Water Rock Research Articles

Identification of the Potential of Acid Rock Drainage in the Tin Mine on Bangka Island

Bangka Belitung is one of the tin-producing areas in the world which is characterized by the large number of granite rocks in the area as the rock carrying cassiterite minerals. Granite rocks found on Bangka Island are rocks formed due to magma activity from acidic volcanic processes. The availability of acidic water is possible due to the presence of acid-carrying minerals from granite which causes acid rock drainage or acid rock water which generally occurs in mining areas, ex-mining and exploration in tin mines. Before making efforts to prevent environmental pollution, identification is needed regarding the potential acidity of the rock so that the pH and dissolved metal content that endangers survival can be prevented to a minimum.

Cenozoic coastal carbonate deposits of Qatar: Evidence for dolomite preservation bias in highly‐arid systems

AbstractIn the ancient rock record, early replacement of metastable marine calcium carbonate deposits by dolomite has long been associated with evidence of arid depositional environments. Such associations led to the development of the seepage reflux dolomitization model, whereby magnesium‐rich marine waters concentrated by evaporation descend into underlying sediments, replacing primary aragonite and calcite deposits with dolomite through rock–water interaction. In the modern arid coastal systems of Qatar, where marine waters concentrate to halite saturation, both aqueous geochemical measurements and mineralogical investigations show that replacement of calcium carbonate deposits by dolomite is not occurring to any consequential degree. At best dolomite formation is minor and localized. Instead, modern and mid‐Holocene coastal deposits retain their original mineralogy, showing little evidence of carbonate precipitation reactions with the notable exception of beachrock formation. Pleistocene coastal deposits are mostly absent in comparison with both Qatar Holocene coastal deposits, and Pleistocene coastal deposits from more humid settings. The lack of onshore Pleistocene‐aged carbonate outcrops in Qatar, as well as regionally, is interpreted to reflect coastal sediment denudation during emergence due to: (i) the absence of coastal marine lithification; and (ii) the absence of meteoric cementation and root stabilization in the highly‐arid realm. In contrast, marine Palaeogene and Miocene carbonate deposits are preserved in outcrop in Qatar, having suffered marine lithification by dolomite, thus promoting retention of carbonate strata through subsequent lowstands. These older deposits formed during times of ocean acidification, which, based on natural system and laboratory investigations, is interpreted to promote metastable carbonate dissolution and dolomite formation. The highly‐arid Holocene and Pleistocene coastal systems of Qatar represent limestone factories, but these deposits are not being retained to the rock record. Based on these observations, the association between the occurrence of dolomite and arid depositional settings may be to some degree a preservation bias.

Carbon Dioxide Production in Bedrock Beneath Soils Substantially Contributes to Forest Carbon Cycling

AbstractSoils are widely considered the primary terrestrial organic matter pool mediating carbon transactions with the atmosphere and groundwater. Because soils are both a host and a product of rhizosphere activity, they are thought to mark the location where photosynthetic fixation of carbon dioxide (CO2) is balanced by the oxidation of organic matter. However, in many terrestrial environments, the rhizosphere extends below soils and into fractured bedrock, and it is unknown if the resulting biological and hydrologic dynamics in bedrock have a significant impact on carbon cycling. Here we show substantial production of CO2 in weathered bedrock at 4–8 m below the thin soils (<0.5 m thick) of a Northern California forest using innovative monitoring technology for sampling gases and water in fractured rock. The deep CO2 production supports a persistent upward flux of CO2(g) year‐round from bedrock to soil, constituting between 2% and 29% of the average daily CO2 efflux from the land surface. When water is rapidly transported across the fractured bedrock vadose zone, nearly 50% of the CO2 produced in the bedrock dissolves into water, promoting water‐rock interaction and export of dissolved inorganic carbon (DIC) from the unsaturated zone to groundwater, constituting as much as 80% of the DIC exiting the hillslope. Such CO2 production in weathered bedrock is subject to unique moisture, temperature, biological, and mineralogical conditions which are currently missing from terrestrial carbon models.

