Coarse Crystalline Research Articles

Investigation of the passive film of nanocrystalline 304 stainless steel in 3.5 wt% NaCl solution under hydrostatic pressure

In this paper, the effect of hydrostatic pressure on the passive film of coarse crystalline 304 stainless steel (304 SS) and sputtered nanocrystalline stainless steel (304 NC) in 3.5 wt% NaCl solution has been investigated using in-situ electrochemical measurement techniques. The results indicate that nanosizing promotes the growth of the passive film. Hydrostatic pressure changes the nucleation mechanism of the passive film, decreases the carrier density and oxygen vacancy diffusivity, and decreases the content of oxides and hydroxides within the film, significantly deteriorating the corrosion resistance of the passive film. The point defect model (PDM) was introduced to elaborate the microscopic process of the surface passivation of stainless steel under hydrostatic pressure.

Effect of Si content on the 1200 - 1300°C steam oxidation and 360°C/18.6MPa autoclave water environmental resistance of Cr-Si coatings on Zry-4

In this study, we applied magnetron sputtering to deposit four Cr-Si coatings on Zry-4, with varying Si content ranging from 0.03 to 0.22 at.%. The main objective was to investigate the influence of Si content on the mechanical properties, steam oxidation resistance at 1200 - 1300 °C, and corrosion resistance in a 360 °C/18.6 MPa autoclave water environment. As the Si content increased, we observed a corresponding enhancement in both the mechanical properties and oxidation resistance of the coating. Notably, at 1300 °C, the oxidation resistance of Cr-Si coated Zry-4 demonstrated improvement when the Si content reached or exceeded 14 at.%, attributed to the formation of an in-situ Zr2Si layer at the coating/substrate interface. However, in the 360 °C/18.6 MPa autoclave water environment, we noted a decrease in the corrosion resistance of the Cr-Si coatings with increasing Si content. This phenomenon was ascribed to the selective dissolution of Si. Moreover, when the Si content surpassed 14 at.%, the surface Cr2O3 underwent a transformation, resulting in the formation of three non-protective sublayers: an amorphous layer, a nanocrystalline layer, and a coarse crystalline layer. These findings provide valuable insights into the overall performance, as well as the advantages and disadvantages, of Cr-Si coatings on Zry-4.

A comparison between deuterium plasma induced blistering of tungsten surface and hillocks grown on tungsten thin film

Tungsten (W) film was prepared by magnetron sputtering, and the coarse crystalline W bulk was used as reference samples. All the samples were exposed to deuterium plasma with the exposure fluence of 1.67 × 1024 D/m2. The films were annealed in-situ at 723 K during deposition and hillocks were found on all film surfaces. Focused ion beam analysis of the subsurface structure of hillocks provides data support for the growth mechanism of hillocks. The formation of hillocks suggested that the underlying force is released the intrinsic compressive stress caused by thermal cycling during the magnetron sputtering. After deuterium plasma exposure, the W bulk showed obvious stepped high-dome deuterium blisters. The micrographs revealed the microscopic morphology characteristics of deuterium blisters and hillocks, and analyzed the similarities and differences between hillocks and surface deuterium blisters. By comparing the growth mechanism of hillocks on the W film with the surface blistering on the W bulk, the stress growth model of deuterium blisters on the surface of coarse crystalline W bulk is proposed. This work provides a new perspective for the transverse stress model of deuterium-induced surface blistering.

Effect of Pressure and Temperature Variation on Wax Precipitation in the Wellbore of Ultradeep Gas Condensate Reservoirs

