Geochemical Techniques Research Articles

Petrographic and geochemical analysis of Barmer Basin Paleogene lignite deposits: Insights into depositional environment and paleo-climate

The current study attempts to characterize the samples from Kapurdi, Giral and Sonari lignite mines of Barmer Basin within Rajasthan Tertiary Lignite deposits using petrographic and geochemical techniques. The data generated has been studied in order to better understand the geochemical properties, hydrocarbon potential, depositional environment and paleo-climatic condition of the paleo-mires of these lignites. The proximate analysis of the samples reveals that the average ash content of the Barmer Basin is 11.93 %, the average moisture content is 14.08 %, average volatile matter yield is 42.03 % and the average fixed carbon is 31.95 %, which suggesting that the physical properties of lignite are dominated by volatile matter on dry basis. The ultimate investigation reveals the chemical properties of the lignite with the average carbon content found to be 58.79 wt%, hydrogen value 3.83 wt%, nitrogen percentage 1.60 wt% and sulphur content 2.75 wt%. This clearly indicates high sulphur concentration in Barmer lignite deposits, based on dry basis. The lignite samples subjected to FTIR studies identified aliphatic CH group, aromatic CO group, hydroxyl OH and Aldehyde HCO group. The Rock-Eval pyrolysis studies have been carried out to know the coalification profile of the deposits and hydrocarbon source rock potential. The varying behaviour between brown coal lithotype are primarily reflected by changes in oxygen index values, whereas hydrogen index values demonstrate a more pronounced correlation with coal type rather than the level of maturation. The results show the average total organic carbon (TOC) 47.29 %, S1 peak 2.18 mg HC/g, S2 peak 88.70 mg HC/g, S3 peak 19.22 % mg CO2/g, Tmax 410.53 °C, hydrogen index 219.2 mg HC/g TOC and oxygen index 46.33 mg CO2/g TOC. According to petrographic investigations, the huminite macerals dominate followed by liptinite and inertinite maceral groups in mineral matter-free basis. In all the three different lignite mines, the huminite group dominates with preserved sub-maceral ulminite indicating less transformation of structured plant matter. Reconstruction of depositional environment and paleo-climatic condition of the paleo-mires has been attempted by using organic petrographic indices. The high gelification index (GI) and low tissue preservation index (TPI) values suggest a prolonged wet environment during the decomposition of organic material, accompanied by a gradual subsidence process. The ground water influence index (GWI) and vegetation index (VI) denote ombrotrophic to mesotrophic hydrological conditions of basin at the time of deposition.

Assessment of some bottled natural mineral waters and spring waters in Algeria using multivariate statistical analysis, hydrogeochemical approaches and water quality index (WQI)

ABSTRACT In Algeria, the consumption of mineral waters has grown enormously, indicating that these waters have safe quality for drinking use. The objectives of the present study are to evaluate the physicochemical characteristics of 43 bottled mineral waters and to identify the main hydrogeochemical processes governing water chemistry using a combination of geochemical techniques and multivariate statistical approaches. The results revealed that the abundance order of cations and anions (mg/L) are Ca2+> Na+> Mg2+> K+, HCO3 −> SO4 2−> Cl−> NO3 −. In addition, the comparison between the obtained results and World Health Organization (WHO) standards showed that the analysed physicochemical parameters (pH, Na+, Cl−, SO4 2−, NO3 −) are within the acceptable limits of the World Health Organization (WHO) for drinking except TDS, Ca 2+, Mg2+, K+, HCO3 −, which exceed the WHO permissible limits in few water samples. Hydrogeochemical types in the study area were Ca2+-HCO3 −, Ca2+-Mg2+-HCO3 −, Ca-Mg2+-SO4 2—Cl-, Na+-HCO3 − and Na+-Cl−types, with a low mineral and intermediate mineral contents based on Van der Aa’s classification. The Gibbs plot specifies that almost all samples (93%) fall in water–rock interaction dominance. The major hydrogeochemical processes acting are dissolution of carbonate minerals, ion-exchange mechanisms and silicate weathering. Principal component analysis (PCA) was applied to hydrochemical data of mineral water samples. The results suggest that hydrochemistry in the region is affected not only by geogenic processes but also is impacted by anthropogenic activities. The comparative evaluation of the different water quality indices (WQI) shows that there is a difference between indices values for the same water sample, which may be attributed to the weighting methods, aggregation methods, and the limits of classes used in the calculation of each index. The results from this study can provide the basis for local decision-makers to develop suitable water management strategies and protection against any pollution risk.