Thermodynamic Modeling of the Rock–Water–Organic Matter Systems and Origin of Hydrocarbons

Chemical interactions in carbonate rock–seawater, silty sand–seawater, clay rock–seawater, basalt–seawater, and granite–seawater systems, where the term “seawater” denotes the compositions of halite, epsomite, and sylvinite stages of seawater densification, were simulated at 25, 100, 200, and 300°С and various pressures in order to assess the ability of rocks to generate hydrocarbons. Based on the efficiency of hydrocarbon generation, the rocks are arranged in the following series: clay > silty sandstone > carbonate > mafic rocks; felsic rocks are unproductive. It is shown that with an increase in the weight rock/water ratio (R/W), which may be taken as the conditional time (degree) of metamorphism, the reduction potential (lgfH2) of rocks, i.e., their ability to generate hydrocarbons, increases. At R/W → 1, the reduction potentials (lgfH2) for carbonate, clay, and silty sandstone are –2.74, –2.45, –2.57 at 100°С, –1.2, –1.1, –1.0 at 200°С, and –0.5, +0.3, –1.2 at 300°С, respectively, which shows a clear advantage of clay at high temperatures (pressures) in terms of its ability to reduce chemical elements and generate hydrocarbons. Thermodynamic modeling of interactions in a closed water–mineral precipitate–natural organic matter system at the T–P parameters of diagenesis was performed. A mature type of kerogen and associated substances (water-dissolved hydrocarbons, nitrogen compounds) are formed in the system in the course of the reactions. It is shown that the removal of CO2 (g) and N2 (g) from the system promotes hydrocarbon and kerogen formation reactions. It was found that the water phase changes insignificantly during kerogen formation. In general, the effect of desalination and changes in pH and Eh, as well as the increase in the content of CO2 dissolved in the water, is significant.

Hydrochemical characterization and quality assessment of groundwater in Meki River Basin, Ethiopian Rift

The present study was carried out in Meki River Basin (Ethiopian Rift) aiming at characterizing the hydrochemical composition of groundwater and evaluating the water quality status for drinking and irrigation uses. For this purpose, 63 primary groundwater samples from springs, hand-dug wells, and boreholes were collected and subjected to major ions analysis besides the in situ tests. The analysis result illustrates that Na+ and HCO3− are the principal cation and anion in the study area. The spatial investigation of the physiochemical parameters revealed that temperature, pH, TDS, EC, Na+, K+, HCO3−, Cl−, SO42−, and F− show a positive trend from the highland towards the rift floor along the groundwater flow direction. On the contrary, Ca2+ and Mg2+ show a negative tendency along the groundwater flow path. The groundwater of the study area generally evolves from predominantly fresh (TDS 750 mg/l) Na–HCO3 water type in the rift floor following the regional groundwater flow path. Gibbs diagram supported by ionic ratio (Na+ + K+/Ca2+ + Mg2+ vs total cations (TZ+) and Chloro-Alkaline Indices (CAIs) suggests that rock–water interaction (silicate hydrolysis and cation exchange) is the major hydrochemical processes controlling the evolution of the groundwater in the study area. 19% of TDS, 11% of EC, 83% of K+, 84% of HCO3−, and 52% of F− of the total water samples were unsuitable for the drinking uses compared with WHO water quality guideline. Spatial distribution maps of major ions (Ca2+, Mg2+, Na+, K+, Cl−, HCO3−, SO42−, and F−) and binary plots of physical parameters (temperature, pH, TDS, and EC) with elevation were produced. Both the spatial maps and binary plots generally show a water quality drop rift wards. Similarly, using multiple agriculture water quality criteria such as EC, SAR, RSC, PI, and Na%, the suitability of the groundwater for agricultural use was evaluated. Except a few samples in the rift floor, the majority of the water samples are found to be suitable for irrigation uses. As the study area is located where active geothermal activity and fluid circulation through fault systems, it is highly advised to carry out further toxic trace elements analysis to investigate the possible influence on the water quality.