Summary To investigate the wax precipitation mechanism of condensate in a wellbore during the ultradeep gas condensate reservoir development, condensate samples were prepared in this work. Changes in the temperature and pressure of fluid flow in the wellbore are simulated by a high-temperature and high-pressure pressure/volume/temperature (PVT) system. This simulation explores their influences on the wax precipitation of the condensate produced from the target reservoir. The results show that the temperature decrease weakens the wax molecular movement activity and promotes the precipitation of wax, resulting in the expansion of the pressure range in which wax precipitation occurs in the system. Meanwhile, decreasing the pressure promotes wax aggregation by increasing van der Waals forces between wax molecules, thereby increasing the wax precipitation rate. At different temperatures, the wax precipitate amount first increases and then decreases with decreasing pressure, which is determined by the wax solubility and remaining content in the system. Since the solubility of a low carbon number component is more sensitive to temperature and pressure changes than that of a high carbon number component, in the early stages of experimental temperature and pressure decreases, the precipitation of coarse crystalline wax with carbon numbers ranging from C16 to C30 is more active than that of microcrystalline wax with carbon numbers exceeding C30. The remaining amount of the former component in the system decreases rapidly, and its precipitation capacity weakens, thus increasing the amount of the latter component in the precipitated wax during the later stage of experiments; this trend corresponds to the shift of the curve peak of the wax carbon number distribution to an abscissa interval with the relatively high carbon numbers. This work can provide reference data for the prediction of the well depth at which the wax precipitation occurs and the wax composition, aiming to promote the implementation of wellbore wax blockage prevention programs.

Effect of WC particle size on the microstructure and mechanical properties of Ni–Co coarse grain cemented carbide

AbstractThe effect of different WC grain size additions on the microstructure and grain distribution of Ni–Co coarse crystalline cemented carbide was studied. And then the effect of grain distribution on the mechanical properties of cemented carbide was discussed. The effect of WC grain size on the grain size and coherency of cemented carbide was analyzed by microstructure. And the distribution of grains in the microstructure was investigated by the truncation method. The addition of fine (1.1–1.4 μm), medium (2.3–2.7 μm), and coarse WC (5.6–6.0 μm) particles can increase the nucleation rate of WC grains in the bonded phase. And the higher grain growth driving force can produce the theoretical limitation of nucleation and inhibit the coarsening of WC grains to a certain extent. The WC grain size has an insignificant effect on the frequency of the occurrence of super‐coarse grains in coarse crystalline cemented carbide. The average grain size and super coarse grains in microstructure gradually decrease, which promotes the improvement of transverse rupture strength. The increase of the adjacent degree and the decrease of the mean free path reduce which is beneficial to the improvement of the corrosion resistance of the alloy. The best overall performance of the alloy is achieved when fine‐grained WC is added.

Effect of original crystal size of kaolinite on the formation of intercalation compounds of coal-measure kaolinite

Coarse crystalline (14.8–19.8 µm) and crypto crystalline (0.51–0.92 µm) coal-measure kaolinite were selected to explore the effect of original crystal sizes on intercalation. Characterization methods of SEM, XRF, XRD, FT-IR, and TG-DTG were utilized to study the original crystal size distribution, chemical composition, crystal structure changes, vibrational characteristics of functional groups, and thermal stability before and after intercalation. The test results reflected that the original crystal size significantly affects the formation of intercalated compounds. Coal-measure kaolinite intercalation compounds have been successfully prepared. Nonlinear fitting curves between the different characterization methods and the original average crystal size showed a significant positive correlation. The results showed that the intercalation effect of coarse crystalline was more significant than those of crypto crystalline, that is to say, the larger the original crystal sizes of coal-measure kaolinite, the higher the intercalation rate, the higher the grafting rate and the more pronounced the mass loss rate. Based on the theory of surface energy and surface charge of mineral particles, the electrical double layer theory which was different from the previous researchers was proposed to explain the intrinsic mechanism of the effect of original crystal size on intercalation.

Influencing factors of rock thermal conductivity and applicability evaluation of its mixing law predictive models

