Solubility Of Calcite Research Articles

Calcium-rich seawater affects the mechanical properties of echinoderm skeleton

Shifts in the magnesium to calcium ratio of seawater in the geological history are thought to have profoundly affected biomineralization of marine invertebrates, including some echinoderms, which changed their skeletal mineralogy from high-magnesium to low-magnesium calcite and vice versa. Here we report on experiments that aimed to investigate the effect of ambient seawater magnesium to calcium ratio on magnesium to calcium ratio and nanomechanical properties in the spines of two echinoid species (Arbacia lixula and Paracentrotus lividus). We found that echinoids cultured in seawater with a low magnesium to calcium ratio produced a skeleton with lower both magnesium content and nanohardness than those of the control specimens incubated under normal (high) magnesium to calcium ratio conditions. These results may suggest that at certain times in the geological past (during the so-called calcite seas) sea urchins with decreased skeletal magnesium contents were more susceptible to damage due to physical disturbances, predation and post-mortem taphonomic processes. Increased skeletal hardness of echinoids from the so-called aragonite seas is expected to enhance their taphonomic potential, thus, to some extent, mitigates the preservation bias related to increased solubility of high-magnesium calcite.

Effects of fluid salinity and composition on subcritical crack growth in marble

Subcritical fracture growth of rocks in fluid-chemical environments played a crucial role in the weathering process of rocks and the preservation of stone building heritage. Fracture mechanics properties of marble under different fluid compositions and salinity conditions were investigated by carrying out double torsion tests. The subcritical crack growth index (SCI) exhibited different salinity dependencies in two salt solutions. In NaCl solution, the SCI decreased by 1.97 % – 40.50 % with increasing salinity due to the increase in solubility of calcite. The SCI decreased by 4.60 % and 14.01 % respectively as the Na2SO4 salinity increases from 0.01 mol/L to 1 mol/L, and then increased with the increase in salinity, which was related to the relationship between calcite solubility and salinity. Compared to Na2SO4 solution, the weakening effect of NaCl solution on Ka was smaller. In contrast, the fracture toughness (KIC) was insensitive to fluid composition and salinity in the short term, with KIC ranging from 0.65 to 0.79 MPa m1/2 in all salt solutions. The three-dimensional morphology results of the fracture surfaces indicated that the effect of salinity on the roughness of both fracture types was negligible. However, the microstructure of the marble was significantly affected by salinity, and apparent dissolution was observed. The results highlighted the dependence of the subcritical fracture behavior of marble on fluid chemistry, which had implications for the weathering assessment of stone masonry buildings and the permanent protection of stone heritage monuments. In these applications, fluid chemistry could either strengthen or weaken the rock, depending on variations in fluid composition and salinity.

Effect of white mud on carbonation resistance of alkali activated slag

White mud (WM) is a solid waste produced in the process of papermaking and it remains to be effectively utilized. It contains a large amount of CaCO3 and residual alkali metal ions. This paper aims to explore the effect of WM on carbonation resistance of alkali activated slag. The changes in mechanical properties and microstructure of alkali activated white mud/slag (AAWS) after natural carbonation and accelerated carbonation were analyzed. The results indicate that the mechanisms of natural carbonation and accelerated carbonation are different. The carbonation depth achieved in 90 days of natural carbonation can be reached in just 14 days of accelerated carbonation. Samples with 15 wt% WM blended possesses the smallest carbonation depth and the highest compressive strength. WM can effectively mitigate the natural carbonation of AAWS by dissolving Mg2+ and Ca2+. Mg2+ can migrate to increase the solubility of calcite, promote the generation of hydrotalcite to absorb carbon dioxide, and reduce the carbonation degree. Ca2+ will migrate after the carbonation and decalcification of the gel product and reduce the decalcification sensitivity. This study offers a sustainable approach for improving the carbonation resistance of AAWS.

Skeletal Mg content in common echinoderm species from Deception and Livingston Islands (South Shetland Islands, Antarctica) in the context of global change

Echinoderms with high levels of magnesium (Mg) in their skeletons may be especially sensitive to ocean acidification, as the solubility of calcite increases with its Mg content. However, other structural characteristics and environmental/biological factors may affect skeletal solubility. To better understand which factors can influence skeletal mineralogy, we analyzed the Mg content of Antarctic echinoderms from Deception Island, an active volcano with reduced pH and relatively warm water temperatures, and Livingston Island. We found significant interclass and inter- and intraspecific differences in the Mg content, with asteroids exhibiting the highest levels, followed by ophiuroids and echinoids. Specimens exposed to hydrothermal fluids showed lower Mg levels, which may indicate local environmental effects. These patterns suggest that environmental factors such as seawater Mg2+/Ca2+ ratio and temperature may influence the Mg content of some echinoderms and affect their susceptibility to future environmental changes.