Wettability alteration and oil recovery by surfactant assisted low salinity water in carbonate rock: The impact of nonionic/anionic surfactants

Combining low salinity water (LSW) and chemicals to enhance oil recovery has recently received more attention in the oil industry. In this study, a systematic experimental procedure was conducted to evaluate the performance of low salinity nonionic surfactant with/without anionic surfactant in wettability alteration and oil recovery of oil-wet carbonate having high salinity formation water (FW) (196 g/L) and moderate temperature (75 °C). A polyethoxylated nonionic surfactant (C13EO12) and two anionic surfactants: sulfonate (IOS 20–24) and carboxylate (AEC 938) were used in this study. Contact angle (CA) results showed that low salinity nonionic surfactant was effective in altering the wettability of oil-wet calcite toward water-wet state. While the low salinity anionic surfactants' systems were only able to reduce the oil-wetness of the oil-wet calcite. When nonionic surfactant is mixed with anionic surfactant, the wettability of oil-wet calcite was altered toward intermediate-wet or only a reduction of its oil-wetness occurred depending on the type of the anionic surfactant. Spontaneous imbibition tests using oil-wet limestone cores showed that among the low salinity single surfactants’ systems, carboxylate anionic surfactant resulted in the highest oil recovery (61% of oil initially in place (OIIP)) and sulfonate anionic surfactant resulted in the lowest oil recovery (31% of OIIP). The low salinity nonionic surfactant recovered 51% of OIIP by spontaneous imbibition. Addition of sulfonate anionic surfactant to the nonionic surfactant resulted in an oil recovery of 49% of OIIP while addition of carboxylate anionic surfactant to the nonionic surfactant considerably improved the oil recovery to 74% of OIIP. Hence, selection of proper surfactant class is crucial for a successful oil recovery.

Excavation of underground research laboratory ramp in granite using tunnel boring machine: Feasibility study

Underground research laboratory (URL) plays an important role in safe disposal of high-level radioactive waste (HLW). At present, the Xinchang site, located in Gansu Province of China, has been selected as the final site for China’s first URL, named Beishan URL. For this, a preliminary design of the Beishan URL has been proposed, including one spiral ramp, three shafts and two experimental levels. With advantages of fast advancing and limited disturbance to surrounding rock mass, the tunnel boring machine (TBM) method could be one of the excavation methods considered for the URL ramp. This paper introduces the feasibility study on using TBM to excavation of the Beishan URL ramp. The technical challenges for using TBM in Beishan URL are identified on the base of geological condition and specific layout of the spiral ramp. Then, the technical feasibility study on the specific issues, i.e. extremely hard rock mass, high abrasiveness, TBM operation, muck transportation, water drainage and material transportation, is investigated. This study demonstrates that TBM technology is a feasible method for the Beishan URL excavation. The results can also provide a reference for the design and construction of HLW disposal engineering in similar geological conditions. © 2020 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Investigation on the influence of thermophysical properties of working fluid on heat extraction from hot dry rock

High pressure hydraulic fracturing is a safe and environment-friendly method for the utilization of hot dry rock. In present work, the heat transfer characteristics of water and helium in hot dry rock are probed with numerical simulation. The results show that reducing the injection temperature, increasing the pressure difference between the injection well and producing well, can increase the heat extraction rate and the total heat extraction. Furthermore, under the condition of same pressure difference and injection temperature, the heat extraction rate of helium is greater than that of water, which indicates that helium is more suitable for hot dry rock heat extraction.

