Pore Fluid Chemistry Research Articles

Impact of pore fluid chemistry on the thermal conductivity of bentonite–sand mixture

Thermal conductivity is an important parameter to consider when designing clay-based barriers for use in deep geological repositories (DGR). In the DGR environment, the infiltration of local saline groundwater can potentially change the pore fluid chemistry of a barrier over its lifetime. This change in chemistry is known to alter the thermal properties of the barrier materials. In order to examine the impact of pore fluid salinity on thermal conductivity, experiments were conducted under both distilled water and saline pore fluid conditions. The material mixtures were prepared at two different dry densities using two different salt types. Furthermore, five different thermal conductivity prediction models were selected and evaluated on their performance with respect to the experimental outcomes. In general, these results indicated that an increase in the constituent pore fluid’s salt concentration leads to a decrease in the thermal conductivity of the material. Additionally, the thermal conductivity values of the materials prepared at a high dry density were greater than of those compacted at a low dry density.

A chemo-mechanical insight into the failure mechanism of frequently occurred landslides in the Loess Plateau, Gansu Province, China

Thick loess deposits are considered problematic soils due to their susceptibility to collapse suddenly and in large volumes upon increase of water content. In the past decades, a large number of landslides occurred in the Loess Plateau in Gansu Province, north-western China, triggered by the extensive irrigation. The increase of water content has been identified as a key factor controlling the loess strength. However, the role of long-term saturation and pore fluid chemistry changes has not been investigated systematically. This paper reports on an experimental study on loess samples from Heitai loess terrace (Yongjing, Gansu) carried out through chemical analyses, oedometer and ring shear tests. The natural pore fluid was found to be a concentrated saline solution in unsaturated soil condition. Upon saturation, the pore ion concentration drop can contribute to shear strength loss in the clay component and volume decrease. A prolonged exposure to the irrigation water might facilitate cement dissolution, which could result in further weakening.

Experimental evidence for chemo-mechanical coupling during carbon mineralization in ultramafic rocks

Storing carbon dioxide in the subsurface as carbonate minerals has the benefit of long-term stability and immobility. Ultramafic rock formations have been suggested as a potential reservoir for this type of storage due to the availability of cations to react with dissolved carbon dioxide and the fast reaction rates associated with minerals common in ultramafic formations; however, the rapid reactions have the potential to couple with the mechanical and hydraulic behavior of the rocks and little is known about the extent and mechanisms of this coupling. In this study, we argue that the dissolution of primary minerals and the precipitation of secondary minerals along pre-existing fractures in samples lead to reductions in both the apparent Young's modulus and shear strength of aggregates, accompanied by reduction in permeability. Hydrostatic and triaxial deformation experiments were run on dunite samples saturated with de-ionized water and carbon dioxide-rich solutions while stress, strain, permeability and pore fluid chemistry were monitored. Sample microstructures were examined after reaction and deformation using scanning electron microscopy (SEM). The results show that channelized dissolution and carbonate mineral precipitation in the samples saturated with carbon dioxide-rich solutions modify the structure of grain boundaries, leading to the observed reductions in stiffness, strength and permeability. A geochemical model was run to help interpret fluid chemical data, and we find that the apparent reaction rates in our experiments are faster than rates calculated from powder reactors, suggesting mechanically enhanced reaction rates. In conclusion, we find that chemo-mechanical coupling during carbon mineralization in dunites leads to substantial modification of mechanical and hydraulic behavior that needs to be accounted for in future modeling efforts of in situ carbon mineralization projects.

How phyllosilicate mineral structure affects fault strength in Mg‐rich fault systems

AbstractThe clay mineralogy of fault gouges has important implications for the frictional properties of faults, often identified as a major factor contributing to profound fault weakness. This work compares the frictional strength of a group of Mg‐rich minerals common in the Mg‐Al‐Si‐O compositional space (talc, saponite, sepiolite, and palygorskite) by conducting triaxial frictional tests with water or argon as pore fluid. The studied minerals are chemically similar but differ in their crystallographic structure. Results show that fibrous Mg‐rich phyllosilicates are stronger than their planar equivalents. Frictional strength in this group of minerals is highly influenced by strength of the atomic bonds, continuity of water layers within the crystals, and interactions of mineral surfaces with water molecules, all of which are dictated by crystal structure. The formation and stability of the minerals studied are mainly controlled by small changes in pore fluid chemistry, which can lead to significant differences in fault strength.

