Rock Reactions Research Articles

Garnet growth in a geological blink of an eye

Mineral reactions determine the physical and rheological properties of rocks, but whether these reactions occur close to or far from equilibrium and whether they are continuous or pulsed is challenging to unravel. This introduces significant uncertainty in determining the thermomechanical properties and behavior of the crust and estimating the pressure and temperature conditions that rocks underwent during their tectonic history. Here, we employ elemental mapping and high-precision Lu-Hf chronology to investigate whether and to what extent garnet—one of the most important recorders of pressure, temperature, deformation, and time in the lithosphere—keeps up with tectonic processes. The analysis was done on a single 1.2-cm-sized garnet grain from a carbonate-rich mica schist from the Schneeberg Complex (Italy). Five compositionally distinct zones were identified and dated separately. The four inner zones, characterized by trace-elements oscillations, yielded identical ages with a weighted mean of 98.4 ± 0.1 Ma (2σ), whereas the outermost zone yielded 97.8 ± 0.3 Ma. During the first growth pulse, garnet grew at an average radial growth rate of at least 6.2 cm m.y.−1. Nucleation initiated out of equilibrium conditions and resulted in high fluid production that, in turn, boosted garnet growth, episodically limited by the rock’s elements transport permeabilities. This pulsed, ultrafast garnet growth must have occurred over a very limited pressure-temperature window. This example provides a rare glimpse into the discontinuous nature of mineral reactions in metamorphic rocks and highlights garnet as a unique recorder of the processes that occur when such rocks push toward equilibrium.

Modeling Complex Interactions Between Acid–Rock Reactions and Fracture Propagation in Heterogeneous Layered Formations

Acid fracturing is essential in enhancing recovery efficiency, especially within carbonate reservoirs. Although extensive studies have been conducted on hydraulic fracturing, understanding the intricate dynamics between acid–rock reactions and fracture propagation in heterogeneous layered reservoirs remains limited. This study employs a comprehensive coupled hydro-mechanical-chemical flow framework to investigate acid fracturing processes in layered geological formations. The model incorporates a two-stage homogenization approach to account for rock heterogeneity, a dual-scale continuum framework for fluid flow and acid transport, and a phase field method for examining fracture propagation. We thoroughly examine how treatment parameters, particularly acid concentration and injection rate, affect fracture propagation modes. The analysis identifies three distinct propagation patterns: crossing, diversion, and arresting. These are influenced by the interplay between pressure buildup and wormhole formation. Initially, higher acid concentration aids in fracture crossing by lowering the peak pressure required for initiation, but excessive concentration results in arresting because it causes extensive wormhole development, which reduces fluid pressure. Similarly, the injection rate plays a crucial role in fracture movement across layer interfaces, with moderate rates optimizing propagation by balancing pressure and wormhole growth. This comprehensive modeling framework serves as a valuable prediction and control tool for acid fracture behavior in complex layered formations.

Assessment of reactive surface and kinetic parameters of basaltic rocks during CO2 storage

Carbon capture and storage (CCS) is a novel technology that aims to reduce the presence of carbon dioxide from the atmosphere. This technology involves capturing CO2 from industrial sources or directly from the air, treating, transporting, and storing it in long-term safe rock formations. Basaltic rock comprises reactive minerals and glassy phases, which trap CO2 permanently through the mineralization mechanism. However, this method is complex mainly due to the rapid interaction between solid and liquid phases. The mineralization occurs at the interface between the reactive fluid and the basaltic rock surface, converting the dissolved CO2 into solid carbonate mineral that precipitates in the pores and fractures of the rock matrix. The reaction rate of a basaltic rock depends significantly on the CO2 wettability and rock-fluid interfacial interactions. However, there is limited information about the influence of the reactive surface on the reaction rate of minerals present in basalt formations. This work investigates the influence of kinetics parameters such as pH, temperature, and reactive surface area in the reaction rate of basaltic rocks. Basaltic rock dissolution and precipitation is assessed using the geochemical software PHREEQC. The proposed numerical model solves the reactive transport problem and provides feedback on the influence of the kinetics reaction parameters. The dynamics of the reactive surface during the reaction of basalt rocks is evaluated. The numerical results show the potential of basaltic rock for CO2 mineral storage as solid carbonates and identify the main factors that limit the mineralization process. Finally, this work provides a deeper understanding of CO2 mineralization that can provide valuable findings to guide Brazilian CCS projects.