Investigation into fluid-fluid interaction phenomena during low salinity waterflooding using a reservoir-on-a-chip microfluidic model

Injection of modified salinity brines (MSB), i.e. brine with seawater-like salinity (SWS) and low salinity water (LSW) in oil-wet carbonate rocks has proven to be relevant to improved oil recovery operations. Many reports in the literature related the underlying mechanisms to rock-fluid interactions such as ionic exchange and electrical double layer expansions, which caused wettability alterations at the rock surface. Little attention appears to have been paid to fluid-fluid interactions as a potential mechanism in displacement processes.In this work, we investigated the role of fluid-fluid interactions in improved oil recovery using MSBs. Interfacial tension and surface elasticity calculations were correlated to visual observations of displacement processes in order to investigate the role of crude oil snap-off. Microfluidic devices featuring pore throats 50 μm in diameter were used to observe snap-off as a function of salinity of the displacing fluid. Flow experiments suggested that, in a water-wet constricted pore throat, SWS brines suppressed crude oil snap-off as compared to formation water brine (FWS) brine. This behavior was correlated to the higher surface elasticity of oil-SWS interfaces than that of oil-FWS interfaces. Higher surface elasticity suppressed the expansion of the thin water film coating pore throat walls and hence it increased the capillary number at which snap-off of the crude oil phase was expected to occur.Moreover, water interacted with the polar components to form reverse micelles called microdispersions. These microdispersions were observed in both aged and non-aged microfluidic devices near oil-brine interfaces in the pore-network. Similarly, in a vial test performed by Tetteh and Barati (2019), microdispersion formation was only observed very close to oil-brine interfaces, caused by transport of water molecules into the oil phase due to reduced intermolecular forces at oil-LSW interfaces. This microdispersion formation was visualized using environmental scanning electron microscopy. These microdispersions remobilized, redistributed the oil, and along with a slight change in wettability in the medium, they improved the observed recovery. In the pore-network flow experiments, the use of SWS brines resulted in the formation of relatively larger oil droplets, which is attributed to the suppression of crude oil snap-off and enhanced oil coalescence resulting from changes in oil-brine interfaces. The integrated experimental study presented in this work demonstrates the importance of fluid-fluid interactions in improved oil recovery using MSBs.

Geochemical processes influencing stream water chemistry: a case study of Ala River, Akure, Southwestern Nigeria

Ala River is the main river that drains Akure metropolis in southwestern Nigeria. The river takes its sources from deep-seated fractures in granite and charnockite rock bodies at the North and North-western regions of Akure town, flowing through quartzite and granite gneiss exposures. This study was carried out to assess the geochemical processes influencing the quality of Ala river water. The dendritic river system, covering an area of about 427 km2, was studied and water was sampled at thirty-seven (37) points for in-situ determination of some physicochemical parameters and dissolved concentrations of the major ions. pH values obtained varied between 7.16 and 7.75, electrical conductivity ranged from 123 to 520 µs/cm, total dissolved solids varied between 62 and 260 mg/l-CaCO3 while average temperature value was 26.65 °C. Relative concentration of cations and anions were in the order of Ca2+ > Mg2+ > Na+ > K+ and HCO3− > SO42− > Cl− > NO3−. Mean values of dissolved Na+, K+, Ca2+, Mg2+, Fe2+, Cl−, HCO3−, SO42−, NO3−, and PO42− were 34.028, 8.872, 34.175, 18.289, 0.428, 16.543, 56.41, 12.503, 0.495 and 2.029 mg/l, respectively. Two hydochemical facies namely Calcium-Bicarbonate facies and mixed calcium–magnesium–chloride facies dominated the chemistry of the water. CaHCO3 facies revealed the contribution of geogenic processes while the mixed Ca(Mg)-Cl type reflected domestically induced anthropogenic activities influencing chemistry of the water. Gibbs diagrams identified rock–water interaction as an important geochemical process in the study area. Silicate weathering of rocks and carbonate weathering were identified as the important geochemical processes which influence the water chemistry of the study area.

