Chalk Samples Research Articles

Improving the method of low‐temperature anisotropy of magnetic susceptibility (LT‐AMS) measurements in air

AbstractThis study examines the limitations of the method of low‐temperature anisotropy of magnetic susceptibility (LT‐AMS) measurements in air and presents technical improvements that significantly reduce the instrumental drift and measurement errors. We analyzed the temperature profile of porous chalk core after cooling in liquid nitrogen and found that the average temperature of the sample during the LT‐AMS measurement in air is higher than 77K and close to 92K. This analysis indicates that the susceptibility of the paramagnetic minerals are amplified by a factor ∼3.2 relative to that of room temperature AMS (RT‐AMS). In addition, it was found that liquid nitrogen was absorbed in the samples during immersing and contributed diamagnetic component of ∼−9 × 10−6 SI to the total mean susceptibility. We showed that silicone sheet placed around and at the bottom of the measuring coil is an effective thermal protection, preventing instrument drift by the cold sample. In this way, the measuring errors of LT‐AMS reduced to the level of RT‐AMS, allowing accurate comparison with standard AMS measurements. We examined the applicability of the LT‐AMS measurements on chalk samples that consist <5% (weight) of paramagnetic minerals and showed that it helps to efficiently enhance the paramagnetic fabric. The present study offers a practical approach, which can be applied to various types of rocks to better delineate the paramagnetic phase using conventional equipment.

Unraveling chalk microtextural properties from indentation tests

The petrographical, petrophysical and geomechanical properties of the less commonly studied low permeability or tight chalks are presented in this study. The latter are relevant as potential unconventional reservoirs or intra-reservoir seals. Tight chalks encompass different lithotypes, in which the main factors controlling the petrophysical properties as shown in this study are the non-carbonate content and the degree of cementation. Those parameters strongly modify chalk microtexture and thus its porous network, reducing pore-sizes hence altering poroperm properties. In order to better understand the characteristics of tight chalks, an integrated petrographical, petrophysical and geomechanical study was carried out on a set of 65 chalk samples from Northwestern European outcrops, covering a wide range of lithotypes. The dataset gathered covers a broad spectrum of values for the determined petrophysical (e.g. porosities from 9 to 45%) and geomechanical properties (e.g. strengths from 3 to 60MPa). In the framework of this study, indentation tests were performed on the chalk samples. This technique proved to be a successful method to quickly estimate rock strength. Indeed, a good linear correlation (R2=0.90) has been established between indentation strength and UCS. Furthermore, indentation tests yielded valuable information about the chalk properties, both in terms of petrographical (cementation/clay-content), petrophysical (exponential relationship with porosity) and geomechanical (in relation to the elastic parameter and plasticity index) properties. This cheap and easy-to-operate method is a promising tool to indirectly estimate the mechanical parameters of chalks, when core samples are unavailable for laboratory testing in oil-field wells.

New insight into the microtexture of chalks from NMR analysis

An integrated petrographical and petrophysical study was carried out on a set of 35 outcrop chalk samples, covering a wide range of lithologies and textures. In this study various chalk rock-types have been characterized, in terms of microtextures and porous network, by integrating both geological, sediment-petrological and petrophysical data, including porosity, permeability, low-field NMR (Nuclear Magnetic Resonance), MICP and specific surface area (BET) measurements. The data allow an in depth understanding of the NMR signal of chalks, with a focus on tight chalks, including all low reservoir quality chalks independently of their sedimentological and/or diagenetic history. The study aims to develop an NMR-based approach to characterize a broad range of chalk samples. The provided laboratory low-field NMR chalk classification can be used as a guide to interpret NMR logging data.Based on the petrographical and petrophysical analysis, 6 groups of samples were identified, each of them characterized by a unique NMR signature: (1) micritic chalks, (2) grainy chalks, (3) cemented chalks, (4) marl-seam chalks, (5) argillaceous chalks and (6) silicified chalk. NMR T2 distributions were linked to pore body size and T2 logarithmic (T2lm) was calculated. It is apparent that tight chalks, whether their characteristics are sedimentological or diagenetic, yield smaller pore body sizes (T2lm < 20 ms), as well as narrower pore throats (average radius < 150 nm) and lower permeability values (typically below 0.2 mD). Grainy chalks possess T2 distributions reflecting larger pore sizes (T2lm > 60 ms) and pore throats (average radius > 290 nm) and higher permeabilities (up to 13 mD). The marl-seam chalk samples yield bimodal T2 distributions, with a first peak related to the micritic matrix pores and a second peak related to intraparticle pores within fossils. For all samples, permeability was inferred from NMR spectra using SDR (Schlumberger Doll Research) model.