Long-term groundwater geochemical evolution induced by coal mining activities-a case study of floor confined limestone aquifer in Yaoqiao Coal Mine, Jiangsu, China.

Groundwater chemical composition can be changed due to long-term coal mining activities, but it was unclear how it was induced in Taiyuan Formation limestone (TFL) regarding the lack of relevant quantitative studies. The aim of this research is to improve understanding of the chemical composition changes in groundwater of L4 limestone in the coal mining area based on the available hydrochemical and hydrodynamical reports and studies during the period 1978-2020. The systematical analysis of the groundwater composition and field allows to make the hydrogeological characterization with the relatively independent blocks by the factor groups "Planar division & Vertical zonation" and "High water pressure, Poor recharge & Little water inflow," which determines different hydrochemical types and high TDS concentration. The long-term groundwater drainage has caused the eastern and southern limestone aquifer to demonstrate a wide range of depression cones and depletion of groundwater resources, the majority areas were dewatered, and the karstification process changed significantly. An analysis of chemical compositions changes due to extensive permanent drainage of L4 limestone water revealed the decrease in the TDS concentration. The solubility of calcite, dolomite, and gypsum changed, which resulted in the decreasing tendency of Ca2+ + Mg2+ ions. Evaporation and concentration were found to be the main factors determining the L4 limestone water composition, whereas ion exchange was the primary factor for rock-water interaction. These findings are helpful for mine enterprises to take necessary measures for preventing and controlling the groundwater quality degradation from the extensive coalmine drainage.

Dissolution and solubility of Pb-substituted calcite, Ca-substituted cerussite and their mixtures at 25 °C

A series of Pb-substituted calcite, Ca-substituted cerussite and their mixtures with the bulk solid Pb/(Ca + Pb) atom fractions (XPbCO3) of 0.00–1.00 were synthesized and their dissolution in water for one year was experimentally studied at 25 °C. During dissolution of the solids (XPbCO3 = 0.01–0.90) in the N2-degassed water and the air-saturated water, the aqueous Pb concentrations increased rapidly to 0.136–2.095 μmol/L in 1 h and 0.140–3.431 μmol/L in 1–6 h, which were followed by a slight decrease-increase fluctuation to a steady state of 0.235–0.961 μmol/L and 0.177–0.483 μmol/L after 300–360 d, respectively. During dissolution in the CO2-saturated water, the aqueous Pb concentrations increased quickly up to the peak value of 1.351–89.107 μmol/L in <12 h, and subsequently declined slowly to a steady state of 0.194–0.515 μmol/L after 300–360 d. The aqueous Pb/(Ca + Pb) molar ratios (XPb2+,aq) declined with time and were considerably lower than the solid XPbCO3. During dissolution in the N2-degassed water, the air-saturated water and the CO2-saturated water, the mean values of log IAP at the steady state (≈log Ksp) were calculated to be −8.55 ± 0.16 ∼ −8.54 ± 0.11, −8.35 ± 0.21 ∼ −8.35 ± 0.17 and − 8.34 ± 0.07 ∼ −8.31 ± 0.13 for calcite [CaCO3]; −13.07 ± 0.53 ∼ −12.97 ± 0.52, −13.23 ± 0.34 ∼ −13.11 ± 0.20 and − 13.56 ± 0.36 ∼ −13.29 ± 0.26 for cerussite [PbCO3], respectively. In terms of the bulk composition, the calcite-type crystals and the cerussite-type crystals, the log IAP values of the solids at the steady state declined almost linearly with the increasing XPbCO3. The highest XPbCO3 value in the calcite-type crystals and the lowest XPbCO3 value in the cerussite-type crystals were measured to be 0.226 and 0.648, respectively. Thereout, the Guggenheim parameters were estimated to be a0 = 0.405 and a1 = −1.49 for the calcite side, and a0 = 1.77 and a1 = −0.474 for the cerussite side of the calcite-cerussite solid solutions. In the Lippmann diagrams constructed for the Calcite–PbCO3 (R3¯c) system, the Aragonite–Cerussite (Pmcn) system and the Calcite–Cerussite system with the estimated Guggenheim coefficients, the solids dissolved non-stoichiometrically and moved gradually up to the quasi-equilibrium curve for the solids with lower XPbCO3, and then along this curve from right to left, approached and crossed the solutus curve and the saturation curve for calcite, and sequentially moved up along the quasi-equilibrium curve for the solids with higher XPbCO3. Finally, the considerably Pb-poor water was simultaneously in equilibrium with both the Pb-richer cerussite-type crystals and the Pb-poorer calcite-type crystals. The result can provide a deeper insight into the environmental and geochemical cycle of lead.