Mechanistic study to investigate the injection of surfactant assisted smart water in carbonate rocks for enhanced oil recovery: An experimental approach

More than half of the world's discovered oil is held in carbonate reservoirs, most of which are naturally oil-wet fractured reservoirs. Oil Recovery efficiency can be improved noticeably if the rock wettability is changed from an oil-wet to a water-wet state. However, what factors control the wettability alteration are not clearly specified. In this study, a comprehensive mechanistic study is performed using different experimental tools to investigate the effects of active ions, non-active ions, CTAB, and different combinations of ions and CTAB on the sample rock's wettability. The results indicate that using CTAB and a smart water solution, in which the sodium and chloride ions are eliminated and the concentration of sulfate ions is increased, (SW-0NaCl-4SO42− + 1CTAB) reduced the contact angle to 43.58°. The zeta potential value of the oil-wet calcite powder increased from −61.12 to −7.6 mV after treatment with SW-0NaCl-4SO42− + 1CTAB. Moreover, the mean roughness value of oil-wet calcite powder increased from 5.02 to 25.89 nm after treatment with SW-0NaCl-4SO42− + 1CTAB. In fact, sulfate ions are capable of removing the strongly adsorbed carboxylic groups from the surface and changing the wettability of the calcite surface to a more water-wet state. Also, the cationic surfactant monomers tend to ionically react with carboxylic groups and separate them from the calcite surface. Moreover, the removal of sodium and chloride ions also leads to significant changes in the wettability. The imbibition results showed that the change of wettability from an oil-wet to a more water-wet state results in a critical increase in oil recovery efficiency during imbibition of distilled water into the calcite rock slice. High oil recovery efficiency can be obtained by optimizing the smart water solution composition and using a proper concentration of surfactant.

Impact of urbanization on hydrogeochemistry and trace metal distribution on five major ponds in the holy city of Gaya, India

Gaya, a prominent city of Bihar (India) with rich cultural and religious significance has been susceptible to massive urbanization, population growth and pollution which have huge impact on its surface water bodies. The study was conducted on five major ponds of Gaya namely Bisar, Dighi, Vaitarni, Ramsagar and Suryakund. This paper attempts to evaluate their drinking and irrigational water quality status, trace metal contamination in water and sediments (except Suryakund), hydrogeochemical characterization and evolutionary trends and processes involved in the water chemistry. The WQI values (>130) revealed that the ponds are facing heavy pollution load and the water is not fit for drinking purposes; however, irrigational indices indicates that the water of these ponds is suitable for irrigational purposes. The ponds' water and sediments are heavily contaminated with trace metals particularly cobalt (CF and PI >17) and lead (CF>1.4 and PI>5) in sediments. The PCA and HCA were also performed to find the relevant sources, trends and groups in trace metal contamination in their water. The hydrogeochemical profile of surface water (Piper's plot, Durov's diagram, Gibbs diagram and IBE) indicated that they are of mixed water type with most abundant facies being Na–Ca–Mg–Cl, Ca–Na–Mg–Cl and Ca–Na–Mg–Cl–HCO3. SI values showed ponds to be oversaturated with Ca–Mg based minerals and dissolution of halite, magnesite and anhydrite indicating high degree of rock water interaction and reverse cation exchange process dominating the water chemistry. However extensive mixing of pollutants and dissolution has caused the overall geochemical character of water to change. The overall study shows that urbanization may further increase the rate of anthropogenic activities overtime which could enhance trace metal accumulation in the ponds and pose a serious health risk.

Evaluation of drinking and irrigation suitability of groundwater with special emphasizing the health risk posed by nitrate contamination using nitrate pollution index (NPI) and human health risk assessment (HHRA)

Groundwater is widely recognized as an essential source of water for drinking and irrigation uses in the South India. It is essential to evaluate the characterization of groundwater for drinking and irrigation uses. A total of 67 samples were collected in different locations of study area from tube wells for physio-chemical analysis. Water quality index (WQI), nitrate pollution index (NPI), human health risk assessment (HHRA), and irrigation water quality index (IWQI) efficient tools have been used to evaluate the quality of groundwater in the present study. The Piper and Gibbs diagram revealed that weathering of parent rocks, evaporation, rock water interaction, and ion exchange process are influencing the nature of groundwater. The result of WQI showed that, 20.89% and 7.46% of the sample locations are moderate and poor quality of water for drinking purpose. In order to evaluate the nitrate contamination, NPI divulged that seven sample locations are significant very significant type of pollution. Based on HHRA, the children are at high risk compared to male and female in the study region. The higher percentage of the sample locations are suitable for irrigation uses. The study helps to identify the contaminated zones and also to follow emerging remedial measures to control the source of contamination in the region.

