Argillaceous Formations Research Articles

Lithostratigraphy of the Kweekvlei Formation (Witteberg Group), Cape Supergroup

AbstractThe Lower Carboniferous, probably Tournaisian, Kweekvlei Formation is part of the Witteberg Group (Cape Supergroup) of South Africa. Together with the overlying Floriskraal Formation, it forms an upward-coarsening succession within the Lake Mentz Subgroup. Sedimentary features of the Kweekvlei Formation suggest deposition in a storm-wave dominated marine setting, within the storm-influenced, distal part of an offshore transition zone environment. This predominantly argillaceous formation preserves a low diversity trace fossil assemblage. Reworked vascular plant debris (including the problematic genus Praeramunculus sp.) and a shark spine have been reported for the Kweekvlei Formation. There are no known stratigraphic equivalents in South Africa.

Hazard susceptibility related to clay shrinkage–swelling phenomena in north-eastern Tunisia (Grombalia area)

The investigation of the shrinkage–swelling phenomena in argillaceous formations of the Grombalia area (north-eastern Tunisia) has allowed the identification of three classes of clays. The first class contains three argillaceous formations and has a low susceptibility towards shrinkage–swelling phenomena. The second class, represented by four argillaceous formations, has an average susceptibility. The third class, comprises four argillaceous formations that have a high susceptibility. Therefore, in the study region, the hazard susceptibility towards the constructions can be significant for certain zones, because of the extension of constructions which is the result of the development of demography and industry in the recent years. Three indices have been determined to obtain these classes: the lithology indices, the mineral composition indices and the geotechnical indices. A description of the lithology of geological formations and X-ray diffraction results from analysis on bulk samples allow recognising the amount of clays in each formation. However, argillaceous formations composed essentially by clays does not mean that it has a high susceptibility towards shrinkage–swelling phenomena. To improve interpretation, XRD results reveal the volume proportion of minerals that exists in each argillaceous formation. Indeed, formations having high susceptibility towards shrinkage–swelling phenomena show a high volume of smectites and/or interstratified. The additional data provided from geotechnical study on argillaceous formations have allowed an inference about the degree of the shrinkage–swelling susceptibility for all the argillaceous formations in the Grombalia area. In fact, geotechnical results have allowed determining the plasticity index value, the methylene blue value and the linear shrinkage value. Determining the degree of the shrinkage–swelling susceptibility must be inferred from the three indices (lithology, mineralogy and geotechnical), because applying only the results of one feature can lead to a false decision.

Forward and back diffusion through argillaceous formations

AbstractThe exchange of solutes between aquifers and lower‐permeability argillaceous formations is of considerable interest for solute and contaminant fate and transport. We present a synthesis of analytical solutions for solute diffusion between aquifers and single aquitard systems, validated in well‐controlled experiments, and applied to several data sets from laboratory and field‐scale problems with diffusion time and length scales ranging from 10−2 to 108 years and 10−2 to 102 m. One‐dimensional diffusion models were applied using the method of images to consider the general cases of a finite aquitard bounded by two aquifers at the top and bottom, or a semiinfinite aquitard bounded by an aquifer. The simpler semiinfinite equations are appropriate for all domains with dimensionless relative diffusion length, ZD < 0.7. At dimensionless length scales above this threshold, application of semiinfinite equations to aquitards of finite thickness leads to increasing errors and solutions based on the method of images are required. Measured resident solute concentration profiles in aquitards and flux‐averaged solute concentrations in surrounding aquifers were accurately modeled by appropriately accounting for generalized dynamic aquifer‐aquitard boundary conditions, including concentration gradient reversals. Dimensionless diffusion length scales were used to illustrate the transferability of these relatively simple models to physical systems with dimensions that spanned 10 orders of magnitude. The results of this study offer guidance on the application of a simplified analytical approach to environmentally important layered problems with one or two diffusion interfaces.