Investigation of Potential Drivers of Elevated Uranium Prevalence in Indian Groundwaters with a Unified Speciation Model.

Elevated uranium (U) (>WHO limit of 30 μg L-1) in Indian groundwaters is primarily considered geogenic, but the specific mineralogical sources and mechanisms for U mobilization are poorly understood. In this contribution, statistical and geochemical analyses of well-constrained metadata of Indian groundwater quality (n = 342 of 8543) were performed to identify key parameters and processes that influence U concentrations. For geochemical predictions, a unified speciation model was developed from a carefully compiled and updated thermodynamic database of inorganic, organic (Stockholm Humic model), and surface complexation reactions and associated constants. Critical U contamination was found at shallow depths (<100 m) within the Indo-Gangetic plain, as determined by bivariate nonparametric Kendall's Taub and probability-based association tests. Analysis of aquifer redox states, multivariate hierarchical clusters, and principal components indicated that U contamination was predominant not just in oxic but mixed (oxic-anoxic) aquifers under high Fe, Mn, and SO4 concentrations, presumably due to U release from dissolution of Fe/Mn oxides or Fe sulfides and silicate weathering. Most groundwaters were undersaturated with respect to relevant U-bearing solids despite being supersaturated with respect to atmospheric CO2 (average pCO2 of reported dissolved inorganic carbonate (DIC) data = 10-1.57 atm). Yet, dissolved U did not appear to be mass limited, as predicted solubilities from reported sediment concentrations of U were ∼3 orders of magnitude higher. Integration of surface complexation models of U on typical aquifer adsorbents, ferrihydrite, goethite, and manganese dioxide, was necessary to explain dissolved U concentrations. Uranium contamination probabilities with increasing dissolved Ca and Mn exhibited minima at equilibrium solubilities of calcite [∼50 mg L-1] and rhodochrosite [∼0.14 mg L-1], respectively, at an average groundwater pH of ∼7.5. A potential indirect control of such U-free carbonate solids on U mobilization was suggested. For locations (n = 37) where dissolved organic carbon was also reported, organic complexes of U contributed negligibly to dominant U speciation at the groundwater pH. Overall, the unified model suggested competitive dissolution-precipitation and adsorption-desorption controls on U speciation. The model provides a quantitative framework that can be extended to understand dominant mobilization mechanisms of geogenic U in aquifers worldwide after suitable modifications to the relevant aquifer parameters.

Dense and strong calcite ceramics prepared by room‐temperature cold sintering based on high‐pressure‐enhanced solubility

AbstractDense and strong calcite (CaCO3) ceramics were prepared by room‐temperature cold sintering with the aid of water and high pressure of up to 900 MPa. Under atmospheric pressure, calcite is barely soluble in water. However, the microstructure evolution and stress‐strain analysis during cold sintering revealed that the dissolution‐precipitation, plastic deformation, and pressure‐solution‐creep mechanisms played a crucial role in the densification and mechanical robustness of calcite ceramics, which was attributed to the significantly enhanced solubility of calcite in water under high pressure. The calcite ceramic cold sintered under 900 MPa from micron powder exhibited the highest relative density of 92.1% and best mechanical properties with compressive strength, flexural strength, hardness, and Young's modulus of 276.5 MPa, 52.5 MPa, 1.64 GPa, and 53.7 GPa, respectively. The as‐prepared calcite ceramic was stronger and harder than most stones and cement, indicating its promising application as novel building and biomimetic materials. The present study also provides a new strategy for densifying ceramics with low solubility by cold sintering.

