Dolomitic Rocks Research Articles

High geogenic soil thallium shows limited impact on bacterial community

Thallium (Tl) is a highly toxic trace metal, included in the US EPA list of priority pollutants. Even though its toxicity is potentially higher or comparable to Cd or Hg, its environmental impact is largely unknown. Despite its toxicity, only a few recent studies are mapping the impact of recently introduced Tl on soil microbial communities, namely in agricultural systems but no studies focus on its long term effect. To complement the understanding of the impact of Tl on soil, this study aims to describe the influence of extremely high naturally occurring Tl concentration (50 mg/kg of potentially bioavailable Tl) on soil microbial communities. Our investigation concentrated on samples collected at Buus (Erzmatt, Swiss Jura, Switzerland), encompassing forest and meadow soil profiles of the local soil formed on hydrothermally mineralized dolomite rock, which is naturally rich in Tl. The soil profiles showed a significant proportion of potentially bioavailable Tl. Yet, even this high concentration of Tl has a limited impact on the richness of the soil bacterial community. Only the meadow soil samples show a reduced richness compared to control samples. Furthermore, our analysis of geogenic Tl contamination in the region unveiled a surprising finding: compared to other soils of Switzerland and in stark contrast to soils affected by recent mining activities, the structure of the bacterial community in Buus remained relatively unaffected. This observation highlights the unique ability of soil microbial communities to withstand extreme Tl contamination. Our study advances the understanding of Tl's environmental impact and underscores the resilience of soil microbes in the face of severe long-term contamination.

Response of trace and rare earth elements to environmental changes in a stalagmite from southern India for the last deglaciation

Speleothems, particularly stalagmites are extensively used to reconstruct paleoclimatic and paleomonsoon changes by using stable oxygen and carbon isotopes along the growth profile of a stalagmite sample. Trace and rare earth elements (REEs) variations in stalagmites are widely recognized as indicators of past precipitation and local hydrology. The amalgamation of isotopic and trace element proxies in speleothems has been regarded as an important tool to infer past climate and hydro-chemical fluctuations. Current advancements in geochemical techniques have enabled us to generate high-resolution paleo-records of almost all trace and REEs from stalagmites. However, their assessment is dependent on numerous factors that control the formation of a stalagmite.Here we present a geochemical record from a well dated stalagmite (VSPM1) from a cave located in the southern India. The stalagmite grew between 15,610 and 13,160 yr BP as revealed by its StalAge modelled ages from eight U–Th dates. This study demonstrates significant variations in trace and REEs during the last deglacial time interval of 2100 years and suggests variations in drip water chemistry. The relative amount of trace elements in colloidal solutions originating from the soil organics and weathered particles of host dolomitic rock may have altered with climatic changes. It appears that trace and REEs of VSPM1 stalagmite have responded to fluctuations in Indian Summer Monsoon (ISM) intensity during the time interval of this study.

Origin of heavy rare earth element enrichment in carbonatites

Heavy rare earth elements (HREE) are currently in high demand for use in high technology, renewable energy and low-carbon transport, but they are the least abundant in nature. Carbonatites are the primary source of REE; however, they are dominated by light REE (LREE). It remains unknown whether carbonatites have the potential to form economic HREE mineralization. Here we report a xenotime-bearing carbonatite in the Bachu REE deposit, northwestern Tarim Large Igneous Province (TLIP), China, and infer the origin of HREE in carbonatites. The rocks evolved from dolomite to calcite carbonatites, and their HREE content correspondingly increased. Both types of rocks have similar monazite U-Pb ages (ca. 300 Ma), and are older than the major eruption of flood basalt of the TLIP, and associated alkaline complexes. They contain higher εNd(t) (2.4–4.1) and lower initial Sr isotopic ratios [(87Sr/86Sr)i = 0.7036–0.7041] than the basalts but similar values to those of younger alkaline rocks. The carbonatites are inferred to be directly derived from low-degree melting of lithospheric mantle sources induced by a deep-seated mantle plume. Calcite carbonatites contain characteristic xenotime, which is associated with burbankite, sulfates, and minor quartz. The rock-forming calcite shows high HREE abundance and flat REE patterns (La/Ybcn = 0.3–2.1). Apatite and LREE minerals in calcite carbonatites also have a higher HREE content (e.g., Y2O3 up to 2 wt%) than those in dolomite rocks. This finding indicates that the early dolomite carbonatite underwent strong fractionation of dolomite and LREE minerals, resulting in HREE and alkali enrichment in the evolved calcite rocks. High amounts of alkalis further enhance the solubility of REE, particularly HREE, in the residual melts. Silica assimilation from the country rocks facilitates the HREE mineralization by sequestering alkalis. Therefore, HREE enrichment in carbonatites may require substantial fractional crystallization of initial melts as well as alkali conservation during ascent.