Evaluation of porosity and permeability of sandstones within the Oti Group of the Volta Basin using petrophysical and petrographic techniques

Evaluation of porosity and permeability of sandstones within the Oti Group of the Volta Basin using petrophysical and petrographic techniques

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

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

Organic facies variability and paleoenvironmental characterization of the Codó and Itapecuru formations (Aptian-Albian) of Parnaíba Basin, Brazil

The Aptian-Albian sedimentary record of the Parnaíba Basin (NE Brazil), represented by the Codó and Itapecuru formations, is characterized by near-shore, shallow marine, and fluvio-lacustrine clastic sediments deposited in a large shallow sag basin that developed during the breakup of northwestern Gondwana associated with the early opening stages of the South Atlantic. This study aims to precisely characterize the nature, variability, paleoenvironmental significance and preservation conditions of the organic matter of the Aptian-Albian succession of the 2-TV-1-MA borehole (270 m). With these premises, organic petrographic and geochemical techniques were applied for the definition of the organic facies, allowing a better understanding of the Parnaíba Basin evolution during the Aptian-Albian interval. The 2-TV-1-MA borehole presents, at the base, a lacustrine system, with a high contribution of continental components deposited in a high energy, oxic environment, with incipient marine influence. This is intercalated by periods of restriction, with deposition occurring in a dysoxic-anoxic, low energy environment, with high contribution of higher plants. To the top, a relative decrease in the water-column leads to an increase in restriction, the emplacement of a stratified water-column, and the development of microbial mats. This is topped by a return to a high energy, oxic environment, with marine influence, and dominance of higher plants organic components.

From Desiccation to Re‐Integration of the Yellow River Since the Last Glaciation

AbstractThe desiccation (extreme drying) of rivers has important implications for the broader Earth System. However, the desiccation history and its linkage to climate are rarely known for numerous major river systems, primarily due to difficulties in recognizing desiccation events from available stratigraphic records. Here, using a combination of geochemical techniques (major and rare‐earth element geochemistry, detrital zircon geochronology, and optically stimulated luminescence dating), we demonstrate that the Yellow River, which maintains the highest sediment load on Earth, became desiccated during the Last Glacial Maximum at approximately 20 thousand years ago. This finding implies that transportation of sediments and dissolved constituents to the oceans via the Yellow River may have decreased substantially or ceased during glacials, which would have ramifications for ocean chemistry and biology. Furthermore, our work highlights the importance of desiccated riverbed sediments as potential dust sources during glacial periods, a finding that is different from what is observed today.

Machine Learning (ML)-Based Copper Mineralization Prospectivity Mapping (MPM) Using Mining Geochemistry Method and Remote Sensing Satellite Data

