Search Results (16)

This study investigates the acid–rock reaction kinetics and their implications for enhancing tight limestone reservoir stimulation through systematic experiments. Using 14 tight limestone cores, we evaluate the dynamic behavior of single-phase and gelled acids (12%, 15%, and 20% HCl) under controlled reservoir conditions (80 °C; 10–180 min). Three key findings emerge: (1) gelled acids initially exhibit higher reaction rates (0.897%/min) compared to single-phase acids (0.453%/min at 10 min), but their efficiency converges over extended durations; (2) reaction rates for both acid types follow the quadratic decay pattern over time (R² > 0.95), contrasting with conventional linear assumptions; and (3) reaction time is identified as the primary factor governing permeability enhancement (up to 29,200% improvement), outweighing acid concentration and type. The results demonstrate that concentrations above 15% significantly enhance etching efficiency, while single-phase acids with moderate reaction rates achieve an optimal balance between penetration depth and surface integrity. By integrating gravimetric analysis with permeability–porosity mapping, this work provides a predictive framework for acidizing process design in low-permeability reservoirs. The findings offer practical insights for optimizing acid fracturing operations, emphasizing time-controlled strategies over traditional concentration-focused approaches. Full article

Acid mine drainage (AMD), wherein acidic water is generated from pyrite-containing waste rock, can be mitigated by encapsulating pyritic waste rock with cover materials to restrict the inflow of oxygen and water. However, acidic water inevitably forms during the construction of waste rock dumps before applying cover materials. Considering that the presence of waste rock containing carbonate minerals contributes to acid neutralization, a mixture of carbonate minerals and pyritic waste rock can be utilized to reduce AMD generation before the completion of the cover system as a temporary management strategy. This paper examines waste rock management using blending scenarios. Kinetic NAG and column leaching tests were employed to evaluate the blending ratio necessary to prevent acidic water generation. Geochemical analyses were conducted on rock and leachate samples, including pH and temperature measurements, XRD and XRF analyses, and Ion Chromatography. Consequently, the pH and temperature measurement results obtained during the kinetic NAG test are valuable for expressing the balance between acid generation and acid neutralization by the mixture material. Furthermore, the column leaching test demonstrated that the pH of the leachate remained neutral when the acid generation and acid neutralization reactions were well balanced. Blending waste rocks is an effective method for AMD reduction during the construction of waste rock dumps. Full article

In this work, a kinetic study and modeling of the decomposition of a rock sample in an ascorbic acid medium with a high content of lepidolite phase were carried out, the results of which are of great importance due to the sample’s high lithium (Li) content. The rock sample was characterized by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS), and the mineral species detected in the sample were lepidolite, at 65.3%, quartz, at 30.6%, and muscovite, at 4.1%, with a quantitative chemical analysis indicating the presence of elements such as Li, Si, K, Na, O, Al and, to a lesser extent, Fe and Ti; this highlights that the Li content present in the sample was 3.38%. Lithium was the element with which the chemical analysis of the kinetics was performed, resulting in decomposition curves comprising the induction period, progressive conversion and stabilization; this highlighted that the reaction progressed during the first two periods, obtaining a reaction order (n) of 0.4307 for the induction period and an activation energy (Ea) of 48.58 kJ mol⁻¹, followed by a progressive conversion period with n = 0.309 and Ea = 25.161 kJ mol⁻¹. This suggested a mixed control regime present in the lower temperature ranges, with a transition from chemical control to transport control present at high temperatures, with the study of the nature of the reaction and the concentration effect showing that chemical control predominates. The kinetic parameters and kinetic expressions for both periods were obtained, with the modeling showing that the calculated and experimental data do not present a major discrepancy. Full article