Oil-water pore occupancy in the Vaca Muerta source-rocks by NMR cryoporometry

Abstract The main motivation of this work is to determine quantitatively the pore occupancy of water and oil in some source rocks. The pore occupancy might be imposed by differences in chemical composition, wettability behavior and sorption of fluids in organic and inorganic porosities and will dramatically affect the hydrocarbons flow through the porous medium. We address this issue using NMR cryoporometry in two phase situations complemented by other NMR measurements. Using oil-wet samples originating from the Vaca Muerta formation, oil saturation as large as 70% were obtained by simply immersing fully water saturated samples into decane. At 100% water saturation, the measured pore size distributions indicate two main peaks around 2 and 80 nm. After immersion into oil, the pores occupied by water in the presence of decane are mostly around 2 nm and less. The pore sizes occupied by decane in the presence of water can then be deduced by subtracting the distributions obtained at 100% water saturation and after spontaneous drainage. Oil is mainly located in pores around 80 nm. These measurements are confirmed by high resolution SEM images showing the presence of porosity in the organic matter (sponge-like structure). Most of the oil can be associated with the porous organic matter network. These observations are complemented by the determination of the porosity below 2 nm and the water connectivity. From D2O diffusion experiments at 100% water saturation, we observed that about 19% of the total porosity is non-exchangeable with D2O. From the measurements of the liquid signal at −29 °C, we observed that on average 58% of the total porosity is located in pores smaller than 2 nm.

ОЦЕНКА ГОРНО-ГЕОЛОГИЧЕСКИХ И ГОРНОТЕХНИЧЕСКИХ УСЛОВИЙ КАРЬЕРА «СЕВЕРНЫЙ» С ПОМОЩЬЮ МАТЕМАТИЧЕСКИХ МОДЕЛЕЙ

One of the most important indicators characterizing the operating conditions of the fields is the water cut. It negatively affects the way of mining and the possibility of effective use of modern mining technologies. The high water cut of the cover and ore-hosting rocks often serves as the main reason for a decrease in their stability and the manifestation of negative processes (quicksand properties of rocks, caving), as a result of which the safety of miners deteriorates and high-performance mining methods become inapplicable, which generally leads to a decrease in the technical and economic indicators of the open pit. Thus, the study of the regularities of the formation of water inflows in the “Severny” open pit, based on the use of factual material and the development of a sound forecasting methodology are relevant. Purpose of the study. Analyze and assess the mininggeological and mining-technical conditions of the open pit “Severny” using mathematical models. Research methodology. The work uses a modeling method to predict water inflow and calculate the drainage of a quarry field in difficult mining conditions. Devices simulating natural mining conditions were used: a device for electrohydrodynamic analogies (EGDA). Research results: An analogy has been drawn between the phenomenon of laminar steady-state filtration of water in rocks and the passage of current in an electrically conductive medium in the form of electrically conductive paper, less often in liquid electrolytes. The EGDA device was used to determine the water inflows into the quarry, taking into account the factors that complicate the calculations of groundwater filtration (for example, taking into account the movement of the walls of the quarry, the operation of drainage devices, the infiltration of atmospheric precipitation, the movement of water in neighboring aquifers of different permeability), modeling of objects with a complex configuration boundary contours. Conclusion. The modeling method has been improved, which makes it possible to substantiate the use of a specific mining method under certain hydrogeological conditions and to select the optimal drainage scheme to increase the operational reliability of the open pit. The conducted research, observation, study of the existing dam showed the technical feasibility of further development of the deposit with minimization of financial costs. In order to ensure the safety of mining operations, it is envisaged to conduct constant and systemic mining and technical monitoring of mining operations and study the state of the water protection dam and pit walls.