Tectonostratigraphic and paleoenvironmental settings of host-replacing phreatic calcrete hardpans developed at basin margins in the Upper Devonian Kinnesswood Formation of southwest Scotland

Abstract In the Firth of Clyde area of southwest Scotland, the Famennian Kinnesswood Formation includes an interval of massive, host-replacing phreatic calcrete hardpan (HRPCH), the likes of which have been documented only at few locations and few intervals in geological history. The HRPCH is found only at basin-margin shoulders, where the Kinnesswood Formation succession is thin and incomplete. The isles of Bute and Great Cumbrae provide well exposed sections in which adjacent shoulder and trough successions can be correlated and compared to clarify the tectonostratigraphic and paleoenvironmental settings of the HRPCHs. In the Cumbraes Trough, above a thin interval of peritidal limestone, the middle part of the Kinnesswood Formation (lower part of the Foul Port Member) is pervasively disturbed by large syndepositional dewatering structures interpreted to be products of the intermittent deposition and dissolution of evaporites. These structures occur at approximately the same stratigraphic interval as the HRPCHs on the isles of Bute and possibly Arran. The HRPCH in Bute is interpreted to have developed on a syndepositional shoulder adjacent to a growth fault (the Kerrycroy Fault) delimiting a trough that accommodated intermittent seawater incursions in a restricted, evaporitic setting. This is consistent with the current model for HRPCH formation, which involves the mixing of fresh groundwater issued from source areas with the high pH groundwater that surrounds evaporitic basins. A significant increase in silica solubility paired with a decrease in calcite solubility occurs in the mixing zone, thus promoting the thorough replacement of silicates with calcrete.

Minimizing calcium lactate precipitation via the addition of gluconate ions for matrix acidizing with lactic acid

Organic acids are commonly used to replace hydrochloric acid (HCl) in high reservoir temperature applications, as they are less corrosive and weaker than HCl. However, organic acids have shown some problems due to acid reaction product solubility. One such organic acid, lactic acid, produces calcium lactate when it reacts with calcite, which has a low solubility in water. However, reaction product solubility can be improved by up to five times when gluconate ions coexist with lactate and calcium ions. The objective of this research is to evaluate lactic and gluconic acid mixtures in term of dissolving calcite, reaction product, corrosion, wettability and generating dominant wormhole.Lactic and gluconic acids were mixed together using deionized water and seawater to conduct calcite solubility tests. Corrosion tests, between 4 and 12 h, were also run under reservoir conditions. A formation response test (FRT) apparatus was used to run different coreflood tests using different combinations of injection rates, total acid concentration, and temperatures. These tests were accompanied with analytical analysis utilizing ICP and IC to measure calcium, iron and sulfate ions in solution.The results showed that mixing lactic and gluconic acids at a 1:1 M ratio provided the optimal results as no precipitation occurred at total acid strengths of 10 wt% and up to 27 wt%. Seawater usage caused calcium sulfate precipitation; therefore, three scale inhibitors were evaluated to determine mitigation rates. Acid-calcite dissolving results were satisfactory when limestone was exposed to a 1:1 and 2:1 M ratio of crushed core-to-acid ratios as at least 50% of the crushed core was dissolved. However, the two-acid mixture showed a corrosion rate that was higher than the acceptable rates and a trace of iron lactate precipitation occurred at 200 and 300 °F. Five gpt from a sulfur-based corrosion inhibitor was enough to mitigate the corrosion rate to allow for 8 h of testing. Coreflood tests showed that the mixture penetrated limestone core with minimal acid pore volume without any face dissolution or salt precipitation on the core faces.This research presents a set of diverse experimental data to confirm that lactic acid accompanied by gluconic acid can penetrate carbonate formation without any by-product precipitation. The two organic acids are less corrosive and less hazardous which can provide a safe operation environment and can decrease replacement and maintenance costs.

Enhanced removal of phosphate by electrogenerated iron combined with mechanically activated calcite

Fe electrocoagulation is efficient for the removal of phosphate with low energy consumption, whereas suffers from the high concentrations of the total dissolved Fe (TDFe) in the effluent. In this study, mechanically activated calcite was used to combine with the electrogenerated Fe to improve the removal efficiency of phosphate and reduce the concentrations of TDFe. The removal efficiency of phosphate (initial concentration 1.0 mg/L) in 30 min was significantly increased (88 %) by mechanically activated calcite combined with electrogenerated Fe method, compared with mechanically activated calcite method (43 %) and electrogenerated Fe method (53 %) separately. The concentration of TDFe in the effluent reduced from 4.9 mg/L with electrogenerated Fe method to 0.2 ∼ 0.5 mg/L with mechanically activated calcite combined with the electrogenerated Fe method. The mechanically activated calcite combined with electrogenerated Fe method was confirmed by the efficient removal of phosphate in the biological treatment effluent from a municipal wastewater treatment plant reached a removal efficiency of approximately 100 % (reduced from 1.33 mg/L to 0.006 mg/L) and in the rainfall runoff from a fertilizer enterprise reached a removal efficiency of 98 % (reduced from 3.86 mg/L to 0.075 mg/L). The removal mechanism was proposed. The Fe-P polymer was formed in the dissolved phase. The mechanical activation improved the solubility of calcite and provided dissolved Ca2+, as well as increased the surface area of calcite and provided more adsorption sites. Therefore, the mechanical activation promoted the adsorption of the Fe-P polymer onto the surface of the mechanically activated calcite. This study provided an efficient method for the removal of phosphate in wastewater and simultaneously reducing the concentrations of TDFe in the effluent.

