Effect Of Mineralogy Research Articles

Incorporation of Geometallurgical Input into Gold Mining System Simulation to Control Cyanide Consumption

The Alhué deposit (Melipilla, Chile) is an example of a hydrothermal Au-Ag-Zn(-Pb) vein system hosted within the volcanic rocks of the Las Chilcas Formation. The dominant ore minerals observed are free electrum and native gold associated with silver sulfosalts, and with magnetite and base metal sulphides, including pyrite +/− sphalerite-galena-chalcopyrite. The alteration assemblage in the veins mainly consists of quartz epidote-chlorite-actinolite with lesser smectite, amphibole, and calcite-kaolinite-garnet. Mineralized veins also contain variable amounts of base metals, some of which (e.g., copper and iron) are considered harmful to the extraction of precious metals. Iron and especially copper minerals are known cyanide consumers; ore type classification schemes that do not consider the detrimental effects of such mineralogy or process elements can ultimately result in metal losses from ore feed restrictions, as well as spikes in cyanide consumption and higher operating costs. Mineralogical and geological variation can nonetheless be managed by applying alternating modes of operation as demonstrated in this paper; the decision to switch between modes is governed by current and forecasted stockpile levels feeding into the process. Simulations based on experiences at the Alhué deposit are provided that demonstrate the importance of standardized operational modes and their potential impact on cyanide consumption control.

Experimental investigation of optimum adhesion properties for anionic emulsions in road maintenance applications

Anionic emulsions are widely used in North America for road maintenance applications but are less popular in Europe. Due to their distinctive characteristics, the use of anionic emulsions is advantageous when local aggregate is excessively dusty and the cost to wash them to meet requirements would be too expensive. However, anionic emulsions’ compatibility, in terms of adhesion, with certain types of aggregate is reported to be limited. This paper presents the results of an experimental study that was conducted firstly to investigate the effect of aggregate mineralogy on the degree of adhesion (i.e. the bond) between the aggregate and the bitumen using anionic and cationic bitumen emulsions, and secondly to evaluate the potential development and use of new adhesion agents/anti-strips for anionic rapid-set emulsions used in chip seal applications. For this purpose, the degree of adhesion that was achieved between the emulsions used and a range of selected aggregates was measured by means of a series of internationally recognised laboratory adhesion tests.The experimental laboratory work confirmed that the degree of adhesion between the aggregate and emulsion is governed to a large extent by aggregate mineralogical composition and, in particular, its associated electrostatic interaction with a given emulsion. The results obtained indicated that a higher degree of adhesion was achieved when an aggregate was combined with an emulsion possessing the opposite surface charge. Further laboratory test results suggest that the addition of amine-based adhesion agents to an anionic emulsion can significantly improve its degree of adhesion with aggregates possessing an electro-negative surface charge.

Effects of Aggregate Shape and Mineralogy on Relationships between Concrete Mechanical Properties

Effects of Aggregate Shape and Mineralogy on Relationships between Concrete Mechanical Properties

Compaction of the Groningen Gas Reservoir Sandstone: Discrete Element Modeling Using Microphysically Based Grain‐Scale Interaction Laws

AbstractReservoir compaction, surface subsidence, and induced seismicity are often associated with prolonged hydrocarbon production. Recent experiments conducted on the Groningen gas field's Slochteren sandstone reservoir rock, at in‐situ conditions, have shown that compaction involves both poroelastic strain and time independent, permanent strain, caused by consolidation and shear of clay films coating the sandstone grains, with grain failure occurring at higher stresses. To model compaction of the reservoir in space and time, numerical approaches, such as the Discrete Element Method (DEM), populated with realistic grain‐scale mechanisms are needed. We developed a new particle‐interaction law (contact model) for classic DEM to explicitly account for the experimentally observed mechanisms of nonlinear elasticity, intergranular clay film deformation, and grain breakage. It was calibrated against both hydrostatic and conventional triaxial compression experiments and validated against an independent set of pore pressure depletion experiments conducted under uniaxial strain conditions, using a range of sample porosities, grain size distributions, and clay contents. The model obtained was used to predict compaction of the Groningen reservoir. These results were compared with field measurements of in‐situ compaction and matched favorably, within field measurement uncertainties. The new model allows systematic investigation of the effects of mineralogy, microstructure, boundary conditions, and loading path on compaction behavior of the reservoir. It also offers a means of generating a data bank suitable for developing generalized constitutive models and for predicting reservoir response to different scenarios of gas extraction, or of fluid injection for stabilization or storage purposes.