Anisotropic modelling of Opalinus Clay behaviour: From triaxial tests to gallery excavation application

Deep repository in geological formations is the preferential solution considered in many countries to manage high-level nuclear wastes. In Switzerland, the Opalinus Clay is a candidate host rock. In this context, in situ and laboratory tests are conducted on Opalinus Clay to demonstrate the feasibility of deep disposal in this argillaceous formation. This paper presents a constitutive model able to fit the experimental data obtained from some triaxial tests conducted by Jahns (2013) on cores from borehole Schlattingen SLA-1. The elasto-plastic behaviour of Opalinus Clay is reproduced thanks to a Drucker-Prager model, taking into account the anisotropy behaviour of this sedimentary rock. The objective is to employ a single set of parameters representative of the material. In a second version of the model, the stress-dependence of the elastic properties and damage are taken into account. Finally, the parameters calibrated with experimental tests are used to simulate the excavation of a gallery with a second gradient approach.

Mont Terri rock laboratory, 20\xa0years of research: introduction, site characteristics and overview of experiments

Geologic repositories for radioactive waste are designed as multi-barrier disposal systems that perform a number of functions including the long-term isolation and containment of waste from the human environment, and the attenuation of radionuclides released to the subsurface. The rock laboratory at Mont Terri (canton Jura, Switzerland) in the Opalinus Clay plays an important role in the development of such repositories. The experimental results gained in the last 20 years are used to study the possible evolution of a repository and investigate processes closely related to the safety functions of a repository hosted in a clay rock. At the same time, these experiments have increased our general knowledge of the complex behaviour of argillaceous formations in response to coupled hydrological, mechanical, thermal, chemical, and biological processes. After presenting the geological setting in and around the Mont Terri rock laboratory and an overview of the mineralogy and key properties of the Opalinus Clay, we give a brief overview of the key experiments that are described in more detail in the following research papers to this Special Issue of the Swiss Journal of Geosciences. These experiments aim to characterise the Opalinus Clay and estimate safety-relevant parameters, test procedures, and technologies for repository construction and waste emplacement. Other aspects covered are: bentonite buffer emplacement, high-pH concrete-clay interaction experiments, anaerobic steel corrosion with hydrogen formation, depletion of hydrogen by microbial activity, and finally, release of radionuclides into the bentonite buffer and the Opalinus Clay barrier. In the case of a spent fuel/high-level waste repository, the time considered in performance assessment for repository evolution is generally 1 million years, starting with a transient phase over the first 10,000 years and followed by an equilibrium phase. Experiments dealing with initial conditions, construction, and waste emplacement do not require the extrapolation of their results over such long timescales. However, experiments like radionuclide transport in the clay barrier have to rely on understanding long-term mechanistic processes together with estimating safety-relevant parameters. The research at Mont Terri carried out in the last 20 years provides valuable information on repository evolution and strong arguments for a sound safety case for a repository in argillaceous formations.

Measuring diffusion coefficients of dissolved He and Ar in three potential clay host formations: Boom Clay, Callovo-Oxfordian Clay and Opalinus Clay

Abstract For the long-term management of high- and intermediate-level radioactive waste and/or spent fuel, many countries prefer disposal in a geological repository. In Belgium, Switzerland and France, argillaceous formations are being explored as potential host formations for this purpose. In this context, knowledge of the diffusion coefficient of He is relevant within two research areas: first, diffusion coefficients are used in safety calculations to evaluate the balance between gas generation (mainly H 2 ) and gas dissipation; and, second, the diffusion coefficients of He and Ar are needed in the diffusion models of natural tracers. Owing to the lack of data on the diffusion coefficients of He and Ar for the different clay host formations, diffusion experiments with dissolved He and Ar were performed on Boom Clay, Opalinus Clay and Callovo-Oxfordian Clay. Samples were confined in a diffusion cell, and diffusion coefficients were measured by using the double through-diffusion technique. The diffusion coefficients ( D p or D pore ) for He in Boom Clay, Callovo-Oxfordian Clay and Opalinus Clay are 12.6×10 −10 , 4.51×10 −10 and 7.13×10 −10 m 2 s −1 , respectively. The diffusion coefficients for Ar in Boom Clay, Callovo-Oxfordian Clay and Opalinus Clay are 18.6×10 −11 , 4.06×10 −11 and 3.65×10 −11 m 2 s −1 , respectively.

