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Copyright of Larhyss Journal is the property of Biskra University, Research Laboratory in Subterranean & Surface Hydraulics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Puebla State, Mexico, stands out with its diverse geological features, ranging from Precambrian and Paleozoic crystalline basements to the Pliocene-Quaternary major volcanoes. It is divided into three distinct regions: the northern region with its predominantly marine successions, where outcrops a volcano-sedimentary marine succession aged between 171.3 ± 0.5 Ma and 168.6 ± 0.4 Ma; the central region, part of the Trans-Mexican Volcanic Belt; and the southern region, mainly characterized by a multitude of continental units on crystalline basements.BULLETS:Geological regionalization, geological provinces, genetic-chronostratigraphic units, key successions tableGeological records contrast between the northern and southern regionsFirst report of Middle Jurassic marine volcano-sedimentary succession in the Sierra Madre Oriental Range

Copyright of EMERG: Energy. Environment. Efficiency. Resources. Globalization is the property of Romanian National Committee of World Energy Council and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Development of oil and gas deposits in fractured reservoirs entails certain risks due to peculiarities of geological structure. Classification and identification of fractures in reservoirs is of high-priority importance and makes it possible to assess the impact of both fractured systems and matrix blocks on field development parameters.This article presents the results of statistical and qualitative analysis of the influence of fracture systems and fracture heterogeneity to classify reservoirs in crystalline basement granitoids using the example of the White Tiger (Bach Ho) and Dragon (Rong) fields located on the southern shelf of the South China Sea (Viet Nam). Field classification of fractured reservoirs is based on a well-marked difference in parameters between wells within a field, due to fracture heterogeneity. In order to solve the tasks set, construction and analysis of graphs of well performance parameters distribution (productivity, flow rates, accumulated indicators, etc.) as well as Lorenz curves were carried out. According to the results, all the objects under study are characterized by asymmetrical shape of distribution curves, which indicates a significant influence of fracturing.Based on the calculated values of the fracture influence coefficient, it is found that fractured reservoirs in crystalline basement, as a first approximation, belong to type 2. This fact is inconsistent with the earlier works on crystalline basement, in which rocks are classified as reservoirs of type 1. Such contradiction is explained by the fact that the microfracture systems and the blocky low-permeability part exhibit matrix properties, but are not fully matrix. This part of the reservoir is proposed to be called a “pseudomatrix”. If macrocracks dominate in the section, the basement rocks are identified as type 1 fractured reservoirs, but if microfracture systems (“pseudo-matrix”) dominate in some parts of the void space, they may show the properties of type 2 reservoirs forming a mixed type of fractured reservoirs.

Despite several geological and geophysical studies that have focused on the estimation of the geometry of the sedimentary basins, the seismic documentation of sediment thickness is inadequately constrained due to the sparse spatial resolution of the expensive seismic and borehole measurements. To provide a new complementary insight into the morphology of the crystalline basement, I have re-examined the radially averaged power spectrum of magnetic anomalies for mapping depth to magnetic basement (DMB). DMB is a proxy of the non-magnetized sediment cover thickness over the magnetized crystalline basement. Synthetic models suggest that the accuracy of the method is not significantly influenced by the unknown magnetic fractal parameter and depth to the bottom of the magnetic slab. The windowing and window size effect on the estimated DMB can be substantial. Our synthetic tests suggest that the uncertainty of the calculated DMB increases with depth if the chosen window size is less than eight times the real DMB. I applied this method to the European, Greenland and North Atlantic regions because of the availability of seismically constrained sediment thickness or depth to the seismic basement (DSB), which allows comparison between DMB and DSB. The estimation of DMB was done by assuming a constant fractal parameter of three within a sliding window and with a variable size from 100 × 100 km in 10 km steps to a maximum size of 200 × 200 km until the estimated DMB is less than one eighth times of the window size. Comparison of DMB with DSB indicates a striking long-wavelength correlation along major sedimentary basins, while discrepancies may indicate limitations in the estimation methods for DMB and DSB. [ABSTRACT FROM AUTHOR]

Copyright of Mineralia Slovaca is the property of State Geological Institute of Dionyz Stur and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Puebla State, Mexico, stands out with its diverse geological features, ranging from Precambrian and Paleozoic crystalline basements to the Pliocene-Quaternary major volcanoes. It is divided into three distinct regions: the northern region with its predominantly marine successions, where outcrops a volcano-sedimentary marine succession aged between 171.3 ± 0.5 Ma and 168.6 ± 0.4 Ma; the central region, part of the Trans-Mexican Volcanic Belt; and the southern region, mainly characterized by a multitude of continental units on crystalline basements. BULLETS: Geological regionalization, geological provinces, genetic-chronostratigraphic units, key successions table Geological records contrast between the northern and southern regions First report of Middle Jurassic marine volcano-sedimentary succession in the Sierra Madre Oriental Range [ABSTRACT FROM AUTHOR]

Copyright of Instituto Superior de Correlacion Geologica, Serie Correlacion Geologica is the property of Instituto Superior de Correlacion Geologica (INSUGEO-CONICET) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydro‐geochemical characterization is challenging in dyke intruded complex geological setting. The comparison between self‐organizing map (SOM) classification and principal component analysis (PCA) is used for better understanding of hydrogeological process surrounding Amarpur dyke in Dhanbad district, Jharkhand. Total 30 water samples were collected and tested for 12 physicochemical parameters. The K‐means clustering with SOM grouped the water quality data into cluster 1 (46.67%, low mineralization), cluster 2 (36.67%, moderate mineralization) and cluster 3 (16.67%, high mineralization). The clusters of the majority of samples identified by PCA analysis is almost same as identified by SOM with little difficulty in discriminating between cluster 2 and cluster 3. The transformation of Ca‐HCO3 to Ca‐Cl‐SO4 occurred because of exchange of Ca2+ with Na+ adsorbed in the aquifer leading excess of sulphate ions. The results of this study suggest that SOM is an effective tool for a better understanding of patterns and processes driving water quality. [ABSTRACT FROM AUTHOR]

Globally, the largest geothermal resources are linked to the crystalline basement, which could be exploited using Enhanced Geothermal Systems (EGS). The planned underground laboratory GeoLaB aims to facilitate the large-scale application of EGS technologies by performing in-situ high-flowrate experiments on fault zones. The Tromm Granite at the northwestern margin of the Upper Rhine Graben was preselected as one of two potential sites for GeoLaB. To improve the understanding of the natural fault network in the target area, a drone-based aeromagnetic survey was conducted in March 2022, covering an area of about 13.3 km2 in the center of the pluton. A selection of eight filters to enhance the signal was tested against each other using a synthetic model. Based on this comparison, the tilt derivative appears to be the most reliable method for mapping and characterizing natural fault zones. The filtered aeromagnetic dataset reveals a network of linear anomalies interpreted as altered fault zones. The relative abundance of magnetic lineaments correlates broadly with slip tendency in the current stress field. Thus, the aeromagnetic may provide insights into the reactivation potential and deformation history of fault zones, which significantly influence the hydraulic properties. However, additional geophysical surveys or exploration wells are needed to validate the results. [ABSTRACT FROM AUTHOR]