The exploration of buried mineral deposits is required to generate innovative approaches and the integration of multi-source geoscientific datasets. Mining geochemistry methods have been generated based on the theory of multi-formational geochemical dispersion haloes. Satellite remote sensing data is a form of surficial geoscience datasets and can be considered as big data in terms of veracity and volume. The different alteration zones extracted using remote sensing methods have not been yet categorized based on the mineralogical and geochemical types (MGT) of anomalies and cannot discriminate blind mineralization (BM) from zone dispersed mineralization (ZDM). In this research, an innovative approach was developed to optimize remote sensing-based evidential variables using some constructed mining geochemistry models for a machine learning (ML)-based copper prospectivity mapping. Accordingly, several main steps were implemented and analyzed. Initially, the MGT model was executed by studying the distribution of indicator elements of lithogeochemical data extracted from 50 copper deposits from Commonwealth of Independent States (CIS) countries to identify the MGT of geochemical anomalies associated with copper mineralization. Then, the geochemical zonality model was constructed using the database of the porphyry copper deposits of Iran and Kazakhstan to evaluate the geochemical anomalies related to porphyry copper mineralization (e.g., the Saghari deposit located around the Chah-Musa deposit, Toroud-Chah Shirin belt, central north Iran). Subsequently, the results of mining geochemistry models were used to produce the geochemical evidential variable by vertical geochemical zonality (Vz) (Pb × Zn/Cu × Mo) and to optimize the remote sensing-based evidential variables. Finally, a random forest algorithm was applied to integrate the evidential variables for generating a provincial-scale prospectivity mapping of porphyry copper deposits in the Toroud-Chah Shirin belt. The results of this investigation substantiated that the machine learning (ML)-based integration of multi-source geoscientific datasets, such as mining geochemistry techniques and satellite remote sensing data, is an innovative and applicable approach for copper mineralization prospectivity mapping in metallogenic provinces.

Organic matter input, paleovegetation and paleoclimate of Upper Cretaceous lignite from Maiganga coalfield, Upper Benue Trough, Nigeria: Insights from biomarkers and stable isotopes

Upper Cretaceous Gombe Formation coals from Maiganga coalfield, Upper Benue Trough, Nigeria were investigated to evaluate the thermal maturity, organic matter input, paleovegetation, paleoclimate, and depositional environment using bulk and molecular geochemical techniques. Vitrinite reflectance (<0.40 %Ro) and biomarker maturity indicators (C31 homohopane 22S/(22S + 22R) < 0.3; 16(H) β/(β+α) phyllocladane <0.5; MPI-1 < 0.5; MPR <2.65) generally signify low thermal maturity. Source-related aliphatic and aromatic hydrocarbon ratios indicate that the coals are derived mainly from terrestrial organic matter but with considerable input from marine algal organic matter. The higher abundance of diterpenoids over triterpenoids and sesquiterpenoids suggests a prevailing contribution of gymnosperms to the Maiganga paleoflora. This is corroborated by the relatively heavier carbon isotopic composition (δ13C = −25.9‰ to −25.0‰) and low angiosperm/gymnosperm ratios. A new proxy, the polycyclic aromatic hydrocarbon ratio (PAHr) which is calculated from PAHr = (phenanthrene + pyrene + fluoranthene + perylene)/(phenanthrene + pyrene + fluoranthene + perylene + retene + cadalene), was proposed to evaluate the abundance and origin of combustion-derived polycyclic aromatic hydrocarbons (PAHs). The mostly high (>0.9) PAHr values for the coals are characteristic of a pyrogenic/combustion origin. Combustion-derived PAHs are abundant in the coals and their ratios indicate a mixed petrogenic/pyrogenic to dominantly pyrogenic origin. However, the high proportion of unburnt organic matter and low abundance of 7-ring PAHs such as coronene indicates limited, high-temperature wildfires. The coronene index values suggest burning temperature in the 700–1000 °C range, which is consistent with the estimated high pO2 of ∼26.5% in the Maastrichtian. n-Alkane proxies (Pwax, Paq, n-C23/n-C29, n-C27/n-C31, etc.) and hydrogen isotope ratios (−117‰ to −112‰) are suggestive of humid paleoclimate with frequent dry periods and lower paleopeat water levels. Moderately high pristane/phytane ratios (2.0–4.8) indicate deposition under sub-oxic to oxic freshwater settings. Additionally, low total sulphur content (0.29–0.90) and dibenzothiophene/phenanthrene ratios (0.05–0.17) imply peat accumulation in lacustrine-swamp to fluvial/deltaic depositional environments with minor post-depositional marine influence.