Very early diagenesis in a calcareous, organic-rich mudrock from Jordan

The diagenesis in the organic-rich Cretaceous to Eocene Al Hisa Phosphorite Formation (AHP), Muwaqqar Chalk Marl Formation (MCM) and Umm Rijam Chert-Limestone Formation (URC) formations of Jordan can be linked directly to the fluctuating sedimentary environment of this shelf depositional system in the Middle to Late Eocene, and its influence on the composition of the deposited sediment and the early burial diagenetic environment. Most cementation was early, mostly within the first 10 m of burial, perhaps entirely within the first 100 m of burial. We propose that the siliceous cements are derived from biogenic silica, probably of diatoms, deposited in a shelf of enhanced productivity. Volumetrically, the most important processes were the redistribution of biogenic opal-A (diatoms) and calcite to form pervasive, layered and nodular cements. The formation of the silica and carbonate cements is closely linked through the effects their dissolution and precipitation have on pore fluid chemistry and pH. The chert beds have a biogenic silica origin, formed through replacement of diatoms and radiolaria by opal-CT, and subsequently by quartz. Calcite cement has carbonate derived from microbial diagenesis of organic matter and calcium derived from seawater. The Mg for early dolomite may have been generated by replacement of opal-CT by quartz, ore dissolution of unstable high Mg calcite bioclasts. The silica and carbonate diagenetic processes are both linked to microbial diagenesis of organic matter, and are intimately linked in both time and space, with pH possibly influencing whether a silica or a carbonate mineral precipitates. The paucity of metal cations capable of precipitating as sulphides is crucial to the creation of acidic pore water favourable to silica precipitation, either as opal-CT, chalcedony or quartz. The lack of clay minerals as a sink for the Mg required for opal-CT polymerisation is the principal factor responsible for the remarkably early silica cementation. All the diagenetic processes, with the probable exception of the opal-CT to quartz transition are early, almost certainly within the first 10 m of burial, possibly much less. A paragenetic sequence is presented here based on these two cores that should be tested against a wider core distribution to see whether this diagenetic history can be generalised throughout the basin. Warm bottom water temperatures probably led to silica diagenesis at much shallower burial depths than occurs in many other sedimentary basins. Silicified layers, in turn, commonly host fractures, suggesting that mechanical properties of the strata began to differentiate at a very early stage in the burial cycle. This has wide implications for processes linking diagenesis to deformation.

Mineral dissolution in porous media: An experimental and modeling study on kinetics, porosity and surface area evolution

Mineral and rock dissolution was studied experimentally using flow-through reactors and reactive transport modeling. The porous media were forsterite, crystalline basalt, and amorphous basalt, dissolved in HCl solutions at pH ∼2.5 and 25 °C. Solution composition, particle surface area, and porosity were determined as a function of travel distance within the reactor and time, using in situ X-ray computed tomography (XMT) and solution chemical composition. The obtained bulk dissolution rates, normalized to the initial geometric surface area, were: log r+,Si −7.59 ± 0.05 for forsterite, −7.64 ± 0.12 for basaltic glass and −8.12 ± 0.24 (mol/m2/s) for crystalline basalt, at 25 °C and pH ∼2.5, similar to those previously obtained using mixed flow reactors and for conditions far from equilibrium. Mineral and rock dissolution resulted in increased porosity and specific surface area of the solids; these changes were not uniformly distributed along the fluid flow path or with time. Similar trends were predicted by reactive transport modeling, however, the exact values of pore volume and surface area were difficult to predict. The results were found to be independent of the method applied in the surface area calculations: either the simple spherical model or the sugar lump model. Also, in the models, stoichiometric mineral dissolution is commonly assumed, but was not observed to occur for either glassy or crystalline basalt. It shows that accurate prediction capabilities of simple reactive transport modeling may be limited for calculating pore volume, mineral and rock surface area changes, and pore fluid chemistry with time and along flow paths. These, in turn, are key parameters in determining dissolution rates, overall chemical mass movement in the system, and fluid flow paths and velocities.