The Sidi Ifni region in southwest Morocco is mainly composed of crystalline rocks with limited groundwater storage capacity. These water resources drain in particular fault zones with high fracture permeability. The main objective of this study is to describe the geological structure of the region to optimize future drilling locations. The gravity data were processed using various techniques, such as total horizontal gradient, tilt derivative, and Euler deconvolution, in conjunction with the interpretation of the geological data, to create a new structural map. This map confirms the presence of many previously identified or inferred faults and identifies significant new faults with their respective trends and depths. Analysis of this map shows that major faults are oriented NNE-SSW and NE-SW, while minor faults are oriented E-W, NW-SE, and NNW-SSE. The superposition of the hydrogeological data and the structural map reveals that the high groundwater flow values in the boreholes are located in the vicinity of the major faults and talwegs. The structures deduced from the filtering and interpretation of the gravity data suggest that the hydrogeological system of the Ifni Inlier is controlled by its structures. To confirm this impact, a high-resolution electrical resistivity map (7200 Hz) was used, with penetration depths ranging from 84 to 187 m. Negative boreholes, located in high resistivity ranges corresponding to sound basement formations without fault crossings, showed high resistivity values. The positive holes, located in anomalies with low linear resistivity, revealed the impact of fault crossings, which drain water and tend to decrease the resistivity values of the formations. Therefore, these new structural maps will assist in planning future hydrogeological studies in this area. [ABSTRACT FROM AUTHOR]

The Sichuan basin, located adjacent to the eastern margin of the Tibetan Plateau, serves as an ideal marker for testing the extrusion process of the plateau. The basin is seismically active, with the strongest earthquake, the 2008 Mw 7.9 Wenchuan earthquake, occurring in the Longmen Shan range along its northwestern edge. A new regional compilation of focal mechanism solutions of earthquakes in and surrounding the basin reveals that a large fraction of the events have focal depths ranging between 8 and 25 km, corresponding to the crystalline basement of the basin. Seismic deformation involves right‐lateral oblique reverse faults, mostly trending northeast–southwest, similar to the kinematics of the mainshock of the Wenchuan earthquake. Shallow earthquakes (3–8 km) suggest that some of the seismic faults rupturing the crystalline basement are growing toward the surface. To the southwest, the seismicity transitions to activity along the left‐lateral Xianshuihe–Xiaojiang fault zone. The spatial relationship between these two sets of fault zones is consistent with a model in which the Sichuan basin responds to the southeast extrusion of the Chuan‐Dian block at the southeast margin of the plateau by a counterclockwise bookshelf rotation of the crystalline basement. This deformation pattern initiated ∼4–2 Ma, as shown by the age of the Xiaojiang fault segment. The history of left‐lateral movement along the Xianshuihe‐Xiaojiang fault can be traced back to ∼12 Ma when the eastward growth of the Tibetan Plateau resulted in the shortening of both the Longmen Shan thrust belt and the sedimentary over the Sichuan basin. Plain Language Summary: This Sichuan basin bounds the Tibetan Plateau on the east. A catastrophic earthquake (Mw 7.9) occurred along its boundary in 2008. However, the driving mechanism for this earthquake remains debated. We combine geologic and seismic studies to elucidate the origin of tectonic and seismic activity in the basin. By interpreting the focal mechanism solutions of basin‐internal earthquakes and the surface deformation, and considering the timing of the plateau's extrusion, we propose that the Sichuan basin experienced two stages of counterclockwise rotation in response to the southeastward extrusion of the plateau. The early stage, occurring at ∼12 Ma, involved deformation of the sedimentary cover, while the late stage, initiated ∼4–2 Ma, involved bookshelf rotation of the crystalline basement of the basin. Key Points: The seismicity of the Sichuan basin is restricted to a depth range of 8–25 km, dominated by the counterclockwise rotation of the basementThe internal deformation is attributed to the southeastward extrusion of the Chuan‐Dian block along the Xianshuihe‐Xiaojiang faultThe rotation history of the Sichuan basin initiated 12 and 4–2 Ma, involving the sedimentary cover and bookshelf rotation of the basement [ABSTRACT FROM AUTHOR]

The present work focuses on the volcanic basement rock geochemistry of Mount Makabaï (Maroua-Cameroon city) in relation to groundwater geochemistry. Investigations were centered on an approach involving an association of several methods such as geological cartography, hydrogeology, and geochemistry. Three rock samples, four disturbed soil samples, three undisturbed soil samples, and 20 samples of groundwater in 10 wells were collected during fieldwork and prepared for laboratory analyses. Bedrocks exhibit porphyritic, aphyric, and sub-aphiric textures. The phenocryst phases are mainly olivine, clinopyroxene, and plagioclase. Based on whole rock major element chemical compositions, the Makabaï samples, plotted on Na2O + K2O versus SiO2 diagram, are mugearite, hawaiite, and basalt. The ratio of (MgO + CaO)/(Na2O + K2O) exceeds unity and shows dominance of alkaline Earth metals (MgO: 2.99–4.48 %; CaO: 6.19–9.80 %) relatively to alkali metals (Na2O: 2.27–4.46 %; K2O: 2.09–2.51 %). Exchangeable base contents are high, mostly represented by Ca and Mg, whose contents vary from 14.6 to 35.28 cmol(+) kg−1 and from 3.28 to 9.48 cmol(+) kg−1 respectively. The CECclay is likewise high, fluctuating between 116.80 and 181.38 cmol(+) kg−1, values in line with the presence of 2:1 clay minerals represented in the study area by montmorillonite. In the water samples, the Ca2+ and Na+ contents are generally higher than K+ and Mg2+, reflecting the relative abundance of Na2O and CaO oxides to K2O and MgO oxides in rocks where different waters were sampled. The waters of Makabaï are acidic to neutral (6.3 ≤ pH ≤ 7.4) and weakly to highly mineralized (110.0 ≤ EC ≤ 1190.0 µS/cm). Hydro-geochemical classification by using the Piper diagram revealed two water types: (1) CaMg–HCO3 (40%) and (2) CaMg–Cl or CaMg–SO4 (60%). The average content of ions in all the analyzed samples was HCO3− ≫ NO3− > SO42− > Cl− for anions and Ca2+ ≫ Mg2+ > Na+ > K+ for cations. Major mechanisms governing ionic constituents of groundwater in the study area are water–rock interactions, silicate weathering, and ion exchange. [ABSTRACT FROM AUTHOR]