Investigation on the synergistic effect of pH and pyridinium-based ionic liquid on the wettability alteration of dolomite rock and IFT of formation brine/alkaline crude oil at the presence and absence of SiO2 nanoparticles

Investigation on the hybrid enhanced oil recovery solutions and methods is gaining attention during the last decade since they can activate multiple mechanisms such as viscosity reduction, interfacial tension (IFT) reduction, and wettability alteration. So, the current work is concentrated on the application of 1-octyl-3-methyl pyridinium chloride ([C8py][Cl]) and 1-dodecyl-3-methyl pyridinium chloride ([C12py][Cl]) as novel surfactants in the absence and presence of SiO2 nanoparticles (SiO2-NPs) for the first time for possible IFT reduction and rock wettability change (contact angle (CA) measurement). In this way, the concentration of ionic liquids (ILs) and SiO2-NPs ranged between 0–2000 ppm and 0–1000 ppm, respectively, to see the influence of these chemicals on the wettability change and IFT reduction. The point is that the higher concentrations of these chemicals were not examined since using higher concentrations makes it expensive and uneconomic for field-scale applications. The obtained results revealed that as the pH increases from 3 to 11 in the absence of different chemicals (formation brine/basic crude oil), the IFT experiences an increase from 20.3 to 31.2 mN/m, while the situation for CA is more complicated. In detail, the results revealed that increasing the pH in the range of 3–11 leads to an increase in the CA from 103.2° to 121.3° (increasing pH from 3 to 7) while a further increase in the pH leads to a reduction in CA value from 121.3° to 118.3°. Moreover, the results revealed that increasing the concentration of [C8py][Cl] from 0 to 2000 ppm led to a reduction in IFT value from 20.3 to 0.95 mN/m for pH of 3, from 27.3 to 2.2 mN/m for pH of 7 and from 31.2 to 5.4 mN/m for pH of 11. Besides, the measurements for [C12py][Cl] revealed that increasing the concentration from 0 to 2000 ppm leads to IFT reduction from 20.3 to 0.74 mN/m for pH of 3, from 27.3 to 0.9 for pH of 7, and from 31.2 to 1.4 mN/m for pH of 11. The results demonstrated a higher influence of [C12py][Cl] on the IFT reduction compared with the [C8py][Cl] due to the longer alkyl chain length of [C12py][Cl] which means more detergency power. Furthermore, the effects of these two ILs are examined on the wettability change which showed that both of the examined ILs are capable to manipulate the wettability of the rock surface toward water-wet conditions (53.3°) from oil-wet conditions (121.3°). Also, the influence of SiO2-NPs in the range of 0–1000 ppm is investigated on the IFT reduction and wettability change while the concentration of ILs is held constant at 2000 ppm since the concentration of 2000 ppm leading to the lowest CA and IFT values for both examined ILs. The obtained results reveal that not only the presence of SiO2-NPs with a maximum concentration of 1000 ppm leads to a reducing trend on the IFT in particular for the pH of 11 regardless of the used IL but also it changes the surface wettability to strongly water-wet condition with minimum CA value of 28.5°. In the last stage, the efficiency of the optimum chemical formulations was examined through core flooding experiments using conventional core flooding procedure and the core flooding experiments concomitant with the soaking time (30 days). The experiments revealed that the chemical formulation under a pH of 3 leads to the highest oil recovery factors while the lowest oil recovery factors are obtained under a pH of 11. Besides, the core flooding experiments followed by soaking reveal the ultimate oil recovery of 10.1 and 13.3% based on the original oil in place (OOIP) due to better activation of the wettability change mechanism which was 46% higher than the situation no soaking was performed. The findings of this study can help for a better understanding of the feasibility and applicability of using new hybrid surfactant-NPs-based EOR methods to activate wettability alteration and IFT reduction, especially with a main focus on one specific fraction of crude oil (resin fraction) instead of crude oil.

