Swelling Of Bentonite Research Articles

Can we generate stable pickering emulsions activating naturally occurring nanoparticles in the reservoir for cost effective heavy-oil recovery?

Activating naturally occurring nanoparticles in the reservoir (clays) to generate Pickering emulsions results in low-cost heavy oil recovery. In this study, we tested the stability of emulsions generated using different types of clays and performed a parametric analysis on salinity, pH, water to oil ratio (WOR), and particle concentration; additionally, we report on a formulation of injected water used to activate the clays found in sandstones to improve oil recovery.First, oil-in-water (O/W) emulsions generated by bentonite and kaolinite clays were prepared for bottle tests and zeta potentials of clay suspensions were measured, then the stability of dispersion was measured under various conditions (pH, salinity and WOR). Heavy crude oils (15,640 cP) were used for all experiments. Second, sandpacks with different clay compositions were saturated with heavy-oil samples. Aqueous solutions with various salinity and pH were injected into the oil-saturated sandpacks with a pump. The recoveries were monitored while analyzing the produced samples. Third, glass bead micromodels with known amounts of clays were also prepared to visualize the in-situ behavior of clay particles under various salinity conditions. The transparent mineral oil instead of opaque heavy oil was used in these micromodel tests for better visualization results.The bottle tests showed that 3% bentonite stabilized O/W emulsions under a high WOR (9:1) condition. The addition of 0.04% of NaOH further improved the emulsion stability which was attributed to the reduction of interfacial tension (0.17 mN/M) between the oil and alkali solution. The sandpack flood experiments showed an improved sweep efficiency caused by the swelling of bentonite when injecting low salinity fluid (e.g., DIW). The micromodel tests indicated a wettability change to be more oil-wet under high salinity conditions, and the swelling of bentonite would divert incoming water flow to other unswept areas thus improving sweep efficiency.This paper presents new ideas and recommendations for further research as well as practical applications to generate stable emulsions for improved waterflooding as a cost-effective approach.

Hydro-chemo-mechanical modelling of long-term evolution of bentonite swelling

The swelling properties of compacted bentonite have typically been studied by means of hydro-mechanical models. The question of how these properties are affected by changes in its chemical composition has been given much less attention. However, cation exchange reactions in montmorillonite interlayer or changes in salinity are known to affect the swelling properties of bentonite. In this paper, a hydro-chemo-mechanical (HCM) model is proposed to study the effects of reactive transport processes on the long-term evolution of swelling pressure of compacted bentonite under confined and partially saturated conditions. The HCM model is implemented in iCP, an interface between Comsol Multiphysics and PHREEQC and is calibrated using available experimental data. At the constitutive level, the hydro-mechanical Barcelona Basic model is extended to include the effects of cation exchange reactions between interlayer and bulk water, changes in salinity, and montmorillonite dissolution in highly alkaline environments. The geochemistry of bentonite is based on an advanced reactive transport model that couples solute transport by diffusion and advection with chemical reactions. An application case is presented to demonstrate the main HCM model features and its ability to predict long-term changes in bentonite swelling pressure. The performance of the sealing system for closure of the repository for radioactive waste in France is simulated under unsaturated and isothermal conditions over a period of 50,000 years. The HCM interactions of MX-80 bentonite with other near-field materials such as concrete and claystone are simulated to predict the evolution of the swelling pressure of the seal. The results show the potential of the proposed model for the performance assessment of repository components. Overall, the model predicts limited impact of geochemical alteration on the swelling pressure of the bentonite seals, which is mainly driven by cation exchange reactions between the Na-rich bentonite, the Ca-rich claystone, and the calcium and alkalis from concrete porewater.

Preparation and performance of ammonium-malic salts as shale swelling inhibitor and a mechanism study

A series of ammonium-malic salts (AMS) was prepared with malic acid and amines as small molecular shale swelling inhibitor. The inhibitors were screened by the linear expansion test of bentonite firstly, and the result shows that the inhibitor prepared by malic acid and tetraethylenepentamine with the mole ratio of 1:3 (AMS-9) displays excellent inhibition on the hydration expansion of bentonite. The results show that AMS-9 has superior performance to inhibit the hydration swelling and dispersion of bentonite, and the swelling rate of 0.5% AMS-9 reaches down to 57.14%. Then the efficiency AMS-9 in water based drilling fluid was investigated, which shows AMS-9 is compatible with the conventional additive, modified starch and PAM. Besides the inhibition mechanism of the AMS was discussed using FT-IR and cation exchange. The inhibition mechanism of AMS-9 to bentonite should be due to the ion exchange of ammonium and the Ca2+, hydrogen bonding and surface modification.