Quantitative characterization of synergistic effect in CO2 storage and enhanced recovery systems with considering CO2–water–salinity–rock reactions

Quantitative characterization of synergistic effect in CO2 storage and enhanced recovery systems with considering CO2–water–salinity–rock reactions

Effect of hydro-chemical corrosion on mechanical properties of red sandstone under uniaxial and triaxial compression

The degradation of mechanical characteristics of sandstone, a common engineering material in acid environment, is directly related to the project service life forecast. In order to investigate the influence of water–rock interaction on the mechanical properties of red sandstone, a series of uniaxial and triaxial compression tests were conducted on sandstone immersed in solutions of different pH values and immersion times. Moreover, the effects of acid chemical corrosion on the microscopic structure of the sandstone were analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) tests. A chemical damage strength model was then formulated within the theoretical framework of chemical reaction kinetics theory. The results indicate that the different hydro-chemical solutions have a significant deterioration effect on the sandstone. In immersion tests, the water–rock reaction of sandstone is essentially completed after 30 days of immersion. With increasing immersion time, the uniaxial compressive strength of sandstone immersed in neutral and weakly acidic saline solutions shows an initial rapid decrease followed by a slow increase, while sandstone immersed in distilled water and strongly acidic solutions shows varying degrees of decrease over time. High confining pressure weakens the corrosion effect of the solutions on the sandstone, particularly, the neutral solution. In the triaxial compression tests, strong acid has a great corrosion effect on sandstone. The average peak strength of sandstone immersed in pH2, pH4, pH7, and distilled water decreased by 30.2%, 28.7%, 25.1%, and 22.8%, respectively. The model considers calcium precipitation not only reflects the change in pH value of the immersion solution with time but also effectively predicts the strength of sandstone immersed in different solutions. The results deepen our understanding of the deterioration mechanism of silicon-based porous rock under different chemical solutions and would be of importance for the long-term stability analysis of rock engineering in complex groundwater environments.

Effect of amygdala on the pore-crack structure and mechanical properties of Permian tuff and breccia during hydration

The Permian volcanic rocks in the Sichuan Basin are rich in oil and gas resources. However, during volcanic rock exploitation, the working fluid fully contacts with the volcanic rocks, and hydration reaction will occur, which destroys the pore structure of the rock, makes the rock layer loose and fragile, increases the risk of wellbore collapse, and causes the loss of volcanic rock production. However, the reasons for the change of pore structure of volcanic rocks after hydration and the understanding of the hydration mechanism of volcanic rocks are not clear. Therefore, this paper uses microscopic and mechanical experimental testing methods combined with digital core technology to study the changes of pore-crack structure, amygdale structure and mechanical characteristics of Permian tuff and breccia in Sichuan Basin before and after hydration. The research results show that during the hydration process of volcanic rocks, pores, cracks, and amygdales are transformed into each other. The hydration process of the volcanic rocks is characterized by the disappearance of isolated pores, the generation of small cracks, and the generation and transformation of new pores into amygdales. Amygdales also have an important impact on the mechanical properties and hydration of volcanic rocks. When the content of amygdales in volcanic rocks is high, the rocks are more prone to breakage. In addition, amygdales promote the hydration reaction of volcanic rocks, and the size and number of amygdales determine the strength of volcanic rock hydration ability. When the content of amygdales in the rock is higher, the rock is more prone to hydration reactions. Therefore, in the process of gas reservoir development, understanding the distribution and characteristics of amygdale is helpful to optimize the composition of the working fluid and enhance drilling technology. It aims to maximize the productivity gas wells.