Understanding groundwater storage and drainage dynamics of a high mountain catchment with complex geology using a semi-distributed process-based modelling approach

Mountainous groundwater systems are usually characterized by great geological complexity and highly heterogeneous hydraulic properties. For that reason, proper system characterization, monitoring and modelling remain challenging. In this study, we investigated a geologically complex alpine catchment (from 1400 to 2900 m asl) in the Dolomites (Italian Alps) by combining hydrogeological field investigation, hydrological monitoring and modelling. A semi-distributed process-based hydrological model was applied to simulate the continuous measured catchment discharge in a period of three years, which covers a large variation of hydrodynamic conditions. The model structure couples the sequential hydrogeological units within the studied catchment: (1) the fractured dolomitic rocks as bedrock aquifer and 2) the unconsolidated deposits accumulating on the slopes and at the valley floor as porous aquifer. In order to evaluate the model structure and parameterization in depth, we applied a multi-step evaluation approach considering both parameter sensitivity and uncertainty. The modelling results demonstrate that the newly developed model can reproduce most discharge behavior of aquifers. The model indicates a seasonal dynamic linkage between surface and subsurface storage units during different flow conditions. Besides the matrix and conduit flow in fractured dolomitic aquifer, it highlights the important role of unconsolidated sediments (porous aquifer) to the storage and discharge behavior of the entire groundwater system. Furthermore, with the comprehensive model evaluation we learned the model performance deficit during extreme high flow conditions and proposed a more detailed hydrogeological conceptual model. We believe that the proposed modelling approach can be transferred to other high mountain catchments with similar hydro(geo)logical characteristics to characterize the collective behavior of aquifer systems, explore conceptual model weakness and optimize catchment monitoring work.

An experimental assessment of seawater alternating near-miscible CO2 for EOR in pre-salt carbonate reservoirs

Enhanced oil recovery (EOR) methods considering the injection of seawater and CO2 have been widely investigated and applied in the Brazilian pre-salt fields. The high availability of these fluids in offshore facilities makes seawater alternating CO2 (CO2WAG) a viable and environmentally friendly EOR method. It combines the advantages of seawater injection and CO2 injection to improve fluid mobility control and viscous fingering attenuation. In this study, in addition to the core flooding test of secondary seawater flooding and the tertiary CO2WAG, different experimental determinations provided a better understanding of the mechanisms related to the EOR methods applied to a carbonate core composed mainly of dolomite, and their interactions with pre-salt oil, brines and CO2. A 13.30% incremental oil recovery was achieved by alternating seawater with CO2. Considering formation brine, non-carbonated seawater, or seawater saturated with CO2, contact angle measurements revealed that the wettability alteration is not significant when dolomite is slightly water-wet, even in the presence of CO2. On the other hand, measures of brine/oil, brine/CO2/oil and CO2/oil interfacial tension emphasize the beneficial effects of this gas for EOR, in near-miscible conditions. This is achieved by the reduction of capillary and interfacial forces that act by trapping the oil in the pores of the medium. The brine salinity, the presence of magnesium in dolomite and the oil's low TAN/TBN ratio proved to be essential factors in determining the slightly water-wet wettability of the dolomitic rock and the interfacial tension between the phases. Furthermore, for the experiments carried out in the presence of brine with solubilized CO2, a considerable variation in the oil drop volume was observed due to the mass transfer of CO2 between the phases. Finally, experimental results showed that the additional oil recovery was mainly associated with oil swelling, viscosity reduction, and mobility increase, which occur even in near-miscible conditions during CO2WAG.