Metal sulfides in waste rocks and tailings are susceptible to serious soil and water contamination due to the generation of acid mine drainage (AMD) during stockpiling. The hydrometallurgical process is one of the most essential heavy metal remediation technologies through harmless disposal and resource utilization of the waste sulfides. However, atmospheric hydrometallurgy of sulfides still faces great challenges due to low leaching efficiency and high cost. In this work, we proposed a cooperative leaching system (Fe₂(SO₄)₃-O₃) and investigated the oxidative dissolution process of sphalerite (ZnS). Under the optimal conditions, the extracted zinc reached 97.8%. Reactive oxygen species (ROS) (·OH, ¹O₂ and ·O₂⁻) were identified in the radical quenching experiments. The dissolution of sphalerite did not show passivation due to the ozone’s capability to oxidize the sulfur in sphalerite to sulfate. In addition, stirring rate, O₃ inlet concentration, and Fe₂(SO₄)₃ concentration had a significant effect on the dissolution of sphalerite. Meanwhile, the apparent activation energy was 24.11 kJ/mol based on kinetic fitting, which indicated that the controlling step of the reaction was mainly a diffusion process. This work demonstrated the cooperative effect of sphalerite leaching in the O₃-Fe₂(SO₄)₃ system and provided a theoretical reference for efficient and atmospheric dissolution of sphalerite. Full article

The kinetics of the dissolution of Estonian phosphate rock and the governing reaction mechanisms in hydrochloric acid in technological processes were investigated. The influences of particle size and acid concentrations of 0.5–1.5 M on the reaction rate and the pH variation during the process were studied at a dosage of 2.1 moles of HCl per mole of calcium for 60 min. The results indicated that the solubility of phosphorus reached 94%–100% for the fine samples and 82%–99% for the coarse samples. The time required to achieve an apparent steady-state pH reduced with the increasing acid concentrations and decreasing particle sizes. It was determined that the CaF₂ precipitation in solutions starting at 1 M was faster at higher concentrations. The SEM surface analysis of the insoluble particles proved the existence of etch pit formation. The XPS and EDX analyses affirmed that the dissolution was incongruent. The surface composition of the unreacted particles gave a stoichiometry of CaF_1.8, showing the formation of CaF₂ on the surface. The dissolution kinetics were analyzed using the shrinking core model and showed a combination of chemical reaction, diffusion or interfacial transfer, and diffusion, sequentially for coarse particles or simultaneously for fine fractions. Full article

The conventional liquid acid has several shortcomings in the acidizing process of fractured-vuggy carbonate reservoirs, including high filtration loss, fast reaction rate, high friction resistance, and difficult flowback. To address these issues, a new atomizing acid acidizing technology is proposed, combining the gas injection development practice from the fractured-vuggy carbonate reservoir in the Tahe oilfield. The laboratory experiments were conducted to optimize the type and concentration of atomized acid, iron ion stabilizer, corrosion inhibitor, and atomization stabilizer. The acid atomization rate was evaluated under different combinations of gas and liquid injection flows using a self-made atomized acid well migration simulator, and the best atomization scheme was selected. Furthermore, a kinetic experiment for the acid–rock reaction was carried out to evaluate the retarding performance of the atomized acid. The optimized formula for the atomizing acid system consists of 15~25% hydrochloric acid, 0.005% atomizing stabilizer (AEO-7), 1% iron ion stabilizer (EET), 1.5% corrosion inhibitor (EEH-160), and water. The optimal gas and acid injection scheme is gas injection at 2m3/min and acid injection at 10 mL/min, which maintains an atomization rate of over 80% after the acid mist migrates through the wellbore. Compared with gelling acid, the acid–rock reaction rate of atomized acid is 8.5, 9.1, and 10.6 times slower under acid concentrations of 15%, 20%, and 25% respectively. The retarding effect of atomized acid is superior, facilitating etching and initiating underdeveloped gas drive channels and thereby increasing the probability of gas communication with new reservoirs. The research findings presented in this paper establish a theoretical foundation for the practical implementation of the atomized acid acidizing process in the field. Full article