Zircon Coupled Dissolution–Precipitation Replacement During Melt–Rock Interaction Modifies Chemical Signatures Resulting in Misleading Ages

ABSTRACTMelt migration through Earth's crust drives well‐documented melt–rock reactions, locally changing rock assemblage and geochemistry. However, melt–zircon interaction remains understudied. We report on three zircon‐melt interaction events from the Pembroke Granulite, New Zealand. Primary zircon from gabbroic gneiss which was subject to minor post‐emplacement melt migration and primary zircon from younger dykes exhibit straightforward microstructures, microchemistry, and age data. In contrast, zircon from melt‐mediated reaction halos adjacent to the dykes and from melt‐fluxed high‐strain zones display dissolution modification of grains, micro‐porosity and blurred or truncated internal zoning typical of replacement by coupled dissolution‐precipitation. Replaced zircon domains show changed rare earth element patterns and redistributed or lost radiogenic Pb that generates ambiguous apparent spot date arrays, smeared over tens of millions of years. We conclude that the metamorphism and three melt–rock interaction events were brief, and the arrays misrepresent the true age and duration of the metamorphism. Pb‐loss persisted beyond the metamorphism, with porosity and inclusions formed during coupled dissolution‐precipitation making replaced zircon domains more susceptible to subsequent Pb‐loss compared to the structurally intact, primary magmatic zircon in the host gabbroic gneiss or dykes. We recommend conducting high‐resolution microstructural investigations upon recognition of spot date arrays observed in single samples to rule out the possibility of spurious arrays resulting from coupled dissolution‐precipitation.

Hydrochemical Characteristics and Formation Mechanism of Geothermal Fluids in Zuogong County, Southeastern Tibet

Zuogong County is located in the southeast of Tibet, which is rich in hot spring geothermal resources, but its development and utilization degree are low, and the genetic mechanism of the geothermal system is not clear. Hydrogeochemical characteristics of geothermal water are of great significance in elucidating the genesis and evolution of geothermal systems, as well as the sustainable development and utilization of geothermal resources. The hydrogeochemical characteristics and genesis of the geothermal water in Zuogong County were investigated using hydrogeochemical analysis, a stable isotope (δD, δ18O) approach, and an inverse simulation model for water–rock reactions using the PHREEQC. The results indicated that the Zuogong geothermal system is a deep circulation heating type without a magmatic heat source. The chemical types present in the geothermal water from the Zuogong area are HCO3 and HCO3·SO4, and the main cations are Na+ and Ca2+. The groundwater is replenished by atmospheric precipitation and glacier meltwater. The salt content of geothermal water mainly comes from the interaction between water and surrounding rocks during the deep circulation process. The reservoir temperature of geothermal water in Zuogong is 120–176 °C before mixing with non-geothermal water and drops to 62–98 °C after mixing with 58 to 79% of non-geothermal water. According to the proposed conceptual model, geothermal water mainly produces water–rock interaction with aluminosilicate minerals in the deep formation, while in shallow areas it interacts mainly with sulfate minerals. These findings contribute to a better understanding of the geothermal system in Zuogong County, Tibet.

Study on A New Type of High Temperature Resistant Adsorption Type Retarded Acid System

Abstract Deep carbonate reservoirs present significant hurdles for reservoir stimulation due to extreme temperatures and rapid acid-rock reactions. The dense adsorption layer has the ability to postpone the interaction between rock and hydrogen ions, which is crucial for lowering the acid rock reaction rate. Based on the surfactant and film-forming agent’s synergistic impact, the retarding agent SH-1—which has the ability to generate a dense adsorption film on the surface of rock samples—was chosen for this study. After adding synergist and corrosion inhibitor, a new type of high temperature resistant adsorption type retarding acid system ’ 0.9% SH-1 + 20% HCl + 0.1% synergist + 1.5% corrosion inhibitor ’ was developed. The retarding performance of the retarding acid system at high temperature and various parameters of acid rock reaction kinetics were studied. The results show that the new adsorption-type retarded acid system can achieve good retarding effect at high temperature and ultra-high temperature, and the retarding rate is 90 % at 180 °C. In comparison to traditional hydrochloric acid, the new adsorption-type retarded acid exhibits a lower hydrogen ion mass transfer rate and a higher acid-rock reaction activation energy. These differences can effectively lower the acid-rock reaction rate. Additionally, an examination of the etching morphology reveals that the retarded acid is more easily etched along the cracks leading to the deep core. The novel adsorption-delayed acid offers excellent retarding power, high temperature resistance, and minimal damage. Consequently, it has certain reference value for the study of acidification transformation of ultra-high temperature deep carbonate reservoirs.