The trace element composition of bitumoids extracted from Archean crystalline basement rocks uncovered by the 20009-Novolkhovskaya borehole was studied. It was established that the rocks of the Bolshechermshanskaya series are characterized by a higher content of hydrocarbons in comparison with those of the Otradnenskaya series. The trace element composition was examined separately in chloroform and alcohol-benzene extracts. The rocks of the Bolshechermshanskaya series contain organic matter in higher amounts. Bitumoids extracted from the rocks of the Otradnenskaya series are characterized by higher concentrations of trace elements. [ABSTRACT FROM AUTHOR]

The Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province, located in the southwestern margin of the Yangtze Block, is the most intensively developed region of carbonate-hosted Pb-Zn deposits in China. Both the number of Pb-Zn deposits/spots (more than 500) and the amount of Pb and Zn metal reserves(more than 2000×104 t)play an important role in the Pb-Zn metallogenic regions/belts of China. Although the previous research has made fruitful theoretical understanding and prospecting achievements, there has been a dispute on the source of ore-forming materials of the Pb-Zn deposits in the study area. A systematic In-situ Pb isotope analysis of galena from nine Pb-Zn deposits hosted in the Sinian(Wusihe, Chipu, Yinchanggou and Maozu deposits), Devonian (Huodehong, Maoping and Maozachang deposits) and Carboniferous(Maoping, Huize, Liangyan and Maozachang deposits)carbonate rocks was carried out. The results show that ① the In-situ Pb isotopes of galena in all deposits have an obvious linear relationship, and their Pb-Pb isochron age is about 2.5 Ga ((2 574±30)Ma); it is suggested that the sources of ore-forming metals for these deposits are the same, and the Archean-Paleoproterozoic crystalline basement rocks are the most likely major metal source; ② in the age of ore-bearing strata, the Pb isotopes gradually increase from the old (Sinian) to the new (Carboniferous); in the space of ore-bearing horizon, the Pb isotopes gradually increase from Wusihe, Chipu deposits in N(W) to Maozachang, Liangyan deposits in S(E); it is indicated that they are the evolvement products of the same ore-forming fluids in different stages, and the crystalline basement-derived and/or flowed ore-forming fluids evolve and migrate from deep to shallow, and from N(W)to S(E)on a regional scale. [ABSTRACT FROM AUTHOR]

Abstract Drilling of the Gotthard Rail Base Tunnel through the Central Alps from 2005 to 2010 opened up fractured basement units and frequent water inflows provided access to the major fluid-rock interactions processes in orogenic crystalline upper crust. Construction of the 57 km long tunnel was divided into five different sections. Here we report data and observations from the 10 km long central Sedrun section 211 water samples were collected at inflow points 900 to 2350 m below the surface. The exceptional samples and data provide a comprehension of the hydrochemical evolution and solute acquisition of deep groundwater in basement units. The investigated tunnel section drilled through steeply dipping rock units and vertical fracture systems at high angle. It cuts across granite, gneiss and schist of the pre-Alpine basement and across two narrow zones of meta-sediments. Rock temperature along the Sedrun section varies from 30 to 45 °C depending on the thickness of the overburden. The fracture water is of meteoric origin and acquires its composition exclusively by chemical interaction with the surrounding rocks along the flow path. Water from inflow points in the basement of the Gotthard Massif has typically a high pH of about 10 and total dissolved solids in the range of 100 to 300 mg L−1. Sodium is the prime cation of most waters. Although plentiful in the rocks, calcium, potassium and magnesium are low to very low in water. The anions associated with Na are carbonate/bicarbonate, sulfate, fluoride and chloride in widely varying proportions. High fluoride concentrations of up to 15.4 mg L−1 are characteristic for most waters. As a result of the high pH dissolved silica (SiO2) reached concentrations of up to 58 mg L−1 and represents 25—30 wt% of the solutes. The meteoric recharge provides dissolved O2 and CO2 to the fluid-rock interaction processes. The solutes derive from the dissolution of feldspar (Na+, SiO2aq), oxidation of sulfides to sulfate (SO4 2−), alteration of biotite (F−), and fluid inclusions opened by brittle deformation (Cl−). The solids formed during fluid-rock interaction, mainly zeolites, chlorite (and other clay minerals) and secondary Fe-minerals, remove Mg, Fe, and K almost quantitatively from the water. The high pH results from hydrolysis of silicates. The data distinctly show that within the depth interval of 1.0–2.5 km below surface deep water in continental basement evolves to a low TDS, high pH, sodium carbonate and silica solution by interaction of gneiss and granite with infiltrating pristine meteoric water, snow and rain.

Deep geothermal energy represents an essential component of the future energy supply because the resources greatly exceed the demand, and the base load capability can compensate for temporal fluctuations in wind and solar power. By far, the largest amount of heat is contained in the crystalline basement, accessible almost everywhere through deep drilling. An interdisciplinary approach for a techno-economic resource assessment was applied to provide stakeholders with a more reliable basis for decision-making in the Northern Upper Rhine Graben. This approach incorporated data from various sources such as boreholes, outcrops, geophysical surveys, geomechanical models, and operating geothermal power plants. Emphasis was placed on resources tied to large-scale fault zones, exhibiting preferential hydraulic properties. Uncertainties in the calculations were quantified using Monte Carlo simulations. The resource base in the basement of the Northern Upper Rhine Graben is about 830 PWhth, of which about 8.2–16.1 PWhth could potentially be extracted with current technologies in enhanced geothermal systems. A comprehensive sensitivity analysis was carried out, examining the economic influence of nine parameters. Considering the reference power plant and the energy prices before the Ukraine war began in February 2022, the geothermal reserves are about 65% of the resources. However, given the massive recent increase in heat and electricity prices, a higher percentage is also possible. Finally, a socio-economic-environmental assessment shows that in the Northern Upper Rhine Graben, geothermal resources largely coincide with favorable conditions at the surface, making the region a preferred target for geothermal utilization. [ABSTRACT FROM AUTHOR]