Laboratory testing the grindability of carbonate mineral raw material of the site Spasina Brdjani: Chalk samples

Laboratory testing the grindability of carbonate mineral raw material of the site Spasina Brdjani: Chalk samples

Late Maastrichtian foraminiferal response to sea-level change and organic flux, Central Graben area, Danish North Sea

Abstract Foraminiferal palaeoecological analyses were carried out on 124 upper Maastrichtian chalk samples from the M-10X and E-5X wells of the Danish Central Graben. The two wells demonstrate similar trends, with some notable differences. Both are strongly dominated by planktic foraminifers, of which the small, biserial Heterohelix globulosa is by far the most common species. Based on variations within five significant, benthic foraminiferal morphogroups and the plankton/benthos ratio, eight specific foraminiferal intervals have been described. The faunal and palaeoenvironmental changes observed during the late Maastrichtian period were, in most places and especially in the lower part, not very distinct, and it is believed that the palaeoenvironment during the majority of the interval was a mostly stable, deep outer-shelf environment characterized mainly by pelagic sedimentation under temperate, suboxic conditions. More unstable conditions characterized the latest Maastrichtian. The analyses show that the sediments in the M-10X well were deposited in a generally deeper palaeoenvironment than those from E-5X. The influx of common Pseudotextularia elegans (three acmes), together with scattered specimens of the typical Tethyan species Abathomphalus mayaroensis and Pseudoguembelina hariaensis (in E-5X only), indicate that relatively warm conditions prevailed, at least periodically, during the latest part of the late Maastrichtian in both areas.

The effect of divalent ions on the elasticity and pore collapse of chalk evaluated from compressional wave velocity and low-field Nuclear Magnetic Resonance (NMR)

Abstract The effects of divalent ions on the elasticity and the pore collapse of chalk were studied through rock-mechanical testing and low-field Nuclear Magnetic Resonance (NMR) measurements. Chalk samples saturated with deionized water and brines containing sodium, magnesium, calcium and sulfate ions were subjected to petrophysical experiments, rock mechanical testing and low-field NMR spectroscopy. Petrophysical characterization involving ultrasonic elastic wave velocities in unconfined conditions, porosity and permeability measurements, specific surface and carbonate content determination and backscatter electron microscopy of the materials were conducted prior to the experiments. The iso-frame model was used to predict the bulk moduli in dry and saturated conditions from the compressional modulus of water-saturated rocks. The effective stress coefficient, as introduced by Biot, was also determined from density and ultrasonic velocities measured on core plugs. Low-field NMR spectroscopy was used in addition to the mechanical testing to prove any changes observed after the saturation related to the surface-to-volume ratio of the pore space in each of the samples or to surface relaxivity. Backscatter-electron (BSE) images were recorded in order to identify the texture of the core plugs under investigation. The experimental results revealed that both elasticity and pore collapse are influenced by the presence of divalent ions in distinct ways. Compressional wave velocities indicate that saturation with water rich in magnesium and calcium ions softens the contact among the mineral grains. Pore collapse strength is deteriorating after the saturation of chalk with water rich in divalent ions. The presence of calcium and sulfate ions in the saturating fluid results in pore collapse at lower stresses than in the case when samples are saturated with deionized water or sodium chloride solution. Low field NMR spectrometry revealed precipitation of crystals in the pore space of chalk saturated with Mg-rich brine. The precipitation of Mg-carbonates was not used to explain the deteriorating pore collapse strength and effects on the elasticity after the saturation since none of the other plugs saturated with divalent ions (Ca2+ and SO 4 2 + ) experienced it.