Matrix acidification is one of the most effective stimulations to dissolve scales and remove damage in carbonate reservoirs. However, existing acid systems are difficult to dissolve organic and inorganic scales simultaneously, and complex multi-stage alternative injection often introduces new precipitation and damages the reservoir. Here, based on the retardation ability of emulsified acid and the stable structure of microemulsion, an oil-phase solvent was preferably selected, and the surfactant and cosurfactant were optimized to prepare an acid-in-oil type microemulsion acid capable of dissolving both organic and inorganic scales and high solubilizing for hydrochloric acid. Based on the rotating disc experiment, scale dissolution experiment and acid driving experiment, the acid-rock reaction kinetics, scale dissolution ability and acidizing and plugging removal performance of microemulsion acid in a carbonate reservoir were systematically studied and compared. The results show that Solvesso 150 (aromatic solvent) has the advantages of low toxicity, high flash point and high-scale dissolving ability. At NP−4: OP−10: A (cosurfactant) = 3:3:4, the microemulsion acid system has the strongest ability to solubilize hydrochloric acid and can solve the problem of low H⁺ concentration. The particle size of microemulsion acid is smaller compared to emulsified acid. At 60 °C, the mass transfer coefficient of microemulsion acid is 3.2 × 10⁻⁸ cm²/s, which is one order of magnitude less than that of emulsified acid. Microemulsion acid shows good solubility performance in dissolving organic and inorganic scales, and the comprehensive solubility of mixed scales can reach 98.28%. The stronger scale solubilization ability and lower acid-rock reaction rate enable microemulsion acid to form a thin and straight main wormhole, thus enhancing the acidizing and plugging removal effect. This study can solve the problem of poor hydrochloric acid solubilization ability of microemulsion acid to a certain extent, which provides theoretical and data support for the research and development of microemulsion acid and the efficient plugging removal technology for carbonate reservoirs. Full article

The Shunbei oil formation is a deep, high-temperature carbonate reservoir. Acid fracturing is an effective technology to stimulate this formation. For acid fracturing, the temperature field is fundamental information for the acid system selection, acid–rock reaction, live acid penetration distance prediction, acid fracturing design, etc. Therefore, in this paper, we conduct a numerical study on the temperature field in acid fracturing to account for the acid–rock reaction in the Shunbei formation. Firstly, a new mathematical model of the fracture temperature field during acid fracturing is established based on the laws of mass and energy conservation and acid–rock reaction kinetics. The fracture model is based on a PKN model, which accounts for a few factors, such as the acid–rock reaction heat, acid–rock reaction rate dependence on the temperature, and the fracture width change with acid erosion. Then, the numerical mode is developed. Next, an extensive numerical study and a parameter analysis are conducted based on the model with the field data from the Shunbei formation. The study shows that the acid–rock reaction in acid fracturing has obvious effects on the temperature field, resulting in a 10~20 °C increase in the Shunbei formation. The acid–rock reaction dependence on temperature is a factor to be accounted for. The rock dissolution increases first and then decreases from the inlet to the tip of the fracture, unlike the monotonous decrease without temperature dependence. The temperature gradient is high near the inlet and then decreases gradually. Beyond half of the fracture, the temperature is close to the formation temperature. The temperature drops fast in the initial injection stage and tends to stabilize at about 50 min. Full article

There are abundant geothermal resources in the Xiong’an New Area, China. Drilling has revealed a greater potential in the deep Gaoyuzhuang geothermal reservoir. However, the reservoir required acidification to increase its water production. In this study, three types of core samples with different mineral compositions from different depths in the target boreholes were selected for acid rock reaction experiments at the temperature of 40 °C, 60 °C, 80 °C and 100 °C, and pressure of 30 MPa. The kinetics of the acid rock reaction of the major minerals were modeled based on the transitional state theory. The kinetic parameters were obtained by comparing the modelling and experimental results. The results show that the lithology of the Gaoyuzhuang reservoir is primarily dolomite. The dissolution ratio for 15 wt.% HCl reached 84.1% on average for the rock fragments. Temperature has a significant effect on the dissolution rate of the minerals. In the presence of HCl (acidic mechanism), the reaction rate constants of the dolomite, calcite and illite reached 2.4 × 10⁻⁴ mol/m²/s, 5.3 × 10⁻¹ mol/m²/s and 9.5 × 10⁻² mol/m²/s, respectively. The results of this study provide the basic parameters for the design and evaluation of field acidizing. Full article