Evaluating the role of salts on wettability alteration in dolomite rocks: Possibility of water based oil mobilization application

While many low salinity studies have been conducted on chalks, calcite minerals and sandstone rocks, few research articles have explored the same for applications in dolomite rocks. To explore the effect of mineralogy, a comparative study on the wettability alteration in the presence of low salinity brines for 2 carbonate rocks of varying composition was studied. The contact-angle experiments were performed for two carbonate samples. One carbonate sample was composed of ∼100 % dolomite mineral whereas the other carbonate rock sample was composed of both dolomite and calcite mineral (5 % calcite and 95 % dolomite). The ionic solutions were composed of NaCl, MgCl2, CaCl2 and CaSO4 single salt solutions of concentration (500 ppm to 5000 ppm). The contact angle reduction was observed in the following order CaSO4 > MgCl2 > CaCl2 > NaCl for the carbonate sample containing calcite and dolomite minerals and the maximum reduction in contact angle for the carbonate sample containing dolomite and calcite minerals was observed for CaSO4 brines was 26.13 % for 1000 ppm concentration. The contact angle reduction observed for the carbonate sample containing dolomite mineral was found to be in the following order MgCl2 > CaCl2 > CaSO4 > NaCl and the maximum reduction in contact angle was observed for MgCl2 brines was 24.58 % for 3000 ppm concentration. The wettability alteration observed in the carbonate sample containing dolomite mineral was less as compared to the carbonate sample containing calcite and dolomite mineral. In the presence of MgCl2 brines, the pH of the brines dominates the mineral dissolution, thereby improving or reducing the extent of wettability alteration. However, the complete wettability reversal has not been observed in this study. An increase in temperature (from 70 to 90 °C) was found to be favourable for wettability alteration while the presence of calcites, along with dolomites has the potential to further improve oil recovery.

Natural fractures in deep continental shale oil reservoirs: A case study from the Permian Lucaogou formation in the Eastern Junggar Basin, Northwest China

The deep continental shale of the Permian Lucaogou Formation in the eastern Junggar Basin is abundant in oil resources, characterized by extensive development and various types of natural fractures. Based on core observations, image log interpretation, and thin section analyses, this study identified fracture types and analyzed the development characteristics of different types in deep continental shales. Moreover, the main controlling factors affecting fracture development and distribution were discussed by integrating statistical and experimental analysis. Results show that natural fractures in deep continental shale oil reservoirs can be grouped as non-bed-parallel and bed-parallel fractures based on their relationship with bedding. Non-bed-parallel fractures are subdivided into subvertical fractures (≥80°) (translayer and intralayer fractures) and moderately dipping fractures (<80°), and bed-parallel fractures are further divided into bedding fractures and stylolites. Since silty and dolomitic rocks appear widely as interlayers and increase the rock brittleness, the deep continental shales are more prone to developing non-bed-parallel fractures. Moreover, intralayer fractures with high dip angles are more developed within these thinner mechanical units and commonly terminate at the mechanical interface, while the translayer fractures are usually less developed. Deep continental shales with higher TOC and argillaceous content are more conducive to forming bed-parallel fractures because of their stronger plasticity, more densely developed laminar structure, and easier formation of abnormally high pressure during the hydrocarbon generation and evolution. In addition, due to the frequent interaction of different types of laminae and the stronger compaction and pressure solution produced by the larger burial depth, the bed-parallel fractures, especially the stylolites, are more developed as a prominent feature in deep continental shales.

A novel and simple approach of rare earth ions (Y3+ and La3+) decorated nano calcium carbonate/ polyethylene glycol for photocatalytic degradation of organic pollutants in wastewater