The Influence of Rock Composition and pH on Reservoir Wettability for Low-Salinity Water-CO2 Enhanced Oil Recovery Applications in Brazilian Reservoirs

SummaryLow-salinity waterflooding and carbon dioxide (CO2) injection are enhanced oil recovery (EOR) methods that are currently increasing in use worldwide. Linking these two EOR methods is a promising approach in the exploration of mature fields and for post- and presalt basins in Brazil. Moreover, the latter reservoirs already exhibit a high CO2 content by nature. Interfacial phenomena between fluids and rock in a low-salinity water-CO2 (LSW-CO2) environment remain unclear, particularly the wettability behavior that is related to the pH of the medium, among others. This study investigates the influence of rock composition and pH of the brine on reservoir wettability through coreflooding and zeta potential experiments in LSW and determination of contact angles and interfacial tension (IFT) in the crude oil-LSW-CO2 system at reservoir conditions. Brazilian light crude oil, pure CO2, and brine solutions of different concentrations and compositions were used to represent the fluids in actual oil reservoirs. The experiments were carried out on Botucatu sandstone, Indiana limestone, and calcite crystal samples, with mineralogy determined by energy dispersive X-ray (EDX) analysis. Coreflooding experiments were conducted by the injection of 10 pore volumes (PVs) of fourfold diluted synthetic reservoir brine (SRB), followed by 10 PVs of 40-fold diluted SRB to evaluate the low-salinity effects. Interfacial properties, such as contact angle and IFT, as well as density and pH, were determined at elevated pressures to evaluate the synergistic effects between CO2 and salt content. In addition, geochemical modeling using PH REdox EQuilibrium (in C language) (PHREEQC) was performed to predict the in-situ pH and match with the experimental data. An increase in oil recovery and pH of the effluent was observed in the coreflooding experiments during diluted SRB injection. The ionic concentrations of the effluent samples also indicated illite dissolution. Furthermore, zeta potential measurements confirmed the expansion of the water film and shift from positive to negative surface charge of Botucatu sandstone for salt concentrations less than 80,000 mg/L at pH > 7, whereas in Indiana limestone, negative surface charge was only observed in deionized water at pH > 9. These observations indicate that during LSW injection alone, an increase in pH will favor a thicker water layer on the Botucatu sandstone surface that in turn increases water wettability and results in increased oil recovery. Conversely, the presence of CO2 in LSW causes a decrease in the pH of the medium, which is related to further enhancing water wettability when linking pH with contact angle measurements. It seems that a change in the pH of the brine induced by CO2 solubility in LSW enhanced interactions between the rock surface and water molecules. The respective interfacial energy then decreased, resulting in a decreasing water contact angle. It was also noticed that seawater-CO2 systems caused salt precipitation and mineralogical changes in carbonate and sandstone rock induced by calcite and kaolinite dissolution, respectively. This study contributes substantially to the understanding of interfacial properties and wettability behavior in LSW-CO2 systems, facilitating the design of LSW-CO2 EOR applications in Brazilian fields or even CO2 storage. Moreover, the study provides useful data for oil companies that have acquired mature wells and exploration blocks in Brazil, supporting them in operational and investment decisions.

An elastoplastic model of frost deformation for the porous rock under freeze-thaw