Effect of grain sorting, mineralogy and cementation attributes on the localized deformation in porous rocks: A numerical study

Practical attempts are made to develop a generalized framework that is capable of characterizing the diverse forms of deformation band. A distinct element model enabling grain fracture and pore collapse is presented, to quantify attributes such as porosity, grain size, mineralogy, cementation, and boundary constraint. The micro-cracking activity, grain fragmentation and energy components are tracked to inspect the tempo-spatial development of localization under contractional regimes. Typically, the porosity exerts the first-order control on the evolution of failure mode with confining pressure: the low-confinement response is always dilatant with the generation of axial split or shear band, and the high-confinement behaviors depend on porosity, where distributed cataclasis dominates at low porosity and collapsed pores often coalesce into a compaction band at high porosity. The nucleation and propagation of localization relate closely to the micro-cracking activity and energy budget, on which grain sorting, boundary constraint, mineralogy and cementation attributes have a direct impact. When the maximum grain size is not more than five times the minimum, the relative abundance of coarser grains facilitates the compaction localization, which is accompanied by a smaller magnitude in both fragmentation and energy release. The mineralogy and cementation generally affect the competition of tensile and shear cracking events on the grain interior and boundary, and have minor effect on the rupture morphology; the frictional boundary does little to the cracking rate while seriously impact the low-confinement performance. Numerical results suggest that the compaction band may originate from the intrinsic defect characterized by pore structure, and the other attributes are of secondary importance.

Effects of surface roughness and mineralogy on the sorption of Cm(III) on crystalline rock

Crystalline rock is one of the host rocks considered for a future deep geological repository for highly active radiotoxic nuclear waste. The safety assessment requires reliable information on the retention behavior of minor actinides. In this work, we applied various spatially resolved techniques to investigate the sorption of Curium onto crystalline rock (granite, gneiss) thin sections from Eibenstock, Germany and Bukov, Czech Republic. We combined Raman-microscopy, calibrated autoradiography and µTRLFS (micro-focus time-resolved fluorescence spectroscopy) with vertical scanning interferometry to study in situ the impact of mineralogy and surface roughness on Cm(III) uptake and molecular speciation on the surface. Heterogeneous sorption of Cm(III) on the surface depends primarily on the mineralogy. However, for the same mineral class sorption uptake and strength of Cm(III) increases with growing surface roughness around surface holes or grain boundaries. When competitive sorption between multiple mineral phases occurs, surface roughness becomes the major retention parameter on low sorption uptake minerals. In high surface roughness areas primarily Cm(III) inner-sphere sorption complexation and surface incorporation are prominent and in selected sites formation of stable Cm(III) ternary complexes is observed. Our molecular findings confirm that predictive radionuclide modelling should implement surface roughness as a key parameter in simulations.

Influence of mineralogy and surfactant concentration on zeta potential in intact sandstone at high pressure

Hypothesis:Zeta-potential in the presence of brine has been studied for its application within hydrocarbon reservoirs. These studies have shown that sandstone’s zeta-potential remains negatively charged, non-zero, and levels-off at salinities > 0.4 mol.dm−3, thus becoming independent of salinity when ionic strength is increased further. However, research conducted to date has not yet considered clay-rich (i.e. clay ≥ 5 wt%) sandstones. Experiments:Firstly, streaming potential measurements were conducted on Bandera Gray sandstones (clay-rich and clay-poor) with 0.6 and 2 mol.dm−3 NaCl brine-saturated in pressurised environments (6.895 MPa overburden and 3.447 MPa back-pressure). Secondly, the streaming potential was determined at identical conditions for the effect of two surfactants, SDBS and CTAB, at concentrations of 0.01 and 0.1 wt% on the clay-poor sample in 0.6 mol.dm−3 NaCl. Thirdly, a comparison of zeta potentials determined via electrophoretic and streaming potential was conducted. Accordingly, this work analyses the effects of mineralogy and surfactants within this process. Findings:Clay-rich sandstone possessed lower zeta-potentials than clay-poor sandstone at the two tested salinities. SDBS reduced zeta-potential and yielded higher repulsive forces rendering the rock more hydrophilic. Additionally, electrophoretic zeta-potentials were higher when compared to streaming zeta-potentials. Mechanisms for the observed phenomena are also provided.