Stone Monuments Consolidation with Nanomaterials

Historical monuments suffer different forms of degradation, due to some improper works on architecture structure, vibrations caused by blasting, traffic, the inadequate restoration, the phenomenon of freeze-thaw, air pollution, humidity and temperature variations, friable mortar, deposits adhering impurities (dust, smoke, tar), soluble efflorescence, poorly soluble or insoluble salts (nitrate, sulfate, chloride, carbonate), and the action of microorganisms. Nowadays, the nanomaterials represent an alternative in architecture conservation, mainly due to their improved mechanical properties, their compatibility as consolidating materials, and because they obey the principle of authenticity of historical monuments. In this paper, hydroxyapatite nanoparticles (HAp) are applied to the chalk samples prelevated from Basarabi monument. Some physico-chemical and mechanical properties have been evaluated and discussed for untreated chalk stone and for the treated one with HAp.

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.

Particle Diffusion in Complex Nanoscale Pore Networks

We studied the diffusion of particles in the highly irregular pore networks of chalk, a very fine-grained rock, by combining three-dimensional X-ray imaging and dissipative particle dynamics (DPD) simulations. X-ray imaging data were collected at 25 nm voxel dimension for two chalk samples with very different porosities (4% and 26%). The three-dimensional pore systems derived from the tomograms were imported into DPD simulations and filled with spherical particles of variable diameter and with an optional attractive interaction to the pore surfaces. We found that diffusion significantly decreased to as much as 60% when particle size increased from 1% to 35% of the average pore diameter. When particles were attracted to the pore surfaces, even very small particles, diffusion was drastically inhibited, by as much as a factor of 100. Thus, the size of particles and their interaction with the pore surface strongly influence particle mobility and must be taken into account for predicting permeability in nanoporous rocks from primary petrophysical parameters such as surface area, porosity, and tortuosity.

Smaller Calcite Lattice Deformation Caused by Occluded Organic Material in Coccoliths than in Mollusk Shell

The growth and nucleation of biominerals are directed and affected by associated biological molecules. In this paper, we investigate the influence of occluded biomolecules on biogenic calcite from the coccolithophorid Pleurochrysis carterae and from chalk, a rock composed predominantly of fossil coccoliths. We compare the results with data on chalk from the extensively studied mussel Pinna nobilis that served as a control. Using high resolution synchrotron powder X-ray diffraction combined with in situ heating, the influence of organic compounds on the structure of the inorganic phase was probed. Two heating cycles allow us to differentiate the effects of thermal agitation and organic molecules. Single peak analysis and Rietveld refinement were combined to show significant differences resulting from the occluded biomolecules on the mineral phase in biogenic calcite in the mollusk shell and the coccolithophorids. These differences were reflected in lattice deformation (macrostrain), structure (microstrain), and atomic disorder distributions (δorganic). The influence of the biological macromolecules on the inorganic phase was consistently smaller in the P. carterae compared to P. nobilis. This suggests that the interaction between biomolecules and calcite is not as tight in the coccoliths as in the shell. Although the shape of chalk has been preserved over millions of years, no major influence on the crystal lattice was observed in the chalk samples.

Nickel adsorption on chalk and calcite

Nickel uptake from solution by two types of chalk and calcite was investigated in batch sorption studies. The goal was to understand the difference in sorption behavior between synthetic and biogenic calcite. Experiments at atmospheric partial pressure of CO2, in solutions equilibrated with calcite and chalk and pH ranging from 7.7 to 8.8, explored the influence of initial concentration and the amount and type of sorbent on Ni uptake. Adsorption increases with increased surface area and pH. A surface complexation model describes the data well. Stability constants for the Ni surface complex are log KNi=−1.12 on calcite and log KNi=−0.43 and −0.50 on the two chalk samples. The study confirms that synthetic calcite and chalk both take up nickel, but Ni binds more strongly on the biogenic calcite than on inorganically precipitated, synthetic powder, because of the presence of trace amounts of polysaccharides and clay nanoparticles on the chalk surface.