The thermal conductivity (TC) of rocks is a very important parameter in geothermal theory and applied research, its value is related to rock composition, mineral grains characteristics, rock porosity, and pore fluid etc., and simultaneously is affected by formation thermodynamic environment (temperature, pressure,etc.). Statistical analysis results of the thermophysical property parameters of borehole samples from Jizhong Depression indicated that the TC is mainly controlled macroscopically by lithology, compared with sandstone, mudstone, conglomerate, and gneiss, dolomite has a greater TC. In the dry state, the TC of dolomite samples showed a decrease with increasing temperature, the values of TC decreased by 12.3–27.5% in the temperature interval of 30–130 °C. Moreover, under the same temperature conditions, excluding the effects of water content and mineral fraction, the TC of medium–coarse crystalline dolomite, medium–fine crystalline dolomite, microcrystalline dolomite, and mud-powder crystalline dolomite decreased successively, reflecting the influence of the mineral grain size on TC. The validity and applicability of six commonly used mixing law predictive models for TC were evaluated based on X-ray diffraction (XRD) data from 70 borehole samples. The results showed that Geometric mean model displayed the best fit (goodness of fit, R2 = 0.878) for rocks, and Voigt-Ruess-Hill average also showed a good fit, with an R2 of 0.868, and had the best prediction for mudstone (AME = 10.16, RMSE = 0.25). In cases where the calculated values deviate significantly from the measured values, it may reflect the limitation that the mixing models consider only the composition of minerals but ignores the structural characteristics of rocks.

Optimized corrosion resistance in pure copper via surface mechanical attrition treatment and subsequent annealing

Surface mechanical attrition treatment (SMAT) was used on the surface refinement of pure copper mainly to study the electrochemical corrosion behavior of pure copper in a 3.5 wt% NaCl solution, under grain refinement and short-time annealing conditions. Fine crystalline copper showed higher corrosion resistance than coarse crystalline copper, and the samples with grain refinement exhibited increased corrosion resistance under annealing conditions. This improvement may be attributable to the enhanced passivation of the surface passivation film after grain refinement. In addition, the residual stress after annealing reduces the activation energy of atoms leaving the metal lattice and entering the solution, reducing the dissolution rate of the anode. Consequently, the corrosion resistance of fine crystalline copper is improved. Grain refinement and short-time annealing help design corrosion-resistant pure copper.

Influence of a rich sulphur atmosphere on the phase development and kinetic behaviour of differentially processed RNT650 γ - TiAl alloys

The influence of sulphur atmosphere on conventionally cast (CM) and on electron beam melted (EBM) γ - TiAl RNT650 alloy exposed to a 1% (vol.) H2S – air atmosphere at 650 °C for 500 h was investigated. The material produced by CM showed a lower mass gain than the EBM material. XRD and TEM/EDS analyses indicated the formation of rutile-TiO2/(α-Al2O3 + rutile-TiO2)/amorphous-Al2O3 sequence of phases. In EBM a coarse crystalline layer rich in aluminium, oxygen and a small amount of sulphur was found. The higher content of sulphur was in the scale bottom intermixed with amorphous alumina.

A boost of thermoelectric generation performance for polycrystalline InTe by texture modulation.

The new rising binary InTe displays advantageously high electronic conductivity and low thermal conductivity along the [110] direction, providing a high potential of texture modulation for thermoelectric performance improvement. In this work, coarse crystalline InTe material with a high degree of texture along the [110] direction was realized by the oriented crystal hot-deformation method. The coarse grains with high texture not only maintain the preferred orientation of the zone-melting crystal as far as possible, but also greatly depress the grain boundary scattering, thus leading to the highest room temperature power factor of 8.7 μW cm-1 K-1 and a high average figure of merit of 0.71 in the range of 300-623 K. Furthermore, the polycrystalline characteristic with refined grains also promotes the mechanical properties. As a result, an 8-couple thermoelectric generator module consisting of p-type InTe and commercial n-type Bi2Te2.7Se0.3 legs was successfully integrated and a high conversion efficiency of ∼5.0% under the temperature difference of 290 K was achieved, which is comparable to traditional Bi2Te3 based modules. This work not only demonstrates the potential of InTe as a power generator near room temperature, but also provides one more typical example of a texture modulation strategy beyond the traditional Bi2Te3 thermoelectrics.