Copyright of Anuario do Instituto de Geociencias is the property of Universidade Federal do Rio de Janeiro, Instituto de Geociencias and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on remote sensing, geographical information system, multi-criteria decision making and field survey, the map of groundwater potential index (GwPI) in the Centre region of Cameroon, characterised by a crystalline basement, covered by saprolite and pedolith units has been elaborated by overlapping groundwater availability, exploitability and accessibility indicator maps, using eight parameters as slopes, drainage density, lineament density, hydraulic conductivity, static levels, pumping flow rate, drilling depth and altitude, respectively. The achieved data highlight that 68% of the study area of Lekié Division (Centre Region, Cameroon) is characterized by zone with moderate/good GwPI. In these zones, the surface water infiltration and aquifers recharge are promoted by weak slope and fine lineaments density. The borehole depth ranges from 20 to 40 m and the static level is shallow (< 6 m). Consequently, for the 68% of the study area, the rate to drill positive boreholes is high, the groundwater exploitation is favourable, and the lens-shaped aquifer are bounded by gently morphological paleo-depressions of the crystalline basement, playing the role of aquiclude. In the 23.73% of the total area, characterized by poor/fair GwPI, the steepness of the slope favours runoff while the density of coarse lineaments reduces infiltration and aquifer recharge. The boreholes and the static level are deeper than 40–60 m and 10–15 m respectively, while the pumping rate is low. Consequently, the rate of positive drilling in these areas is low and groundwater exploitation is unfavourable. It cannot be excluded that for the 23.73% of the total area, groundwater is stored in scattered deep morphotectonic depressions, probably corresponding to paleo-shear zones of the crystalline basement, acting as aquifers. In summary, by saving time and costs, all the thematic maps developed allow the identification of areas where drilling and groundwater exploitation are favourable, and areas where hydrogeological and resistivity studies are mandatory before drilling. These maps can therefore be powerful tools for local authorities to optimise human and financial resources in aquifer and groundwater exploitation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study is to determine the variation of soil-gas radon concentrations from different rock formations in Ogbomoso, southwestern Nigeria. The radon concentrations at different five geological domains in Ogbomoso are determined with respect to depth. The measurements varied from the surface (0 cm) to 100 cm depth, with an interval of 20 cm. At all the geological domains (Porphyroclastic, Granite, Quartzite, Migmatite and Banded gneiss), radon has its minimum emission over migmatite at 0 cm, while its maximum emissions occured over granite and banded gneiss at 80 cm. The overall soil-gas radon concentrations in Ogbomoso varied from 0.06 to 26.5 kBq/m3, which is within the natural limit of 0.4 to 40 kBq/m3 based on the International Commission on Radiological Protection's recommendation. An F-ratio of 6.989 and a p-value of 0.001 were obtained for the first inferential hypothesis, while an F-ratio of 2.489 and a p-value of 0.076 were obtained for the second inferential hypothesis using ANOVA test. The post hoc (using Tukey HSD and Duncan) tests revealed that at 60 + cm, depth controls the level of radon concentrations being emanated from the subsurface. The pollution index in Ogbomoso is of level 1 at 80 cm and level 0 (safe limit) at other depths. In conclusion, the soil-gas radon emission depends on the local geology and lithological sequences (depths). Cracks that could act as passage for indoor radon at the floors of the buildings around the polluted zones should be avoided in order to have a sustainable city. [ABSTRACT FROM AUTHOR]

The gravitational and magnetic fields of the eastern Aldan anteclise, within the area bounded by longitudes 126° and 138° E and latitudes 58° and 64° N, are analyzed; seismic data along the 3-DV Tommot‒Khandyga reference profile are also considered in order to identify structural features of the Early Precambrian consolidated crust and to assess the diamond potential of the territory. It is shown that the crystalline basement is divided by the Uchur crustal‒mantle fault into the Paleoproterozoic Aldan granulite–gneiss belt and the Archean Batomga granite–greenstone zone; the southern segments of these structures were studied within the Aldan–Stanovoy shield. The formation processes of the Aldan granulite–gneiss belt in the Paleoproterozoic contributed to thickening of its crust (to 50–52 km) compared to the Archean Batomga granite–greenstone region (42–45 km). The Khompu–Maya kimberlite field with the Tuymada pipe is confined to the Bestyakh block of the Batomga granite–greenstone zone. The main regional criteria for the diamond potential of the identified subprovince in the northeast Aldan anteclise include: (i) the presence of a lithospheric root up to 220 km thick, (ii) the granite–greenstone type of the Earth's crust, and (iii) low heat flow values. [ABSTRACT FROM AUTHOR]

The present study investigates geological structures in parts of the crystalline basement and the adjoining middle Niger Basin of Nigeria using high-resolution airborne magnetic and radiometric data. The purpose is to provide additional insights into the contrasting structures of the magnetic basement within the crystalline and the sedimentary terrain. The magnetic and radiometric data of the study area were subjected to standard interpretation techniques. The results obtained showed the entire crystalline basement to be overprinted by younger igneous rocks at extremely shallow depths. The sedimentary basin on the other hand is marked by basement subsidence and volcanic intrusions. Two major shear zones traverse the crystalline basement and the adjoining sedimentary basin. The shear zones cross-cut the entire study area in a NNE direction and exhibit three major dipping contacts, namely, vertical-, north-western- and south-eastern-dipping contacts in specific locations. The shear zones exhibit multiple surface faults mostly within the crystalline basement and are characterized by linear magnetic highs that indicate magnetic minerals precipitate in specific areas. Some parts are characterized by a low-amplitude magnetic anomaly that coincides with high potassium and fairly low thorium concentrations that indicate the presence of younger volcanic rocks and possibly gold mineralization in the shear planes. The zones are parallel to the trans-current Ifewara–Kalangai–Zungeru shear zone already linked to the South Atlantic transform fault system. The structural architecture of the study area and perhaps the entire basement complex displayed a positive prospect for economic minerals in specific locations. [ABSTRACT FROM AUTHOR]

Purpose. Based on the analysis of existing information on the exertions of oil and gas in crystalline rocks of the Dnieper-Donets Basin (DDB), assess the presence of hydrocarbon deposits in certain fields and assess the prospects for the discovery of new ones. Methodology. The study on oil and gas bearing capacity of the crystalline basement was based on the analysis of stock material on oil and gas fields of the Dnieper-Donets Basin, the study on petrographic composition of rocks in sections, analysis of results of well logging, petrophysical studies on rock samples from promising intervals of wells. The peculiarities of the structure of structural-tectonic models of hydrocarbon deposits with oil and gas exertions in the upper parts of the crystalline basement were also taken into account. Findings. A significant number of drilling and well testing results, lithological-petrographic and petrophysical studies were analyzed, which allowed making objective conclusions about the existence of independent oil or gas deposits in the weathering crust of the crystalline basement at already known deposits. The conclusions also concerned the assessment of the industrial (commercial) attractiveness of the discovered deposits or oil and gas exertions in the upper parts of the crystalline basement of the DDB fields. Originality. At the current level of study, it can be argued that within the Eastern Ukrainian oil and gas basin in the Archean-Proterozoic traps apart from the basal horizons of the cover, oil deposits were found in only three fields: Yuliivske, Ulianivske and Hannivske. Undoubtedly, there are hydrocarbon deposits in the Precambrian formations of DDB, but the most extensive discoveries in this direction of exploration and involvement in the development of already discovered accumulations seem to be still ahead. The geological situation should be realistically assessed for the presence of potential areas where the existence of common hydrocarbon deposits in the weathering crust of the foundation and the lower horizons of the sedimentary cover in the DDB is possible. Practical value. The main value of this study is the real assessment of the existence of industrial accumulations of hydrocarbons in already discovered oil and gas fields in DDB. The myth of the presence of many oil and gas deposits in DDB in crystalline rocks of the crystalline basement, which without proper justification has repeatedly been found in the professional literature and in scientific reports at specialized conferences of various levels, has been debunked. Certain prospects for the discovery of oil and gas deposits in the crystalline basement of the Dnieper-Donets Basin are unmarked. [ABSTRACT FROM AUTHOR]

