Dissolution Of Chalk Research Articles

Ammonia gas treatment in low cost biological reactor

Ammonia gas contributes to a number of environmental and human health concerns. The use of chalk, a cheap alkalinity source may reduce costs for biological systems. This research studies a closed liquid flow reactor to treat ammonia gas using chalk as biomass media and alkalinity source with high value calcium nitrate fertilizer production.The proposed reactor showed complete ammonia gas removal at high rate (500 mg N/L/day) and with low cost; where chalk dissolution and ammonia gas absorption contributed to alkalinity in the water for nitrification. High calcium ion concentration (up to 10,000 mg Ca2+ as CaCO3/L) showed only minor effects on ammonia absorption and nitrification rate.

Observations on the geology of the country around Chalfont St Giles, Buckinghamshire

This paper presents new field observations from the area around Chalfont St Giles and relates them to existing information from the wider Chiltern Hills region on lithostratigraphy, structural geology, geomorphological and karstic features, and landscape development. In this area the NW-SE aligned valley of the River Misbourne, an internationally rare chalk stream, and flanking interfluve plateaus form a transition zone on the chalk dipslope between the lowest elevations of outcropping chalk around Denham and the characteristic chalk valleys and clay-with-flints capped upland present from Amersham northwards. The area straddles the northernmost extent of both the Paleogene strata, represented by Lambeth Group outliers, and SW–NE aligned pre-Anglian palaeo-Thames River Terrace deposits, and contains an anomalous Lambeth Group, Quarrendon Gap, mid-slope platform. Ground investigations carried out for HS2 have helped substantiate other evidence for significant faulting across the area, with intermittent movement episodes dating from the Mid- to Late Cretaceous onwards, which have affected both the Chalk and Paleogene strata and had a major influence on shaping the valley network and wider landscape. Karstic features are widespread, including contemporary interfluve plateau level streams sinks around the Lambeth Group outliers forming active dolines, together with many concealed chalk dissolution related features. There are numerous, generally small scale, clay, chalk, sand and gravel workings most of which are long abandoned but still provide useful insights into the near surface geology.

Geomorphology and Species Interactions Control Facilitation Cascades in a Salt Marsh Ecosystem.

Facilitation cascades are chains of positive interactions that occur as frequently as trophic cascades and are equally important drivers of ecosystem function, where they involve the overlap of primary and secondary, or dependent, habitat-forming foundation species [1]. Although it is well recognized that the size and configuration of secondary foundation species' patches are critical features modulating the ecological effects of facilitation cascades [2], the mechanisms governing their spatial distribution are often challenging to discern given that they operate across multiple spatial and temporal scales [1, 3]. We therefore combined regional surveys of southeastern US salt marsh geomorphology and invertebrate communities with a predator exclusion experiment to elucidate the drivers, both geomorphic and biotic, controlling the establishment, persistence, and ecosystem functioning impacts of a regionally abundant facilitation cascade involving habitat-forming marsh cordgrass and aggregations of ribbed mussels. We discovered a hierarchy of physical and biological factors predictably controlling the strength and self-organization of this facilitation cascade across creekshed, landscape, and patch scales. These results significantly enhance our capacity to spatially predict coastal ecosystem function across scales based on easily identifiable metrics of geomorphology that are mechanistically linked to ecological processes. Replication of this approach across vegetated coastal ecosystems has the potential to support management efforts by elucidating the multi-scale linkages between geomorphology and ecology that, in turn, define spatially explicit patterns in community assembly and ecosystem functioning.

Identification, investigation and classification of surface depressions and chalk dissolution features using integrated LiDAR and geophysical methods