Coastal groundwater salinization: Focus on the vertical variability in a multi-layered aquifer through a multi-isotope fingerprinting (Roussillon Basin, France)

The Roussillon sedimentary Basin (South France) is a complex multi-layered aquifer, close to the Mediterranean Sea facing seasonally increases of water abstraction and salinization issues. We report geochemical and isotopic vertical variability in this aquifer using groundwater sampled with a Westbay System® at two coastal monitoring sites: Barcarès and Canet. The Westbay sampling allows pointing out and explaining the variation of water quality along vertical profiles, both in productive layers and in the less permeable ones where most of the chemical processes are susceptible to take place.The aquifer layers are not equally impacted by salinization, with electrical conductivity ranging from 460 to 43,000μS·cm−1. The δ2H–δ18O signatures show mixing between seawater and freshwater components with long water residence time as evidenced by the lack of contribution from modern water using 3H, 14C and CFCs/SF6. S(SO4) isotopes also evidence seawater contribution but some signatures can be related to oxidation of pyrite and/or organically bounded S. In the upper layers 87Sr/86Sr ratios are close to that of seawater and then increase with depth, reflecting water–rock interaction with argillaceous formations while punctual low values reflect interaction with carbonate. Boron isotopes highlight secondary processes such as adsorption/desorption onto clays in addition to mixings. At the Barcarès site (120m deep), the high salinity in some layers appear to be related neither to present day seawater intrusion, nor to Salses-Leucate lagoonwater intrusion. Groundwater chemical composition thus highlights binary mixing between fresh groundwater and inherited salty water together with cation exchange processes, water–rock interactions and, locally, sedimentary organic matter mineralisation probably enhanced by pyrite oxidation.Finally, combining the results of this study and those of Caballero and Ladouche (2015), we discuss the possible future evolution of this aquifer system under global change, as well as the potential management strategies needed to preserve quantitatively and qualitatively this water resource.

Interpreting fluid pressure anomalies in shallow intraplate argillaceous formations

AbstractInvestigations have revealed several instances of apparently isolated highs or lows in pore fluid potential in shallow (< ~ 1 km depth) argillaceous formations in intraplate settings. Formations with the pressure anomalies are distinguished by (1) smaller ratios of hydraulic conductivity to formation thickness and (2) smaller hydraulic (or pressure) diffusivities than those without anomalies. This is consistent with transient Darcian flow caused by strain at rates of ~ 10−17 to 10‐16 s‐1, by significant perturbing events in the past 104 to 106 annum or by some combination of the two. Plausible causes include erosional downwasting, tectonic strain, and glaciation. In this conceptualization the anomalies provide constraints on formation‐scale flow properties, flow history, and local geological forcing in the last 106 annum and in particular indicate zones of low permeability (10−19–10−22 m2) that could be useful for isolation of nuclear waste.

Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, northern Switzerland

Abstract. The stress field at depth is a relevant parameter for the design of subsurface constructions and reservoir management. Yet the distortion of the regional stress field due to local-scale features such as sedimentary and tectonic structures or topography is often poorly constrained. We conduct a stress sensitivity analysis using 3-D numerical geomechanical modelling with an elasto-plastic material law to explore the impact of such site-specific features on the stress field in a sedimentary sequence of the Swiss Alpine foreland. The model's dimensions are 14 × 14 × 3 km3 and it contains 10 units with different mechanical properties, intersected by two regional fault zones. An initial stress state is established involving a semi-empirical relationship between the ratio of horizontal to vertical stress and the overconsolidation ratio of argillaceous sediments. The model results indicate that local topography can affect the stress field significantly to depths greater than the relief contrasts at the surface, especially in conjunction with horizontal tectonic loading. The complexity and frictional properties of faults are also relevant. The greatest variability of the stress field arises across the different sedimentary units. Stress magnitudes and stress anisotropy are much larger in stiffer formations such as massive limestones than in softer argillaceous formations. The stiffer formations essentially carry the load of the far-field forces and are therefore more sensitive to changes of the boundary conditions. This general characteristic of stress distribution in the stiff and soft formations is broadly maintained also with progressive loading towards the plastic limit. The stress field in argillaceous sediments within a stack of formations with strongly contrasting mechanical properties like in the Alpine foreland appears to be relatively insensitive to changes in the tectonic boundary conditions and is largely controlled by the maximum stiffness contrast with respect to the load-bearing formations.