The efficacy of enhancing carbonate weathering for carbon dioxide sequestration

Enhanced weathering is a geoengineering strategy aiming to increase continental weathering rates, thereby increasing the delivery of atmospheric carbon (as HCO3-) to the oceans. Most enhanced weathering studies focus on the capacity of silicate rocks (e.g., basalt) and minerals (e.g., olivine, Mg2SiO4, or wollastonite CaSiO3) to remove atmospheric CO2. However, carbonate minerals (e.g., calcite, CaCO3) could provide an additional, rapid way to increase HCO3- export to the oceans. Recent studies suggest that 0.84 Gt C yr−1 could be removed from the atmosphere through the enhanced dissolution of calcite in soils, provided carbonic acid is the main dissolution agent. What is not clear is whether atmospheric CO2 dissolved in soils can be transported by rivers, which typically have lower [pCO2], to the oceans. This difference in calcite solubility between soils (where weathering occurs) and rivers (where HCO3- is transported) may lead to large amounts of secondary carbonate formation during transport, releasing the CO2 consumed through dissolution. Here, we present a modeling study comparing the estimated soil dissolution capacity (SDC) in 149 of Earth's largest river basins, to the potential transport capacity of carbon (PTCC) in corresponding rivers. We find the SDC can only be exported to the oceans, without secondary carbonate precipitation, if rivers are in disequilibrium with respect to calcite (i.e., SIc = 1). In this instance, 0.92 Gt C yr−1 may be sequestered above background weathering rates, which is ~20% of annual increases in atmospheric carbon. If rivers are at equilibrium with calcite (i.e., SIc = 0), approximately two-thirds of the carbon dissolved in soil waters are lost due to calcite precipitation in rivers, and just 0.26 Gt of additional atmospheric C yr−1 can be transported to the oceans. Overall, the efficacy of enhanced carbonate weathering is a function of the capacity rivers have for transporting the products from carbonate weathering to the oceans, rather than the dissolution capacity of soils. These findings have implications for the efficiency of enhancing silicate weathering for ocean alkalinity enhancement, as secondary carbonate precipitation during transport is not always considered.

Reaction Kinetics Determined from Coreflooding and Steady-State Principles for Stevns Klint and Kansas Chalk Injected with MgCl2 Brine at Reservoir Temperature