Carbonate Nanoparticles Formed by Water–Rock Reactions in Groundwater: Implication of Carbonate Rock Weathering in Carbonate Aquifers

Carbonate rocks are highly reactive and exhibit higher ratios of chemical weathering compared to most other rock types. A chemo-mechanical mechanism, which is particularly effective in groundwater due to higher ion concentrations, is common in fine-grained carbonates at the nanoscale. As a result, the weathering of carbonate aquifers produces a substantial number of carbonate nanoparticles (CNPs). In this study, we utilized high-resolution transmission electron microscopy (HRTEM) to analyze CNPs formed by water–rock reactions in two types of groundwater from Shandong Province, China. Our findings reveal a significant presence of naturally occurring CNPs in groundwater. The HRTEM results show that CNPs display spherical, cubic, hexagonal, and irregular shapes, with some forming aggregates. Energy-dispersive spectrometry indicates that most nanoparticles contain O, C, Ca, and Fe, with some also containing Si, Mg, S, Sr, and Cl. Selected area electron diffraction (SAED) patterns show that CNPs are mainly amorphous, with some crystalline forms. The diverse shapes and complex compositions of these CNPs suggest that they are not man-made but formed through the weathering of carbonate minerals via chemo-mechanical mechanisms. This discovery provides new insights into carbonate mineral evolution and mineralization during weathering. Given their widespread presence, CNPs in groundwater could represent the transportation of elements in the form of particles.

The Indicative Role of Geochemical Characteristics of Fracturing Flowback Fluid in Shale Gas Wells on Production Performance

The geochemical properties of fracturing flowback fluids indirectly indicate the fracturing efficiency of the reservoir, the interaction between the reservoir and injected water, and the preservation of oil and gas, thereby offering robust data support for identifying fracturing flowback fluid sources, assessing fracturing effects, and proposing stimulation strategies. In this study, the ion characteristics, total salinity, and stable isotope ratio of fracturing flowback fluids of the Z202H1 and Z203 wells in Western Chongqing were measured. The findings suggest that with the extension of flowback time, the geochemical properties of fracturing flowback fluids evolve toward higher salinity and heavier stable isotope ratios, ultimately stabilizing. Upon comparing the water–rock reaction intensity and the rate of total salinity increase in the fracturing flowback fluids, it is concluded that fracturing flowback fluids contain a mixture of formation water. Because water–rock reactions elevate the total salinity of fracturing flowback fluids, we introduce the Water–Rock Reaction Intensity Coefficient (IR) to denote the intensity of these reactions. Based on the IR value, the binary mixture model for fracturing fluids in fracturing flowback fluids was adjusted. With the increase in flowback time, the content of fracturing fluids in fracturing flowback fluids of Z202H1 and Z203 stabilized at about 55% and 40% respectively. During the same flowback period, the fracturing flowback fluids of the Z203 well exhibit a higher total salinity, a heavier stable isotope ratio, a greater IR, and a lower fracturing fluid content in fracturing flowback fluids. This suggests that the fracturing effect of the Z203 well is superior to that of the Z202H1 well, leading to a higher production capacity of the Z203 well.