In the Earth studies, discoveries and investigations of impact craters buried beneath thick sediments are sporadic so far and may still remain inefficient, unless geophysical surveys of the areas of interest are initiated. Such studies can provide useful data to develop the knowledge about cosmic events of the past geological eras, as well as contribute to industrial development of the areas. It is known that an impact crater is filled with layered deposits that create specific sequences and are generally thicker that deposits outside the crater. We have investigated a Precambrian crater located in the southern part of the Nepa-Botuoba anteclise of the Siberian platform. This impact crater called Nepsky-1 was discovered by seismic surveys using the common depth point method (CDPM). In our study, we used the geological and geophysical deep-drilling data of three wells, including gamma-ray and neutron logs and lithological core descriptions. With reference to the concepts of regional geological conditions, we reconstructed the conditions of sedimentation in the study area based on a comprehensive analysis of the structural and textural features of the rocks, and logging and seismic survey data. By processing and interpretation of the CDPM 3D seismic survey data, we obtained the structural images and cross-sections of the impact crater and analysed the thickness of its fill deposits. The Nepsky-1 crater is a bowl-shaped structure with a rim composed of allogenic breccia. In the area around the crater, fault systems are detected. Based on the core sample analysis, we identified the lithological members of the crater and its rim and described them in detail. Active compensation with lacustrine-delta sediments took place in the Nepa period of the late Vendian. By the end of the Tira time, the crater was completely leveled up. In our study, we obtained the first data on the structure of the crater section of the Vendian deposits. Sedimentation in the study area was controlled by the sea level changes. The main terrigenous productive horizons are confined to sandstones that accumulated during the sea level low stand, and found at the bottoms of the lower and upper Nepa subsuites, as well as at the bottoms of the lower and upper Tira subsuites. It is established that the study area was tectonically active in the late Tira time. As a result, the sediments filling the crater were removed to subaerial conditions, and the edges of the allogenic breccia rim were partially destroyed and formed granite breccia outgrowths observed in the rim’s cross-section. We conclude that in the Nepa and Tira times, tectonic vertical movements initiated relatively fast weathering and transportation of the terrigenous material from the adjacent hills into the sedimentation basin. The Nepsky-1 crater gives evidence of meteorite bombing of the Siberian paleocontinent in Precambrian. Finding similar crater structures can be reasonably expected in the study region. Considering the increased thicknesses of crater fill deposits, buried craters are promising potential for discovering oil-source and overlying seal rocks, which is important for petroleum industry.

Energy independence is an important component of sustainable development and security of the state. Ukraine has a great hydrocarbon potential of the subsoil, which is why the priority objective is a search and exploration of new deposits of hydrocarbon raw materials. One of the important directions for increase of potential resources and reserves of oil and gas is the development of large deep (over 4500–5000 m) deposits, as hydrocarbon reserves at small and medium depths are quite depleted in many regions. For a long time, hydrocarbon reservoirs in basement rocks were underestimated during geological exploration works. Obtained results indicate that new concepts of the formation of hydrocarbon deposits can dramatically change the system of oil production, methods of prospecting and development of deposits. It is important to assess possible oil-and-gas-bearing capacity of sediments and rocks of the basement by identifying prospective areas of hydrocarbon deposits, including in the rocks of the crystalline basement. In Ukraine, main prospects of discovery of oil and gas deposits at great depths are associated nowadays with the Dnieper-Donets Rift (DDR). Deposits with accumulations of hydrocarbons at depths of more than 5000 m are concentrated in the main oil-and-gas-bearing areas of the Rift that coincide with the central paraxial and marginal zones of the graben. It was in the central segment of the DDR that the main regularities of oil-and-gas-bearing capacity of deep-lying geological formations were first discovered: secondary nature of reservoirs, discovery of the phenomenon of supercollectors and associated huge debits. It is relevant and promising to study the process of recovery/replenishment of gas reserves by the example of deposits that are at the final stage of development.

Oil and gas occurs in basement reservoirs in many parts of the world. The reserves of basement fields are as small as one or two million barrels of oil or gas-equivalent such as the Beruk Northeast pool in Sumatra, Indonesia to over 1.0 billion barrels of oil as in Viet Nam’s Bach Ho field and Libya’s Augila-Naafora field. This paper focuses on three giant-size oil and gas fields and six major-size fields. Exploration for oil and gas in basement has been remarkably successful in the past decade with important discoveries in basement in Indonesia, United Kingdom, Norway, Chad, and Argentina. In order to successfully develop basement oil and gas fields and also to avoid costly mistakes, all available geological, geophysical, reservoir engineering and economic data must be closely studied. Also, it is very important to study analogues worldwide of basement oil and gas fields in order to understand why some fields are very successful and others turn out to be technical and economic failures.

The Sidi Ifni region in southwest Morocco is mainly composed of crystalline rocks with limited groundwater storage capacity. These water resources drain in particular fault zones with high fracture permeability. The main objective of this study is to describe the geological structure of the region to optimize future drilling locations. The gravity data were processed using various techniques, such as total horizontal gradient, tilt derivative, and Euler deconvolution, in conjunction with the interpretation of the geological data, to create a new structural map. This map confirms the presence of many previously identified or inferred faults and identifies significant new faults with their respective trends and depths. Analysis of this map shows that major faults are oriented NNE-SSW and NE-SW, while minor faults are oriented E-W, NW-SE, and NNW-SSE. The superposition of the hydrogeological data and the structural map reveals that the high groundwater flow values in the boreholes are located in the vicinity of the major faults and talwegs. The structures deduced from the filtering and interpretation of the gravity data suggest that the hydrogeological system of the Ifni Inlier is controlled by its structures. To confirm this impact, a high-resolution electrical resistivity map (7200 Hz) was used, with penetration depths ranging from 84 to 187 m. Negative boreholes, located in high resistivity ranges corresponding to sound basement formations without fault crossings, showed high resistivity values. The positive holes, located in anomalies with low linear resistivity, revealed the impact of fault crossings, which drain water and tend to decrease the resistivity values of the formations. Therefore, these new structural maps will assist in planning future hydrogeological studies in this area.