Pristine and rare earth ions (Y3+ and La3+) decorated rhombohedral nano CaCO3/PEG were extracted from natural dolomite rock using a novel green route biomimetic synthesis. XRD analysis confirmed the crystal phase and doping of Y3+ and La3+ in the CaCO3/PEG. The FTIR analysis confirmed the presence of various functional groups in the synthesized nanoparticles. The obtained products exhibited good thermal stability at the temperatures up to 844 °C. The absorption and emission peaks were blue-shifted due to the impact of the doping ion concentration. The surface chemical compositions were analyzed using XPS. The direct and indirect bandgap energies of nCY1 (0.02 M Y3+: CaCO3/PEG) and nCL1 (0.02 M La3+: CaCO3/PEG) were 3.95, 3.27 eV (direct bandgap) and 2.52, 2.09 eV (indirect bandgap) respectively. The measured fluorescence quantum yields of nCY1 and nCL1 were 22% and 26%, respectively. FESEM with EDX mapping and HR-TEM with SAED analysis was used to determine the morphology, elemental mapping, and crystalline behavior. The photocatalytic activity of prepared samples were performed against methylene blue under UV irradiation. Based on photocatalytic results, nCL1 showed extremely high photocatalytic activity (92%). The effects of the scavenging agents were investigated using superoxide radicals, photogenerated holes, electrons, and OH radicals. Hence, the prepared samples could be an effective catalysts for significant environmental issues. This is the first study for preparing Y3+ and La3+ doped CaCO3/PEG nanoparticles from natural dolomite rock using a low-cost and nontoxic biomimetic method to get enhanced photodegradation efficiency.

Main controlling factors of natural fractures in tight reservoirs of the lucaogou formation in the jimsar sag, Xinjiang, China

Natural fractures act as critical flow channels and reservoir space in the Lucaogou Formation tight reservoir of the Jimsar Sag. It is essential to identify the main controlling factors of natural fractures in order to achieve efficient development of tight oil in this area. There are mainly three types of natural fractures, including tectonic fractures, diagenetic fractures, and abnormal overpressure-induced fractures. Diagenetic fractures are predominantly bedding seams. The fracture development is affected by multiple factors including brittle minerals, lithology, tectonic stress, bed thickness, and total organic carbon (TOC). Large tectonic stress, smaller bed thickness, and higher total organic carbon are all favorable for the development of tectonic fractures and bedding seams. The controls of brittle minerals and lithology on fracture development are different for tectonic fractures and bedding seams. Specifically, carbonate minerals stimulate the tectonic fracture development, while brittle minerals have no control over the bedding seam development; tectonic fractures are most developed in the dolomitic rocks, while bedding seams are most developed in the argillaceous rocks. The calculated fracture density variation coefficients reveal that tectonic stress and brittle minerals are the main controlling factors of tectonic fracture development; total organic carbon and lithology are the main control factors of bedding seam development.

Cataclastic Characteristics and Formation Mechanism of Dolomite Rock Mass in Yunnan, China

The dolomite rock mass on the slope of the Yanhe domestic waste incineration power plant was used as the research object. The macro- and micro-structural characteristics of intact rock blocks and rock discontinuities were analyzed qualitatively and quantitatively using in-hole television, wave velocity testing, three-dimensional laser scanning techniques, photogrammetry, image processing techniques, and scanning electron microscopy (SEM). The study shows that the degree of fracturing generally decreases with depth over the exposed borehole depth range, and the rock masses are generally very fractured. The wave velocity of dolomite generally increases with the depth of the borehole, and the integrity of the dolomite is either broken or extremely broken. The excavation profile reveals six sets of discontinuities and joints that are straight, smooth, interconnected, and largely unfilled. The angles of the structural bodies of different grain sizes are sharp, with roundness being angular and sharp-angled. The smaller the blocks, the more complex the surface morphology. SEM observations show that the ultramicroscopic fractures are not flat and smooth, and the fractures are folded. Fracturing mainly occurs along intercrystalline and crystal interfaces. These fracture features suggest that the fracturing of dolomite is mainly related to the original sedimentary construction and tectonism.

Experimental investigation on the application of concrete produced with limestone and dolomitic limestone aggregates in building constructions

Concrete, which is frequently used in the production process of buildings; It is made by mixing cement, water, aggregate and additives in appropriate amounts. It is important that the physical, chemical, mineralogical and especially mechanical properties of the concrete are at the desired level in terms of strength and durability of the built structures. In this direction, the selection of aggregates, which are an important part of the concrete mix, is one of the important factors affecting the concrete properties. The use of limestone and dolomitic rocks, which are rocks of sedimentary origin, in the selection of aggregates, strengthens the adhesion of aggregates with cement and improves the properties of the concrete mixture. In this study, it was aimed to identify and classify the rocks in the Western Anatolian region of Turkey and to investigate the suitability of their use as aggregates in concrete. In this context, when the physical, chemical and mineralogical properties of the rock samples taken from the field area were examined, it was understood that the rock samples were limestone and dolomitic limestone samples. In order to compare the performance of concrete mixtures prepared using limestone and dolomitic limestone aggregates, a total of 18 concrete samples were prepared, including limestone crushed aggregate, dolomitic limestone, and limestone and dolomitic limestone aggregates used together. At the end of the 7 and 28 days curing period, the concrete compressive strengths of the prepared samples with the intention of being used as concrete in building structures were tested and compared.