Integration of petrophysical and geochemical approaches for lower Miocene Euphrates and Jeribe Formations in selected wells in Tawke Oil Field, Northwestern Iraq, Zagros-fold belt

The Lower Miocene Euphrates and Jeribe Formations are among Iraq's potential reservoirs with significant proven reserves. Petrophysical and geochemical techniques were used to investigate these Formations in the recently discovered Tawke Oil Field. Investigation consisted of acquiring a considerable amount of data from eight wells including conventional core analysis, wireline logging data, gas chromatography data and formation water analysis. The Euphrates and Jeribe Formations are considered to have low to moderate porosity (avg. 2.7–20.5%) and low matrix permeability (avg. 0.87–15mD). Secondary porosity is more prevalent than primary depositional porosity and is a significant factor in optimal reservoir properties with an average of 3.7–5.4% Secondary Porosity Index (SPI) for Jeribe and Euphrates Formations respectively. Meanwhile, fractures increased matrix permeability by up to 33mD and 56mD in the Euphrates and Jeribe Formations respectively. Lithology and core analysis revealed that the Dhiban Formation is a non-reservoir rock with maximum 2% He-Porosity and 0.069mD Klinkenberg permeability confirming that the formation is insufficient as a hydrocarbon reservoir, and that the rock properties are primarily controlled by the depositional environment. The Jeribe Formation contains crude oil of intermediate gravity and high sulfur content. According to gas chromatograph analysis the liquid and oil extracted from the Jeribe Formation originated from a matured marine setting that was possibly algae rich (Type-II kerogen) and has been deposited in a reductive environment. It is believed that these hydrocarbons were sourced from the Middle Jurassic Sargelu and Upper Jurassic-Lower Cretaceous Chia Gara Formations. The chloride-calcium water class is determined from the produced water in the Jeribe Formation and the concentration of elements with dissolved salts confirmed that the Jeribe Formation is in contact throughout eight Tawke wells studied.

Preliminary results on the applicability of neutron activation analysis (NAA) to identify cherts from the Munsungun Lake Formation, Maine, USA

AbstractRed chert attributed to the Munsungun Lake Formation, Maine, USA is common in late Pleistocene fluted‐point‐period archaeological sites located throughout the New England states and Quebec, appearing more frequently than any other material type in the region. Despite the assumed association between red Munsungun chert and fluted‐point‐period sites, until recently, it was not possible to link red chert artifacts from these sites to a specific source area within the Munsungun Lake Formation because outcrops of this material associated with direct evidence of past use were not documented. Here, we report the first results of a neutron activation analysis (NAA) study of red Munsungun chert from two quarry areas within the Munsungun Lake Formation. These results suggest that NAA can distinguish between chert source areas within the Munsungun Lake Formation and lookalike materials from the wider region. Additional analyses are required to include more comparative samples and evaluate the efficacy of less destructive geochemical techniques in characterizing cherts from the region. Despite the need for additional research, these results suggest that NAA will be useful for re‐evaluating past identifications of chert from the Munsungun Lake Formation, providing an important foundation for additional geochemical research in the region.

A multi-technique approach to characterization: the Sant Martí de Tous chert as a prehistoric resource for the NE of the Iberian Peninsula

The Sant Genís Formation is located in the NE of the Iberian Peninsula (Catalonia, Spain) and is dated to the Priabonian (upper Eocene), being part of the evaporitic formations of the margin of the Ebro Basin. It is formed by a succession of sandy lutites, occasional limestone layers, marls, and local stratified gypsum and cherts, including the Sant Martí de Tous chert. The Sant Martí de Tous chert type is confirmed by its abundance at specific locations within the territory (NE Iberian Peninsula). This is an important raw material procurement area, as evidenced by the presence of this chert in the main prehistoric sites of the region (e.g., Abric Romaní) and the constant discovery of new sites in the area around the Sant Genís Formation, especially from the Neolithic period onwards (e.g., Cal Sitjo, La Guinardera Nord workshop). All these features, together with the great heterogeneity of the Cenozoic evaporitic cherts, prompted us to carry out a multi-proxy characterization for obtaining a valid criterion by which to identify this chert in the archaeological record. This very heterogeneity hampers the macroscopic characterization of archaeological cherts (e.g., at Abric Romaní), but through petrographic analysis we have been able to identify their origins and, albeit to a lesser extent, their lithostratigraphic unit of provenance within the formation. The complementary mineralogical and geochemical techniques applied in this study show that, although it is difficult to establish an exact origin, through intensive sampling and criteria such as the differential presence of Fe and Ca, some differences among the siliceous varieties within a formation can be detected.