Summary A methodology is presented for determining reaction kinetics from coreflooding: A core is flooded with reactive brine at different compositions with injection rates varied systematically. Each combination is performed until steady state, when effluent concentrations no longer change significantly with time. Lower injection rate gives the brine more time to react. We also propose shut-in tests where brine reacts statically with the core for a defined period and then is flushed out. The residence time and produced brine composition are compared with the flooding experiments. This design allows characterization of the reaction kinetics from a single core. Efficient modeling and matching of the experiments can be performed as the steady-state data are directly comparable to equilibrating the injected brine gradually with time and do not require spatial and temporal modeling of the entire dynamic experiments. Each steady-state data point represents different information that helps constrain parameter selection. The reaction kinetics can predict equilibrium states and time needed to reach equilibrium. Accounting for dispersion increases the complexity by needing to find a spatial distribution of coupled solutions and is recommended as a second step when a first estimate of the kinetics has been obtained. It is still much more efficient than simulating the full dynamic experiment. Experiments were performed injecting 0.0445 and 0.219 mol/L MgCl2 into Stevns Klint (Denmark) and Kansas (USA) chalks at 100 and 130°C (North Sea reservoir temperature). Injection rates varied from 0.25 to 16 pore volume per day (PV/D), while shut-in tests provided equivalent rates down to 1/28 PV/D. The results showed that Ca2+ ions were produced and Mg2+ ions retained (associated with calcite dissolution and magnesite precipitation, respectively). This occurred in a substitution-like manner, where the gain of Ca was similar to the loss of Mg2+. A simple reaction kinetic model based on this substitution with three independent tuning parameters (rate coefficient, reaction order, and equilibrium constant) was implemented together with advection to analytically calculate steady-state effluent concentrations when injected composition, injection rate, and reaction kinetic parameters were stated. By tuning reaction kinetic parameters, the experimental steady-state data were fitted efficiently. The parameters were determined to be relatively accurate for each core. The roles of reaction parameters, pore velocity, and dispersion were illustrated with sensitivity analyses. The determined reaction kinetics could successfully predict the chemical interaction in reservoir chalk and outcrop chalk containing oil with strongly water-wet or mixed-wet state. The steady-state method allows computationally efficient matching even with complex reaction kinetics. Using a comprehensive geochemical description in the software PHREEQC, the kinetics of calcite and magnesite mineral reactions were determined by matching the steady-state concentration changes as function of (residence) time. The simulator predicted close to the identical production of Ca as loss of Mg. The geochemical software predicted much higher calcite solubility in MgCl2 than observed at 100 and 130°C for Stevns Klint and Kansas. The methodology supports reactive flow modeling in general, but especially oil-bearing chalk reservoirs, which are chemically sensitive to injected seawater in terms of wettability and rock strength.

Realization of parallel experiments in a diamond anvil cell and their application to water-mineral interactions at high-pressure and high-temperature conditions.

Parallel experiments are normally used to compare different chemical systems and conditions simultaneously. In the field of high-pressure experimental science, parallel experiments are hard to realize due to very limited reaction chamber size for the generation of high-pressure conditions, especially in diamond anvil cells (DACs). Multiple holes, instead of a single hole, can be drilled into a gasket (i.e., multihole gasket technique) to realize parallel experiments in a DAC. In this study, we conducted a series of systematic calibration experiments on multihole gasket techniques using statistical methods. Multiple (two or three or four) holes 100 µm in diameter were symmetrically drilled into a gasket by a laser drilling instrument with the help of a coded Python program. The pressure deviations among different holes in a gasket at average pressures below 10GPa are constrained to less than 0.2GPa in all calibration experiments at room temperature. We further checked the influences of the gasket material, hole number, pre-indented gasket thickness, and temperature on the pressure deviations among different holes in a gasket. Finally, we applied the multihole gasket technique in a DAC experiment and compared the solubility of calcite in different chemical environments at the same pressure and temperature conditions. The experimental results showed that the multihole gasket technique could be widely applied to study water-mineral interactions at high-P (<10GPa) and high-T (<700°C) conditions because multiple parallel experiments can be efficiently realized simultaneously.

Solubility product constants for natural dolomite (0–200 °C) through a groundwater-based approach using the USGS produced water database

The calculation of a reliable temperature dependent dolomite solubility product constant (K_sp−dol) has been the subject of much research over the last 70 years. This study evaluates log₁₀(^aCa²⁺/^aMg²⁺) values using PHREEQC (Pitzer approach) for a screened subset (n = 11,480) of formation waters in the U.S. Geological Survey National Produced Waters Geochemical Database V2 (PWGD), an extensive inventory of 165,960 formational waters from a range of sedimentary lithologies in North America up to 6.6 km depth (Blondes and others, 2016). Through extensive ground truthing against datasets sourced from Texas Gulf Coast basin and the Mississippi Salt Dome basin we establish both the geochemical data from the PWGD and a new geothermal model of the US that is used to determine temperatures at-formation-depth to be reliable data sources. The vast majority (90%) of PWGD samples have log₁₀(^aCa²⁺/^aMg²⁺)-temperature values that are interpreted to be indicative of calcite-dolomite equilibrium and buffering by the bulk mineral solubilities. Using statistical models with different parameterisations (different Maier-Kelly formulas, mixed-effects models with various random effects and linear models) log₁₀(^aCa²⁺/^aMg²⁺) values are regressed against the estimated at-formation-depth temperatures to determine K_sp−dol between 0 and 200 °C. This process relies on the well constrained calcite solubility product constant (K_sp−cal). Local effects that modify log₁₀(^aCa²⁺/^aMg²⁺) values are evaluated through the addition of random effects to the mixed model which both improves the statistical reliability of the K_sp−dol model and enables the determination of K_sp−dol values for local dolomite phases. The nature of these local effects is open to interpretation, but we suggest the primary influence on log₁₀(^aCa²⁺/^aMg²⁺) values is the stoichiometry of the dolomite phase systematically modifying log₁₀(^aCa²⁺/^aMg²⁺) values. We discount the influence on log₁₀(^aCa²⁺/^aMg²⁺) values of dolomite order, the solution ionic strength, equilibration with anhydrite and chlorite group minerals, illitization of smectite and albitization of feldspar. For the dolomite solubility equation; the mixed-effects model (model J23) chosen as most representative yields a pK_sp−dol (log₁₀K_sp−dol); We determine pK_sp°−dol to be −17.27 ± 0.35 (25 °C, 1 atm) which is close to prior estimates, including the most recent experimental value reported by Bénézeth and others, 2018 (pKs_p°−dol = −17.19 ± 0.3) validating the groundwater regression analysis approach of this study.