The chalk bedrock of the Hampshire Basin, southern England is an important aquifer and is highly susceptible to dissolution, making the development and presence of karstic features a widespread occurrence. These features are hazardous because they provide possible pathways to the underlying aquifer and therefore present potential site-specific contamination risks. There is also evidence of extensive extraction, through both mining and surface quarrying, of chalk, flint and clay over many centuries. Geophysical techniques consisting of electromagnetic (EM31) and ground-penetrating radar surveys were used to identify and characterize target features identified from desk study data. The ground-penetrating radar and EM31 interpretations allowed the classification of non-anthropogenic target features, such as diffuse buried sinkholes with disturbed and subsiding clay-rich infill and varying symmetrical and asymmetrical morphologies. We describe here the investigations of such features identified at Holme Farm, Stansted House, Hampshire. The combination of EM31 data and ground-penetrating radar profiles facilitated the identification of a palaeovalley, cavities and irregular rockhead. This investigation identified locations of aquifer contamination risk as some sinkholes have been sites for the illegal dumping of waste or the infiltration of fertilizers, leaking sewage pipes or animal waste. This potential source of contamination utilizes the sinkhole as a pathway into the highly transmissive White Chalk Subgroup of Hampshire and has caused contamination of the aquifer. We conclude that our integrated approach of geophysical techniques linked to aerial photographs and LiDAR image interpretation was highly effective in the location and characterization of dissolution structures, infilled former quarries and mining features at this site.

Chapter 15 Dissolution – carbonates

Abstract The dissolution of limestone and chalk (soluble carbonates) through geological time can lead to the creation of naturally formed cavities in the rock. The cavities can be air, water, rock or soil infilled and can occur at shallow levels within the carbonate rock surface or at deeper levels below. Depending upon the geological sequence, as the cavities break down and become unstable they can cause overlying rock strata to settle and tilt and also collapse of non-cemented strata and superficial deposits as voids migrate upwards to the surface. Natural cavities can be present in a stable or potentially unstable condition. The latter may be disturbed and triggered to cause ground instability by the action of percolating water, loading or vibration. The outcrops of various limestones and chalk occur widely across the UK, posing a significant subsidence hazard to existing and new land development and people. In addition to subsidence they can also create a variety of other problems such as slope instability, generate pathways for pollutants and soil gas to travel along and impact all manner of engineering works. Knowledge of natural cavities is essential for planning, development control and the construction of safe development.

Evaluation of Nanofiltration Membrane Process for Smartwater Production in Carbonate Reservoirs From Deoiled Produced Water and Seawater

SummaryThis research focuses on membrane-separation efficiencies by adjusting the ionic composition of deoiled produced water (PW) and evaluates the possibility for smartwater production from PW for enhanced oil recovery (EOR) in carbonate reservoirs. Key characteristics of smartwater for carbonate reservoirs are increased concentrations of divalent ions and low concentrations of monovalent ions compared with seawater.In this research, PW was pretreated with media filters, which resulted in 96 to 98% oil removal. This deoiled PW was used as feed for nanofiltration (NF) membranes. Combinations of NF retentate with seawater as feed and NF permeate from PW were considered. PW NF permeate, mixed with seawater spiked with multivalent ions, sulfate (SO42−), or phosphate (PO43−), is expected to alter the wettability of oil reservoirs.NF-membrane performance was evaluated in terms of flux and the separation efficiencies of the key scaling ions calcium (Ca) and barium (Ba). The tested membranes removed 60% of Ca2+ and 53% of Ba2+, thereby reducing the scaling tendency. No membrane fouling was observed during the experiments.NF-treated PW was analyzed for solubility of calcium carbonate (CaCO3). The results showed no Ca dissolution, which could affect chalk-reservoir compaction. This research also reflects the use of nonprecipitating PO43− for smartwater production, simultaneously decreasing the Ba concentration and the scaling potential of PW. The results obtained conclude that spiking PO43− below 12 mM showed no indication of chalk dissolution during equilibration tests at room temperature. Experiments performed with 44 mM of PO43− resulted in calcium phosphate [Ca3(PO4)2] precipitation.A process scheme is proposed for smartwater production by ionic selection from seawater and PW at an operating pressure of 18 bar. Energy-consumption analysis for smartwater production before membrane treatment concluded NF to be economic over other desalination technologies. The power consumed by NF membranes for smartwater production at 18 bar is calculated at 0.88 kW·h/m3, whereas the power consumed is 51.22 and 103.52 kW·h/m3 for reverse osmosis (RO) and multistage flash distillation (MSF), respectively.