The surface reactivity of chalk (biogenic calcite) with hydrophilic and hydrophobic functional groups

The surface properties of calcium carbonate minerals play an important role in a number of industrial and biological processes. Properties such as wettability and adsorption control liquid–solid interface behaviour and thus have a strong influence on processes such as biomineralisation, remediation of aquifers and oil recovery. We investigated how two model molecules of different polarity, namely water and ethanol, interact with reservoir and outcrop chalk samples and we compared their behaviour with that of pure, inorganically precipitated calcite. Thermodynamic quantities, such as the work of wetting, surface energy and isosteric adsorption enthalpy, were determined from vapour adsorption isotherms. The chalks were studied fresh and after extraction of organic residues that were originally present in these samples. The work of wetting correlates with the amount of organic matter present in the chalk samples but we observed a fundamental difference between the adsorption properties of chalk and pure, inorganically precipitated calcite toward the less polar, ethanol molecule. Further analysis of the chemical composition of the organic matter extracted from the chalk samples was made by gas chromatography (GC–MS). Monitoring surface composition by X-ray photoelectron spectroscopy (XPS) before and after extraction of the organic material, and with atomic force microscopy (AFM), showed that nanometer sized clay crystals observed on the chalk particle surfaces could be an important part of the reason for the differences. Removal of the extractable portion of the hydrocarbons liberates adsorption sites that have different wetting properties than the rest of the chalk and these have an energy distribution that is similar to clays. Thus, the results exemplify the complexity of biogenic calcite adsorption behaviour and demonstrate that chalk wetting in drinking water aquifers as well as oil reservoirs is controlled partly by the nanoparticles of clay that have grown on the chalk surfaces and partly by adsorbed organic material.

Use of Descartes Folium Equation for Deriving a Relation between Total Aperture of Fractures after Uniaxial Compression and Strain Parameters of Different Rocks Exhibiting Negative Total Volumetric Strains

The axial, crack and total volumetric strains, porosity, elastic constants, crack damage stresses, uniaxial compressive strengths, as well as fracture apertures and number of fracture traces in rock samples surface after compression were defined for different chalk, basalt, dolomite, granite, limestone and sandstone samples exhibiting negative total volumetric strain at failure. It is established that the total (summed) aperture of vertical fractures obtained on the lateral surface of rock sample is related to three characteristic strain parameters: axial strain at the onset of negative total volumetric strain, axial failure strain and negative total volumetric strain at failure. The relation is based on Descartes folium equation, where the length of the loop of folium is equal to axial strain coordinate at the onset of negative total volumetric strain. This relation shows that the total aperture increases according to power law with increasing difference between axial failure strain and axial strain at the onset of negative total volumetric strain. Simultaneously, an increase in this difference leads to an increase in the value of negative total volumetric strain at failure. It is found that a direct correlation between total aperture of fractures and negative total volumetric strain at failure is relatively weak. Nevertheless, total aperture of fractures tends to increase with increasing absolute value of negative total volumetric strain at failure. It is revealed that there is no connection between the number of fracture traces and negative total volumetric strain at failure.

Nanopore structures, statistically representative elementary volumes, and transport properties of chalk

AbstractDual focused ion beam‐scanning electron microscopy (FIB‐SEM) is frequently being used to characterize nano‐scale pore structures observed in carbonate and shale gas rocks. However, applications are limited to qualitative analysis of nanopore structures. Herein, the concept of statistical representative elementary volumes (SREV) is applied to FIB‐SEM data of a Cretaceous chalk sample. Lattice‐Boltzmann (LB) simulations with multiple relaxation time and topological analysis show that the size of the SREV for this chalk sample can be established at ~ 10 microns based on anisotropic permeability, tortuosity, and specific surface area. This work confirms that the FIB‐SEM technique can be used for the quantitative analysis of nanopore structures and highlights nano‐scale basis for strong anisotropy in the presence of fractures. In addition, nanopores and pore throats are not resolved at voxel dimensions less than ~ 80 nm, resulting in significant underestimation of surface area and permeability.