The Debated Discovery of Dolomite and the Proposal of a New Geosite at Borcola Pass (Eastern Italian Pre-Alps) in Honor of Giovanni Arduino

Within the Venetian Pre-Alps, the Borcola Pass connects the Posina (Vicenza province) and the Terragnolo (Trento province) valleys. The Posina valley is located north of Schio (Vicenza) within the Italian Southern Alps structural unit. In this area, the injection of Paleogene basaltic dykes along fault/fractures in the late Triassic Dolomia Principale unit has produced a local metamorphism of the dolomite rock into a marble characterized by the presence of brucite veins. This marble was studied in the eighteenth century by the famous Italian scientist Giovanni Arduino, who understood its metamorphic origin. In fact, the marble is always associated with sub-vertical basaltic dykes intruded into the carbonate rocks of the Pre-Alps. Arduino performed also chemical experiments on the marble. The reading of the description of the experiments induced later authors (e.g., Maraschini, von Morlot, Mc Kenzie) to infer that Arduino unknowingly discovered the mineral called dolomite. In this work, we propose that the abandoned Borcola Quarry should be nominated as a geosite, to allow its conservation and popularization and to preserve the memory of a probably minor, yet informative step in the long-lived history of the discovery of dolomite. In addition, this site presents other reasons of interest, such as petrography, mineralogy, structural geology, industrial archeology, and eco-geotourism. The proposed geosite is therefore of great importance in terms of its multidisciplinary scientific value, aesthetic appeal, and educational value.

Lacustrine-evaporitic microbial dolomite from a Plio-Pleistocene succession recovered by the SG-1 borehole in the Qaidam Basin, NE Tibetan Plateau

The Plio-Pleistocene evaporitic lacustrine succession in the Qaidam Basin, which was recovered by drill core SG-1, provides the material for understanding the maturation of dolomite since dolomite is present in the core from 7.6 to 870 m depth, spanning a time interval of 0.1–2.8 Ma. Twenty-two samples were collected at different burial depths. The samples were examined by thin-section petrography and SEM for textures, and analyzed for mineralogy (XRD), trace elements and carbon and oxygen isotopes. The main mineral compositions of each sample are dolomite, quartz, halite and gypsum. Dolomite is mostly scattered with spheroidal to ellipsoidal shapes, several microns in diameter, partially encapsulated in gypsum. Microbial micropores and calcified microorganisms are observed on and within the dolomite crystals and in the thin sections. The degree of ordering of the dolomite gradually increases with burial depth, which basically conforms to the first-order reaction function. The crystal constants of dolomite decrease with burial depth, indicating recrystallisation with increasing overburden. The trace elements of the dolomites are significantly different from those of hydrothermal dolomites, but close to lacustrine microbial carbonate. It is concluded that the dolomites in core SG-1 are mainly authigenic, with microbial processes a likely facilitator of dolomite precipitation. The dolomite formed and then evolved in crystal structure during burial, gradually approaching ordered stochiometric dolomite. This study gives clues to link microbial dolomite to the massive ideal dolomite rock encountered in the geological record.

Spiraea decumbens Koch subsp. tomentosa (Poech) Dostál, novelty for the flora of Slovenia and the Dinaric Alps

Abstract In Govci under Mt. Poldanovec above the Trebuša Valley we found a new locality of southeastern-Alpine (Alpic) endemic Spiraea decumbens subsp. tomentosa, which is new to the flora of Slovenia and the Dinaric Alps. Its closest known localities are in the western Julian Prealps in Northeastern Italy. A small population of several ten shrublets occurs at elevations of about 570 m in shady, almost vertical dolomite rocks, in a stand of the endemic association Phyteumato columnae-Primuletum carniolicae. Despite a very small population we assume there are other localities in this area, where numerous gorges are very difficult to acces and have therefore not yet been sufficiently studied.