Effects of filler mineralogy on the compressive strength of cementitious mortars

Substituting cement with fillers is crucial to formulate cost-effective cementitious materials with low CO2 emissions. However, despite limestone, there is a lack of knowledge of fillers from other mineralogical sources for use in cementitious pastes. This study investigates the effects of characteristics of fillers from 6 mineralogical sources on the reactivity and compressive strength of the cementitious pastes, which could allow increasing industrial possibilities. The filler density and the paste total bound water content allowed to determine the paste porosity, which has a much better fit with the compressive strength than the water-binder ratio.

Reducing lead solubility in kaolinitic and oxidic soils by application of limed sewage sludge

AbstractLittle attention has been paid to the effects of soil mineralogy on remediation efficiency of sewage sludge. To fill this gap, we applied limed sewage sludge to Pb‐contaminated soil samples of an Oxisol rich in hematite (309 g kg−1) and gibbsite (322 g kg−1) and to an Inceptisol rich in kaolinite (683 g kg−1). Soil samples were collected from B horizon, being both of them acid, clayey, and poor in organic matter. Soil samples were incubated for 40 days and evaluated for Pb after fractioning. Limed sewage sludge neutralized the soluble and exchangeable‐Pb forms in the kaolinitic and oxidic soils primarily as a result of pH increase. It was measured increased concentrations of unavailable forms of Pb such as precipitated‐Pb, Fe and Mn oxide‐Pb, gibbsite and kaolinite‐Pb, and residual‐Pb in the kaolinitic Inceptisol. Likewise, it measured increased concentrations of precipitated‐Pb, organic matter‐Pb, Fe and Mn oxide‐Pb, and residual‐Pb in the Oxisol. Results have demonstrated that limed sewage sludge decreases concentrations of Pb fractions more susceptible to leaching or more bioavailable, while increasing Pb fractions that pose lower risks to the environment. Such results indicate that limed sewage sludge can be used for the remediation of Pb‐contaminated soils regardless of soil mineralogy.

Effects of mineralogy, chemistry and physical properties of basalts on carbon capture potential and plant-nutrient element release via enhanced weathering

Mafic igneous rocks, such as basalt, are composed of abundant calcium- and magnesium-rich silicate minerals widely proposed to be suitable for scalable carbon dioxide removal (CDR) by enhanced rock weathering (ERW). Here, we report a detailed characterization of the mineralogy, chemistry, particle size and surface area of six mined basalts being used in large-scale ERW field trials. We use 1-D reactive transport modelling (RTM) of soil profile processes to simulate inorganic CDR potential via cation flux (Mg2+, Ca2+, K+ and Na+) and assess the release of the essential plant nutrients phosphorus (P) and potassium (K) for a typical clay-loam agricultural soil. The basalts are primarily composed of pyroxene and plagioclase feldspar (up to 71 wt%), with accessory olivine, quartz, glass and alkali feldspar. Mean crushed particle size varies by a factor of 10, owing to differences in the mining operations and grinding processes. RTM simulations, based on measured mineral composition and N2-gas BET specific surface area (SSA), yielded potential CDR values of between c. 1.3 and 8.5 t CO2 ha−1 after 15 years following a baseline application of 50 t ha−1 basalt. The RTM results are comparative for the range of inputs that are described and should be considered illustrative for an agricultural soil. Nevertheless, they indicate that increasing the surface area for slow-weathering basalts through energy intensive grinding prior to field application in an ERW context may not be warranted in terms of additional CDR gains. We developed a function to convert CDR based on widely available and easily measured rock chemistry measures to more realistic determinations based on mineralogy. When applied to a chemistry dataset for >1300 basalt analyses from 25 large igneous provinces, we simulated cumulative CDR potentials of up to c. 8.5 t CO2 ha−1 after 30 years of weathering, assuming a single application of basalt with a SSA of 1 m2 g−1. Our RTM simulations suggest that ERW with basalt releases sufficient phosphorus (P) to substitute for typical arable crop P-fertiliser usage in Europe and the USA offering potential to reduce demand for expensive rock-derived P.