Effect of Additives on Dispersed System Structure Formation

Results are provided for a study of the effect of complex additives on critical concentration for argillaceous suspension structure formation. Curves are presented for the dependence of suspension limiting dynamic shear stress on solid phase content and additive concentration. It is revealed that the most effective complexes at low concentration are those containing oxyphenolfurfural oligomers. These complexes may be used as diluting additives for argillaceous suspensions.

Can argillaceous formations isolate nuclear waste? Insights from isotopic, noble gas, and geochemical profiles

AbstractThere is considerable interest in the use of thick argillaceous geologic formations to contain nuclear waste. Here, we show that diffusion can be the controlling transport process in these formations and diffusional time scales for δ18O and δ2H in water, dissolved He, and Cl transport in shale‐dominated aquitards are typically over 106 years, well exceeding the regulatory requirements for isolation in most countries. Our scientific understanding of diffusive solute transport processes through argillaceous formations would benefit from the application of additional isotopic tracers (e.g., using new 4He sampling technology), multidimensional diffusive‐dispersive modeling of groundwater flow and diffusive‐dispersive solute transport over long geologic time scales, and an improved understanding of spatial heterogeneity as well as time‐dependent changes in the subsurface conditions and properties of argillaceous formations in response to events such as glaciation. Based on our current isotopic and geochemical understanding of transport, we argue that argillaceous formations can provide favorable long‐term conditions for isolating nuclear wastes.

Simulation of coupled THM process in surrounding rock mass of nuclear waste repository in argillaceous formation

To investigate and analyze the thermo-hydro-mechanical (THM) coupling phenomena of a surrounding rock mass in an argillaceous formation, a nuclear waste disposal concept in drifts was represented physically in an in-situ test way. A transversely isotropic model was employed to reproduce the whole test process numerically. Parameters of the rock mass were determined by laboratory and in-situ experiments. Based on the numerical simulation results and in-situ test data, the variation processes of pore water pressure, temperature and deformation of surrounding rock were analyzed. Both the measured data and numerical results reveal that the thermal perturbation is the principal driving force which leads to the variation of pore water pressure and deformations in the surrounding rock. The temperature, pore pressure and deformation of rock mass change rapidly at each initial heating stage with a constant heating power. The temperature field near the heater borehole is relatively steady in the subsequent stages of the heating phase. However, the pore pressure and deformation fields decrease gradually with temperature remaining unchanged condition. It also shows that a transversely isotropic model can reproduce the THM coupling effects generating in the near-field of a nuclear waste repository in an argillaceous formation.

Model evaluation of geochemically induced swelling/shrinkage in argillaceous formations for nuclear waste disposal

Argillaceous formations are being considered as host rocks for geologic disposal of nuclear waste in a number of countries. One advantage of emplacing nuclear waste in such formations is the potential self-sealing capability of clay due to swelling, which is of particular importance for the sealing and healing of disturbed rock zones (DRZ). It is therefore necessary to understand and be able to predict the changes in swelling properties within clay rock near the waste-emplacement tunnel. In this paper, considering that the clay rock formation is mostly under saturated conditions and the swelling property changes are mostly due to geochemical changes, we propose a modeling method that links a THC simulator with a swelling module that is based on diffuse double layer theory. Simulations were conducted to evaluate the geochemically induced changes in the swelling properties of the clay rock. Our findings are as follows: (1) geochemically induced swelling/shrinkage occurs exclusively in the EBS–clay formation interface, within a few meters from the waste-emplacement tunnels; (2) swelling/shrinkage-induced porosity changes are generally much smaller than those caused by mineral precipitation/dissolution processes; (3) geochemically induced swelling/shrinkage of the host clay rock is affected by variations in the pore water chemistry, exchangeable cations, and smectite abundance. Neglecting any of these three factors might lead to a miscalculation of the geochemically induced swelling pressure.

Reactive Formations: Characterization and Capacity Expansion

During the drilling of oil wells is common the presence of layers consisting of clay minerals with high degree of hydration and arranged in laminar packages. When in contact with water, the packets of the clay are separated as the water enters in the basal spacing. Argillaceous formations such as shales containing smectite are sensitive to the presence of water and the greater the amount of smectite, higher reactivity in the presence of water. This phenomenon is known as expansion or swelling. So, the aim of this paper is to characterize the shales from two different regions of the country and to explain the susceptibility of hydration of each of these formations. The characterization was done by making use of CEC, XRF and XRD. The obtained results showed that among the studied shales, those with the greatest degree of clay fractions (smectite) in its composition showed higher swelling index according to the methodology of Foster.