Scale effect and impact of discontinuities in the dynamic elastic constants of the Campanian chalk of Bougival (France)

Abstract Physical properties of in situ rock mass are usually estimated from results obtained through laboratory tests on intact rock samples because the access to in situ rock may be quite challenging. This approach however raises some questions concerning the number of samples needed for reliable result, the validity of the extrapolation of the parameters from centimetre scale to a large rock mass and finally the effect of discontinuities contained in the rock mass. An underground quarry in Bougival with easy access to metre-scale pillars and the possibility to collect large number of samples has been chosen to analyse the scale effect and the anisotropy of the Campanian chalk. Different experiments have been designed to determine the dynamic elastic properties (Young’s modulus and Poisson’s ratio) based on geophysical approaches: ultrasonic measurements on laboratory samples, and “hammer” seismic measurements in situ. The static Young’s modulus and Poisson’s ratio have been determined through uniaxial compression tests on centimetre core samples. Pillars with and without visible discontinuities, as well as with various overburden rock thicknesses, have been chosen in order to analyse the possible impact of different heterogeneities on the elastic properties. Core samples of intact chalk, with 40mm to 100mm diameters, have been studied in laboratory. The high dispersion observed on the different results suggests that if only a few tests are analysed, the conclusions may not be representative. A statistical approach is more appropriate to analyse the mechanical properties of the chalk. The dynamic Young’s Modulus and Poisson’s ratio calculated from laboratory samples (centimetres) and in situ rocks (about ten metres) do not reveal any clear impact of size on these elastic properties. The presence of discontinuities has a major impact on both the dynamic Young’s modulus and Poisson’s ratio. Decreasing values of these properties have been observed where discontinuities (fractures, flints) have been detected. Finally, the overburden rock thickness above the underground quarries (from 14m to 50m) seems to have no effect on the mechanical properties; the uncertainty of the measurements, partly due to the heterogeneity of the chalk mass, is likely to be more important than the effect of load on the pillars.

Preferential Adsorption of Hydrocarbons to Nanometer-Sized Clay on Chalk Particle Surfaces

The demand for oil is increasing, but many reservoirs are reaching the end of their productive lifetime. A clearer understanding of the fundamental chemical and physical controls on the wetting behavior of reservoir pore surfaces would provide clues for developing methods to improve, or enhance, recovery of the currently inaccessible oil (improved/enhanced oil recovery, IOR/EOR). In this work, the surfaces of chalk were investigated to understand hydrophobicity at nanometer scale spatial resolution. Chalk samples from the gas and water zones of the Danish sector in the North Sea Basin were used. With inverse gas chromatography (IGC), the surface characteristics were compared. Chalk from the gas zone has a lower surface energy, dispersive as well as specific, than chalk from the water zone, clearly indicating that the gas zone pore surfaces are more hydrophobic. X-ray photoelectron spectroscopy shows that the concentration of hydrocarbons is higher in gas zone chalk than in water zone chalk, which is consistent with IGC measurements. With combined atomic force microscopy and chemical force mapping, we demonstrated that the hydrophobicity of chalk is not correlated spatially with the calcite of the coccolith elements, but rather with nanometer-sized authigenic clay crystals that decorate the surfaces of the coccoliths. Our results suggest that clay and adsorbed organic material, not calcite, are responsible for wettability alterations in chalk during the introduction of hydrocarbons. Furthermore, we show that surface hydrophobicity is heterogeneous, even within single-clay laths.

Human Geophagia, Calabash Chalk and Undongo: Mineral Element Nutritional Implications