Potential of fusion technique in production of mesoporous zeolite A powder from poor kaolin through modification by boehmite: Effect of clay mineralogy on particle morphology

The aim of present study is to investigate the modification of poor kaolin by boehmite to produce zeolite A via fusion techniques. The processed kaolins containing considerable content of quartz, as a major impurity, were employed, and alkalinity, boehmite content, fusion temperature, and ageing time were changed to achieve zeolite A. Regardless of the starting material composition, the sodium hydroxide/kaolin ratio should be fixed in the range of 2.00–2.33 to delete quartz. Boehmite was added to material mixtures for compensating aluminum deficit followed by thermal treatment at 700, and 800 °C. The presence of boehmite in the precursors is very crucial for the formation of zeolite A. The maximum relative crystallinity was obtained by control of the boehmite/kaolin ratio at the level of 0.26. The zeolite A produced from clay containing illite + kaolinite + pyrophyllite indicated the semi-cubic particles with rounded edges, and lower surface area, 17.5 m2.g−1 while the application of kaolinite-rich clay resulted in the mesoporous product with an average pore size of 8 nm, and larger surface area of about 59.6 m2.g−1.

Effect of coarse aggregate mineralogy on micro-texture deterioration and polished stone value

The objective of the study presented in the paper is to identify the mineralogical parameters that influence both micro-texture deterioration and Polished Stone Value (PSV), which are the two most important properties of the aggregates that control the pavement skid resistance. The study was carried out on fourteen sources of aggregates which belong to either igneous or metamorphic rock category, the two most commonly used aggregate categories for surface course mixtures in India. PSV of aggregates was determined as per BS EN 1097-8: 2009. To investigate the progressive extent of polishing, the British Pendulum Number (BPN) of the aggregate was determined after every hour of polishing. Simultaneously, the mineralogical parameters were also obtained based on the microscopic observations of the thin sections of the aggregates. From accelerated polishing tests, it was observed that igneous aggregates, especially granites, were found to have relatively high PSV and good polishing resistance. Nevertheless, granite aggregates with altered minerals witnessed poor polishing resistance. Correlation analysis on the combined data for igneous and metamorphic aggregates suggested that the mineralogical parameters such as Relative Hardness (RHD) of aggregates, Differential Hardness (DH) between major minerals within the aggregate, and degree of alteration (DA) influence micro-texture deterioration rate (BPN3-BPN6). PSV showed a good correlation with RHD and DH. It was also noted that altered granite aggregates of igneous type significantly influenced the correlation. In general, it was observed that fundamental mineralogical parameters can better predict BPN3-BPN6 than PSV.

The effect of mineralogy and grain size of fine aggregate and different surface textures on the durability of the RCCP surface toward abrasion conditions

The roller-compacted concrete pavement (RCCP) surface is almost smooth and without texture due to the vibrating rollers in the construction process. The lack of texturing causes a decrease in skid resistance in RCCP. For this purpose, different scenarios were proposed to create surface texture at micro and macro levels and provide the necessary friction. To provide friction at micro-scale, siliceous and calcareous sand and a combination of 50-50 of them with broken and natural aggregate shape was used in the construction of 8 RCCP mixing designs. In addition, in order to provide macro-texture, each of the eight mixing designs was texturing by methods such as seeding (three cases), stamping (two cases), and brooming (two cases). The purpose of this paper is to investigate the durability of various micro and macro textures created on RCCP surfaces by the simulation method proposed in the ASTM C 944 standard. The results showed that different textures have almost the same abrasion resistance. Among these, the seeding texture with the grain size of 4.75-9.5 mm has the weakest, and the stamp texture of 4 x 4 cm has the most durable abrasion resistance. Changes in abrasion resistance were associated with more changes in the mixing design. This means that crushed silica sand had the highest and natural lime sand had the lowest abrasion resistance. The results demonstrated that the combination of calcareous and siliceous materials improves abrasion resistance. In this regard, the higher the fracture rates of combined sand, the better the abrasion resistance.