GEOGRAPHICAL CONTROLS ON SEDIMENT ACCRETION OF THE CENOZOIC ALGOA GROUP BETWEEN OYSTER BAY AND ST. FRANCIS, EASTERN CAPE COASTLINE, SOUTH AFRICA

Borehole data provide an opportunity to explore the thickness distribution of Late Cenozoic Algoa Group sediments along the southern Eastern Cape coastline, between Oyster Bay and Cape St. Francis, South Africa. Bedrock lithology, bedrock elevation, surface relief and sediment supply are factors considered to influence thickness variations locally. Variations in accretion values allow recognition of four coast-parallel trending zones, referred to here as zones A to D. Zones A and B are characterised by a general trend of increasing thickness, with increasing distance from the coastal margin and occur in the first few hundred metres from shore. Zone A occurs closest to the shoreline and records the lowest sediment thicknesses. At Thyspunt zone A extends inland from the coastal margin for ~250 m and sediment thicknesses here range between 3 to 12 m. Zone B defines the inland area between ~250 to 750 m from the shoreline. A clear progression from zone A accretion values into thicker zone B sediment thicknesses is recognized at Thyspunt, where sediment thickness typically range between 12 to 26 m. Further inland, zone C, a zone of peak thickness values (61 m) occurs where the Algoa Group is underlain by the argillaceous Goudini and Cederberg Formations. Bedrock elevations below sea-level and the occurrence of fluvial deposits above these argillaceous bedrock lithologies indicate the presence of a possible palaeo-valley near Thyspunt and Cape St. Francis. Such a palaeo-valley allowed for greater accretion of sediments. Greatest accretion values occur in these areas especially where coupled with elevated surface relief as is the case towards the northwestern regions of the study area where elevated dune heights occur close to the area’s upwind sand supply. Furthermore here the occurrence of the Cape St. Francis anticline cored by quartzite of the Peninsula Formation form a bedrock ridge impeding sediment transfer to the east, concentration dune mass along the western limb of the anticline. The transition to zone D is marked by the dramatic decline from peak sediment thickness values to thinner accretion values (

Modeling of oxygen gas diffusion and consumption during the oxic transient in a disposal cell of radioactive waste

The oxic transient in geological radioactive waste disposals is a key issue for the performance of metallic components that may undergo high corrosion rates under such conditions. A previous study carried out in situ in the argillite formation of Tournemire (France) has suggested that oxic conditions could have lasted several years. In this study, a multiphase reactive transport model is performed with the code HYTEC to analyze the balance between the kinetics of pyrite oxidative dissolution, the kinetics of carbon steel corrosion and oxygen gas diffusion when carbon steel components are emplaced in the geological medium. Two cases were modeled: firstly, the observations made in situ have been reproduced, and the model established was then applied to a disposal cell for high-level waste (HLW) in an argillaceous formation, taking into account carbon steel components and excavated damaged zones (EDZ).In a closed system, modeling leads to a complete and fast consumption of oxygen in both cases. Modeling results are more consistent with the in situ test while considering residual voids between materials and/or a water unsaturated state allowing for oxygen gas diffusion (open conditions). Under similar open conditions and considering ventilation of the handling drifts, a redox contrast occurs between reducing conditions at the back of the disposal cell (with anoxic corrosion of steel and H2 production) and oxidizing conditions at the front of the cell (with oxic corrosion of steel). The extent of the oxidizing/reducing front in the disposal cell is strongly dependent on the gas diffusion coefficient in partially saturated zones.