Transient increase in reactive surface and the macroscopic Damköhler number in chalk dissolution

Surface area is an important input parameter for reactive transport modelling and it changes with time when rocks dissolve. Here we show direct observations of increased surface area due to chalk (predominantly CaCO3) dissolution, using 3D in situ X-ray microtomography. This transient increase cannot be explained by changes in fluid accessibility or by surface roughening that arises from preferential leaching. We use model simulations to explain how this increase in surface area correlates with the size of the Damköhler space, defined macroscopically using a phenomenological dissolution rate law and the cumulative surface of the microstructure. We attribute this transient increase to the coupling between fluid flow and mineral dissolution and argue that the extent is determined by the advective penetration distance of the reactants. We conclude that using a macroscopic dimensionless number as a qualitative indicator for microstructure evolution has limited applicability.

Strontium dynamics in soil and assimilation by plants during dissolution of conversion chalk

In an experiment carried out on Soddy-podzolic soil, limed with conversion chalk in a wide range of doses, the rate of dissolution of strontium-containing chalk and its effect on soil and plant were studied. Here we show that the complete decomposition of chalk applied to soil is achieved in the 3–4 years after its application. Increase in the concentration of plant available strontium in soil lasts until the chalk is completely dissolved. The dose of applied chalk determined the assimilation of strontium by rapeseed plants. We have found differences in accumulation of strontium by rapeseed in the year of application of chalk and in the third and fourth year of its aftereffect. We conclude that chalkmeliorated soil will generate strontium streams into plants for a longer period. We further propose empirical models that adequately describe: a) the processes of chalk dissolution in the soil; b) the dynamics of the content of strontium compounds accessible to plants in the process of interaction between chalk and soil; c) strontium accumulation in vegetative mass of rapeseed at different stages of chalk dissolution.

On the nature and significance of two mega Chalk dissolution pipe infills, Goring Gap, Chiltern Hills, south Oxfordshire, UK

Two partially exposed infilled pipes hosted by chalk were revealed in excavations into a hillside some 50m above the modern River Thames. The pipes are interpreted as collapse features induced by voids originating at depth rather than classical stream fed sinkholes. Two kinds of infill could be distinguished, sands tentatively assigned to the early Eocene Reading Formation (Lambeth Group) and gravels associated with the mid-Pleistocene Beaconsfield Terrace. The age of development can be constrained by the Thames terrace chronology and this implies major landscape changes due to fluvial erosion since initiation of the pipes some 2Ma and a reactivation event about 1Ma.

Evaluation of the compositional changes during flooding of reactive fluids using scanning electron microscopy, nano-secondary ion mass spectrometry, x-ray diffraction and whole rock geochemistry

Outcrop chalk of late Campanian age (Gulpen Formation) from Liege (Belgium) was flooded with in a triaxial cell for 516 days under reservoir conditions to understand how the non-equilibrium nature of the fluids altered the chalks. The study is motivated by enhanced oil recovery (EOR) processes because dissolution and precipitation change the way in which oils are trapped in chalk reservoirs. Relative to initial composition, the first centimeter of the flooded chalk sample shows an increase in MgO by approximately 100, from a weight percent of 0.33% to 33.03% and a corresponding depletion of CaO by more than 70% from 52.22 to 14.43 wt.%. Except for Sr, other major or trace elements do not show a significant change in concentration. Magnesite was identified as the major newly grown mineral phase. At the same time, porosity was reduced by approximately 20%. The amount of in the effluent brine remained unchanged, whereas was depleted and enriched. The loss of and gain in are attributed to precipitation of new minerals and leaching the tested core by approximately 20%, respectively. Dramatic mineralogical and geochemical changes are observed with scanning electron microscopy–energy-dispersive x-ray spectroscopy, nano secondary ion mass spectrometry, x-ray diffraction, and whole-rock geochemistry techniques. The understanding of how fluids interact with rocks is important to, for example, EOR, because textural changes in the pore space affect how water will imbibe and expel oil from the rock. The mechanisms of dissolution and mineralization of fine-grained chalk can be described and quantified and, when understood, offer numerous possibilities in the engineering of carbonate reservoirs.

Chemostratigraphy and provenance of clays and other non-carbonate minerals in chalks of Campanian age (Upper Cretaceous) from Sussex, southern England

AbstractGeochemical analysis of acid-insoluble residues derived from white chalks and marl seams of Campanian age from Sussex, UK, has been undertaken. All display a broadly similar <2 μm mineralogical composition consisting of smectite or smectite-rich illite-smectite with subordinate illite and minor amounts of talc. Plots of K2O/Al2O3 and TiO2/Al2O3 indicate that most marl seams have an acid-insoluble residue composition which is slightly different to that of the over- and underlying white chalk, implying that marl seams are primary sedimentary features not formed through white chalk dissolution. On the basis of a negative Eu anomaly and trace element geochemistry one marl seam, the Old Nore Marl, is considered to be volcanically derived and best classified as a bentonite; it is considered to correlate with the bentonite M1 of the north German succession.