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Closure to “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Closure to “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Fil: Montoro, Marcos Alexis. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Estudios Avanzados En Ingenieria y Tecnologia. Universidad Nacional de Cordoba. Facultad de Ciencias exactas Fisicas y Naturales. Instituto de Estudios Avanzados En Ingenieria y Tecnologia; Argentina; Argentina. Facultad de Ciencias Exactas, Fisicas y Naturales, Universidad Nacional de Cordoba; Argentina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Discussion of “Fines Classification Based on Sensitivity to Pore-Fluid Chemistry” by Junbong Jang and J. Carlos Santamarina

Liquid limit and hydraulic conductivity of brown coal composites

Adequate waste disposal is currently under high demand in Australia, due to a rapid growth in population. Australia’s scarcity and cost for the use of clays (most commonly used landfill liner material) have resulted in a search for alternative materials to achieve satisfactory performance in landfill design. This study explored liquid limit and hydraulic conductivity (HC) of coal composites for potential landfill liner use. Brown coal (lignite) was mixed with polyacrylamide (PAM) or sodium bentonite (Bt) to investigate liquid limits (LL), HC, and swelling behaviour. Each additive was subject to distilled water and sodium chloride solution (50 g/l) to investigate the effects of pore fluid chemistry. The addition of 2 wt% PAM resulted in approximately 82 percentage point (pp) increase in the LL of lignite with distilled water and 76 pp increase with 50 g/l sodium chloride (NaCl) solution. The HC of lignite also decreased by more than two orders of magnitude as the PAM content increased. The swell index of lignite composites increased with the addition of PAM. This exploratory study has found the unique property of brown coal and its composites that the LL, HC and swell index do not deteriorate significantly in the presence of highly concentrated electrolyte solution (50 g/l NaCl). Such distinct properties will be beneficial over currently used landfill liner materials.

IDENTIFICATION OF CLAY SOIL MINERALOGY AND SWELLING BY THE FREE SWELL RATIO METHOD

The paper presents the results of free swell measurements of Neogene clays and model clay mixtures composed of Wyoming bentonite and Sedlec kaolinite. Modified free swell index (MFSI) as well as free swell ratio (FSR) were determined and analyzed with respect to pore fluid chemistry, mineral composition and clay content. The FSR, defined as the ratio of the equilibrium sediment volume of 10-g oven dried soil in 0.0025% NaCl solution to that in kerosene, has proved to provide only a rough prediction of clay mineralogy in natural soils.

Constitutive Model of Unsaturated Soils Considering the Effect of Intergranular Physicochemical Forces

AbstractA clayey soil is an electrically charged porous medium whose behavior is sensitive to the variations in the composition and concentration of pore water. Pronounced physicochemical interaction can occur between the solid particle and the pore water so that the clayey soil shows strong chemomechanical coupling effects and complex mechanical behaviors. If the degree of saturation varies the pore-water composition and concentration can also vary, resulting in intensive physicochemical effects in the soil. In this paper, a conceptual constitutive model for unsaturated soils is proposed to explain the influence of pore-fluid chemistry on the chemomechanical behavior of unsaturated clayey soils. A new intergranular stress which can effectively account for the physicochemical effects including osmosis, capillarity, and adsorption is introduced as the stress-state variable. The formulation of the proposed model can lead to a remarkable unification of the experimental results obtained under complex chemomec...

Fines Classification Based on Sensitivity to Pore-Fluid Chemistry

AbstractThe 75-μm particle size is used to discriminate between fine and coarse grains. Further analysis of fine grains is typically based on the plasticity chart. Whereas pore-fluid-chemistry-dependent soil response is a salient and distinguishing characteristic of fine grains, pore-fluid chemistry is not addressed in current classification systems. Liquid limits obtained with electrically contrasting pore fluids (deionized water, 2-M NaCl brine, and kerosene) are combined to define the soil “electrical sensitivity.” Liquid limit and electrical sensitivity can be effectively used to classify fine grains according to their fluid-soil response into no-, low-, intermediate-, or high-plasticity fine grains of low, intermediate, or high electrical sensitivity. The proposed methodology benefits from the accumulated experience with liquid limit in the field and addresses the needs of a broader range of geotechnical engineering problems.