Effect of construction and demolition waste on the long-term geo-environmental behaviour of cemented paste backfill

The construction and demolition waste (CDW) could be used as backfill material to fill the voids created during the ore production in underground mining. However, there is a need to clarify the impact of CDW on groundwater pollution when it is used as backfill material in cemented paste backfill (CPB) of sulphide-rich tailings (S-rT). This study presents the influence of CDW on the long-term geo-environmental behaviour of CPB samples (CPBs) when used as replacement (10 wt.%) to S-rT. For this reason, the dynamic-tank leaching test was conducted on CPBs and pH, conductivity (Ec), sulphate (SO42−) and heavy metals (HMs) analyses were executed for leachates over 30–360 days of leaching period. The effects of mineralogy and microstructure on the geo-environmental behaviour of CPBs were also analysed via X-ray fluorescence (XRD) and mercury intrusion porosimeter (MIP). The utilisation of CDW in CPB mixtures was found to reduce the SO42− release (up to 13.89%), neutralise the acid generated and lower the Ec (up to 22.16%). Furthermore, the HMs releases (except As, Cu and Zn) were prevented (Ni and Cr) or reduced up to 92%, which is compatible with the improved CPB microstructure. Only the release of arsenic (As) exceeded the limit value for groundwater in CPB of CDW leachate. These findings suggest that not only the cost, strength and stability but also the impact on groundwater pollution should be considered when disposing of CDW as CPB material in underground voids.

Enhancing oil recovery using silica nanoparticles: Nanoscale wettability alteration effects and implications for shale oil recovery

Enhanced oil recovery (EOR) techniques have the potential to improve recovery in unconventional shale oil reservoirs which have prolific short-term success but elusive near-to-long term outlook. The use of silicon dioxide nanoparticles for enhancing shale oil recovery has recently gained significant attention in the oil industry. However, the technique remains novel partly due to inadequate fundamental understanding of oil release mechanisms. Herein, the oil recovery potential of untreated and treated silica nanoparticles is investigated using an atomic force microscope (AFM) by studying nanoscale interactions between different crude oil functional species and substrates of pure minerals found in a shale oil reservoir. Quartz and muscovite mica (clay substitute) were employed as substrates as these are the dominant rock minerals identified in the most productive zone of Tuscaloosa Marine Shale (TMS). Thiolates of undecane (CH3) and phenyl (C6H5) compounds were used to simulate alkane and aromatic fractions of TMS crude oil respectively, while undecanoic acid (COOH) thiol was used to represent carboxylic acid found in asphaltene and resin components. Following our in-house experimental protocol for liquid cell force spectroscopy, adhesion forces and surface energies between functionalized AFM probes and mineral substrates were characterized in untreated and amino-treated silica nanoparticle dispersions. Zeta potential of respective nanofluid solutions was measured and AFM adsorption data were supported with scanning electron microscope (SEM) micrographs of TMS rock samples. Results showed that aqueous dispersions of hydrophilic silicon dioxide nanoparticles promote wettability towards a less oil-wet state by significantly lowering the adhesion force and energy barrier to spontaneously detach oil molecules from clay and quartz mineral surfaces in shale reservoirs, shown at the nanoscale with AFM studies. However, the grafting of aminosilanes onto surfaces of silica nanoparticles generally increased adhesion forces and surface energies due to surface charge effect and hydrophobicity. Findings pertinent to nanoparticle silanization were consistent in molecular interactions on mica in nanofluids but not necessarily predictable with quartz surfaces, highlighting mineralogical effects. The irreversible adsorption of silica nanoparticles was also observed. Adhesion force and energy are resolved in various intermolecular forces such as electric double layer repulsion, non-electrostatic interaction and structural forces. The scientific significance and broad engineering implications of results were comprehensively discussed in the context of previously reported core-to-field scale observations of nanofluid EOR. This study pitches new light on the scientific understanding of silica-based nanofluid EOR by probing nanoscale wetting effects of silica nanoparticles with implications for shale oil recovery. The findings herein can help for better understanding of the design of nanofluid EOR reagents and the conditions that favor application of silica nanofluid EOR.