Reactive transport modelling of groundwater chemistry in a chalk aquifer at the watershed scale

This study investigates thermodynamics and kinetics of water–rock interactions in a carbonate aquifer at the watershed scale. A reactive transport model is applied to the unconfined chalk aquifer of the Champagne Mounts (France), by considering both the chalk matrix and the interconnected fracture network. Major element concentrations and main chemical parameters calculated in groundwater and their evolution along flow lines are in fair agreement with field data. A relative homogeneity of the aquifer baseline chemistry is rapidly reached in terms of pH, alkalinity and Ca concentration since calcite equilibrium is achieved over the first metres of the vadose zone. However, incongruent chalk dissolution slowly releases Ba, Mg and Sr in groundwater. Introducing dilution effect by rainwater infiltration and a local occurrence of dolomite improves the agreement between modelling and field data. The dissolution of illite and opal-CT, controlling K and SiO2 concentrations in the model, can be approximately tackled by classical kinetic rate laws, but not the incongruent chalk dissolution. An apparent kinetic rate has therefore been fitted on field data by inverse modelling: 1.5×10−5 molchalkL −1wateryear −1. Sensitivity analysis indicates that the CO2 partial pressure of the unsaturated zone is a critical parameter for modelling the baseline chemistry over the whole chalk aquifer.

The nature, formation and engineering significance of sinkholes related to dissolution of chalk in SE Hampshire, England

An area around Horndean in SE Hampshire, England, has been studied to determine the reasons for an unusually high density of sinkholes related to dissolution of the underlying chalk. Ground investigations and excavations for a variety of engineering and construction projects in this area have provided detailed information that gives an insight into their formation and development. Contouring of the chalk surface indicates the presence of a north–south-trending palaeovalley, beneath Tertiary cover deposits, to the south of Horndean. The significance of this feature to chalk karstification and continuing sinkhole development is discussed, along with the significance of other geological factors, such as fracture zones in the chalk and the nature and distribution of cover deposits. This forms the basis of a risk assessment of ground subsidence in this area, with particular reference to collapse. The engineering significance of the sinkholes and the design of ground investigations are discussed in the light of experience gained from past projects in this area and the established risk of pollution of the chalk aquifer

Non-tectonic deformations of Pleistocene sediments in the eastern Paris basin, France

Abstract Deformations observed within Quaternary alluvium in the Champagne region (Paris Basin) comprise faults, folds and soft-sediment deformation structures. Their occurrence is linked to the subjacent weathered chalk. Previously interpreted as neotectonic features, the deformations are reinterpreted as karst subsidence features or/and soil displacements due to periglacial processes. Dissolution of chalk has produced superficial subsidence, explaining the geometry of some faults and their large offsets within surface deposits. The freezing-thawing cycles in the porous superficial layers have also favoured gravity instability and deformations, and this can explain local small-scale deformations but also mass movement (sliding). The seismotectonic hypothesis is rejected, because of the absence of regional faults able to generate such large co-seismic offsets. The fault directions and the apparent vertical offsets are not homogeneous at regional scale and they are often inconsistent with the Quaternary stress field. Moreover, the rooting of faults into the basement is not documented and therefore, the neotectonic origin is very doubtful.

A spatial analysis of structural controls on Karst groundwater geochemistry at a regional scale

