an extension of the HTR algorithm, was developed for identifying gas hydrate types, cage structures, and grain boundaries (GBs) within polycrystalline structures. Utilizing molecular dynamics trajectories of polycrystalline hydrates, the accuracy of the HTR+ algorithm is validated in identifying sI, sII and sH hydrate types, hydrate grains, and GBs in multi-hydrate polycrystals, as well as clathrate cages at GBs. Additionally, during the hydrate nucleation and growth processes, clathrate cages, hydrate type, hydrate grains and ice structures are accurately recognized. Significantly, this algorithm demonstrates high efficiency, particularly for large hydrate systems. HTR+ algorithm emerges a powerful tool for identifying micro/mesoscopic structures of gas hydrates, enabling an in-depth understanding of the formation mechanisms and properties of gas hydrates.

Greenhouse gas (GHG) transport as solid natural gas (SNG) hydrate Pellets: Assessment of Self-Preservation & dissociation controls

Safe greenhouse gas (GHG) transport is an integral part of any carbon capture, utilization, and storage (CCUS) operations. This manuscript discusses the assessment of solid natural gas (SNG) hydrate technology to safely transport GHG utilizing the self-preservation capability of hydrates around 248 K. Ice shielding around hydrate grains has been previously implicated as a key mechanism for self-preservation of hydrates. However, there is a lack of thorough understanding of the hydrate grains sintering and compaction effects on self-preservation prior to the ice crust formation around the grains. In a first of its kind study, the promotional effects of hydrate grains compaction and sintering via pellet porosities, aging times, and formation times on self-preservation are presented. Furthermore, real time operational variables such as depressurization rates and system pressure build-up are studied. A unique integrated apparatus was designed to assess in-situ hydrate pellets formation, compaction, and dissociation. This method eliminated the uncertainties of possible hydrate dissociation during material transfer between the operational stages. Around 248 K, hydrate pellet stability occurs in two states: pre-self-preservation (initial fast hydrate dissociation) and extended self-preservation (slow hydrate dissociation over 200 + hours). Decreasing porosity via compaction and increasing formation and pellet-aging times via prolonged sintering increases hydrate pellet stability. The pellet stability can be further promoted by slowly depressurizing the pellet to ambient pressure and allowing pressure build-up from the dissociating hydrates. Additional transport risks are assessed through a sudden loss of temperature from 248 K, which are missing in the literature. Refrigeration failure of the pellet progresses in two stages: (1) a safe insulation stage characterized by slow dissociation and minimal gas evolution, followed by (2) a rapid dissociation stage during which complete dissociation of the pellet took place. Overall, this work elucidates the transportation factors governing self-preservation and dissociation, thus indicating the feasibility for safe GHG transport via SNG technology.

A hypoplastic model for hydrate‐bearing sand considering hydrate saturation and grain breakage

AbstractWe present a hypoplastic model to capture the mechanical responses of hydrate‐bearing sands by incorporating hydrate saturation and grain breakage. In our model, a new degradation scalar is introduced to account for the effects of hydrate bonding evolution on strength. We also adopt the variable critical state line to assess the effects of hydrate saturation and relative breakage ratio at high confining pressure. This model is validated by modeling a series of laboratory tests.

Coupled thermo-hydro-mechanical-chemical modeling of fines migration in hydrate-bearing sediments with CFD-DEM

Fines migration associated with the multiphase flow in the exploitation of hydrate-bearing sediments (HBS) usually induces local clogging and sand production around wells, and thus its behavior with multi-field coupling is of vital importance but still poorly discovered. This paper establishes a coupled thermo-hydro-mechanical-chemical (THMC) model incorporating fines migration in HBS from micro- to macro-scale. Two typical hydrate pore habits, i.e., grain coating and pore filling, are simulated with the discrete element method (DEM) under different depressurization modes, water flow is simulated using computational fluid dynamics (CFD), and heat transfer and chemical reactions are also considered in coupled CFD-DEM simulations. Two distinct fines migration modes and their consequence on the mechanical and hydromechanical properties are revealed. For the grain-coating habit, the coarse particle size reduction induced by hydrate dissociation under an intense depressurization decreases the constriction size, increasing the local pore-clogging probability and reducing the growth rate of the hydraulic conductivity. Conversely, the fine particle size reduction in the pore-filling habit facilitates fines migration and thus sand production, with hydromechanical properties of HBS evolving oppositely compared to the clogging case.