140 years-long sedimentary records of PAHs and CN stable isotopes from Ninomiya River, Japan

Anthropogenic activities' impacts over 140 years were studied at West Nanao Bay using a variety of geochemical techniques on sedimentary records. The bay is influenced by the Ninomiya River which is fed by a small watershed at which Tatzuruhama Town is located. Sedimentation rate was calculated using 210Pb-excess and 137Cs activities. C/N decreased after 1975, indicating a decrease in lignin-rich organic matter. From δ13C, δ15N and biogenic silica it was indicated that the population increased sewage-discharges until the construction of waste-water treatment plant in 1986. Several recorded changes in the landuse matched with the variation of the particle size. Total PAHs concentration was 1.17–62.78 μg g−1, being highest during Japan's fastest economic growth period (1946–1975). Using diagnostic ratios and PCA analysis, PAHs' sources were identified as pyrogenic for all depths, varying from coal combustion (90.7 %) before 1946 to a mixture of biomass and vehicle combustion after 1961.

New insight into geochemical characterization of Paleogene coals from Jarain coalfield, Meghalaya, N-E India: Hydrocarbon potential and organic petrographic analysis

In the present work, geochemical techniques such as Rock-Eval pyrolysis, TOC, Organic petrographic analysis, and statistical investigation have been performed to conclude hydrocarbon generation potential and thermal maturity of studied source rocks samples. Thermal maturity measurement of source rock samples has been assessed by calculated VRo and pyrolysis temperature Tmax (400–418 °C). The result demonstrates that samples are thermal immature in nature and cannot produce hydrocarbons at the commercial level. Modified Van Krevelen diagram (HI versus Tmax) and hydrogen indices (HI) plotted against OI. The study of samples demonstrates that Type II and mixed Type II-III kerogens exist in almost all investigated samples; the HI varies from 203 to 447 mg HC/g TOC and thus can be considered fair oil source and gas/oil source rock. The plot between HI vs Tmax also evaluated the above result. The result of HI vs Tmax is also confirmed by the hydrocarbon richness value (S2/S3), which indicates the emphatic possibility for oil and gas generation in all studied samples. The ternary diagram obtained from microscopic petrographic data typifies that coal forms in platform regions during the coalification process under alternating oxic and anoxic moor conditions. The finding of statistical techniques like Pearson's correlation and cluster analysis also demonstrated that the source rock has tremendous potential for producing hydrocarbons, with a negative correlation between TOC and HI and a decent association between S2 and HI.

Phoenician–Punic amphorae in northern coastal Etruria: New evidence from Pisa (Italy)

AbstractThis study outlines the circulation of Phoenician–Punic amphorae in northern coastal Etruria, with a particular focus on Pisa (Italy), where their presence has been attested since the mid‐eighth century BCE. A set of specimens from Piazza del Duomo was analysed by minero‐petrographic and geochemical techniques. The results were compared with literature data from Mediterranean production areas. The research allowed a better definition of the role of Etruscan Pisa in the frame of commercial and cultural routes in the Mediterranean, specifically in the Tyrrhenian area, also providing the opportunity to review the attestations of Phoenician–Punic amphora on a regional scale.