Research on the solution of the thermo-hydro-mechanical-chemical coupling model based on the unified finite volume method framework

Heat extraction from hot dry rock (HDR) reservoirs involves complex thermal–hydraulic-mechanical-chemical (THMC) coupling processes, which pose significant challenges for efficient geothermal energy utilization. The current frameworks that combine the finite volume method (FVM) and finite element method (FEM) for THMC modeling based on the embedded discrete fracture model (EDFM) are separate, leading to complex implementations and hindering the development of efficient solutions. To address these issues, we propose an FVM-based THMC coupling model that solves fluid flow, heat transfer, and chemical reactions using the finite volume method (FVM), while mechanical deformation is addressed using the extended finite volume method (XFVM). The reaction module incorporates PHREEQC for multicomponent reactions under high-temperature and high-pressure conditions. The model is validated against experimental data for mineral reactions under high-temperature and high-pressure conditions, as well as XFEM and COMSOL simulations for displacement fields, confirming its accuracy and computational performance. Application results show that the temperature deviation between multicomponent and single-component models can reach up to 14 °C, underscoring the importance of incorporating multicomponent water–rock reactions in THMC coupling. This model accurately captures the spatiotemporal evolution of THMC processes and efficiently predicts long-term heat production in enhanced geothermal systems (EGS) reservoirs. It could significantly advance the ability to achieve more accurate and reliable predictions for the engineering development and efficient utilization of EGS reservoirs.

Effect of two-phase viscosity difference and natural fractures on the wormhole morphology formed by two-phase acidizing with self-diverting acid in carbonate rocks

Different types of acids are needed in the field to achieve various acidizing goals. Currently, there are no reliable acidizing models for multiphase flows and complex multiphysics coupling. This paper derives mathematical formulas for the oil–water acidizing process of a situ self-diverting acid combined with thermal–chemical–fracture interactions and discusses the influence of two-phase oil–water mixture and fractures on the wormhole morphology produced by self-diverting acid. The results show that the spent acid following the acid–rock reaction forms a high-viscosity sealing zone, causing the injected acid to be redirected. The self-diverting acid forms more numerous and longer branches than a conventional acid during single-phase acidizing. In the case of two-phase acidizing, the high viscosity difference produces distinct effects when using self-diverting acid compared with conventional acid. Specifically, the self-diverting acid extends the breakthrough time and forms a wormhole morphology with longer and more complex branches, whereas the conventional acid accelerates the breakthrough of the rock. As the viscosity difference decreases, the wormhole morphology of the self-diverting acid gradually approaches that of a single-phase acid. Large-aperture fractures completely determine the wormhole morphology, while smaller apertures determine the branch morphology of the wormhole. Fractures have a negative acidizing effect in the case of the self-diverting acid, unlike conventional acid. The proposed model accurately simulates the complex acidizing process of a self-diverting acid.

Feasibility Research on Surface Water Reinjection into the Sandstone Geothermal Reservoir of the Guantao Formation in Tianjin Based on Laboratory Experiments

Tianjin possesses abundant geothermal resources, and geothermal reinjection is an effective strategy for maintaining the sustainable development and utilization of these resources. However, several issues have arisen in the reinjection of sandstone geothermal reservoirs in the Tianjin area, including a mismatch between the reinjection capacity and effluent capacity, as well as challenges related to continuous reinjection. Therefore, it is crucial to investigate the reinjection of exogenous water into sandstone pore-type geothermal reservoirs. This study focuses on the geothermal reservoir of the Guantao Formation in the Binhai New Area. The surface water treatment process for reinjection into sandstone geothermal reservoirs was determined through water treatment simulation experiments. Additionally, experiments examining the interaction between the reinjected water and reservoir rock were conducted to assess the feasibility of using treated surface water for reinjection into sandstone geothermal reservoirs. The hydrogeochemical response mechanisms and the impact on the reservoir under reinjection conditions were also investigated. The results indicate that a nanofiltration module and tubular microfiltration membrane are essential to ensure the stability of the system. The pH and TDS of water samples decreased after reinjecting mixed water (HHS) into the sandstone reservoir. The hydrochemical type consistently remained Cl-Na. The conventional water chemistry components and trace elements were influenced by the corresponding water–rock reactions. The reservoir minerals exhibited minimal precipitation, primarily consisting of K-feldspar and Fe-dolomite. The minerals produced during the experiment accounted for only 0.08% of the total cuttings’ mass, indicating a negligible impact on the reservoir structure. PHREEQC was employed to simulate the changes in mineral saturation index before and after the reinjection of mixed water and geothermal water, respectively. Notably, similar hydrogeochemical changes were observed in the geothermal fluids. Thus, this study demonstrates the feasibility of reinjecting treated surface water into sandstone geothermal reservoirs from a hydrogeochemical perspective. This research provides valuable insights for the development of external water reinjection projects in hot spring health care units, contributing effectively to the achievement of carbon peaking and carbon neutrality goals.