Freeze-thaw action has caused many engineering geology disasters in cold regions, such as frost cracking of tunnel and pavement, rockfall of rock slope, falling off of building materials. The freeze-thaw damage of porous rock is mainly induced by the frost heaving pressure due to pore water freezing. Although some elastic crystallization theories have been proposed to model the freezing process of pore water, the long-term frost heave characteristics under cyclic freeze-thaw are rarely studied. The ice crystallization and frost heave theory under freeze-thaw have been developed in the elastoplastic regime in this study. A novel elastoplastic model has been proposed to estimate the long-term frost heave and frost damage under freeze-thaw. This model has considered the influence of the pore size, yield stress of matrix and degree of water saturation on the development of the frost heaving pressure in pores. During freezing, a plastic region will produce inside the matrix around the pore. This plastic region gradually expands outwards with the increase of this pressure. During thawing, the elastic deformation will be recovered but a considerable residual plastic strain is accumulated. However, the growth rate of the residual plastic strain will decrease under freeze-thaw due to the production of new empty voids. Therefore, the freezing of pore water in porous rock is an elastoplastic problem. Besides, the water saturation and mechanical properties of the porous rock are very important to quantify the frost heave. This study provides a better understanding of the frost damage of the porous rock and a reference for the stability of rock engineering under freeze-thaw in cold regions.

A global-scale data set of mining areas

The area used for mineral extraction is a key indicator for understanding and mitigating the environmental impacts caused by the extractive sector. To date, worldwide data products on mineral extraction do not report the area used by mining activities. In this paper, we contribute to filling this gap by presenting a new data set of mining extents derived by visual interpretation of satellite images. We delineated mining areas within a 10 km buffer from the approximate geographical coordinates of more than six thousand active mining sites across the globe. The result is a global-scale data set consisting of 21,060 polygons that add up to 57,277 km2. The polygons cover all mining above-ground features that could be identified from the satellite images, including open cuts, tailings dams, waste rock dumps, water ponds, and processing infrastructure. The data set is available for download from https://doi.org/10.1594/PANGAEA.910894 and visualization at www.fineprint.global/viewer.

Hydrochemistry and multivariate statistical analysis of the quality of water from Lake Bosomtwe for agricultural and human consumption

Abstract One of the six major meteoric lakes in the world, Lake Bosomtwe, is of great ecological significance for Ghanaians and the scientific community, most importantly for agricultural and human consumption. Water samples (n = 30) were collected to analyze the hydrogeochemical characteristics and water quality of the lake. Statistical methods including correlation, principal component, cluster analysis, Gibbs ratio, and the Piper–Trilinear diagram were used to analyze parameters. The Water Quality Index revealed that the lake water is not suitable for human consumption because measured pH, temperature, total dissolved solids, color, and bicarbonate exceeded their respective thresholds on all occasions. The calculated sodium absorption ratio (13.7–14.8) and soluble sodium percentage (94.43–95.43%) showed that the lake is not appropriate for irrigation as they exceeded their respective limit of 2 and 60%. The Gibbs ratio revealed that rock–water interaction is the underlying mechanism for water evolution. The Piper–Trilinear diagram revealed that alkalies earth and weak acids dominate the water chemistry of the lake. The dominant cation is sodium (82.22%), while the dominant anion is bicarbonate (79.39%). Five monitoring stations were identified, and the water quality was influenced by diverse anthropogenic and natural sources. The findings will provide a reference for policymakers and decision-makers at Lake Bosomtwe.

An assessment of the potential health risks associated with the use of spring waters in crystalline basement rocks in Oke-Igbo in south-western Nigeria

Challenges of water scarcity (quantity and quality) in a basement terrain have prompted the study on the rate of discharge and water quality of springs in the Oke-Igbo area in south-western Nigeria. Discharges from all the spring sites were found to range between 1.50 and 30.42 l/s and only suitable for small water supplies. All the dissolved ions were found to be within the WHO standard tolerable limit except for Pb and Fe which were present in spring discharges at levels of 0.18 to 0.62 mg/l and 0.07 to 2.4 mg/l, respectively. An assessment of water quality using a Piper plot, Gibbs plots, ionic ratios and Chloro-Alkaline Indices classified the spring water as Ca–HCO3 water-type facies, suggesting that the principal controls on the chemical composition of the water are water–rock reactions in the basement aquifers. Health Index (HI) and Probability Cancer Risk (PCR) result for adults and children presented that all the springs portend traceable chronic risk to consumers due to elevated lead concentrations. Secondary treatment is required and highly suggested to reduce the concentrations of lead and iron before consumption of the spring waters.