Defining quality indicators for sugar pasteswith demineralized whey during storage

This paper considers the changes in quality indicators of sugar pastes with dry demineralized whey and glycerin during storage in order to establish their technological shelf life. Based on the results of studying changes in the mass fraction of moisture of sugar pastes over 30 days, a decrease in this indicator in the control sample was established, by 80 %, and in the experimental one – by 30 %. Examining the sensory characteristics of consistency according to the devised descriptors has made it possible to establish that the control sample of sugar pastes onday 10 of storage is technologically unsuitable. Its consistency is characterized as too dense, hard, brittle, not uniform, with lumps. Accordingly, the molding ability, which received 3.45 points, decreases. The prototype, even on day 30 of storage, has acceptable consistency characteristics: moderately hard and dense, softish, homogeneous with the presence of barely perceptible small inclusions. A high molding ability is retained, which received 4.3 points. Experimental studies of the fractional composition of the solid phase and the dispersion of sugar pastes are consistent with studies into the sensory characteristics of the consistency. It was established that on day 10 of storage, in the control sample the fractional composition of particles with a size of 21 to 30 µm prevails, the content of which is 62 %, which characterizes the structure as coarse crystalline. In the prototype on day 30 of storage, thecontent of particles the size of 11 to 20 µmwas 72 %, which preserves the quality of the paste and characterizes its structure as finely crystalline. The results of the study made it possible to establish a tendency to slow down the build-up of solid particles of the developed sugar pastes, and their growth to a critical size of 22.6 µm.The data obtained have made it possible to establish the technological shelf life of the developed sugar pastes, which was 30 days, which is 3 times more than that of the control. Consequently, the introduction into the formulation composition of sugar pastes of demineralized whey at a concentration of 50 % and glycerin at a concentration of 5 % makes it possible to extend their technological shelf life. This is important from a practical point of view and solves the problem set.

Dolomitization evolution and its effects on hydrocarbon reservoir formation from penecontemporaneous to deep burial environment

Aiming at the scientific problem that only part of dolomite acts as dolomite reservoir, this paper takes the multiple dolomite-bearing formations in the Tarim and Ordos basins, NW China and Sichuan Basin, SW China as the study object, by means of mineral petrological analysis and geochemical methods including carbonate clumped isotope, U-Pb isotopic dating, etc., to rebuild the dolomitization pathway and evaluate its effects on reservoir formation. On the basis of detailed rock thin section observation, five dolomitic structural components are identified, including original fabric-retained dolomite (microbial and/or micrite structure), buried metasomatic dolomite I (subhedral–euhedral fine, medium and coarse crystalline structure), buried metasomatic dolomite II (allotriomorphic–subhedral fine, medium and coarse crystalline structure), buried precipitation dolomite and coarse crystalline saddle dolomite. Among them, the first three exist in the form of rocks, the latter two occur as dolomite minerals filling in pores and fractures. The corresponding petrological and geochemical identification templates for them are established. Based on the identification of the five dolomitic structural components, six dolomitization pathways for three types of reservoirs (preserved dolomite, reworked dolomite and limestone buried dolomitization) are distinguished. The initial porosity of the original rock before dolomitization and the dolomitization pathway are the main factors controlling the development of dolomite reservoirs. The preserved dolomite and reworked dolomite types have the most favorable dolomitization pathway for reservoir formation, and are large scale and controlled by sedimentary facies in development and distribution, making them the first choices for oil and gas exploration in deep carbonate formations.

Dolomitization Mechanism in the Chorgali Formation (Eocene), Pakistan: Evidences from Field observations, Petrography, Mineralogical and SEM analysis

The subject of dolomite formation has always put researchers in the challenge. In this study, the origin of the dolomites of the Chorgali Formation near Chorgali Pass was explored through field observation, petrographic characteristics, mineralogical and geochemical analysis. Analytical analyses used in the present studies include XRD, SEM-EDS, and stable isotopes studies. The dolomites were categorized into three major genetic types based on their textural and structural features showing their distinct origins. These dolomites are named fine crystalline dolomite (Df), medium crystalline dolomite (Dm), and coarse crystalline dolomite (Dc). The analytical approaches linked with field observations and petrographic examinations identified that; the first type of dolomites (i.e., Df) is related to the early stage of diagenesis and contain the presence of mineral dolomite (40%), gypsum (27%), quartz (17%) and albite (16%) and are low stochiometric low ordered in character as recognized by XRD results. The SEM-EDS analysis identified low Mg, Ca, O, Na, Si, and Fe concentrations. Further, the stable isotopes (δ18O) values for Df (i.e., -5.95 to -396‰V-PDB) are less depleted. Moreover, Dm and Dc revealed 100% mineral dolomite and are stochiometric ordered dolomites. High concentrations of Mg, Ca and O are observed in Dm and Dc respectively. Stable isotopes (δ18O) result in exhibiting highly depleted values for Dm (-7.947‰V-PDB) and Dc (-9.227 to -8.302‰V-PDB) showing its formation with the elevated temperature at depth. In addition, δ13C values of Df, Dm, and Dc lie in the range of the original marine signature of Eocene times.