Effects of functional groups in polymers on rate of acid–rock reaction in reservoir stimulation

The focus of research on acid stimulation is to reduce the rate of the acid–rock reaction, which involves the infiltration of acid into deep formations. Gelled acids with high viscosity can decelerate the diffusion of hydrogen ions to decrease the rate of the acid–rock reaction. However, there have been few reports on the interactions between functional groups in polymers and rocks. In this study, three polymers (AA7, AA24, and AAS) with different functional groups were synthesized, and their effects on the acid–rock reaction were investigated. The results showed that the order of the abilities of the three polymers to delay the acid–rock reaction was as follows: AA24 > AA7 > AAS. The retardation rate for AA24, AA7, and AAS was 79.31%, 66.67%, and 40.23%, respectively. Adsorption experiments illustrated that AA7 and AA24 were adsorbed on the surface of calcite via hydrogen bonds formed by ethoxy groups, whereas AAS relied on the hydrophobic effect of the benzene ring. The anionic polymer AAS was subjected to a strong electrostatic effect in an acid solution, which caused the molecular chains to curl and impaired the retarding performance. This was proved by the fact that the viscosity dramatically decreased from 66.00 mPa s in an aqueous solution to 7.50 mPa s in an acid solution and the effective diameter decreased from 322.2 nm in an aqueous solution to 102.2 nm in an acid solution. In the cases of the nonionic polymers AA7 and AA24, there was little change in viscosity or effective diameter, whether in an acid solution or an aqueous solution. Scanning electron microscopy confirmed that the film formed by the adsorption of AA24 on the surface of calcite was denser than that formed by AA7 because more ethoxy groups were present in AA24, but the film exhibited some narrow cracks in the case of AAS. Atomic force microscopy demonstrated that the surface roughness of calcite etched by a retarding acid solution of AA24 was only 78 nm, whereas it was as high as 130 nm in the case of AAS, which was consistent with the retarding performance with regard to the acid–rock reaction. This research could contribute to improvements in carbonate acidizing for reservoir stimulation.

Origin of porosity in evaporite platform dolostone in the middle Cambrian Shaelek Formation, NW Tarim Basin, China: constraints from petrology, mineralogy and geochemistry

The extensive middle Cambrian evaporite platform dolostone represents a significant area for hydrocarbon exploration in the Tarim Basin with recent advances indicating promising exploration prospects. However, owing to its considerable depth and the limited exploration, the genesis and distribution of evaporite-related dolostone reservoirs from the middle Cambrian remain poorly understood. This study includes detailed field investigations along with petrological, mineralogical and geochemical analyses to characterise the secondary porosity of the middle Cambrian Shaelek Formation evaporite platform dolostone and to explore the origin of the diagenetic fluids responsible for these features. The results show that gypsum dissolution vugs are the main secondary porosity in the evaporite platform dolostone reservoirs, with their development and distribution strongly controlled by sedimentary facies. Meteoric dissolution during the penecontemporaneous period is responsible for this secondary porosity. The frequent fluctuation in sea-levels and the transient exposure of the dolostone reservoirs provide favourable conditions for the dissolution of unstable gypsum. The multiple stages of calcite filling in the vugs result from supersaturated precipitation from fluids during the late stage of meteoric diagenesis. Variations in δ13C, δ18O and rare earth element compositions between the two types of calcite reflect different stages of fluid evolution and varying degrees of water–rock reaction. The vug-filling fluorite is of non-hydrothermal genesis but results from the highly evaporative concentrated seawater and terrigenous input. The highly concentrated F– in evaporative seawater, combined with F– from fluvial input (if any) during subaerial exposure, most likely provides the F– necessary for fluorite precipitation. A model of reservoir formation and evolution has been established that will be beneficial for hydrocarbon exploration and prediction of the deeply buried Cambrian evaporite platform dolostone reservoir.