The coupled spatial investigation of the geometrical and geochemical properties of a chalk karstic aquifer provides information on the degree to which geologic structure controls aquifer functioning and groundwater quality. Major ion concentrations in the chalk aquifer of the Haute-Normandie region (France) were measured at a high spatial resolution (more than 100 sampling sites over a 6000 km2 area) and mapped. The first observation is a continuity of the geochemical properties, in spite of the karstic properties of the aquifer principal components analysis of geochemical maps revealed two types of spatial distributions: ions with an autochthonous origin (Ca2+, HCO3), and ions with a principally allochthonous origin (Cl−, Na+, NO3-, SO42-). Mg2+ was categorised as both autochthonous (chalk dissolution) and allochthonous (brought in by infiltration of Tertiary deposits). To better understand the spatial distribution of the geochemistry, the aquifer geochemistry was compared to the physical properties of the aquifer, in particular aquifer thickness (representing aquifer geometry) and piezometric level (representing aquifer flow). Use of spatial correlation between the geochemical and the geometrical properties provided insight regarding the directional structure of the data and give evidence of directional relations between geochemical and geometrical properties. The degree of mineralisation (principally composed of Ca2+ and HCO3- ions) increased along the direction of flow, corresponding to an increase in chalk dissolution rate along the flowpath. The steepest mineralisation gradients were related to an increase in the Mg/Ca ratio, evidence of longer residence times and corresponding to zones where aquifer flow capacity is limited because of a decrease of the thickness of the flow section (anticlines or faults). These results highlight the dominant role played by the geometry and the structural context in controlling aquifer geochemistry.

Wettability of chalk: impact of silica, clay content and mechanical properties

The success of improved oil recovery from natural fractured chalk fields by injection of water depends largely on the wetting conditions of the reservoir rock and also, to some extent, on the compaction due to water weakening of the formation. Samples from outcrops are often used to mimic the reservoir properties in laboratory work. The present study illustrates that care must be taken when selecting outcrop material; in particular, the content of silica will affect these important properties. Chalk samples from Aalborg, which contained significant amounts of silica and minor amounts of clay (6.3 wt% Si), were studied by SEM and the mineral properties of the silica characterized. The surface chemistry of the porous medium was different from chalk containing smaller amounts of silica and clay (1.4–2.8 wt%). In the presence of a crude oil with high acid number and initial formation water, the water-wet fraction of Aalborg chalk remained close to 1.0 after aging for four weeks at 90°C in the crude oil. The Amott–Harvey wetting index showed, however, the wetting condition to be close to neutral, and only small amounts of water and oil imbibed spontaneously at the residual saturations. The difference in wetting conditions due to different content of silica and clay is also reflected in differences in the mechanical properties. It appeared that the mechanical strength, as studied by a large number of tests, became weaker as the water wetness decreased. The effect of wettability on the water weakening of chalk is discussed in terms of chalk dissolution and the chemistry associated with thin water films. As an overall conclusion and recommendation, a careful comparison should be made of the Si-content in the reservoir rock and outcrop chalk when picking material for laboratory experiments.

Nitrification in a Biofilm at Low pH Values: Role of In Situ Microenvironments and Acid Tolerance

The sensitivity of nitrifying bacteria to acidic conditions is a well-known phenomenon and generally attributed to the lack and/or toxicity of substrates (NH3 and HNO2) with decreasing pHs. In contrast, we observed strong nitrification at a pH around 4 in biofilms grown on chalk particles and investigated the following hypotheses: the presence of less acidic microenvironments and/or the existence of acid-tolerant nitrifiers. Microelectrode measurements (in situ and under various experimental conditions) showed no evidence of a neutral microenvironment, either within the highly active biofilm colonizing the chalk surface or within a control biofilm grown on a nonbuffering (i.e., sintered glass) surface under acidic pH. A 16S rRNA approach (clone libraries and fluorescence in situ hybridizations) did not reveal uncommon nitrifying (potentially acid-tolerant) strains. Instead, we found a strongly acidic microenvironment, evidence for a clear adaptation to the low pH in situ, and the presence of nitrifying populations related to subgroups with low Km s for ammonia (Nitrosopira spp., Nitrosomonas oligotropha, and Nitrospira spp.). Acid-consuming (chalk dissolution) and acid-producing (ammonia oxidation) processes are equilibrated on a low-pH steady state that is controlled by mass transfer limitation through the biofilm. Strong affinity to ammonia and possibly the expression of additional functions, e.g., ammonium transporters, are adaptations that allow nitrifiers to cope with acidic conditions in biofilms and other habitats.