Material composition and characteristics of bentonite clays used as a binder in the production of iron ore pellets

In the production of iron ore pellets, binding additives are used, in particular, bentonite clays. At present, instead of alkaline bentonite clays used before, the alkaline-earth bentonite clays modified by soda ash are used, supplied from abroad. There is a whole number of bentonite clays deposits in Russia and Ukraine having reserves of the raw material accounting hundreds of million tons, which are not used in the industry because of absence of planned and proper studies of their applicability for pellets production. The analysis of chemical composition carried out and requirements to rheological characteristics of bentonite clays used in the iron ore pellets production at steel-works of Russia and Ukraine determined. Indicators of swelling and water absorption of mono-ionic forms of bentonite of some deposits in water of various hardness presented. Quality of pellets with bentonites, having different exchange complex when using technical water of various hardness considered. Analysis of mineralogical and chemical compositions, as well as value and content of exchange complex of alkaline-earth bentonite clays of Cherkassk deposition, Ukraine, accomplished. The deposition has the largest reserves of such clays in CIS. It was shown, that clays suitable for pellets production, are located near the earth surface. Comparative analysis of strength indicators of pellets, produced with bentonite application with alkaline and alkaline-earth complexes, carried out. It was shown, that despite the low swelling of alkaline-earth bentonites, the quality of pellets, produced with those bentonites is sometimes a little lower, but under definite conditions does not yield to the quality of pellets with alkaline bentonites at the same their consumption.

Sensitivity of bentonite swelling to pore water activity

The deformability of bentonites is strongly conditioned by their salinity conditions. Consequently, the chemomechanical coupling must be taken into account to characterise correctly the deformational behaviour of these materials. Some models have been developed that account for this coupling. These models, which usually assume a double-porosity approach to characterise the structure of compacted bentonite, idealise the geochemical system, commonly using a simplified definition of the activity of the species dissolved in the aqueous solutions present in the bentonite pores. In this paper, the significance of the formulation used to calculate the activities is analysed. As a sensitivity exercise, the extended Debye–Hückel model is applied to estimate the activity coefficients of the species in the macrostructure. The exercise is conducted by simulating vertical free-swelling tests under different salinity conditions. It is shown that when the salinity conditions are not negligible, the results are improved using this illustrative model compared with the case in which the activity of the species was assumed equal to their concentration. Although the formulation of the activity coefficients could be improved for higher-salinity conditions, this study highlights the sensitivity of the bentonite mechanical behaviour to the activity definition.

The potential of using of alkaline earth bentonite clays of Ukraine in the production of iron ore pellets

Objective: to analyze and determine the potential of alkaline earth bentonite clays of Ukraine for use as a binder in the production of iron ore pellets. Methods: performing rheological studies of bentonite clay samples and their chemical analysis, electron microscopic studies of samples. Results: the analysis of the chemical composition and requirements for the rheological characteristics of bentonite clays used in the production of iron ore pellets at metallurgical enterprises of Russia and Ukraine is carried out. The swelling indicators and water absorption of monoionic forms of bentonites of some deposits in water of different hardness are given. The quality of pellets with bentonites, that have a different exchange complex, during an industrial water of various hardness usage is examined. The analysis of the mineralogical and chemical composition, as well as the size and composition of the exchange complex of alkaline-earth bentonite clays of the Cherkassk deposit (Ukraine), which has the largest reserves of such clays in the CIS is carried out. It is shown that clays suitable for the production of pellets are located near the surface of the earth. A comparative analysis of the strength characteristics of pellets using bentonites with an alkaline and alkaline-earth exchange complex is presented. Scientific novelty: it was shown that despite the low swelling of alkaline-earth bentonites, the quality of pellets with these bentonites, in some cases, is slightly lower, and in certain conditions is not inferior to the quality of pellets with alkaline bentonites at the same flow rate. Practical significance: for real industrial conditions it is shown that the increase in water hardness leads to partial or complete (depending on the value of hardness) replacement of alkaline exchange complex with alkaline earth and conversion of alkaline bentonite clay into alkaline earth with corresponding rheological characteristics, deterioration of lumps and the need to increase the content of bentonite in the charge. In the case of increased hardness of water in the concentrate, it is economically feasible to use in the production of alkaline earth pellets bentonite clay, if it is cheaper than alkaline.