Advancing dosimetry for Dating Environmental Materials: Development of an ultra-sensitive beta dosimeter system and potential for beta autoradiography

Beta Dose Rate heterogeneity is a recognized source of uncertainty when applying luminescence dating to heterogeneous samples, such as coarse crystalline rocks and clast-rich sediments. Simulations have shown that a combination of a heterogeneous distribution of minerals and radioactive elements can lead to complex dose distributions, overdispersion and potentially to bias in equivalent dose determinations. However setting realistic conditions for such simulations remains difficult, and there are at present only a few experimental validation cases for such simulated systems. Project ADDEM is investigating means of linking Monte Carlo simulations of dose rate to specific minerals with direct observations using high sensitivity phosphor plates and laser scanning imaging systems in combination with phase mapping. To overcome some of the limitations of autoradiographic imaging of low level beta dose distributions work has been undertaken using Landauer alumina OSL phosphor screens in combination with a laser scanning system developed at the Scottish Universities Environmental Research Centre (SUERC). Preliminary excitation spectra, emission band characterization and time resolved measurements were undertaken, confirming the potential to recording low doses using asynchronous stimulation at 635 nm coupled with blue band detection. Taking advantage of the slow decay of the luminescence signal the scanning equipment has been configured for pulsed stimulation and asynchronous detection to maximise signal to background ratios. Exploratory work was calibrated using a 60Co facility capable of calibrating doses in the μGy to mGy range. A series of powdered granulite/basalt mixtures of known mean activity and dose rate (Dr) have also been used to calibrate the phosphor screens. To reduce background levels during autoradiographic signal accumulation rock slices are being exposed in the Zeplin shield of the STFC Boulby Underground Laboratory, in an environment which is essentially free from cosmic ray muon background.Simulations have been conducted providing preliminary deconvolution parameters in order to either reconstruct the beta dose rate (β Dr) distribution received by the grains in the sample, or retrieve the radioactive element distributions in the minerals of the sample, providing the data required for representative simulations of β Dr.This paper outlines the spectroscopy and sensitivity verification of the autoradiography system, confirming its prospects for measuring spatially resolved β Dr distributions with single pixel lower detection limit of 130 μGy and spatial resolution of 150 μm. Prospects are outlined.

Dolomite–magnesite formation and polymetallic mineralization in a rift-sag basin on the western margin of the Red Sea: Paleoenvironmental, hydrothermal, and tectonic implications