Characterization of the sources of thermal spring‐ and well water in Jordan by rare earth element and yttrium distribution and stable isotopes of H2O

AbstractFour types of thermal groundwater in Jordan were distinguished by Y and rare earth elements (REY) distribution patterns. Complementary to the stratigraphic origin of water in springs or of wells, REY patterns identify either recharge areas covered by basalt, limestones or sandstone, or interaction with basalt‐limestone contact zones. This hydrochemical grouping does not always correspond with “common geological knowledge” of the aquifer lithology of the thermal water. Therefore, comparison of the hydrochemical signatures of REY patterns and the lithological source of water yield insight into transaquifer flow. Out of 44 analysed groundwater, 18 indicated down‐ and 3 upflow of water the latter due to step faults near the Rift system. During transaquifer flow REY patterns of groundwater from basalts and gypsum beds or gypsum‐cemented sandstones are not changed by subsequent interaction with limestones, whereas in groundwater originating from dissolution of chalk and limestones REY patterns are adjusted to those typical for gypsum‐bearing sediments. Cross plots of δ18O vs. δ2H reveal essentially two trends. The main trend of water from limestone aquifers define a mixing line of past to recent meteoric water with negligible contributions of Pleistocene water. Some water from Eocene aquifers plot on the local Mediterranean meteoric water line, others plot together with water from sandstone aquifers at enhanced δ18O values due to hydrothermal overprinting.

The influence of CO 2 gas and carbonate water on the mechanical stability of chalk

The mechanical strength of high porosity chalk is affected by using carbonate water as EOR (Enhanced Oil Recovery) fluid. The water-weakening effect is enhanced due to increased dissolution of chalk in the presence of CO 2(aq). In this study, the mechanical properties of chalk were compared with and without CO 2(aq) present in the injected water. By use of a standard triaxial cell, series of samples with and without pre-flooding at confining pressure of 0.5–1.0 MPa were hydrostatic loaded up to yield point at room temperature or 90 °C. Then a major part of the samples were exposed to subsequent creep and flooding phases at increased stress levels of about 2 MPa above yield point. In all cases flooding experiments were performed without any backpressure and with flooding pressure varying between 0.2 and 0.8 MPa. Injection of pure CO 2 gas into water-saturated chalk resulted in only marginal weakening of the chalk material. At stress levels below the yield point, the chalk exposed to carbonate water becomes considerably weaker than chalk flooded with pure Eq. Water. At a given flooding pressure of carbonate water, an increase in temperature to 90 °C improved the chalk stability. Flooding with CO 2 saturated modified seawater, which contained an enhanced concentration of sulfate, increased the strain significantly due to the precipitation of CaSO 4·2H 2O(s). The preferential oil-wet cores at S or = 0.62 experienced an increased strain of 20% compared to the water-wet test series during flooding with CO 2-saturated Eq. water. Increasing the confining pressure by a factor of 10, strain values of about 10 times higher or even more were observed when flooding with carbonate water. The experimental observations are discussed in terms of chemical and pressure dissolution of chalk.

Pressure solution in chalk

Pressure-solution residues in the Cretaceous to Paleocene chalk from the North Sea area were studied to understand the pressure-solution process and fluid flow. Residue seams reach lengths and thickness of more than 800 and 0.15 m (2625 and 0.5 ft), respectively. Seams can present significant barriers to fluid flow because they have nannodarcy permeability and hold back large pressure differentials. Stylolite amplitudes decrease when they merge, making it difficult to quantify volume loss. Measuring amplitudes allows volume-loss estimates using a new dissolution ratio method. The sum of the thicknesses of all residues is multiplied by the maximum amplitude-to-residue thickness ratio. On average, 30 mm (1.2 in.) of chalk had to be dissolved to produce a 1-mm (0.04-in.)-thick residue. The volume loss of chalk from Flamborough averages about 50% and is 60% in the Machar oil field, United Kingdom Central Graben. The minimum fluid volume required to produce the volume loss in 1 unit volume of preserved chalk on the Machar field is estimated to be 8000 unit volumes. This and the stable isotopes of vein carbonates imply that the pressure-solution process involved an open-fluid system. High illite content in mixed layered illite-smectite and high illite crystallinity of clays in the pressure-solution seams in the Machar reservoir indicate high diagenetic maturity, with implied temperatures in the range of 200–360C (392–680F), which is greater than the present-day reservoir temperature of 85C (185F). The anomalously hot temperatures are interpreted to be produced by deep mineralizing fluids transported from the Central Graben. The lack of abundant veining in the chalk and the large fluid volumes involved in the chalk dissolution suggest that this was an open pressure-solution system.