State of compacted bentonite inside a fractured granite cylinder after infiltration

A small-scale mock-up test was carried out on a fractured hollow granite cylinder with compacted MX80 bentonite inside, to study the interaction between engineered barrier (compacted bentonite) and natural barrier (host rock with the presence of rock fracture). The swelling pressure and relative humidity of bentonite were monitored with respect to the position of the rock fracture during 349 days of infiltration. Herein, the variation of water content, dry density, suction and microstructure along bentonite column after dismantling were reported, focusing on the changes in the vicinity of the rock fracture, to evaluate the effect of the rock fracture on the swelling behaviour of compacted bentonite. Results showed that the presence of rock fracture disturbed the water content distribution, with a lower water content at a position closer to the fracture. A significant decrease in dry density was also observed in the vicinity of the rock fracture; the closer the positions to the fracture the larger the decrease of dry density. This decrease coincided with the reduction of swelling pressure recorded by the pressure sensors, suggesting the occurrence of rock fracture filling-up by bentonite. Further examination showed that when the soil suction was higher than 9 MPa, the decrease in dry density in the near field of rock fracture was mainly attributable to the increase in large pore porosity (>2 μm). This suggests that at this suction the mechanism involving intrusion of bentonite into the rock fracture with fracture width higher than the size of bentonite gains was related to the pushing effect under the swelling of bentonite behind. By contrast, when the suction became lower than 9 MPa, the bentonite gel formed from the exfoliation of clay particles might fill up the rock fracture with smaller aperture width.

Experimental study on the 1-D free swelling of compacted bentonite

This paper presents a new designed 1-D free swelling test of compacted bentonite in glass tubes to simulate the process by which the bentonite cushion in the nuclear waste disposal reservoir swells and squeezes into the crack after absorbing the fissure water from surrounding rock. Deionized water and NaCl, Na2SO4, CaCl2 solutions with different concentrations were used as soaking solutions, and the change of the specimen height with time was recorded until the swelling completed. The effects of initial dry density, initial water content, and soaking solution concentration and type on the swelling deformation of bentonite were analyzed. Results show that the maximum swelling strain, almost independent from initial water content, increases with the initial dry density. The increase in the concentration of the salt solution reduces the free swelling deformation, and the degree of inhibition is related to the type of the salt solution. The effect of the concentration and type of the salt solution on swelling property can be uniformly reflected by the osmotic suction that acts as an additional stress applied on bentonite and is quantified as osmotic pressure item of the total effective stress proposed previously that controls the swelling strain of compacted bentonite. Then, the maximum swelling strains of the compacted bentonite under different soaking solutions in 1-D free swelling test can be predicted by a uniform power-law relationship with the total effective stress.

Swelling characteristics of bentonite after long-term dissolution in alkaline solution

AbstractIn a high-level radioactive waste repository, bentonite may react with the alkaline solution produced by cement degradation. In this study, bentonite was mixed with alkaline solution in a closed system and reacted for 3–24 months. Furthermore, swelling tests were conducted on the alkaline-dissolved bentonite immersed in distilled water. The swelling deformation decreased significantly with increases in the concentration of NaOH solution and reaction time, and this was mainly due to montmorillonite dissolution. The fractal e–p relationship (e is the void ratio and p is the vertical pressure) with two calculation coefficients (the swelling coefficient and the fractal dimension) was employed to determine the swelling of alkaline-dissolved bentonite. The fractal dimension increased slightly with increasing reaction time or concentration of NaOH solution, as the dissolution traces caused by the alkaline solution favoured an increase in the irregularity and fractality of the bentonite surface. The swelling coefficient decreased linearly with decreasing montmorillonite content. In addition, the swelling coefficient and the fractal dimension were related exponentially to the reaction time in alkaline solution. A relationship between the swelling of alkaline-dissolved samples and the reaction time was proposed, which might be used to assess the swelling properties of bentonite barriers that would be affected by long-term dissolution of the alkaline solution in a closed repository.