Insights into the thermal effect on the fracture toughness of calcium silicate hydrate grains: A reactive molecular dynamics study

Cement-based materials behave with brittle properties at the macro scale. By contrast, at the nanoscale, its main phase, the calcium silicate hydrate (C–S–H) grain, shows better ductility. However, the nature of the relationship between the fracture properties and the heating temperature remains elusive. To this end, reactive molecular dynamics simulations on the pre-cracked C–S–H grain with various Ca/Si (C/S) molar ratios (1.10–1.80) are carried out to study the thermal effect on the fracture property. For the first time, we report that heating can enhance the C–S–H grains' fracture toughness and the energy release rate. According to simulation results, we further discuss the evolution of the brittleness of C–S–H grains with temperature. Interestingly, it can be found that heating can make improvements in the brittleness of the C–S–H grain. Nevertheless, the degree of improvement heavily depends on the chemical compositions, wherein a lower C/S ratio can lead to a more thermally stable structure and a higher yielding strength and in turn, a slighter change in the dissipated energy at higher temperature levels. Moreover, we report that heating can induce crack blunting which can enhance the plastic deformation and the dissipated energy and improve ductility. Meanwhile, crack blunting can occur at a lower temperature level for a higher C/S ratio. These new insights into C–S–H grains’ fracture behavior can help formulate multiscale models of designing higher fire-resistant cementitious composites.

Insights into the effect of high temperature on the shear behavior of the calcium silicate hydrate by reactive molecular dynamics simulations

When subjected to fires, cementitious composites can be seriously damaged. However, the mechanical behavior of nanoscale calcium silicate hydrate (C–S–H) grains, which are the main binder of cementitious composites, exposed to elevated temperatures under shear deformations remain poorly investigated. In this paper, considering different calcium/silicate (C/S) molar ratios (i.e., C/S = 1.10, 1.33, and 1.64), the shear behavior of the C–S–H grain after exposure to different high-temperature levels (i.e., 300 K, 500 K, 700 K, 900 K, and 1000 K) is studied by conducting series of reactive molecular dynamics simulations. Results reveal that the C–S–H grain exhibits good plasticity under shear deformation. Furthermore, the shear modulus of the C–S–H grain is between 14 GPa and 17 GPa and exhibits a decrease with the calcium/silicon (C/S) molar ratio at ambient temperature. While the shear strength is around 1.0 GPa and reaches the lowest value at C/S = 1.64. Interestingly, we report that heating can lead to the increase of the shear modulus and shear strength due to the evaporation of the interlayer water which generally acts as the lubricant. Additionally, we show that heating has no clear influence on the shear strain corresponding to the onset of yielding when the C/S ratio is high but can indeed improve the shear strain corresponding to the shear strength. Furthermore, the yielding area of the C–S–H grain under the shear deformation can be enlarged. Finally, factors affecting the strength degradation of cementitious composites after being heated to different temperature levels are further discussed based on the simulation results.

Sustainable hydrate production using intermittent depressurization in hydrate-bearing reservoirs connected with water layers

The intermittent depressurization may sustain hydrate production. But its production features and influencing factors in the real setting have not been clear. Thus, the intermittent depressurization with the participation of the water layers was performed in the laboratory samples. The hydrate production features were studied from pressure changes, temperature changes, gas and water production, multi-phase flow, and residual hydrates. On the other hand, the influencing factors were analyzed from the back pressure, the recovered pressure, and the retarded temperature recovery. The results showed that gas and water production was increased by 44.05 % and 97.14 %, respectively. The abnormal depressurization, the fresh hydrate formation, and the retarded temperature recovery were observed. Moreover, hydrate dissociation and gas flow were weakened by the thickened water films around hydrate grains and the quick depressurization along with the preferential flow channels. Hence, residual hydrates accounting for 49.15 % were still found after the intermittent depressurization. Besides, the back pressure of 2.6 MPa increased gas production by 22.915 L; the recovered pressure of 3.92 MPa reduced water production by 47.85 %; the wait for temperature recovery increased hydrate dissociation rate of 15.29 %. This work may benefit the achievement of the sustainable hydrate production in actual hydrate reservoirs.