ABSTRACTThe present study gives new insight on the formation conditions of dolomite and magnesite in an early–middle Miocene succession related to a half-graben rift-sag basin on the western margin of the Red Sea. The studied Miocene succession comprises two units of siliciclastic–carbonate rocks separated by a magnesite bed. The succession is enriched with epigenetic–supergenetic polymetallic minerals, dominated by zinc-bearing ferromanganese oxides. These represent oxidized Mississippi Valley-type deposits (MVT) formed during uplifting in late Miocene–Pliocene time. Multistage dolomitization (four dolomite types: D1–D4) and magnesite authigenesis, enhanced by tectonic uplifting and faulting related to the Red Sea rifting, have been recorded. The first dolomite phase (D1) is pervasive early diagenetic dolomicrite (replacement type), which is dominant in the lower unit. Magnesite occurs as microcrystalline aggregates exclusive to the lower unit, where its authigenesis was after D1 and before D2. Occurrence of magnesite was mostly related to a restricted environment in a sag fault-bounded basin with shallow evaporative hypersaline conditions in coastal areas. D2 dolomite occurs in the lower and upper units as replacement and/or cement type of medium- to coarse-crystalline dolomite crystals. The three magnesium-rich carbonates (D1, magnesite and D2) are related to successive events of sea-level fall and rise in mesohaline and hypersaline conditions. Enrichment of magnesite and D2 dolomite with Na (up to 2.16 wt.%) and Sr (up to 1483 ppm) supports their formation under more saline evaporative conditions if compared with D1 dolomite which was formed in near-normal sea water or mesohaline fluids. The third and fourth dolomite phases (D3 and D4) are late diagenetic pore-filling coarsely crystalline and zoned, and restricted mainly to faulted areas associated with the polymetallic ore deposits. Elemental analyses of the four dolomite phases show different chemistries, i.e., non-ferroan dolomites (D1 and D2), alternation of manganiferous and non-ferroan zones (D3) and/or ferroan-type dolomite (D4). Stable- isotope values of the four dolomite types (δ18OVPDB of –7.82‰ to –5.88‰) and geochemistry suggest involvement of shallow evaporative conditions in coastal areas, enhanced either by dry and hot climate or by hydrothermal process in their formation. Nonetheless, the localized occurrence of D3 and D4 types along the faults, their concomitant occurrence with the epigenetic–supergenetic polymetallic ore deposits, and the preservation of unaltered feldspar grains ruled out the meteoric-water interaction and reinforce the fault-controlled and deep-seated hot fluid evolution for these two dolomite types. The underlying ultramafic and serpentinite rocks along with the intercalated magnesium-rich clays and/or the modified seawater most probably played a critical role in the diagenesis and/or precipitation of dolomite and magnesite. The proposed model can contribute to better understanding the genetic mechanisms of magnesite and dolomite hosted by mixed siliciclastic–carbonate deposits and their relations with MVT mineralization conditions in rift basins.

The Diagenetic Alteration of the Carbonate Rocks from the Permian Qixia Formation as Response to Two Periods of Hydrothermal Fluids Charging in the Central Uplift of Sichuan Basin, SW China

The hydrothermal fluid–carbonate rock reaction is frequently regarded to occur in deep-burial diagenesis, and the hydrothermal dissolution is usually distributed and takes place along the faults. Previous studies have suggested that there was hydrothermal fluid activity locally in the Permian Qixia Formation in Sichuan Basin, likely related to the Emeishan basalt eruption. However, the effect of hydrothermal fluids on the carbonate rocks of the Qixia Formation in the central uplift of Sichuan Basin is still unclear. Based on the characteristics and geochemical parameters of the diagenetic minerals, this study aims to reveal the diagenetic alteration related to the hydrothermal fluid–rock reaction in the Qixia Formation and reestablish the diagenetic evolution by using the timing of diagenetic mineral precipitation. The methods include petrographic observation; trace and rare earth element (REE) analysis; C, O and Sr isotope measurement; fluid inclusion temperature measurement and cathodoluminescence analysis. According to the petrographic characteristics, the dolostones are mainly of crystalline structure, namely fine-medium crystalline dolostone, meso-coarse crystalline dolostone, and coarse crystalline dolostone, with the cathodoluminescence color becoming brighter in that order. The limestones from the Qixia Formation are of the bioclastic limestone type, with no cathodoluminescence color. Compared with dolostones, limestones have higher Sr content, lower Mn content, and heavier oxygen isotopes. With the crystalline size of dolostone becoming coarser, the oxygen isotopes of dolostones tend to become lighter. The meso-coarse crystalline dolostone has the highest Mn content and negative carbon isotope. Both limestones and dolostones have an obvious positive Eu anomaly in the Qixia Formation. However, the REE patterns of fine-medium crystalline dolostones are very different from those of meso-coarse crystalline dolostones. It is credible that there were two periods of hydrothermal fluid charging, with different chemical compositions. The first period of hydrothermal fluids could laterally migrate along the sequence boundary. Fine-medium crystalline dolostones were almost completely distributed below the sequence boundary and were dolomitized during the shallow burial period. As products of the hydrothermal fluid–dolostone reaction, the saddle-shaped dolomites in the meso-coarse crystalline dolostones were the evidence of the second period of hydrothermal fluids. As a result, the dolomitization model was established according to the timing of diagenetic mineral precipitation, which can improve that the geological understanding of the effect of hydrothermal fluid activities on the carbonate rocks in the Qixia Formation.