Drilling of the Gotthard Rail Base Tunnel through the Central Alps from 2005 to 2010 opened up fractured basement units and frequent water inflows provided access to the major fluid-rock interactions processes in orogenic crystalline upper crust. Construction of the 57 km long tunnel was divided into five different sections. Here we report data and observations from the 10 km long central Sedrun section 211 water samples were collected at inflow points 900 to 2350 m below the surface. The exceptional samples and data provide a comprehension of the hydrochemical evolution and solute acquisition of deep groundwater in basement units. The investigated tunnel section drilled through steeply dipping rock units and vertical fracture systems at high angle. It cuts across granite, gneiss and schist of the pre-Alpine basement and across two narrow zones of meta-sediments. Rock temperature along the Sedrun section varies from 30 to 45 °C depending on the thickness of the overburden. The fracture water is of meteoric origin and acquires its composition exclusively by chemical interaction with the surrounding rocks along the flow path. Water from inflow points in the basement of the Gotthard Massif has typically a high pH of about 10 and total dissolved solids in the range of 100 to 300 mg L−1. Sodium is the prime cation of most waters. Although plentiful in the rocks, calcium, potassium and magnesium are low to very low in water. The anions associated with Na are carbonate/bicarbonate, sulfate, fluoride and chloride in widely varying proportions. High fluoride concentrations of up to 15.4 mg L−1 are characteristic for most waters. As a result of the high pH dissolved silica (SiO2) reached concentrations of up to 58 mg L−1 and represents 25—30 wt% of the solutes. The meteoric recharge provides dissolved O2 and CO2 to the fluid-rock interaction processes. The solutes derive from the dissolution of feldspar (Na+, SiO2aq), oxidation of sulfides to sulfate (SO42−), alteration of biotite (F−), and fluid inclusions opened by brittle deformation (Cl−). The solids formed during fluid-rock interaction, mainly zeolites, chlorite (and other clay minerals) and secondary Fe-minerals, remove Mg, Fe, and K almost quantitatively from the water. The high pH results from hydrolysis of silicates. The data distinctly show that within the depth interval of 1.0–2.5 km below surface deep water in continental basement evolves to a low TDS, high pH, sodium carbonate and silica solution by interaction of gneiss and granite with infiltrating pristine meteoric water, snow and rain. [ABSTRACT FROM AUTHOR]

Crystalline basement and Precambrian crustal growth of the continental massifs within the Central Asian Orogenic Belt (CAOB) are still pending problems. Our geological and geochemical investigations identified an Archean (2606 Ma) granitic pluton in the Biliya area of the Erguna Massif. The Neoarchean granitoids show high and positive in‐situ zircon ∊Hf(t) (+0.3 to +10.0), whole‐rock ∊Nd(t) (+4.8) and whole‐rock ∊Hf(t) values (+2.1). They are characterized by high Y + Ce + Zr + Nb (> 220 ppm) and Zr contents and could be classified as A‐type granites. These granitoids are characterized by high Zr saturation temperatures (TZr) (796–836°C). They were derived from partial re‐melting of juvenile mafic lower crust in an intracontinental back‐arc extensional environment. This newly identified Neoarchean granitic pluton may represent the crystalline basement of the several continent massifs within the CAOB, and their high ∊Hf(t)–∊Nd(t) values may also indicate the occurrence of lateral crustal growth events in these massifs during the Neoarchean. [ABSTRACT FROM AUTHOR]

The article demonstrates that the placer gold content of the Vilyui Syneclise is governed by the regional structure of the crystalline basement of the Siberian Platform—the Baikal–Vilyui Paleoproterozoic belt, the boundaries and tectonics of which are substantiated by analysis of the gravitational field structure. The belt includes a system of basement blocks with a common northeastern strike, which form horsts (of the Suntar type) and grabens (of the Kempendyai type). The gold-bearing placers of the Vilyui Syneclise are mainly confined to the Suntar, Tyukyan, and Chybyda blocks of the belt, the metamorphic and igneous rocks of which were the primary gold sources in the sedimentary cover. The suture zone of the Baikal–Vilyui belt was very permeable to deep fluids responsible for gold migration. The types of possible primary gold sources (gold–platinoid, low-sulfidation gold-quartz, and gold–silver) reflect the peculiarities in the evolution of Early Precambrian gold during sedimentation in the Vilyui Syneclise. The areas controlled by the Suntar, Kempendyai, Tyukyan, Chybyda, and Khapchagai blocks of Early Precambrian rocks, which may contain gold objects, should be considered promising for buried gold placers in the Vilyui Syneclise. [ABSTRACT FROM AUTHOR]

Basement rocks are important oil and gas reservoirs in a number of basins in the world. The basement oil and gas play has intensified in the past decade with significant basement discoveries. This paper provides a technical review of select basement oil and gas fields in Asia, Africa and the Americas. “Best practices” for exploring and developing basement fields are reviewed. Failures are also considered since basement reservoirs can be very complicated and unpredictable. Preference scale for basement reservoir rock types is presented. The opinion of this author is that the best rock types are fractured quartzites or granites since they are brittle and thus fracture optimally. Based on international experience, recommendations on the study of crystalline basement for oil and gas and the development of deposits in it are given.

The history of studying the crystalline basement in the Republic of Tatarstan, the state of implementation of the super-deep drilling program is given. The scientific substantiation of the replenishment of exploited oil and oil-gas fields is provided by feeding them with deep hydrocarbons through oil supply channels connecting the deep source of hydrocarbons with sedimentary cover deposits. The crystalline basement is of interest for the search for hydrocarbon deposits, but its role as a transit for replenishing deposits of hydrocarbon sedimentary cover in the process of constant degassing of the Earth is more attractive and justified. To use these processes, a fundamentally new approach to the construction of geological and hydrodynamic models of oil fields is proposed, taking into account the fundamental principles of geological science on the formation and reformation of oil deposits and the deep processes of Earth degassing. Prospects are substantiated for the development of “old” fields that are in long-term development, for the calculation of oil recovery factor taking into account oil entering the reservoir from the depths of the Earth, the need for adjusting methods for calculating and accounting reserves, changing levels of material balance, and scientific and practical suggestions for accounting when calculating reserves and designing the development of fundamental principles of field geology. Further prospects for the introduction of hydrodynamic development methods and their significant expansion due to the opening of the processes of replenishment of sedimentary basin deposits with deep hydrocarbons and the reformation of deposits at a late stage of development are shown.

In this communication, from the perspective of modern views, the following issues are highlighted. A brief overview of the regions – large oil and gas bearing basins, in which hydrocarbon deposits are currently being developed in the deposits of the crystalline basement, is given. The problems of non-anticline-type collector traps, usually non-structural, combined, widely developed in basement deposits, are considered. The existing characteristic features of oils in deposits from a crystalline basement are voiced. As a result of the study, ever-increasing volumes of world oil production from base sediments were noted, the difficulty of identifying and classifying traps in it, and the almost lack of originality of the composition of oils in the foundation compared with oils in the overlying or adjacent parts of the sedimentary section, are shown.