A revision of the Jurassic (Bathonian to Oxfordian) lithostratigraphy of the onshore Moray Firth Basin, north-east Scotland

Abstract Bathonian to Oxfordian strata occur onshore in two principal locations over 30 km apart on the coast of the Moray Firth, at Brora and Balintore. The existing lithostratigraphy has the same formation names applied to both successions despite profound differences, exemplified in their schemes of local members. Furthermore, three of the formation names include the same place name, and use obsolete lithological terms. We consider that all the Bathonian to Oxfordian members are satisfactory, and propose their retention with original names, with one exception, to provide continuity with the superseded formational scheme. We propose retention of the Brora Coal Formation as currently defined. The Brora Argillaceous, Brora Arenaceous and Balintore formations at Brora are unsatisfactory in a modern context and we propose: i) a new Strathsteven Mudstone Formation, which is mudstone-dominated, and generally coarsens-upwards. ii) a Clynekirkton Sandstone Formation, which is sandstone-dominated and generally coarsens upwards. This formation scheme employs unique geographical names and modern and appropriate lithological terminology. Furthermore, the boundary between the Strathsteven and Clynekirkton formations is placed at a junction that is a change from mud- and silt-dominated lithologies to silt- and fine- and medium-grained sand and is mappable. We consider that the Callovian–Oxfordian succession at Balintore should be assigned to a single formation, viz. the revised Balintore Formation. Apart from the basal Brora Roof Bed, the succession at Balintore does not lithologically resemble that at Brora, and the scheme of the Brora Argillaceous Formation, Brora Arenaceous Formation, and the Balintore Formation as previously defined is unworkable here.

Climate change and its influence on shrinkage–swelling clays susceptibility in a semi-arid zone: a case study of Souk Ahras municipality, NE-Algeria

Dry summers and irregular rainfall have been affecting our daily life in the last decades. These climatic changes influence the susceptibility of shrinking and swelling phenomenon of clay and marl formations. Clay soils are found in many areas in north Algeria, but they are more common in the sub-arid highlands belt. By combining intrinsic factors that influence shrink–swell behavior as well as the climatic data, a susceptibility map has been established for Souk Ahras municipality. This map shows sensitive areas, which are going to become the future extension territories, toward shrink and swell phenomenon. The adopted methodology begins with the establishment of a synoptic map of clay and marl formations. This procedure allowed the identification of 17 argillaceous formations. Then, they were subjected to a hierarchy in terms of their susceptibility to the phenomenon. The classification was established by a combination of lithological, mineralogical, and geotechnical criteria. The use of GIS technology has permitted the combination of several predisposing and trigging factors such as the annual average rainfall, the evapotranspiration, the land use, and the orography. The result of the adopted approach was a shrink–swell susceptibility map, which can be used as a regulatory tool in land use and planning procedures.

Simulations of THM processes in buffer-rock barriers of high-level waste disposal in an argillaceous formation

The main objective of this paper is to investigate and analyse the thermo-hydro-mechanical (THM) coupling phenomena and their influences on the repository safety. In this paper, the high-level waste (HLW) disposal concept in drifts in clay formation with backfilled bentonite buffer is represented numerically using the CODE_BRIGHT developed by the Technical University of Catalonia in Barcelona. The parameters of clay and bentonite used in the simulation are determined by laboratory and in situ experiments. The calculation results are presented to show the hydro-mechanical (HM) processes during the operation phase and the THM processes in the after-closure phase. According to the simulation results, the most probable critical processes for the disposal project have been represented and analyzed. The work also provides an input for additional development regarding the design, assessment and validation of the HLW disposal concept.

Approaches for representing hydro-mechanical coupling between sub-surface excavations and argillaceous porous media at the ventilation experiment, Mont Terri

At the Mont Terri Underground Research Laboratory (Switzerland), a field-scale investigation has been conducted in order to investigate the hydro-mechanical and chemical perturbations induced in the argillaceous formation by forced ventilation through a tunnel. This experiment has been selected to be used for processing model development and validation in the international project DECOVALEX-2011. The conceptual and mathematical representation of the engineered void, which itself forms a major part of the experiment and is not simply a boundary condition, is the subject of this paper. A variety of approaches have been examined by the contributors to DECOVALEX and a summary of their findings is presented here. Two major aspects are discussed. Firstly, the approaches for the treatment of the surface condition at the porous media/tunnel interface are examined, with two equivalent but differing formulations successfully demonstrated. Secondly, approaches for representing the tunnel with associated air and water vapour movement, when coupled with the hydro-mechanical (HM) representation of the porous medium, are also examined. It is clearly demonstrated that, for the experimental conditions of the ventilation experiment (VE) that abstracted physical and empirical models of the tunnel, can be used successfully to represent the hydraulic behaviour of the tunnel and the hydraulic interaction between the tunnel and the surrounding rock mass.