Origin of dolomites in Lower-Middle Ordovician carbonate rocks in the Yingshan Formation, Gucheng Area, Tarim Basin: Evidence from petrography and geochemical data

Various degrees of dolomitization are widely present in the Yingshan Formation in the Gucheng area of the Tarim Basin. To determine the petrological characteristics and origin of the massive dolomites present, a rich combination of tools was well used, including previous research results, core and thin-section samples, cathodoluminescence, carbon (C-) and oxygen (O-) isotopes, strontium (Sr-) isotopes and content, and burial-thermal history data. The results of this analysis successfully reveal three primary matrix dolomites and three special cements, as follows: (1) microcrystalline to very fine crystalline nonplanar-a dolomite (MD1); (2) very fine to fine crystalline planar-s to planar-e dolomite (MD2); (3) medium to coarse crystalline nonplanar-a to planar-s dolomite (MD3); (4) coarse crystalline nonplanar-a saddle dolomite cement (SD) and (5) medium to coarse crystalline calcite cements (C1 and C2). Among them, MD1 precipitated from the reflux of mildly evaporated seawater, and MD2 was formed by the first significant recrystallization of MD1 in shallow burial environments. In particular, some MD3 was formed by the second significant recrystallization of MD1 in medium-burial environments. The others, even SD, were likely the products of the third significant recrystallization and cementation in deep-burial environments that precipitate under the action of a hydrothermal fluid mixture composed of mantle-derived fluid and Cambrian thermal brine. In addition, C1 and C2 would form close to the times in which the Himalayan and Late Caledonian–Early Hercynian hydrocarbon charging events occurred, respectively.

Diagenetic Modifications and Reservoir Heterogeneity Associated with Magmatic Intrusions in the Devonian Khyber Limestone, Peshawar Basin, NW Pakistan

In the present study, an attempt has been made to establish the relationship between diagenetic alterations resulting from magmatic intrusions and their impact on the reservoir properties of the Devonian Khyber Limestone (NW Pakistan). Field observations, petrographic studies, mineralogical analyses, porosity-permeability data, and computed tomography were used to better understand the diagenetic history and petrophysical property evolution. Numerous dolerite intrusions are present in the studied carbonate successions, where the host limestone was altered to dolomite and marble, and fractures and faults developed due to the upwelling of the magmatic/hydrothermal fluids along pathways. Petrographic studies show an early phase of coarse crystalline saddle dolomite (Dol. I), which resulted from Mg-rich hydrothermal fluids originated from the dolerite dykes. Coarse crystalline marble formed due to contact metamorphism at the time of dolerite emplacement. The second phase of dolomitisation (Dol. II) postdates the igneous intrusions and was followed by dedolomitisation, dissolution, and cementation by meteoric calcite. Stable isotope studies likewise confirm two distinct dolomite phases. Dol. I exhibits more depleted δ18O (-15.8 to -9.1‰ V-PDB) and nondepleted δ13C (-2.05 to +1.85‰ V-PDB), whereas Dol. II shows a relatively narrow range of depleted δ18O (-13.9 to -13.8‰) signatures and nondepleted δ13C (+1.58 to +1.89‰ V-PDB). Dolomitic marble shows a marked depletion in δ18O and δ13C (-13.7 to -8.5‰ and -2.3 to 1.95‰, respectively). The initial phase of dolomitisation (Dol. I) did not alter porosity (5.4-6.6%) and permeability (0.0-0.1 mD) with respect to the unaltered limestone (5.6-6.9%; 0.1-0.2 mD). Contact metamorphism resulted in a decrease in porosity and permeability (3.3-4.7%; 0.1 mD). In contrast, an increase in porosity and permeability in Dol. II (7.7-10.5%; 0.8-2.5 mD) and dolomitic marble (6.6-14.7%; 8.2-13.3 mD) is linked to intercrystalline porosity and retainment of fracture porosity in dolomitic marble. Late-stage dissolution and dedolomitization also positively affected the reservoir properties of the studied successions. In conclusion, the aforementioned results reveal the impact of various diagenetic processes resulting from magmatic emplacement and their consequent reservoir heterogeneity.