Bentonite Extrusion into Near-Borehole Fracture

In this paper, we discuss laboratory experiments of bentonite swelling and coupled finite element simulations to explicate bentonite extrusion. For the experiments, we developed a swell cell apparatus to understand the bentonite migration to the near-borehole fracture. We constructed the swell cell using acrylic, which comprised of a borehole and open fracture. Initially, the borehole of the swell cell was filled with bentonite and liquid. Then, the apparatus was sealed for observations. Due to the liquid saturation increase of bentonite, its swelling pressure increased. The developed pressure caused the extrusion of bentonite into the fracture, and the flow of bentonite from the borehole decreased with time. Moreover, for the effectiveness of bentonite-based plugging, there is a limiting condition, which represents the relation between the maximum bentonite migration length with the fracture aperture. Additionally, we also performed the bentonite free swelling test to assess the swelling potential to the fluid salinity, and we observed that with the increase of the salinity, the swelling potential decreased. In addition, we present a fully coupled two-phases fluids flow (e.g., liquid and gas) and deformation flow finite element (FE) model for the bentonite column elements and swell cell model. We also combined the Modified Cam Clay (MCC) model and the swelling model for the bentonite deformation flow model. Then, we also present the validation of the bentonite model. To model other sub-domains, we used the poro-elastic model. Additionally, we obtained the transition between the wetting phase (i.e., liquid) and non-wetting phase (i.e., gas) using the Brooks–Corey model. From the finite element results, we observed that due to the liquid intrusion into the bentonite, the developed capillary pressure gradient results in a change of the hydro-mechanical behavior of the bentonite. Initially, we observed that due to the high capillary pressure gradient, the liquid saturation and the swelling pressure increased, which also decreased with time due to a reduction in the capillary pressure gradient. Thereby, the swelling pressure-induced bentonite migration to the fracture also decreased over time, and after the equilibrium state (for a negligible pressure gradient), there was no significant transport of bentonite into the fracture.

Swelling of unsaturated GMZ07 bentonite at different temperatures

A series of wetting tests on unsaturated compacted GMZ07 sodium bentonite, taken from the Gaomiaozi area, Inner Mongolia, China, was performed to investigate the swelling characteristics of the GMZ07 sodium bentonite at temperatures of 5, 20, 60 and 75 °C. The influences of temperature and initial dry density on swelling deformation and swelling pressure were studied by performing a series of constant-stress and constant-volume tests under the wetting condition. The test results showed that the swelling deformation and swelling pressure due to saturation decreased slightly with increasing temperature. A linear relationship was present between the vertical pressure and corresponding saturated void ratio in the semi-logarithmic coordinate at a given temperature; this line is referred to as a state line. Swelling or collapse due to saturation was found to be dependent on the relative location of the initial state between the state line and initial state. The void ratios after saturation at different initial dry densities were close at the same temperature and vertical pressure.

Effects of NaCl solution on the swelling and shrinkage behavior of compacted bentonite under one-dimensional conditions

Because of its low hydraulic conductivity, high swelling capacity, and good adsorption properties, Gaomiaozi (GMZ) bentonite has been proposed as a suitable buffer/backfill material for construction of artificial barriers in deep geological repositories for high-level nuclear waste (HLW) disposal in China. By varying the concentration of NaCl solution and total suction, the swelling and shrinkage characteristics of compacted GMZ bentonite were studied under one-dimensional conditions. Results show that the swelling strain of compacted GMZ bentonite decreases as the concentration of NaCl solution increases under one-dimensional conditions. During drying with suction control by vapor phase technique, the density increases with suction. Simultaneously, the sample saturated with salt solution has a larger void ratio than that of the sample saturated with distilled water under the same suction. The void ratio and water content of the samples decrease with increasing suction. For a given suction, the sample saturated with salt solution has a higher degree of saturation than the sample saturated with distilled water. With the obtained water content (w), void ratio (e), and the degree of saturation (Sr), soil-water retention curves (SWRCs) were calculated for samples initially hydrated with different concentrations of NaCl solution. The SWRCs reveal that the sample with salt solution has higher water retention capacity than the sample with distilled water. A modified SWRC equation was proposed to account for the effect of NaCl solutions on the drying process of compacted GMZ bentonite under one-dimensional conditions. The results confirm that the modified SWRC equation can effectively describe the SWRCs of compacted GMZ bentonite considering the effects of NaCl solutions.