Deconstructing water sorption isotherms in cement pastes by lattice density functional theory simulations

AbstractThe moisture content in cement pastes influences their mechanical properties and durability. However, the complex, multiscale nature of cement pastes makes it challenging to isolate the contributions of each scale to their macroscopic water sorption isotherms. In particular, the contribution of the calcium–silicate–hydrate gel (the binding phase of cement pastes) remains only partially understood. Here, we introduce a density functional theory lattice model describing water sorption in calcium–silicate–hydrate, which properly reproduces experimental water sorption isotherms in cement pastes. Based on this model, we deconstruct the contribution of each pore scale (interlayer spacing, gel pores, and capillary pores) to the total sorption isotherm. We show that, when the relative humidity is below 80%, the calcium–silicate–hydrate gel accounts for more than 90% of the moisture content adsorbed in cement pastes. In turn, we find that the contribution of the interlayer space within the calcium–silicate–hydrate grains is governed by the competition between the rate of interlayer space opening and the increasing propensity for water to fill larger pores upon increasing relative humidity. Overall, our results highlight the key role played by the calcium–silicate–hydrate in governing the sorption isotherms of cement pastes.

Effects of high temperature on the mechanical behavior of calcium silicate hydrate under uniaxial tension and compression

When subjected to high temperatures, cement-based materials can dehydrate, which, in turn, affects the mechanical property of the main binding phase (calcium silicate hydrate) at the atomic scale. However, the effects of high temperature on the tensile and compressive behavior of calcium silicate hydrate (C−S−H) grains under uniaxial loading remains poorly understood. In this work, based on reactive molecular simulations, the tensile strength, compressive strength, and stress-strain relations of C−S−H grains with four calcium/silicon (C/S) ratios (1.10, 1.33, 164, and 1.80) both under and after (residual properties) high temperatures are investigated. It is shown that C−S−H grains can shrink due to the water loss induced by high temperature, and a low C/S ratio can lead to a thermo-stable molecular structure. Meanwhile, the residual tensile strength can be enhanced, particularly the tensile strength in the z-direction. Upon the residual compressive strength, in the x and y directions, high temperature can decrease the residual compressive strength for C/S = 1.10 or 1.33 but has no apparent effect for C/S = 1.64 or 1.80. While in the z-direction, the residual compressive strength can be enhanced due to the reduction in the interlayer space. In addition, high temperature can improve the residual tensile ductility but has no obvious effect on the residual compressive stress-strain relations. As for the mechanical properties under high temperature, both the tensile and compressive strengths can be weakened except that the tensile strength in the z-direction can undergo an increasing trend when the temperature is below 800 K due to significant shrinkage in the z-direction. Moreover, high temperature can make stress-strain curves exhibit good plasticity. Discussion indicates that the strength degradation of C−S−H gels or cement paste exposure to high temperatures is likely caused by the increasing porosity and coarsening of the void or defect size.

Development, test, and evaluation of exploitation technologies for the application of gas production from natural gas hydrate reservoirs and their potential application in the Danube Delta, Black Sea

One important scientific objective of the national research project SUGAR – Submarine Gas Hydrate Reservoirs was the development, improvement, and test of innovative concepts for the production of methane from natural gas hydrate reservoirs. Therefore, different production methods, such as the thermal stimulation using in situ combustion, the chemical stimulation via injection of CO2 as a gaseous, liquid or supercritical phase and depressurization were tested alone or in combination at different scales. In the laboratory experiments these ranged from pore and hydrate grain scale to 425-L reactor volume, whereas numerical models were applied to describe the related processes from molecular to reservoir scale. In addition, the numerical simulations also evaluated the feasibility and efficiency of the application of these methods in selected areas, such as the Danube Paleodelta in the Black Sea, addressing the two dominant methane hydrate reservoir settings, buried channel-levee and turbidite systems. It turned out, that the injection of CO2 or a CO2–N2 gas mixture is not applicable for the Danube Paleodelta in the Black Sea, because the local pressure and temperature conditions are too close to the equilibrium conditions of both, the CO2 hydrate and a CO2–N2 mixed hydrate stability fields. Experiments using thermal stimulation and depressurization showed promising results but also some issues, such as sufficient heat transfer. In summary it can be said that the applicability and efficiency of each method has to be proven for each specific hydrate reservoir conditions. Based on the results obtained by numerical simulations the most promising and safe method for the production of CH4 from hydrate bearing sediments in the Danube Paleodelta would be the depressurization technique. This study summarizes the main experimental and modeling results.