Application of LithoScanner Logging Technology in CO2 Geological Storage Injection Well

The formation evaluation in a primary formation of a CO2 sequestration project in Western Australia has been very challenging due to the presence of glauconite and other iron rich minerals. The conventional method cannot handle the mineralogy effects, hence the accurate porosity, clay type and clay content cannot be calculated accurately. The latest generation in spectroscopy technology LithoScanner was brought to the project and run in well A for the first time in Australia. The tool has a high output pulse neutron generator and unique cerium-doped lanthanum bromide (LaBr3:Cr) gamma ray detector. This combination enables the tool to measure both inelastic and capture spectra for an expanded set of elements from that of previous-generation tools. We are measuring elements that make up more than 99% of the average abundance in the earth’s crust. Measuring the elements is the starting point to calculate minerals, matrix density and those are key to obtain accurate reserves estimates (porosity) and build an accurate petrophysical and reservoir model. For well A, the LithoScanner elements weight fractions are used in the Techlog QuantiElan module to solve mineralogy that includes quartz, K-feldspar, calcite, siderite, pyrite, illite, kaolinite, glauconite and chlorite. There is a very good agreement between the computed mineralogy and the mineralogy from core measurements. LithoScanner provides a continuous log of matrix density that is used as an input to porosity calculations. This formation evaluation based on Litho Scanner does not require the subjective inputs from the log analysis, but completely rely on the tool’s reading. It can be used for both simple and complex formation to obtain the good consistency and accurate answers.

Mineralogical and structural characterization of the sediments of Krishna Godavari and Mahanadi Basin and their influences on hydrate formation kinetics

Structural and mineralogical characterization of sediment samples of Krishna Godavari (KG) and Mahanadi (MH) basin was performed with the aim of providing in-depth analysis of the effect of mineralogy, grain size and other properties on the hydrate formation. Bulk mineralogy and clay mineralogy of the sediments analyzed through different characterization techniques like X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) that was associated with Energy Dispersive X-Ray (EDX) analysis. Quartz was the main component observed in the sediment samples. A relation between particle size and pore size was also established through particle size (DLS) and pore size characterization (BET) techniques. Finer clay materials were leading in both KG and MH basin samples having slight variation in their quartz content. Illite and smectite were the dominating clay minerals found in the sediments with calcite and albite being the other contributing minerals. Framboids as the pyrites were also observed in sediments and were clearly visible in FESEM observations. Hydrate formation studies were also performed in the sediments to observe the effect of their sedimentology and geology on the occurrence of hydrates in oceanic sediments. Hydrate formation in sediments occurred in less time as compared to pure water system with an accelerated rate of nucleation as per the observations. Kinetic studies were also performed that showed the higher initial rate of hydrate formation in sediments that could be due to the high surface area and additional nucleation sites provided by the sediments as confirmed by BET analysis. Rate constants and other kinetic parameters were also calculated by assuming the first order reaction kinetics of hydrate formation.