Voids effect on the swelling behaviour of compacted bentonite

This paper investigates the swelling behaviour of compacted MX80 bentonite under hydration with the presence of initial voids that simulate the technological voids in real nuclear waste repositories. With water introduced into samples from the initial voids, the swollen bentonite first filled up the initial voids, and then swelling pressure was generated. At different hydration times, the microstructure was investigated at different heights (initial void, top, middle and bottom) using mercury intrusion porosimetry, together with the determination of dry density, water content and suction. It was observed that the microstructure was characterised by the presence of a large- and a small-pore families at bottom and middle layers, but by the creation of a new medium-pore family with dominant pore mode around 0·04–2 μm at the top and initial void layers after the void space was filled by swollen bentonite. From bottom to void, the significant increase in medium pores was accompanied by an increase in inaccessible pores and a decrease in large and small pores. Further examination showed that the sample could be divided into compression and swelling zones based on the variation of void ratio with swelling pressure: at the compression zone, the soil was compressed over time, characterised by a significant reduction of medium and large pores; whereas at the swelling zone, the soil was still undergoing swelling, represented by the increase of inaccessible pores and medium pores. In addition, the changes in microstructure along the sample were found to be well correlated with changes in dry density and water content: the water content was decreasing and the dry density was increasing from the initial void to the bottom positions; over time the dry density of the upper part was increasing due to compression, while the dry density of the lower part was decreasing due to swelling. This provided evidence for the main mechanism of compacted bentonite swelling with the presence of technological voids: the swollen bentonite fills the initial voids first and then undergoes compression by the swelling of the bentonite behind.

An Investigation of the Swelling Kinetics of Bentonite Systems Using Particle Size Analysis

Particles size distribution (PSD) is introduced as a tool for analysis of bentonite aggregation and swelling kinetics. Raw Ca-bentonite was purified using a combined wet sieving and sedimentation processes, followed by thermochemical treatment with Na2CO3 to increase its swelling capacity. The detailed analysis of the PSD shows a strong correlation between the PSD and the swelling process. For the chemically treated raw bentonite, PSD revealed two different peaks representing unswelled and swelled particles along with some aggregates. The swelling is shown to be a kinetically controlled process that depends on time, temperature, and bentonite chemical composition. At the beginning of the chemical treatment, the effect of aggregates was more dominant; therefore, the viscosity did not increase much with particle size. However, the combined chemical and thermal treatment has enhanced the Na-activation process and boosted bentonite swelling. The rheological measurements have shown enhancement in the viscosity and confirmed the PSD findings. The same optimal treatment conditions are obtained from both rheological measurements and PSD analysis. A model is developed based on classical reaction rate kinetics and used to describe the conversion from unswelled to swelled particles. The PSD has a strong correlation with the physical properties of the suspension such as the viscosity. The swelling rate fits a second order model with a rate constant, k, in the range 0.002 to 0.124 h−1 and an activation energy, E, of 87 kJ/mol. PSD analysis together with the developed kinetic model are powerful tools for studying the swelling kinetics of bentonites.

Swelling behavior of compacted bentonite with the presence of rock fracture

In this study, the influence of rock fracture on the swelling behavior of compacted bentonite was investigated experimentally with bentonite compacted inside a hollow cylinder of fractured Beishan granite from China. During the test, hydration was allowed by letting water flowing into the compacted bentonite from the base plate, and air being expelled from the top plate. Along the sample, swelling pressure and relative humidity were monitored at different positions. Results showed that the presence of rock fracture significantly changed the hydration process of compacted bentonite. The evolutions of swelling pressure were directly related to the relative position to the rock fracture. At the same height, for the position closer to the rock fracture, a larger decrease in local dry density occurred, resulting in a larger loss in swelling pressure. This suggests that in field conditions of radioactive waste repository involving bentonite and rock, local filling of rock fracture by bentonite may occur, and the resulted bentonite swelling pressure decrease must be accounted for in the safety evaluation of the whole storage system.