A new multibranch Integrated Catchment (INCA) model INCA-Metals has been developed to simulate the impact of tannery discharges on river systems. The model accounts for the key chemical reaction kinetic processes operating as well as sedimentation, resuspension, dilution, mixing and redistribution of pollutants in rivers downstream of tannery discharge points and for mine discharges or acid rock drainage sites. The model is dynamic and simulates the daily behaviour of hydrology and eight metals, including cadmium, mercury, copper, zinc, lead, arsenic, manganese and chromium, as well as cyanide and ammonia. The model is semi-distributed and can simulate catchments, tributaries and instream river behaviour. The model can also account for diffuse pollution from rural runoff as well as point sources from effluent and trade discharges. The model has been applied to the new Savar tannery complex on the Dhaleshwari River system in Bangladesh to assess the impacts on pollution levels in the river system and to evaluate a set of treatment scenarios for pollution control, particularly in the dry season. It is shown that the new effluent treatment plant at Savar needs to significantly improve its operation and treatment capability in order to alleviate metal pollution in the downstream Dhaleshwari River System and also protect the Meghna River System that falls in the Bay of Bengal. Full article

We studied the effects of supercritical carbon dioxide (scCO₂) on the matrix permeability of reservoir rocks from the Eagle Ford, Utica, and Wolfcamp formations. We measured permeability using argon before exposure of the samples to scCO₂ over time periods ranging from days to weeks. We measured permeability (and the change of permeability with confining pressure) when both argon and scCO₂ were the pore fluids. In all three formations, we generally observe a negative correlation between initial permeability and carbonate content—the higher the carbonate content, the lower the initial permeability. In clay- and organic-rich samples, swelling of the matrix resulting from adsorption decreased the permeability by about 50% when the pore fluid was scCO₂ although this permeability change is largely reversible. In carbonate-rich samples, dissolution of carbonate minerals by carbonic acid irreversibly increased matrix permeability, in some cases by more than one order of magnitude. This dissolution also increases the pressure dependence of permeability apparently due to enhanced mechanical compaction. Despite these trends, we observed no general correlation between mineralogy and the magnitude of the change in permeability with argon before and after exposure to scCO₂. Flow of scCO₂ through μm-scale cracks appears to play an important role in determining matrix permeability and the pressure dependence of permeability. Extended permeability measurements show that while adsorption is nearly instantaneous and reversible, dissolution is time-dependent, probably owing to reaction kinetics. Our results indicate that the composition and microstructure of matrix flow pathways control both the initial permeability and how permeability changes after interaction with scCO₂. Electron microscopy images with Back-Scattered Electron (BSE) and Energy Dispersive Spectroscopy (EDS) revealed dissolution and etching of calcite minerals and precipitation of calcium sulfide resulting from exposure to scCO₂. Full article

Phosphate rock has been considered as one of the most significant secondary rare-earth resource, and the utilization of rare earth elements (REEs) in phosphate rock has attracted increasing attention. In this study, the leaching kinetics of REEs from a phosphate ore from China was studied with the variation of temperature and phosphoric acid concentration under the conditions: ratio of liquid to solid of 12 mL/g, stirring speed of 120 r/min, and phosphate particle size of −0.074 mm amounts 61.1%. The results suggest that there were two distinct stages in leaching process and kinetics of both stages followed shrinking core model. At fast reaction stage, the semi-empirical equation describing the kinetics was 1 − 3(1 − α)^2/3 + 2(1 − α) = 1.885C_H3PO4^0.89exp(−11220/8.31T)t. The semi-empirical equation for slow reaction stage was 1 − 3(1 − α)^2/3 + 2(1 − α) = 0.299C_H3PO4^2.50exp(−18720/8.31T)t. Using shrinking core model and time-to-a-given-fraction method, we found that leaching rate of fast reaction stage was controlled by solid product layer diffusion, and both solid product layer diffusion and chemical reaction determined slow reaction stage. Full article