Water–Rock reactions in the acid leaching of Uranium: Hydrochemical characteristics and reaction mechanisms

Acid in–situ leaching (AISL) mining is used to recover uranium from sandstone using sulphuric acid. However, the evolution of groundwater hydrochemistry, the water–rock reaction mechanisms, and their relationship remain elusive. To effectively address these issues, ore samples were obtained from a sandstone uranium deposit in Inner Mongolia in this work. Soaking tests at different sulphuric acid concentrations were performed to quantify the mining aquifer’s water–rock reaction processes (sulphuric acid and minerals) according to the hydrogeochemical composition analysis and inverse modelling. From our results, it was demonstrated that the water–rock interactions between the sulphuric acid and gangue minerals primarily affect the leachate’s chemical composition. The introduction of sulphuric acid efficiently facilitates the gangue mineral dissolution and the groundwater total dissolved solids (TDS) increases and enhances the formation of uranyl sulphate (predominantly UO2SO4 and UO2(SO4)22– and UO22+, thus stimulating uranium mobility. Mineral precipitation (mirabilite) is primarily responsible for the elevated TDS in the leachate. The leachate’s oxygenation mainly depends on the sulphuric acid concentration and Fe3+ concentration produced by hematite dissolution. During the AISL process, the dissolution of dolomite, calcite, FeO, hematite, pyrite, K–feldspar, anorthite, chlorite, and alunite take place in the groundwater system. In parallel, the precipitation of kaolinite, illite, Ca–Montmorillonite and mirabilite, accompanied by Na–K exchange and Na–Mg exchange occur. The dissolution of dolomite, calcite and illite and Na–Mg exchange mostly affects the hydrochemical evolution, as well as the leachate of Fe mainly from dissolved chlorite. The predominant precipitates were kaolinite and mirabilite, with their precipitation ability increasing with acidity. These findings highlight the importance of clarifying the relationship between the hydrochemical characteristics and the water–rock reaction mechanisms in AISL geochemical processes to elucidate the hydrochemical evolution and mineral corrosion characteristics of ore–bearing aquifers. Finally, K–feldspar, alunite, chlorite, anorthite and dolomite were obtained as the major acid–consuming minerals. Our work provides a novel evaluation method for the prediction of acid consumption that can be used for actual production.

Comparison of mineral transformation in CO2 geological storage under CO2–water–sandstone and mudstone reactions

Carbon dioxide (CO2) mineral trapping was considered the most secure and stable mechanism for CO2 geological storage. The previous studies lacked clarity regarding the mechanisms and processes of transformation for various types of minerals involved in CO2–water–sandstone and mudstone reactions during CO2 geological storage. Additionally, it didn't clear the different stages of mineral reactions in reservoir and caprock. We utilized experimental and numerical simulation methods to analyze the mechanisms, processes, and stages of CO2–water–rock reactions involving various types of minerals in the mudstone from Chang 4 + 5 members and the sandstone from Chang 6 member of the Triassic Yanchang Formation in the Ordos Basin. The experimental simulation demonstrated the dissolution of feldspar minerals in sandstone led to precipitate of carbonate, clay, and other minerals. Contrary, mudstone primarily underwent the dissolution of clay minerals and the precipitation of feldspar minerals, whereas carbonate content remained relatively stable. The numerical simulation consisted of experimental results in the short term, but over a longer timescale, The reaction processes of carbonate and clay minerals in the reservoir and caprock dissolved first and then precipitated. Conversely, other minerals behaved oppositely; feldspar minerals continuously dissolved in the reservoir but precipitated first and then dissolved in the caprock. The reaction stages of mineral change in both the reservoir and caprock could be divided into dissolution, rapid precipitation, and stable precipitation. The reservoir's dissolution stage was shorter than the caprock, which entered the stable precipitation stage earlier. With increasing storage time, continuous CO2–water–rock reactions gradually transformed physically sequestered CO2 in the formation into chemically sequestered mineralized CO2.