Effect of aqueous environment on sedimentation of dredged mud and kaolinite

Port development results in production of large quantities of dredged marine sediments. Once dredged, sediments often have high water contents and are pumped to near-shore or in-water bunded marine impoundments for port expansion. However, dredged material disposal to freshwater onshore or empty impoundments typically changes sedimentation conditions that may change the effective grain-size distribution, mineral specific surface areas, settling particle orientations, resulting in settling rate changes. Salinity, temperature, water content, mineralogy, filling rate, and organic matter content may also influence sediment settlement and resulting consolidation. This study investigates the effect of salinity and sediment mineralogy on sediment settlement behaviour when deposited in saltwater, freshwater, or to empty ponds. For this purpose, slurries of dredged mud and kaolinite with water contents of 1.7 times their liquid limit were prepared and disposed into a series of 1000 mm long, 50 mm wide, and 500 mm high settlement columns. Result shows that the sediments settle faster in saltwater than freshwater or air, through divalent surface complexation and flocculation provided by seawater Ca and Mg. However, this is true if the salinity remains below 10 PSU, but the mixed mineral dredge spoil ultimately provides the densest sediment and lowest water sediment interface.

Effects of short-term high-temperature calcinations on the physico-chemical and mineralogical properties of Ca-bentonites from Ünye (Ordu, NE Turkey)

Three Ca-bentonite samples from Unye (NE Turkey) were calcined up to 1000 °C with 200 °C increments at 25 min. The physico-chemical and mineralogical effects of high-temperature loadings were evaluated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET) and loss on ignition (LOI) analysis. The results of the experiments show that the dehydration up to 400 °C does not alter the properties of Ca-bentonites significantly; however, the endothermic reactions due to dehydroxylation between 400 and 800 °C cause the deformation in the Ca-smectite crystal structure revealed by the collapse of the basal reflection from 1.4 to 1.0 nm and the gradual disappearance of OH stretching of structural hydroxyl groups and decrease in specific surface area and the closure of micropores. By calcination at 1000 °C, the specific surface area reaches the minima of 1.33–2.05 m2 g−1 for all the samples, and the structure of Ca-smectite is almost completely decomposed for CaB2 and CaB3, however, partially decomposed for CaB1 due to incomplete dehydroxylation stage. The crystallinity of opal-CT intensifies, and the formation of amorphous silica phases is promoted for all samples at 1000 °C; however, the formation of mullite is enhanced only for CaB2 and CaB3. The sintering effect is revealed as much larger aggregates with more rounded morphologies. It is also determined that the calcination up to 1000 °C does not affect the mesoporous characteristics of Ca-bentonite samples.

Porosity and permeability variability across a chalk reservoir in the Danish North Sea: Quantitative impacts of depositional and diagenetic processes

Abstract The Upper Cretaceous to Lower Paleocene Chalk Group in the North Sea comprises important reservoir targets for hydrocarbon and energy storage. The quantitative impacts of mineralogy, chalk diagenesis and oil saturation on petrophysics are often based on general trends that cannot be directly applied to reservoir engineering. The present study aims at identifying quantitatively the individual effects of mineralogy, compaction and cementation, and oil saturation on porosity and permeability by means of detailed samplings and mineralogical and petrophysical analyses from base to top of the Kraka reservoir. Special attention is brought to the visual inspection of the rock fabric and its variations across the reservoir in order to better constrain interpretations and establish relationships within an otherwise scattered dataset. Porosity and permeability variations are categorised into two trends, a mineralogical and diagenetic trend, which can both form tight rock. For chalk containing >7% quartz and > 4% clay, porosity decreases linearly from 35% to 21% and permeability from 0.5 mD to 0.07 mD with increasing quartz content. The amount of quartz rather than clay appears as an effective tool to estimate the petrophysical properties of impure chalk. Below 7% quartz and 4% clay, compaction and cementation decrease porosity and permeability in two steps along transects from oil- to water-bearing intervals. A first step of predominantly mechanical compaction reducing porosity and permeability from >41% to 37% and from 3 to 3.5 mD to 1.5–2.5 mD, respectively, is followed by a phase of chemical compaction and cementation that further deteriorates petrophysical properties. In Ekofisk Fm., stylolitised chalk and deposits located adjacent to chert horizons display singular petrophysical properties that do not fit the observed trends. The outliers likely result from phases of local chemical compaction and early cementation associated with chert formation. Porosity-permeability functions and uncertainty analyses are also proposed for the different controlling factors and at different scales of observation. The proposed petrophysical relationships are instrumental in building more realistic reservoir models and can assist geoscientists in interpreting and upscaling the large amount of geological data collected in chalk fields.