Impact of organic pollutants on the macro and microstructure responses of Na-bentonite

Bentonite (Bent) is a favorable buffer material for waste containment barriers, although its properties may be affected by the pore fluid chemistry. Hence, this study investigates the role of different organic pollutants including methanol, acetone, acetic acid, and citric acid on the macro and microstructure responses of Na+-Bent. The chemicals at various concentrations (0 to 80% by the volume of distilled water) were separately added to the soil samples which were then subjected to a set of tests. The results indicate that an increase in the concentration of organic permeants by decreasing the dielectric constant (ε) reduces the plasticity index, compressibility and swelling potential of soil; whereas, the permeability increases. Such changes are ascribed to a tighter packing of the clay particles, as clearly confirmed by the SEM micrographs and XRD patterns. The decrease in the absolute value of soil zeta potential also supports the development of coagulated structure in the artificially contaminated samples upon reducing the ε of solution. However, the results reveal that the sensitivity of soil properties to the variations in the ε value is pronounced at the intermediate stages of concentration (i.e. the organic fluid/water ratio<60%) when the ε is higher than 50. In addition, at relatively low concentration, the acidic permeants dramatically alter the soil fabric due to having lower pH, causing remarkable effects on the hydro-mechanical parameters as compared to the other chemicals. Overall, the organic pollutants, depending on their type and concentration, exert negative impact on the barrier performance of Na+-Bent which are not precisely comparable only with reference to the changes in the dielectric constant of pore fluid, and thereby may not be completely explained by the diffuse double layer (DDL) theory.

Iron biomineralization controls on geophysical signatures of hydrocarbon contaminated sediments

The interpretation of geophysical data from mature hydrocarbon contaminated sites has relied on a conductive plume model where the conductivity of the subsurface contaminant volume is the result of microbial mediated changes in pore fluid chemistry. This conductive anomalous region is characterized by high total dissolved solids and occurs within the water table fluctuation zone where microbial activity is the maximum. Here we update this conductive plume model by providing new insights from recent laboratory investigations and geophysical data from hydrocarbon contaminated sites suggesting the unrecognized role of the impact that microbial-mediated metallic mineral precipitates have on geophysical signatures. We show that microbial redox processes (e.g., iron and sulfate reduction) during the biodegradation process involve mineralogical transformations and the precipitation of new minerals (e.g., magnetite, and pyrite) that can impact the electrical and magnetic properties of contaminated sediments. We provide examples from laboratory experiments and field studies and suggest that knowledge of the dominant redox processes occurring at hydrocarbon contaminated sites and the mineral phases formed is critical for a more robust interpretation of geophysical data associated with microbial-mediated changes at hydrocarbon contaminated sites. We also show that integration of both magnetic and electrical techniques may help reduce ambiguity in data interpretation.

Coupled Behavior of Cemented Paste Backfill at Early Ages

Once cemented paste backfill (CPB) is poured into a mine stope, it is subjected to strong coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes. A laboratory investigation is performed to understand the THMC behavior of CPB at early ages. An experimental setup is developed to study the THMC behavior of CPB. The testing and monitoring are conducted in undrained conditions, with and without pressure application, and take into consideration two types of tailings (artificial and natural). The evolutions of the total pressure, pore pressure, suction, temperature and electrical conductivity are monitored for a period of 7 days. Also, the CPB samples are tested or analyzed with regards to their shear strength properties, hydraulic conductivity, thermal conductivity, and physical and microstructural characteristics at 1, 3 and 7 days. The obtained results show that the THMC properties of CPB are strongly coupled due to several mechanisms, such as curing stress, heat of hydration, self-desiccation and pore fluid chemistry. The results presented in this paper will provide a better understanding of the THMC behavior of CPB at early ages and thus contribute to the better designing of CPB structures.