S-wave attenuation estimation from walkaway vertical seismic profiling data in methane hydrate-bearing sediments at Nankai Trough, Japan

Previous studies have demonstrated that the presence of methane hydrates (MHs) causes high S-wave attenuation (1/Q) at sonic logging frequencies. However, there are extremely few examples with which to estimate S-wave attenuation at seismic frequencies for MH reservoirs because of the low signal-to-noise ratio (SNR) of S-wave events. To elucidate the mechanisms responsible for such attenuation, it is important to obtain S-wave attenuation at various frequencies. We improve the SNR by horizontally stacking traces after linear moveout with fine-tuning over the offset range. Then we select better-quality S-wave events observed in methane hydrate-bearing sediment (MHBS). The better quality is possibly due to better coupling between the geophones and MHBS. Finally, we estimate S-wave intrinsic attenuation at a frequency range from 30 to 100 Hz from walkaway vertical seismic profiling (w-VSP) data. To isolate intrinsic attenuation from total attenuation, scattering attenuation is estimated using one-dimensional synthetic data from sonic velocity and density logs. The estimated intrinsic attenuation ranges from 0.34 to 0.39. By comparing our results with previously published results on S-wave attenuation at sonic frequencies of 0.5–1 kHz, we attribute a possible S-wave attenuation mechanism to the viscous friction due to the elastic contrast between hydrate and sand grains.

Laboratory Insights Into the Effect of Sediment‐Hosted Methane Hydrate Morphology on Elastic Wave Velocity From Time‐Lapse 4‐D Synchrotron X‐Ray Computed Tomography

AbstractA better understanding of the effect of methane hydrate morphology and saturation on elastic wave velocity of hydrate‐bearing sediments is needed for improved seafloor hydrate resource and geohazard assessment. We conducted X‐ray synchrotron time‐lapse 4‐D imaging of methane hydrate evolution in Leighton Buzzard sand and compared the results to analogous hydrate formation and dissociation experiments in Berea sandstone, on which we measured ultrasonic P and S wave velocities and electrical resistivity. The imaging experiment showed that initially hydrate envelops gas bubbles and methane escapes from these bubbles via rupture of hydrate shells, leading to smaller bubbles. This process leads to a transition from pore‐floating to pore‐bridging hydrate morphology. Finally, pore‐bridging hydrate coalesces with that from adjacent pores creating an interpore hydrate framework that interlocks the sand grains. We also observed isolated pockets of gas within hydrate. We observed distinct changes in gradient of P and S wave velocities increase with hydrate saturation. Informed by a theoretical model of idealized hydrate morphology and its influence on elastic wave velocity, we were able to link velocity changes to hydrate morphology progression from initial pore‐floating, then pore‐bridging, to an interpore hydrate framework. The latter observation is the first evidence of this type of hydrate morphology and its measurable effect on velocity. We found anomalously low S wave velocity compared to the effective medium model, probably caused by the presence of a water film between hydrate and mineral grains.