Origin of dolomites in the Permian dolomitic reservoirs of Fengcheng Formation in Mahu Sag, Junggar Basin, NW China

Origin of authigenic dolomites in the dolomitic reservoir of the Permian Fengcheng Formation in the Mahu Sag of Junggar Basin is unclear. Occurrence and genetic evolution of the authigenic dolomites in dolomitic rock reservoir of the Fengcheng Formation in the Mahu Sag were analyzed by polarized and fluorescence thin sections, scanning electron microscope (SEM), electron microprobe (EMP), C, O and Sr isotopes analysis, and other techniques. (1) Dolomites were mainly precipitated in three stages: penecontemporaneous–shallow burial stage (early stage of the Middle Permian), middle burial stage (middle stage of the Middle Permian), and middle–deep burial stage, with the former two stages in dominance. (2) Dolomitization fluid was high-salinity brine originating from alkaline lake. In the penecontemporaneous–shallow burial stage, Mg2+ was mainly supplied by alkaline-lake fluid and devitrification of volcanic glass. In the middle burial stage, Mg2+ mainly came from the transformation of clay minerals, devitrification of volcanic glass and dissolution of aluminosilicates such as feldspar. (3) Regular changes of Mg, Mn, Fe, Sr, Si and other elements during the growth of dolomite were mainly related to the alkaline-lake fluid, and to different influences of devitrification and diagenetic alteration of volcanic materials during the burial. (4) In the penecontemporaneous stage, induced by alkaline-lake microorganisms, the micritic–microcrystalline dolomites were formed by primary precipitation, replacement of aragonite and high-Mg calcite, and other processes; in the shallow burial stage, the silt-sized dolomites were formed by continuous growth of micritic–microcrystalline dolomite and replacement of calcites, tuffs and other substances; in the middle burial stage, the dolomites, mainly silt- and fine-sized, were formed by replacement of volcanic materials. The research results are referential for investigating the formation mechanism and distribution patterns of tight dolomitic reservoirs in the Mahu Sag and other similar oil and gas bearing areas.

Prevention of rock and gas outbursts in super deep-level mining in Internatsionalny Mine

The method of advanced perimeter blasting has found effective application in development heading&nbsp;and stone drivage. The method uses various drilling-and-blasting scenarios subject to the alteration ingeological and geotechnical conditions, and with regard to the spatial location of outburst-hazardous strata relative to the section of a mine road being driven. This article describes the actually implemented prevention of gas-dynamic events using the method of advanced perimeter blasting, and the case-study of the method applied in the outburst-hazardous carbonate rock mass in super deep-level mining in Internatsionalny Mine (depth of 1200 m and more). The records of the gas-dynamic events in the course of drivage with anti-outburst measures are analyzed. The semi-commercial tests of advanced perimeter blasting are described with patterns of drilling and blasting, and designs of charges in shooting outburst-hazardous beds. The effect of blasting on fracturing is estimated by calculation of the blast impact zones as function of the charge mass and length. The observations over variation in the geomechanical and geodynamic behavior of rock mass during drivage with the perimeter blasting efficiency control are analyzed. The studies included examination of geodynamic characteristics of dolomite rock mass susceptible to rock and gas outbursts and the performance evaluation of the preventive advanced perimeter blasting. The quantitative figures on gas-dynamic phenomena and events in striking and intersecting outbursthazardous dolomite beds are given in graphical form. The flow chart of the semi-commercial testing of advanced perimeter blasting is presented, and the fracturing zones induced by the explosion-generated shock in advanced perimeter blasting are calculated.