Geochemical and mineralogical investigation of cemented crusts in the tailings cover at Long Lake Gold Mine, Sudbury, Canada

In mine tailings, precipitation of secondary minerals may cement the tailings material and form cemented crusts or hardpans. Hardpans typically form beneath the surface of reactive tailings. However, at the former Long Lake Gold Mine near Sudbury, Ontario, cemented crusts formed in a clean sand cover above the tailings. We applied mineralogical and geochemical techniques to investigate the formation of these cemented crusts. Representative samples were collected from the sand cover and vertical cores from the underlying tailings. Elevated concentrations of arsenic (As), iron (Fe), and sulfur (S) in the sand cover indicate the upward transport of sulfide-mineral oxidation products. The shallow porewater of the tailings is acidic (pH 4 – 6) and contains elevated concentrations of As (up to 346 mg/L), Fe (up to 1844 mg/L), and SO4 (up to 12,000 mg/L). Mineralogical observations indicate that primary sulfide minerals in the near-surface tailings display moderate to strong oxidation, and secondary Fe-arsenate and jarosite minerals are formed both in the near-surface tailings and the sand cover. Upward migration of sulfide-mineral oxidation products leads to the formation of cemented crusts, which with continuing erosion, represent a long-term source of pollution to the surrounding environment.

Iron oxides act as an alternative electron acceptor for aerobic methanotrophs in anoxic lake sediments

Conventional aerobic CH4-oxidizing bacteria (MOB) are frequently detected in anoxic environments, but their survival strategy and ecological contribution are still enigmatic. Here we explore the role of MOB in enrichment cultures under O2 gradients and an iron-rich lake sediment in situ by combining microbiological and geochemical techniques. We found that enriched MOB consortium used ferric oxides as alternative electron acceptors for oxidizing CH4 with the help of riboflavin when O2 was unavailable. Within the MOB consortium, MOB transformed CH4 to low molecular weight organic matter such as acetate for consortium bacteria as a carbon source, while the latter secrete riboflavin to facilitate extracellular electron transfer (EET). Iron reduction coupled to CH4 oxidation mediated by the MOB consortium was also demonstrated in situ, reducing 40.3% of the CH4 emission in the studied lake sediment. Our study indicates how MOBs survive under anoxia and expands the knowledge of this previously overlooked CH4 sink in iron-rich sediments.

Coaly and lacustrine hydrocarbon source rocks in Permo-Carboniferous graben deposits (Weiach well, Northern Switzerland)

Permo-Carboniferous graben sediments in the North Alpine Foreland Basin (NAFB) include Upper Carboniferous (Stephanian) coal-measures and lower Permian (lower Autunian) lacustrine shales with high organic matter contents. Coals are probably the source for a gas accumulation in Switzerland, while the bituminous shales are potential source rocks for oil. In order to study the hydrocarbon potential of coal and bituminous shales and to contribute to the understanding of their depositional environment, 90 core samples from the Weiach-1 well (northern Switzerland) were investigated using organic petrographic, palynofacies, Rock-Eval pyrolysis, and geochemical techniques (incl. biomarker analysis and compound-specific carbon isotopy). Carboniferous coal seams are up to 10 m thick and were deposited in low-lying freshwater mires. They contain a significant gas potential and reached a maturity stage related to the onset of gas generation. Sapropelic rocks were not observed in the coal-bearing succession. Organic matter-rich Permian shales (Autunian shales) were deposited in anoxic lakes with a stratified water column. The organic matter is of mixed aquatic and terrigenous origin. δ13C values of chlorophyll-derived isoprenoids provide evidence for reworking of organic matter in the water column. The Autunian shales have a strongly varying, but locally very good oil potential. They reached early oil window maturity, but did not yet generate significant amounts of hydrocarbons. The main shale interval in the studied borehole is about 12 m thick and will generate about 0.35 tHC/m2 when mature. A comparison with literature data shows that it is possible to distinguish oils generated from Permian, Jurassic and Oligocene source rocks based on biomarker ratios and isotope data.