Unsaturated permeability of Gaomiaozi bentonite under partially free-swelling conditions

In the deep geological disposal of high-level radioactive wastes (HLW), Na-bentonite produced from Gaomiaozi (GMZ) deposit has been selected as a possible buffer and backfill material for the Beishan repository in China. A sealing buffer is manufactured with bentonite at its hygroscopic water content (initially unsaturated). After taking water from the surrounding geological medium, bentonite under totally free condition is used to seal the technological voids, and then the outer surrounding bentonite (affected by the water mostly) compresses the innermost bentonite under partially free-swelling condition. However, permeability of GMZ bentonite under the partially free-swelling condition is still unknown. In this article, using the instantaneous profile method, we present a laboratory test of the GMZ bentonite unsaturated hydraulic conductivity under partially free-swelling condition. Changes in the cross-sectional area and motion of the sensors (to measure temperature and relative humidity) were considered in computing the unsaturated permeability. Our experimental results show that before the finial hydration stage, although permeability increases locally at some suctions (due to saturation degree increase and bentonite swelling to some extent), unsaturated permeabilities decrease and become constant in general for the reasons as follows. Initially, water is tightly adsorbed to the clay sheet surface and then water film is adsorbed to the tightly adsorbed water which leads to the initial highest permeability, and then diffuse double-layer forces lead to water uptake between the hydrated montmorillonite unit layers which is partially restricted by the confining stress, while capillary water flows on the water adsorbed on the internal surface of the bentonite large pores. For the capillary water flow due to surface tension, complex microstructure evolution (e.g., mesoscopic swelling compacts the inter-aggregate pores due to hydration under the confining stress from the rubber tube) before the finial hydration stage leads to flux decrease if under a certain hydraulic gradient (i.e., permeability decreases). Results show that in the final hydration stage, permeability increases rapidly with decreasing suction, because large pore compacting is complete while saturation degree increases and bentonite swells to some extent. Results show that at the same suctions, the unsaturated permeabilities located at the sensor closest to the water injection device are the largest among the four sensors, which could be explained with “critical gradient” concept for unsaturated expansive clay or effect of hydraulic gradient from boundary water pressure.

Experimental simulation of boundary condition effects on bentonite swelling in HLW repositories

On the basis of textural and hydro-mechanical characteristics, bentonite has been proven to be an effective buffer/backfill material for long-term containment of high-level radioactive waste (HLW) in deep geological repositories. Herein, the results of experiments performed to investigate the swelling equilibrium limit (SEL) of bentonite under various boundary conditions are presented. A special apparatus was employed to simulate various stress–strain boundary conditions, including constant volume (CV), constant vertical stress (CVS), and constant stiffness (CS). Bentonite samples were prepared with various initial dry densities ranging from 1.5 to 1.7 g/cm3 and vertically stressed to different levels. During wetting, they were subjected to different boundary conditions before the swelling strain or swelling pressure reached equilibrium. Test results indicate that stress–strain boundary conditions have significant effects on the measured swelling strain and swelling pressure of the tested bentonite. More specifically, the relationship between the sequence of swelling pressure under different boundary conditions is CV > CS > CVS, while the relationship between the sequence of swelling strain is CVS > CS > CV. In addition, the characteristics of SEL curves are governed by the initial dry density and vertical stress with the effect of dry density being more significant. Based on these results, several SEL curves were developed to index the effects of boundary conditions on swelling potential of bentonite. They can be used to evaluate the final stress and volume states of bentonite during fluid infiltration under the range of boundary conditions possible in HLW repositories.

Microbial Degradation of Cellulosic Material and Gas Generation: Implications for the Management of Low- and Intermediate-Level Radioactive Waste.