Anisotropy of surface morphology of carbonate rocks after reaction with acid

In acid fracturing, acid is injected into artificial fracture to dissolve the rock, and the rock surface is shaped into the non-uniform morphology. This non-uniform morphology is the main cause of fracture conductivity after acid etching. The effects of acid type, flow rate, contact time and rock type on the non-uniform morphology of acid-etched rock surface have been studied. However, when the direction of acid flow is determined, the difference of dissolution characteristics in different directions of rock surface is not investigated. In this paper, acid rock reaction experiment and analysis of rock surface morphology after acid etching are carried out by using rock samples with flat surface. The difference of morphological characteristic parameters of rock surface in different directions under the condition of acid flow is discussed. It was found that the mean drop height, drop height range and roughness coefficient increase with the increase of acid rock reaction rate on flat rock surface. The morphological characteristic parameters of acid-etched rock face of limestone are greater than those of dolomite, which is conducive to forming acid-etched channels. According to the statistics of all experimental data, the larger average drop height of rock surface is distributed in the direction of parallel acid flow, the larger drop height range is distributed in the direction of vertical acid flow and other directions, and the larger roughness coefficient is distributed in other directions.

Geochemistry and clay mineralogy of shales in the Sulu Orogenic Belt, East China: suggestion for continental weathering during an Early Cretaceous hyperthermal interval

ABSTRACT Understanding past weathering–climate feedback mechanisms under greenhouse conditions has significance for guiding the development of climate mitigation strategies. The continental paleoweathering state of Early Cretaceous shales in the Sulu Orogenic Belt of East China during a hyperthermal interval related to oceanic anoxic event 1a (OAE1a) was investigated via geochemical and clay mineralogical analyses of shale samples. The resulting diagrams of ternary 15Al2O3–Zr–300TiO2 discrimination, Th/Sc and Zr/Sc show that the geochemical composition was mainly controlled by source composition. This is supported by observations of low Zr contents, high indexes of compositional variability (ICV; > 1), and micropetrological characteristics. All samples showed narrow SiO2/Al2O3 and (Fe2O3 + MgO)/Al2O3 ranges that were within the predicted weathering trends of the ternary A-CN-K diagram, indicating that the shale geochemistry was not influenced by silicification and K-metasomatism. The chondrite-normalized rare-earth-element pattern suggests that all samples had the same felsic igneous parent rock. The geochemistry of whole rocks and their silicate fractions indicates that the shale had low chemical indexes of alteration (CIA) but high ICV values compared to post-Archean Australian Shale, indicating low sediment maturity and extremely weak chemical weathering in the source terrane and/or sedimentary basin under hot-dry conditions. Moreover, the clay minerals in the shale were mainly illite, suggesting low mineral weathering. Thus, during the OAE1a-related hyperthermal interval, chemical weathering was relatively weak in some mid-latitude arid inland areas. This may be mainly due to aridification decreasing water–rock reactions. Chemostratigraphic analysis suggests that the CIA, Ga/Rb, and Rb/Sr values of shales from the upper strata of the Yangjiazhuang and Shuinan formations were greater than those from lower strata. Moreover, the opposite trend in K2O/Al2O3 ratios was found. These indices suggest gradual increases in chemical weathering as the climate changed from hot-dry to warm-humid. In contrast, proxy indices of shale from the Zhifengzhuang Formation showed the opposite trend, suggesting a gradual decrease in chemical weathering as the climate changed from warm-humid to hot-dry. Considering the composition of the clay minerals, it is speculated that continental weathering was dependent on atmospheric humidity rather than temperature under the extreme greenhouse conditions, resulting in ineffective climate regulation by chemical weathering. This comprehensive study advances our understanding of the weathering–climate feedback mechanism under greenhouse regimes.