Geochemical techniques to identify fluid sources in highly pressured casing-casing annuli (CCA)

The buildup of high pressure in the casing-casing annulus (CCA) threatens well integrity and can cause serious incidents in case of left untreated. Either, trapped water in the cement column or a dynamic water inflow represent potential fluid sources for the elevated CCA pressure. This study presents a sequential methodology to determine the provenance of CCA effluent as trigger for high pressure in newly drilled wells. Single fluid types, multicomponent mixing, and secondary fluid alteration processes were identified through inorganic geochemical techniques; in detail by monitoring the hydrochemical (major, minor, and trace elements) and stable isotopic (δ2H, δ18O) relationship between fluid candidates. As a proof-of-concept, geochemical signatures of CCA effluent from three wells were linked with potential source candidates, i.e., utilized drilling fluids (mud filtrate, supply water) from the prospect well site, groundwater from Lower - Upper Cretaceous aquifers, and Upper Jurassic - Upper Triassic formation waters from adjacent wells and fields. The detection of geochemical affinities of CCA water with groundwater from a Lower Cretaceous aquifer postulates one single lithological unit as source for active groundwater inflow. Nonreactive elements (Na+, Cl−) and environmental isotopes (δ2H, δ18O) were found to be most suited tools for primary fluid identification. The 2H/1H and 18O/16O ratios of supply water and mud filtrate are generally close to global meteoric water and Tertiary groundwater composition, while formation water from Mesozoic units (Cretaceous, Jurassic, and Triassic) can individually be distinguished through increasing ratios in δ18O and δ2H. Compositional anomalies in SO42− and K+, and extreme alkaline conditions for CCA water indicate the occurrence of secondary fluid alteration processes, likely caused by the contact of inflowing groundwater with alkaline minerals in the cement column or by fluid mixing with residuals of potassium chloride (KCl) additives from the drilling process. The geochemical techniques from this study facilitate the detection of high CCA pressure and fluid leakages sources. As a practical benefit, workover engineers are enabled to plan for potential remedial actions prior to moving the rig to affected well sites; thereby significantly reducing operational costs. Appropriate remedial solutions can be induced for safe well abandonment, plus to resume operation at the earliest time.

Integrating electrical resistivity, geotechnical and geochemical techniques to assess soil and groundwater resources near Warri refinery, Niger Delta, Nigeria

Integrating electrical resistivity, geotechnical and geochemical techniques to assess soil and groundwater resources near Warri refinery, Niger Delta, Nigeria

Mapping the spatiotemporal evolution of seawater intrusion in the Moroccan coastal aquifer of Ghiss-Nekor using GIS-based modeling

The impact of seawater intrusion on coastal aquifers is a major concern in managing groundwater resources. The unconfined coastal aquifer of Ghiss-Nekor, located in a semi-arid area, is particularly vulnerable to seawater intrusion (SWI) because of excessive groundwater pumping and climate change impacts. Therefore, the main goal of the present work is to track the spatiotemporal evolution of SWI in the Ghiss-Nekor aquifer by analyzing data from the years 2015 and 2022 using appropriate geochemical approaches. Accordingly, a range of geochemical techniques were employed, including the Piper diagram, Chadha's diagram, Gibbs diagram, Stiff diagram, major ions variation maps, Hydrochemical Facies Evolution Diagrams (HFE-D), and seawater fraction (fsea). As a result, Gibbs diagram clearly indicates the contribution of seawater to the salinization of the Ghiss-Nekor aquifer. Further information is provided by the Piper, Chadha, and Stiff diagrams, which reveal that 29%–38% of the wells studied display Na–Cl water type, a characteristic feature of seawater facies. Additionally, statistical analysis shows a significant increase in salinity levels between 2015 and 2022. Furthermore, the spatiotemporal analysis using the differential mapping technique (DMT) confirmed the increase of salinity, particularly near the shoreline. Additionally, the HFE-D showed that the region impacted by SWI increased from 14% to 20% between 2015 and 2022, and the maximum fsea value rose from 14.84% to 25.77% over the same time frame. Our findings reinforce the assumption that SWI is worsening over time in the Ghiss-Nekor aquifer. In summary, the techniques used in this study were effective in tracking the spatiotemporal evolution of SWI in the aquifer and in quantifying it. The results of this study can inform the development of effective strategies for managing SWI in coastal aquifers.