A fast method to infer Nuclear Magnetic Resonance based effective porosity in carbonate rocks using machine learning techniques

A better estimation of the effective porosity of the reservoir rock is a critical task for petrophysicist and well logs analyst. A majority of the current approaches to estimate the effective porosity of the reservoir rocks from well logs are based on the information of the Density-Neutron logs. These approaches usually resulted in the inaccurate estimation of the rock porosity particularly in the naturally fractured carbonates or dolomite rocks. The Nuclear Magnetic Resonance (NMR) based effective porosity is independent of the rock matrix and mineralogy, on contrary it depends on the number of hydrogen nuclei in the pore spaces of the rock. In this study, we have used six machine learning (ML) techniques to predict the NMR based effective porosity in carbonate rocks. The ML models to predict the effective porosity includes deep neural networks (DNN), random forest regressor (RF), decision trees (DT), K-Nearest Neighbors algorithm (KNN), extreme gradient boosting (XGB), and adaptive gradient boosting (AdaBoost). These models were trained on the geophysical well logs such as Gamma ray log (GR), caliper log (Cali), neutron porosity log (NPHI), photoelectric factor log (PE), and bulk density log (RHOB). A total of 4002 data points were obtained from the five wells located in the carbonate field. The tuning of ML models hyperparameters were conducted using a ‘GridSearchCv’ method. Furthermore, the K-fold cross-validation criterion was implemented to improve the accuracy of the ML models. The ML models performances were evaluated using multiple graphical and goodness of fit tests including prediction cross-plots, average absolute percentage error (AAPE), root means square error (RMSE), and coefficient of determination (R2) methods. The prediction results showed that the DNN, RF, and XGB models performed better than the other implemented ML techniques. These methods resulted in a significantly low error and high (R2). The achieved accuracy was above 85% when validated on a blind dataset. This study also offered an empirical model that can be used to quickly estimate the NMR based effective porosity using afore-mentioned well logs. The model can also be used as a standalone package that can be coupled with any logging software for quick evaluation of NMR based effective porosity.

Metamorphic dolomitic marble-hosted talc from the Mulvoj area in the Western Pamir Mountains, Tajikistan

Abstract Talc is crystallized in the metamorphic dolomitic rocks of the southwest Pamir mountains in the Mulvoj area, Tajikistan. Field studies show that talc is restricted to metamorphic dolomitic marble layers in the garnet-mica schist and gneiss. The layers are parallel to the original sedimentary bedding and schistosity of the metamorphic rocks. Petrography and whole rock geochemistry reveal calcite, tremolite, quartz and dolomite as the main mineral phases in the talc-bearing metamorphosed dolomitic rocks, while calcite is absent in the samples without talc. XRD studies show that talc samples are almost pure, and geochemistry indicates very low Fe and Cr and very high Mg contents. Geochemical features along with field observations clearly shows that Mulvoj talc is not originated from peridotite. Based on phase relations studies in the CaO-MgO-SiO2-H2O-CO2 system, the reaction between dolomite, quartz, and water at pressure greater than 2 kbar and temperature up to ~460°C and XCO2 up to 0.6 was the main talc forming reaction. Talc and calcite consuming reaction produced tremolite, dolomite and binary (CO2-H2O) fluid.

Determining the optimal conditions for the synthesis nano CaTiO3 square prepared from natural dolomite rocks

Due to the importance of ceramic materials, especially of the perovskite type, this study included the synthesis of calcium titanate using dolomite as a natural calcium source from the Iraqi environment. Firstly, the work included preparing of calcium sulfate dihydrate from dolomite using dilute sulfuric acid, and then studying the optimal conditions for the formation of calcium titanate (CaTiO3) through the reaction of titanium dioxide with calcium sulfate dihydrate. The optimum conditions included: the ratio of titanium to calcium which was 1:0.5, 1:1, 1:1.5 and 1:2, respectively, as well as, the calcination temperature (1000, 1200 and 1300 °C) and finally the calcination time (1 and 2 h). The formation of calcium titanate was tracked by X-ray diffraction, and the results demonstrated that the optimum conditions are 1:1 at a calcination temperature of 1300 °C for 2 h. Moreover, the work included converting calcium titanate into calcium titanate nanoparticles using an environmentally friendly method which was achieved by using ultrasound on a liquid composed of calcium titanate in deionized water. The formation of calcium titanate nanoparticles was proved by TEM, which showed the formation of regular and irregular square-like nanoparticles with an average particle size of 55 nm. From an industrial point of view, this method is considered to be of low cost for the production of high cost nano-calcium titanate.