Abstract Weathered and fractured crystalline basement is known as the important unconventional reservoir in the Cuu Long Basin. Naturally fractured reservoir plays a crucial role in oil exploration to contribute for hydrocarbon production in Vietnam. However, the complexity and heterogeneity of the fractures system in the basement reservoir are challenges for oil and gas production. They require the realistic simulation scenarios to estimate the hydrocarbon potential as well as field development plan of these reservoirs. Thus, this paper aims to propose the feasibility development scenarios to improve oil recovery factor for crystalline basement reservoir, X field, Cuu Long Basin, Vietnam. First, history matching process is validated for the model to fit the actual production data (reservoir pressure, pressure, water cut in each well) in order to approach closer the fluid flow behavior through the reservoir. The manual matching was selected to adjust the actual aquifer size and permeability distribution with limit simulation runs. Next, the highest reliability matching model which approximately reflects the actual fluid flow behavior can be used as the base case to forecast the future reservoir performance through the field development plan. The most potential scenario is to add six new infill production wells, two side track wells and two water injection wells. The forecasted results indicate that this scenario yields 8% more oil recovery factor compared to the natural drive with thirteen producers. This result suggests that the precise field development plan is to increase the efficiency of the production process by increasing the displacement parameters of residual oil and reservoir sweep efficiency by stimulation. The major contribution of this paper demonstrates the merits of the field development plan in fractured basement reservoir. The findings of this study can help better understand the fluid flow behavior using the production history profiles and field development scenarios of crystalline basement reservoir of Cuu Long Basin.

Abstract The bedrock of Skåne, the southernmost province of Sweden, has been targeted for geothermal feasibility studies since the late 1970s. An exploration project concerning the geothermal potential in the Romeleåsen Fault Zone was launched outside the town of Lund in 2001. Besides geophysical imaging of the thrust fault zone, the investigations included drilling and investigations of a 3701.8-m-deep exploration well, DGE-1, with the aim to find > 100 °C warm and hydraulically conductive fractured crystalline bedrock associated to the fault zone. The well penetrates a heavily thrusted and predominantly strongly inclined sedimentary succession in hanging rock blocks along the main fault before entering the fractured crystalline basement at 1946 m, primarily composed of gneiss, granite, and metabasite. This paper represents the first comprehensive description and evaluation of the geological, physical, and hydrological properties of the bedrock at these depths in the Romeleåsen Fault Zone coupled to a geothermal assessment. In addition, the applicability of the four drilling methods used in the crystalline basement section is discussed. The outcome of the DGE-1 well shows significant fracturing in the crystalline bedrock at target depth. The investigations show an average thermal gradient of 22 °C/km, an average heat flow of 58 mW/m2, and an average heat production of 5.8 µW/m3. The values are relatively high in comparison to thermal conditions noted in other deep wells in the Fennoscandian Shield. However, a bottomhole temperature of around 85 °C and insufficient fluid production rate made a commercial geothermal system unviable. Despite this, the experiences from drilling and investigations of the crystalline bedrock at several kilometers depth constitute important proxies for assessing the geothermal potential in similar geological settings and for engineered geothermal systems in the crystalline bedrock of south Sweden.

Abstract Injection‐induced seismicity across the US midcontinent has almost exclusively occurred in the crystalline basement that underlies the Arbuckle Group aquifer and its equivalents, the primary wastewater disposal zone in this region. However, the properties of the basement are not well known. Newly compiled data, from Class I wells in Kansas, provide a unique record of pressures in the Arbuckle and an opportunity to constrain the reservoir‐scale properties of the basement such as permeability, diffusivity, and specific storage. Constraints on these parameters are critical for modeling fluid flow and pressures across the entire Arbuckle‐basement system, and are necessary for accurate evaluation and prediction of injection‐induced earthquakes. Here, we present a detailed, three‐dimensional geological and pressure history‐matched numerical model for the Arbuckle and basement, based on data from >400 wells covering a large region in south‐central Kansas, where injection‐induced seismicity has been concentrated since 2014. Simulations of dynamic data from 319 wells indicate that Arbuckle pressures have increased by 1.1 MPa in high injection rate areas and an overpressure of

This study aims to compare hydrological processes in the Liptako-Gourma crystalline basement and the Iullemeden sedimentary zone in Western Niger. These two sites were equipped to quantify water infiltration, runoff and water retention within the beds of the ravines. We found that for the same surface type, while hydraulic conductivity was similar in both sites, surface runoff was 15–50% higher in the crystalline site compared to the sedimentary site. Within the sedimentary basin, we assume that runoff mainly originated from the tiger bush (typical vegetation and bare soil stripes found on plateaus). We suggest that the main reason for differences in stream flow was the stream storage capacity, which was four-fold higher in the sedimentary area compared to the crystalline domain. We thus conclude that the crystalline area functions as a water production and draining zone whereas the sedimentary basin is an accumulator of this resource. [ABSTRACT FROM AUTHOR]

Here we report U-Pb zircon age data, obtained using LA-ICP-MS, from a total of 14 rocks of the Pass and Elbrus sub-zones of the Main Range Zone of the Greater Caucasus, which differ quite significantly from each other in composition of sedimentary and igneous rocks. Both exotic (detrital) zircons, and those formed within the Greater Caucasus are revealed. The ages of detrital zircons range from 2981 to 668 Ma. On the basis of weighted mean age data among in situ zircons from meta-sedimentary rocks in both sub-zones figures of 626± 2 Ma and 627± 19 Ma were detected, which corresponds to the earliest - Cadomian stage of high temperature regional metamorphism. From meta-sedimentary rocks of the Elbrus sub-zone figures - 461±5.3 Ma, 457±12 Ma indicate manifestation of the Ordovician (tectonically associated with Caledonian orogeny) stage of high temperature prograde regional metamorphism. Figures from granitoid rocks of both sub-zones - 454±9 Ma, 468±5 Ma and 471.7±4.6 Ma were obtained, which also correspond to the Caledonian stage of synmetamorphic granitoid formation. Besides, figures from the meta-sedimentary rocks of the Pass sub-zone - 312.5±4 Ma, 317.0±8.3 Ma correspond to Late Variscan regressive regional metamorphism. In addition, figures obtained from the granitoid rocks of both sub-zones - 309±8 Ma, 310.9 Ma, 325±4 Ma, 311±5.9 Ma and 357±5.9 Ma correspond to the Late Variscan stage of synmetamorphic granitoid formation. These results are in good agreement with geological and petrological data for the Greater Caucasus. [ABSTRACT FROM AUTHOR]