Well stimulation using hydrochloric acid (HCl) is a common practice in carbonate reservoirs to overcome formation damage in the near wellbore area. Using HCl for matrix acidizing has many limitations at high-temperature (HT) conditions, such as tubulars corrosion and face dissolution due to the fast reaction rate. Chelating agents, such as L-glutamic acid-N,N-diacetic acid (GLDA), are alternatives to HCl to overcome these problems. We studied the effect of diluting GLDA in seawater on the reaction kinetics with carbonate rocks under HT conditions at low pH (3.8). Results of the reaction of carbonate at 1000 psi and 150, 200, and 250 °F with GLDA prepared in both fresh and seawater, GLDA/DI and GLDA/SW, respectively, are presented. The reaction kinetics experiments were carried out in HT rotating disk apparatus (RDA) at rotational speeds ranging from 500 to 2000 revolutions per minute (RPM) at a fixed temperature. Indiana limestone and Austin chalk were used to studying the effect of rock facies on the reaction of GLDA with rock samples. In both GLDA/DI and GLDA/SW, the reaction regime of 20 wt% GLDA (3.8 pH) with Indiana limestone was mass transfer limited. The reaction rate and diffusion coefficient were highly dependent on the temperature. For Austin chalk, at 200 °F and 1000 psi the diffusion coefficient of GLDA/SW is an order of magnitude of its value with Indiana limestone using the same fluid. Diffusion coefficients were used to estimate the optimum injection rate for stimulating HT carbonate formation and compared with coreflooding results. The data presented in this paper will support the numerical simulation of the acid flow in carbonate reservoirs. Full article

The oxidation of pyrite is one of the near field processes of the chemical evolution of clay rock planned to host a deep geological radioactive waste repository during operation. Indeed, this process can lead to transitory acidic conditions in the medium (i.e., production of sulphuric acid, carbonic acid) which may influence the corrosion kinetics of the carbon steel components of some disposal cells. In order to improve the geochemical modelling of the long-term disposal, the oxidation of pyrite in contact with clays and carbonates at 100 °C must be evaluated. In this study, special attention was paid to the pyrite oxidation rate thanks to an original experimental set-up, involving several pyrite/mineral mixtures and a reactor coupled to a micro gas chromatograph (P_O2 and P_CO2 monitoring). Although thermodynamic modelling expects that hematite is the most stable phase in a pure pyrite heated system (low pH), experiments show the formation of native sulfur as an intermediate product of the reaction. In the presence of calcite, the pH is neutralized and drives the lower reactivity of pyrite in the absence of native sulfur. The addition of clay phases or other detrital silicates from the claystone had no impact on pyrite oxidation rate. The discrepancies between experiments and thermodynamic modelling are explained by kinetic effects. Two laws were deduced at 100 °C. The first concerns a pure pyrite system, with the following law: $r_{Py}={10}^{-4.8}·P_{O_2}^{0.5}·t^{-0.5}$ . The second concerns a pyrite/carbonates system: $r_{Py+Ca}={10}^{-5.1}·P_{O_2}^{0.5}·t^{-0.5}$ where P_O2 corresponds to the partial pressure of O₂ (in bar) and t is time in seconds. Different mechanisms are proposed to explain the evolution with time of the O₂ consumption during pyrite oxidation: (i) decrease of the specific or reactive surface area after oxidation of fine grains of pyrite, (ii) decrease of O₂ pressure, (iii) growing up of secondary minerals (Fe-oxides or anhydrite in the presence of calcium in the system) on the surface of pyrite limiting the access of O₂ to the fresh surface of pyrite, and (iv) change in the pH of the solution. Full article

The acidification of agricultural soils in high rainfall regions is usually countered by the application of finely ground calcite or dolomite. As this carbonate dissolves, soil pH is raised, but CO₂ is released. Mining activities often produce large quantities of very fine silicate rock-derived powders that are commonly deposited in stockpiles. However, the dissolution of such powders can also result in an increase in pH, without any direct release of CO₂. Of particular interest are those silicate powders that have a high reactivity and higher capacity for raising pH. In this contribution, we report experimental work addressing the dissolution of various silicate rock-derived powders that were produced during mining activities in Norway under conditions that were representative of weathering in agricultural soils. Three different powders—derived from Åheim dunite, Stjernøya nepheline syenite, or Tellnes ilmenite norite—were exposed to different acids at pH 4 in unstirred flow cells, and dissolution or leaching kinetics were determined from the changes in the fluid composition. Based on these kinetics, pH neutralization rates were determined for the individual powders and compared to expected values for carbonates. Based on this comparison, it is concluded that the application of silicate rock-derived powder dissolution to replace carbonate-based liming may not be feasible due to slower reaction rates, unless larger quantities of a finer particle size than normal are used. The application of larger volumes of slower-reacting silicates may have the additional benefit of reducing the required frequency of liming. Full article