Experimental Study of Mixed Gas Hydrates from Gas Feed Containing CH4, CO2 and N2: Phase Equilibrium in the Presence of Excess Water and Gas Exchange

This article presents gas hydrate experimental measurements for mixtures containing methane (CH4), carbon dioxide (CO2) and nitrogen (N2) with the aim to better understand the impact of water (H2O) on the phase equilibrium. Some of these phase equilibrium experiments were carried out with a very high water-to-gas ratio that shifts the gas hydrate dissociation points to higher pressures. This is due to the significantly different solubilities of the different guest molecules in liquid H2O. A second experiment focused on CH4-CO2 exchange between the hydrate and the vapor phases at moderate pressures. The results show a high retention of CO2 in the gas hydrate phase with small pressure variations within the first hours. However, for our system containing 10.2 g of H2O full conversion of the CH4 hydrate grains to CO2 hydrate is estimated to require 40 days. This delay is attributed to the shrinking core effect, where initially an outer layer of CO2-rich hydrate is formed that effectively slows down the further gas exchange between the vapor phase and the inner core of the CH4-rich hydrate grain.

Compressibility and particle crushing of Krishna-Godavari Basin sediments from offshore India: Implications for gas production from deep-water gas hydrate deposits

Abstract Depressurizing a gas hydrate reservoir to extract methane induces high effective stresses that act to compress the reservoir. Predicting whether a gas hydrate reservoir is viable as an energy resource requires enhanced understanding of the reservoir's compressibility and susceptibility to particle crushing in response to elevated effective stress because of their impact on the long-term permeability and geomechanical stability of the reservoir. This study investigates physical and geomechanical properties of natural sediments with and without tetrahydrofuran (THF) hydrate subjected to high effective stresses of up to 25 MPa. Experimental results show the stiffness of hydrate-free sediments is mainly governed by the stress state and history, while the stiffness of hydrate-bearing sediments reflects both the grain supporting nature of the interconnected hydrate phase and stress effects. The Poisson's ratio of hydrate-bearing sediments at low stresses is dominated by the Poisson's ratio of the interconnected pore-filling phases, and dominated at high stresses by elastic properties of both the skeleton and pore-filling phases. The stress-void ratio responses of hydrate-bearing sediments above the pre-consolidation stress yields a slightly convex-downward trend, suggesting compressibility is influenced by the stiffness of THF hydrate and sediment grains rather than only by void space reduction. The shape of the compression index (Cc) trend may be attributed to an increasing effective gas hydrate saturation as the total pore volume decreases under loading. The results also show that the presence of THF hydrate in sediments can mitigate particle crushing by suppressing particle rearrangement and supporting a portion of the load that would otherwise have to be carried by the sediment. Therefore, the loss of hydrate crystals during gas production may exacerbate sand crushing.

PCATS triaxial testing: Geomechanical properties of sediments from pressure cores recovered from the Bay of Bengal during expedition NGHP-02

Abstract The Indian National Gas Hydrate Program Expedition 02 (NGHP-02) was the most comprehensive gas hydrate drilling expedition carried out to date. From 74 pressure cores that were successfully recovered from various site locations offshore India, 19 subsamples were obtained for further detailed geotechnical analysis using the PCATS Triaxial apparatus to investigate the geomechanical behaviour of the cores, including small-strain stiffness, Gmax, undrained shear strength, Su, as well as direct-flow measurements of permeability, k. Samples tested included fine-grained muds with no appreciable hydrate through to coarse-grained sands that contained extensive hydrate within the pore space. Although the subsampling and transfer of pressure cores into the PCATS Triaxial under zero effective confining stress, σ′, remains challenging, 12 samples were successfully transferred and underwent detailed geotechnical characterization. During consolidation, after reapplication of in-situ σ′, all samples experienced axial and radial consolidation, with variations between samples seemingly dependent on the degree of sample disturbance, stress relaxation between coring and testing, hydrate saturation, Sh and grain size, D50. The largest values of Gmax were obtained from samples with high Sh in the pore space, with values much higher than that expected for similar sediments without hydrate under comparable σ’. Samples with high permeability had both high Sh and larger grain size, suggesting that in coarse-grained sediments sufficient pathways are available for reasonable fluid flow even with high hydrate saturations. Triaxial testing and unconfined compression tests highlighted the influence of hydrate on increasing sediment strength, although the size of the sediment grains appeared to have an important control on the magnitude of the strength increase and the overall stress-strain behaviour. The results from the detailed geotechnical characterization of the recovered pressure cores will be invaluable in helping India identify potential locations for future gas production wells, and assess the long-term performance of such reservoirs.