Fluoride in thermal and non-thermal groundwater: Insights from geochemical modeling

High fluoride (F) groundwaters (>1 mg/L) have been recognized as a water quality problem for nearly a century and occur in many countries worldwide. The affected aquifers can be sedimentary, metamorphic or igneous rocks, but the process giving rise to high-F concentrations has been studied with geochemical modeling and an examination of the rock sources. The association of high-F with silicic igneous rocks such as granites and rhyolites results from magmatic differentiation (fractional crystallization, fractional melting, and crustal assimilation) wherein F is enriched in the liquid phase because of its incompatibility in the mafic minerals that crystallize early during cooling. Further development of F-rich groundwaters occurs during the evolution of Na-HCO3 waters because of removal of Ca through ion-exchange and calcite precipitation, thereby raising the F concentration from minerals like fluorite and fluorapatite to maintain solubility equilibrium. Increasing temperatures enhance this effect because of the retrograde solubility of calcite. From geochemical modeling using the PhreeqcI code, the primary variables controlling F concentrations are DIC (dissolved inorganic carbon), salinity (ionic strength), PCO2, and temperature. Complexing is also important but plays a more secondary role. Considering these variables, an improved set of plotting parameters, F/Cl vs. HCO3/Cl, are shown to be effective in interpreting groundwater analyses. This approach is demonstrated by examining case studies from the Black Creek aquifer, South Carolina, USA, the Madison regional aquifer, midwestern USA, the Mizunami Underground Research Laboratory, Japan, New Zealand thermal waters, the San Luis Valley groundwaters, Colorado, USA, and the Aquia aquifer, Maryland, USA.

Interactive effect of salinity and Ca to Mg ratio of irrigation water on pistachio growth parameters and its ionic composition in a calcareous soil

ABSTRACT This study investigated the effect of different salinity (EC≈6 and 9 dS/m) and Ca/Mg ratios (≈0.95,0.50, and 0.25) in irrigation water on the chemical composition of soil solution and growth of pistachio (Pistacia vera L.). The physiological, biochemical, and yield-related responses of pistachio seedlings were measured within ≈30 weeks in a greenhouse pot experiment. The EC of the soil solutions rapidly approached the one in the irrigation waters while the Ca/Mg ratios slowly altered, as such the final ratios were ≈50-100% larger than the one in the irrigation waters. The slower change in the Ca/Mg ratio is due to the fact that Ca concentration is dominantly controlled by the calcite solubility but the Mg concentration by the ion-exchange reaction. With increasing EC of the soil solution from 5.8–10.4 dS/m, we found 4-fold reduction in shoot dry weight and 62% increase in electrolyte leakage. In each salinity level, the highest yield and membrane stability were achieved at the Ca/Mg ratio of ≈1 in the soil solution. Overall, a Ca/Mg ratio < 1 in the irrigation water shifted the ionic composition of the soil solution, even in calcareous soil, towards a ratio < 1 and negatively affected pistachio growth.