Middle Permian dolomites of the SW Sichuan Basin and the role of the Emeishan Large Igneous Province in their origin

Dolomitization of the Middle Permian carbonate platform in South China occurred in successive phases, partially influenced by the emplacement of the Emeishan Large Igneous Province. The main replacement dolomites are: (1) finely crystalline (˂50 μm) Md I, (2) mesocrystalline (50–250 μm), non-planar-a to non-planar-s Md II; and (3) coarse crystalline (250–500 μm), non-planar-s to non-planar-a Md III. Dolomite cement (Cd) is characterized by pores and/or fractures filled with saddle crystals within the Md III dolomites. The Md I dolomites share similar rare earth element patterns and carbon and strontium isotopes to host limestones and δ18O values that are in equilibrium with the limestone. These characteristics indicate that Md I dolomite was formed via the seepage/reflux dolomitization of evaporated seawater during the penecontemporaneous phase. The Md II dolomites share δ13C values and 87Sr/86Sr ratios similar to those of typical Permian carbonates, characterized by a range of low δ18O values. Analyses of fluid inclusions in these Md II dolomites showed homogenization temperatures of 90–130 °C and salinities of 4–9 wt% NaCl equivalent. These results suggest that Md II represents typical replacive dolomitization occurring within convective half-cells under geothermal conditions. They are particularly pervasive when the platform is heated by magmatic underplating and/or igneous emplacement to form thermal convection. The coarser Md III dolomites are characterized by high porosity and subsequently partially filled with saddle dolomite cement (Cd). These Md III and Cd dolomites are rich in radiogenic strontium, have low δ13C values, very low δ18O values, positive Eu anomalies, and contain fluid inclusions indicating high homogenization temperatures and salinities. These characteristics suggest that the Md III and Cd dolomites precipitated from high-temperature hydrothermal fluids, potentially associated with the emplacement of the Emeishan Large Igneous Province (LIP). Regional heating from the Emeishan LIP induced basin uplift and faulting. These were important in channeling the upwelling deep brine fluids into the overlying platform carbonates, leading to the localized intense dolomitization. This suite of Middle Permian dolomites is an excellent example of the successive phases of different dolomitization processes, including that associated with hydrothermal and thermal convection during the emplacement of a LIP.

Assessment of damage on geo-mechanical and micro-structural properties of weak calcareous rocks exposed to fires using thermal treatment coefficient

In most studies focusing on the engineering behaviour of rocks exposed to high temperatures, thermal procedure tends to apply a slow and linear heating rate, and constant exposure time. Also, granite, marble, limestone, and sandstone are generally used because many mineralogical features of these rocks such as texture, mineral size and mineral content can be easily determined under polarized microscope. Contrary of literature, engineering behaviours of the highly porous calcareous rocks (calcarenites and chalk) were evaluated considering logarithmic/exponential heating rates and different exposure times as in a real fire in this study. The porous structure of the carbonate rocks depending on the primary voids was observed in SEM images for initial condition. SEM images of the samples exposed to high temperatures indicated that thermal treatment plays an important role on developing of secondary porosity due to the grain clumping in calcarenites and forming of new micro fissures in chalks. Lumping of minerals observed in calcarenite samples due to increasing temperatures is the main reason for the continuous decrease in strength. Decrease in porosity due to the sintering and fusing between clay minerals up to 600 °C caused the increase in strength of the chalks unlike coarse grained calcarenites. While high temperatures caused strength decrease in coarse crystalline calcarenites by creating thermal stress in the crystal grains due to expansion, on the contrary, fine crystalline chalks were more resilient to this stress because smaller crystals acted as expansion hinges during heating. Also, exposure time was insignificant in fine crystalline rocks, whereas coarse crystalline rocks showed great thermal damage. Depending on the increased temperatures, considering to the strength of some rocks increases while some decreases, a new thermal treatment coefficient graph was suggested to evaluate the rocks with different behaviours together. Because P-wave velocity tends to decrease in almost all rocks whether the strength increases or decreases, it was proposed to use tensile strength as an input parameter in the suggested approach. • Highly porous clayey calcareous rocks were subjected to high temperatures. • Logarithmic/exponential heating rates are used to simulate a real fire. • A new thermal treatment coefficient was proposed to define thermal damage.