Deep geologic repositories (DGR) in Canada are designed to contain and isolate low- and intermediate-level radioactive waste. Microbial degradation of the waste potentially produces methane, carbon dioxide and hydrogen gas. The generation of these gases increase rock cavity pressure and limit water ingress which delays the mobility of water soluble radionuclides. The objective of this study was to measure gas pressure and composition over 7 years in experiments containing cellulosic material with various starting conditions relevant to a DGR and to identify micro-organisms generating gas. For this purpose, we conducted experiments in glass bottles containing (1) wet cellulosic material, (2) wet cellulosic material with compost Maker, and (3) wet cellulosic material with compost Accelerator. Results demonstrated that compost accelerated the pressure build-up in the containers and that methane gas was produced in one experiment with compost and one experiment without compost because the pH remained neutral for the duration of the 464 days experiment. Methane was not formed in the other experiment because the pH became acidic. Once the pressure became similar in all containers after 464 days, we then monitored gas pressure and composition in glass bottle containing wet cellulosic material in (1) acidic conditions, (2) neutral conditions, and (3) with an enzyme that accelerated degradation of cellulose over 1965 days. In these experiments, acetogenic bacteria degraded cellulose and produced acetic acid, which acidity suppressed methane production. Microbial community analyses suggested a diverse community of archaea, bacteria and fungi actively degrading cellulose. DNA analyses also confirmed the presence of methanogens and acetogens in our experiments. This study suggests that methane gas will be generated in DGRs if pH remains neutral. However, our results showed that microbial degradation of cellulose not only generated gas, but also generated acidity. This finding is important as acids can limit bentonite swelling and potentially degrade cement and rock barriers, thus this requires consideration in the safety case as appropriate.

Rock mechanical modelling of the Bentonite Rock Interaction Experiment, Äspö Hard Rock Laboratory, Sweden

The Bentonite Rock Interaction Experiment (BRIE) was performed in a tunnel at a depth of 420 m at the Äspö Hard Rock Laboratory in Sweden. The experiment focused on the hydraulic properties of rock and bentonite aiming at investigating the exchange of water across a bentonite-rock interface. The hypothesis for the mechanical modelling presented here was that changes in flow (observed in rock and on bentonite parcels) were due to local mechanical deformation. Induced stresses related to the construction (and experimental) stages for the BRIE site such as excavation of tunnels, drilling and over-coring of two vertical, tunnel-floor boreholes and, finally, installation and swelling of bentonite, were expected to be the main causes of these deformations. We assumed that this could be investigated using a step-wise rock mechanical modelling approach (with a relevant modelling sequence) and validated by using a transdisciplinary approach including field structural geological mapping (geometric, kinematic and dynamic interpretation of the exposed fracture sets) and hydrogeological investigations.For key fractures intersecting the boreholes, the modelled fracture normal and shear displacements were found to be local, small, and in line with field observations and measurements for BRIE. Results point at an agreement between the spatial locations of changes in flow identified from the bentonite parcels and the locations of inelastic deformation indicated by mechanical modelling for a reverse stress regime. Besides providing information about the key fractures, the structural mapping allowed to establish solid relationships between brittle structural features in the tunnel and in the cores, which were used as, or compared to, the main fracture input to the rock mechanical modelling. The identified fracture sets were found to be structurally reconcilable with the larger-scale tectonic picture of the area.

The Synthesis of Cationic Gelatin Derivative and its Effect on the Swelling of Sodium Bentonite

In this study, a cationic gelatin derivative (denoted as GCTA) was synthesized and its effect on the swelling of sodium bentonite (Na-BT) was investigated. The inhibitive properties of GCTA were evaluated through linear swelling test and hot-rolling recovery test. Results suggested that GCTA displayed better inhibitive ability than KCl and polyether amine (PEA). The underlying inhibitive mechanisms were also investigated by measuring interlayer spacing through X-ray diffraction, observing shale cuttings through scanning electron microscope and measuring the change of zeta potential of Na-BT dispersion. GCTA could strongly adsorb on the surface of clay particles and coat the particles. Meanwhile, the molecules entered the interlayer space, expelled water and decreased the interlayer spacing. This study can provide new insights into the design of environmentally friendly and highly effective clay inhibitors for water-based drilling fluids.