Improving chemical composition of smart water by investigating performance of active cations for injection in carbonate Reservoirs: A mechanistic study

Laboratory experiments have shown that smart water (low salinity water with electrolyte additive) can improve the carbonate reservoir wettability toward a favorable condition to enhance oil recovery. Several hypotheses have been introduced in previous studies to explain the underlying mechanisms, but there are still some contradictions among those mechanisms. In this research, throughout a comprehensive laboratory study, we investigated cationic surfactant to explore why the conventional method of reducing the salinity of injection solutions is not always effective. Then for the preparation of smart water, several conclusive remarks are introduced for more effective application in carbonate reservoirs. In our experimental study, first, the effect of change in electric charge was studied using zeta potential measurement. From the generated lab data, an equation was developed for the zeta potential at the calcite-brine and oil-brine interfaces. Next, the effect of cationic surfactant on wettability alteration was tested. It was observed that the required time to activate the wettability alteration was significantly reduced from around 63 days to approximately 40 days in the presence of cationic surfactant. In addition, we showed that the interfacial tension between oil and water is changed by both reducing the salinity and cationic surfactant additive. Furthermore, using Attenuated Total Reflectance (ATR), it was observed that the negatively functional groups of oil were adsorbed on the calcite surfaces confirming that the crude oil properties were essential parameters in this EOR method. Finally, we developed a geochemical model that shows calcite's solubility is not the only factor for the wettability alteration mechanism.

Case Study: Single-Aqueous-Phase Retarded Acid Performance Offshore Sarawak

The purpose of acid stimulation of carbonate formations is to increase production. The essential component for these stimulation fluids is the carbonate-dissolving agent, which creates conductivity channels connecting the reservoir with the wellbore. Controlling the reactivity of hydrochloric acid (HCl), the most-used dissolving agent due to its high dissolving capacity, wide availability, and low unit cost, is the most viable approach to successfully stimulate a high-temperature carbonate reservoir. It is essential to retard the HCl-carbonate rock reaction to achieve the optimum balance between total fluid used and enhanced well production. It is well documented that the conventional emulsified acid exhibits high friction pressure, is cumbersome to prepare, and performs with sensitivity to a multitude of parameters. These drawbacks have prevented the industrywide adoption of this method. The recently developed single-aqueous-phase retarded acid (SAPRA) designed for primarily 15–25% HCl solutions represents a significant step forward. The first successful field implementation of SAPRA took place offshore the Malaysian state of Sarawak in early 2021. At Sarawak, the HCl reactivity was regulated and retarded by a single potent low- dosage additive, which is compatible with selected acid corrosion inhibitors, nonemulsifiers, H2S scavengers, other commonly used additives, and if necessary, friction reducers. Improving Acid Stimulation Efficiency The technical approach behind SAPRA is based on chemical technology that enables the reduction of the reaction rate and allows the control of the diffusion/mass transfer mechanism. This is key in designing the acid treatment to optimize chemical program cost and well production and has been extensively studied (Al Moajil et al. 2020; Czupski et al. 2020; Daeffler et al. 2018; and Abdrazakov et al. 2018). The technology was developed utilizing a surface barrier concept where transiently adsorbed retarder molecules adhere to a carbonate surface and thus, delay the hydrogen ion carbonate reaction over a range of acid concentrations and operating temperatures. Due to the complexity of the chemical interactions among all the additives in the acid fluid system, the selected additives must be screened to ensure mutual compatibility before conducting performance testing such as corrosion rate, calcite solubility capacity characterization, and coreflow measurements. Incompatible chemistry could lead to severe corrosion issues such as the examples shown in Table 1.

Constraining fluid-rock interactions during eogenetic karst and their impacts on carbonate reservoirs: Insights from reactive transport modeling

Eogenetic karst has been regarded as a dominant origin of hydrocarbon reservoirs, whereas quantifying the fluid-rock interactions and their impacts on porosity evolution during the palaeokarst process remain persistent challenges that limit the accuracy of reservoir quality prediction. This study investigates the dissolution of carbonate rocks with potential controlling factors by reactive transport modeling that couples fluid flow, mineral reactions and porosity changes in a one-dimensional vadose meteoric water-rock system. Simulation results of base case scenario and sensitivity analyses show that the duration of subaerial exposure and recharge capacity of rainwater significantly determine the karst-affected depth and porosity increment. The amount of calcite dissolution is also affected by a downward decrease in calcite solubility (temperature-dependent) and the enrichment of Ca2+ and HCO3− in the lower part. The atmospheric carbon dioxide concentration has a minor impact on the vertical extent of karst, while it facilitates the dissolution rate under high pCO2 conditions. The influence of atmospheric pCO2 variation over geological time on the porosity increment was reconstructed under hydrogeological conditions of the base case scenario (exposure time = 130 ka; rainfall = 628 mm/a). The differences in the dissolution rates and extent of karst between limestone and dolostone can be interpreted as the results of different rate-determining reaction mechanisms, i.e., thermodynamically controlled calcite and kinetically controlled dolomite.