The prime aim of our work is to report and comment on the bioaccessible concentrations – i.e., the soluble content of chemical elements in the gastrointestinal environment that is available for absorption – of a number of essential mineral nutrients and potentially harmful elements (PHEs) associated with the deliberate ingestion of African geophagical materials, namely Calabash chalk and Undongo. The pseudo-total concentrations of 13 mineral nutrients/PHEs were quantified following a nitric-perchloric acid digestion of nine different Calabash chalk samples, and bioaccessible contents of eight of these chemical elements were determined in simulated saliva/gastric and intestinal solutions obtained via use of the Fed ORganic Estimation human Simulation Test (FOREhST) in vitro procedure. The Calabash chalk pseudo-total content of the chemical elements is often below what may be regarded as average for soils/shales, and no concentration is excessively high. The in vitro leachate solutions had concentrations that were often lower than those of the blanks used in our experimental procedure, indicative of effective adsorption: lead, a PHE about which concern has been previously raised in connection with the consumption of Calabash chalk, was one such chemical element where this was evident. However, some concentrations in the leachate solutions are suggestive that Calabash chalk can be a source of chemical elements to humans in bioaccessible form, although generally the materials appear to be only a modest supplier: this applies even to iron, a mineral nutrient that has often been linked to the benefits of geophagia in previous academic literature. Our investigations indicate that at the reported rates of ingestion, Calabash chalk on the whole is not an important source of mineral nutrients or PHEs to humans. Similarly, although Undongo contains elevated pseudo-total concentrations of chromium and nickel, this soil is not a significant source to humans for any of the bioaccessible elements investigated.

In-situ and Laboratory Tests to Evaluate the Impact of Water Table Fluctuations on Stability of Underground Chalk Mines

Shallow underground mines can be flooded if there is a rise in the water table, which reduces pillar strength and increases risk of collapse and surface subsidence. To prevent this, INERIS is studying rock behavior in two underground chalk mines in northern France. In the first mine, the water content of a flooded pillar is almost constant (∼20%) in its internal zone, while it varies from 14% to 22% in its external zone, due to variations in the groundwater table. In the second mine, the pillar is episodically flooded and, even if no flooding occurs, the groundwater table variations cause simultaneous fluctuations of the pillar extension rates due to capillarity: from 4-5% in the middle to 10-14% in the external zone. In parallel, laboratory tests have been carried out on chalk samples. They show differences between the geomechanical behavior of these chalks: one is dolomitic and has a higher inherent strength (i.e, more resistant to water) than the other, which has a glauconitic composition.

Measurements of spontaneous potential in chalk with application to aquifer characterization in the southern UK

We report the first measured values of the streaming potential coupling coefficient in chalk samples saturated with natural groundwater, and preliminary field measurements of the spontaneous potential (SP), at both ambient and pumped conditions, at a test site in the Berkshire Chalk aquifer in the southern UK. The ultimate aim of the work is to use measurements of SP, in conjunction with borehole data, to characterize groundwater flow and aquifer properties. Laboratory measurements yield a value of the streaming potential coupling coefficient of −60 ± 4 mV MPa −1 and a corresponding zeta potential of −13 ± 1 mV. A negative zeta potential contrasts with previous published open-system measurements on artificial calcite, and may reflect the presence of organic material in the natural chalk samples or HCO 3 and SO 4 ions in the groundwater. Field measurements at ambient conditions show temporal variations in SP consistent with flow processes within the aquifer, but no coherent spatial variations. Measurements during water abstraction demonstrate that voltages at the ground surface and in monitoring boreholes become more positive during pressure drawdown and more negative during pressure build-up, consistent with the negative values of streaming potential coupling coefficient and zeta potential observed in the laboratory. Moreover, the magnitude of the change in voltage is similar to that estimated using the laboratory value of the coupling coefficient. Our results suggest that measurements of SP may make a valuable contribution to characterizing groundwater flow in the UK Chalk aquifer.

Improved segmentation of X-ray tomography data from porous rocks using a dual filtering approach

We present a new method for image segmentation of X-ray microtomography data that is especially adapted for samples where the feature of interest, in this case the pore size is about the same order of magnitude as the resolution of the data. It combines two filters that are widely used in image processing, Unsharp Mask and Median Filter, to preprocess the tomography data before applying regular Otsu thresholding. For assessing performance, two types of simulated data were constructed, where the true segmentation is known. One data set was purely generic, with tuneable blurring and noise, and a second set used presegmented tomography data taken from chalk samples, where noise was added. Comparison with standard Otsu thresholding and region growing showed superior segmentation results for almost all levels of noise and blurring using the dual filtering approach. It is far more resistant to noise but most important, it retains all the main structural parameters (pore volume, surface area and material volume), even at high noise levels and it provides reliable results across a set of chalk samples with a range of microstructures.