Ultrasonic attenuation of pure tetrahydrofuran hydrate

ABSTRACTImproved estimates of the amount of subsurface gas hydrates are needed for natural resource, geohazard, and climate impact assessments. To evaluate gas hydrate saturation from seismic methods, the properties of pure gas hydrates need to be known. Whereas the properties of sediments, specifically sands, and hydrate‐bearing sediments are well studied, the properties of pure hydrates are largely unknown. Hence, we present laboratory ultrasonic P‐wave velocity and attenuation measurements on pure tetrahydrofuran hydrates as they form with reducing temperatures from 25°C to 1°C under atmospheric pressure conditions. Tetrahydrofuran hydrates, with structure II symmetry, are considered as proxies for the structure I methane hydrates because both have similar effects on elastic properties of hydrate‐bearing sediments. We find that although velocity increased, the waveform frequency content and amplitude decreased after the hydrate formation reaction was complete, indicating an increase in P‐wave attenuation after hydrate formation. When the tetrahydrofuran hydrate was cooled below the freezing point of water, velocity and quality factor increased. Nuclear Magnetic Resonance results indicate the presence of water in the “pure hydrate” samples above the water freezing point, but none below. The presence of liquid water between hydrate grains most likely causes heightened attenuation in tetrahydrofuran hydrates above the freezing point of water. In naturally occurring hydrates, a similarly high attenuation might relate to the presence of water.

Direct numerical simulation of the thermal dehydration reaction in a TGA experiment

This work presents a detailed mathematical model of the coupled mass and heat transfer processes in salt hydrate grains in a TGA experiment. The purpose of developing this numerical model is to get a more fundamental understanding of the influence of parameters like particle size, nucleation rate and vapor pressure on the dehydration reaction in a TGA experiment. Such a model needs a detailed description of the fluid flow and water vapor distribution between the particles. The dehydration reaction of grains of TCMs is described by the nucleation and nuclei growth model presented in our earlier work. The flow around grains is solved by means of the finite volume method using OpenFOAM including heat and mass transfer. Direct numerical simulations of TGA-experiments under various conditions are performed. Such simulations provide direct insight into the physics of mass and heat transport processes coupled with detailed reaction kinetics at grain scale. The numerical results are compared to the experimental results. The developed CFD model can be a promising tool to calculate the overall kinetics for dehydration reactions under realistic heat storage conditions. To that end, the effect of buoyancy should also be included in the model to get a more accurate description of convection within the sample.

Improvement of gas hydrate preservation by increasing compression pressure to simple hydrates of methane, ethane, and propane

In this report, we describe the dissociation behavior of gas hydrate grains pressed at 1 and 6 MPa. Certain simple gas hydrates in powder form show anomalous preservation phenomenon under their thermodynamic unstable condition. Investigation of simple hydrates of methane, ethane, and propane reveals that high pressure applied to the gas hydrate particles enhances their preservation effects. Application of high pressure increases the dissociation temperature of methane hydrate and has a restrictive effect against the dissociation of ethane and propane hydrate grains. These improvements of gas hydrate preservation by increasing pressure to the initial gas hydrate particles imply that appropriate pressure applied to gas hydrate particles enhances gas hydrate preservation effects.

Concrete creep mechanism explained

Concrete is ubiquitous as a building material, but it suffers from “creep,” long-term deformations caused by its own weight, that damage its integrity and make it susceptible to cracking and crumbling. Now, scientists have evidence this creeping phenomenon stems from nanoscale dissolving of concrete’s primary phase, calcium silicate hydrate (CSH) grains, under high stress (J. Chem. Phys. 2016, DOI: 10.1063/1.4955429). The discovery, by a team led by Gaurav Sant, Mathieu Bauchy, and Isabella Pignatelli at UCLA, could allow further study to devise concrete compositions that are more resistant to creep. Concrete—various mixtures of sand or gravel with a binder and water—has been used as a building material for thousands of years, and today, next to water, it’s the most widely used material in the world. Scientists have proposed models for concrete creep mechanisms, but none have been able to explain all of the physical manifestations of creep. In the new