Groundwater in crystalline basement is highly mineralized. The chemistry of bedrocks in crystalline basement of Ogbomosho in relation to chemical composition of groundwater in the area was, therefore, investigated employing a combined approach involving hydrogeological, geological mapping and geochemical method. A total of seventy five (75) water samples collected from wells; shallow and deep, bore within rock exposures (6) and other locations within the study area were analyzed for elemental composition using Inductive Coupled Plasma-Mass Spectrometry (ICP-MS). Physico-chemical parameters, temperature, electrical conductivity (EC), total dissolved solids (TDS) and acidity (pH), were measured in situ using HANNA HI9813-6 hand-held meter. Six rock samples representative of the main geological units of the study area were also collected and analyzed for major oxides and rare earth elements (REE) concentrations using ICP-MS. Thin sections of the rock samples were prepared and observed under petrological microscope for mineralogical compositions of the rocks. Acidity ions/TDS model of groundwater in the area was also established to determine the reactivity of the rock minerals and groundwater evolution pattern. The results of in-situ physico-chemical tests of the water samples indicate the temperature, EC, TDS and pH ranged within 26.6–31.7 °C, 72–1491 mS/cm, 36–747 ppm and 6.15–9.3, respectively. The petrographical analysis revealed biotite, quartz, potassic feldspar (microcline), perthite, albite, hornblende, plagioclase, myrmekite, topaz and muscovite. The major oxides, SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, TiO2, P2O5 and MnO, varied with median values of 72.21%, 14.99%, 1.17%, 0.375%, 2.245%, 4.215%, 3.46%, 0.16%, 0.045% and 0.015%. These indicate dorminance of SiO2 and Al2O3 suggesting acidic and metamorphic/acidic igneous rocks, respectively. The median percentage oxide compositions of the cations in rocks were, therefore, of the order: Na2O > K2O > CaO > MgO. The dissolved cations consequent upon weathering of the minerals were also of the order Na+ (26.9 mg/l) > K+ (4.69 mg/l) > Mg2+ (4.57 mg/l) > Ca2+ (4.23 mg/l) in groundwater based on their median values. These indicate solute concentration in groundwater is proportional to the reactivity of the bedrock minerals. The major anions, HCO3−, Cl− and NO3−, varied within 5.0–455 mg/l, 14.18–184.34 mg/l and 0.02–0.21 mg/l, respectively, in groundwater. The cross-plots of TDS against Ca2+, Na+, Cl− and HCO3− indicate the groundwater in the area is moderately to highly mineralized. The ionic reactivity based on pH ions/TDS plots indicated six-type models. The ionic concentration at low pH within 6.4–7.2 increases with pH for Type-1 (Ca2+), Type-5 (NO3−) and Type-6 (HCO3−,TDS), decreases for Type-2 (Mg2+, K+) but constant as pH increases for Type-4 (Cl−). At high pH, greater than 7.2 but less than 9, ionic concentration increases with pH for Type-1, Type-2 and Type-4, decreases with pH for Type-6 and constant for Type-5. However, the ionic concentration of Na+ (Type-3) momentarily increased, decreased and subsequently increased through low to high pH. These indicate varied degree of reactivity of the bedrock minerals and groundwater evolution pattern. Thus, the composition of dissolved ions in groundwater is controlled by weathering of Ca-feldspar (plagioclase), K-feldspar (orthoclase), Na-feldspar (albite) and biotite found in host rocks. The similarity in trend of cations in groundwater and their oxides in rock samples suggests the influences of local rock chemistry on the groundwater chemistry and hence, groundwater–rock interaction in the study area. The groundwater evolution pattern in the area depends on pH and reactivity of the ions produced from the weathering of the minerals. The chemical compositions of natural waters are, therefore, a direct indication of the geology of their catchment. [ABSTRACT FROM AUTHOR]

Weathered and fractured crystalline basement is known as the important unconventional reservoir in the Cuu Long Basin. Naturally fractured reservoir plays a crucial role in oil exploration to contribute for hydrocarbon production in Vietnam. However, the complexity and heterogeneity of the fractures system in the basement reservoir are challenges for oil and gas production. They require the realistic simulation scenarios to estimate the hydrocarbon potential as well as field development plan of these reservoirs. Thus, this paper aims to propose the feasibility development scenarios to improve oil recovery factor for crystalline basement reservoir, X field, Cuu Long Basin, Vietnam. First, history matching process is validated for the model to fit the actual production data (reservoir pressure, pressure, water cut in each well) in order to approach closer the fluid flow behavior through the reservoir. The manual matching was selected to adjust the actual aquifer size and permeability distribution with limit simulation runs. Next, the highest reliability matching model which approximately reflects the actual fluid flow behavior can be used as the base case to forecast the future reservoir performance through the field development plan. The most potential scenario is to add six new infill production wells, two side track wells and two water injection wells. The forecasted results indicate that this scenario yields 8% more oil recovery factor compared to the natural drive with thirteen producers. This result suggests that the precise field development plan is to increase the efficiency of the production process by increasing the displacement parameters of residual oil and reservoir sweep efficiency by stimulation. The major contribution of this paper demonstrates the merits of the field development plan in fractured basement reservoir. The findings of this study can help better understand the fluid flow behavior using the production history profiles and field development scenarios of crystalline basement reservoir of Cuu Long Basin. [ABSTRACT FROM AUTHOR]

Geothermal systems in amagmatic orogens involve topography‐driven infiltration of meteoric water up to 10 km deep into regional‐scale faults and exfiltration of the heated water in surface springs. The thermal anomalies along the upflow zones have not been quantified, yet they are key to estimating the geothermal exploitation potential of such systems. Here we quantify the three‐dimensional heat anomaly below the orogenic geothermal system at Grimsel Pass, Swiss Alps, where warm springs emanate from an exhumed, fossil hydrothermal zone. We use discharge rates and temperatures of the springs, temperature measurements along a shallow tunnel, and the formation temperature and depth of the fossil system to constrain coupled thermal–hydraulic numerical simulations of the upflow zone. The simulations reveal that upflow rates act as a first‐order control on the temperature distribution and that the site is underlain by an ellipsoidal thermal plume enclosing 102–103 PJ of anomalous heat per km depth. When the fossil system was active (3.3 Ma), the thermal plume was double its present size, corresponding to a theoretical petrothermal power output of 30–220 MW, with the 120 °C threshold for geothermal electricity production situated at less than 2‐km depth. We conclude that mountainous orogenic belts without igneous activity and even with only low background geothermal gradients typical of waning orogens are surprisingly promising plays for petrothermal power production. Our study implies exploration should focus on major valley floors because there the hydraulic head gradients and thus upflow rates and heat anomalies reach maximum values. Key Points: Quantification of the heat anomaly below an orogenic geothermal system, combining geochemical observations with numerical simulationsCalibrated simulations yield large thermal anomalies of 102–103 PJ per km depthAmagmatic orogens are surprisingly promising plays for geothermal power production [ABSTRACT FROM AUTHOR]

The aim of this work was to establish the structure of a crystalline basement along the previously constructed regional cross-section located in the westernmost part of the Polish Outer Carpathians. The analysis of the gravity and magnetic data, additionally constrained by the borehole information, geological maps and seismic profile was carried out to anticipate the depth to the crystalline basement. Based on the qualitative interpretation, several basement-rooted faults were delineated that in some cases most probably affected the structural evolution of the Carpathians Fold and Thrust Belt. Moreover, along the entire cross-section, the basement seems to be located much deeper than previously anticipated. Lastly, the 2D potential fields modelling indicates that a continuous sedimentary cover, most probably represented by the Devonian and Carboniferous sequence or Miocene sediments of the Carpathian foredeep, may be expected below the Carpathian nappes along the whole cross-section length. [ABSTRACT FROM AUTHOR]

Results of a depth-to-basement study are presented for the East European Craton and the Teisseyre-Tornquist Zone (TTZ) in Poland. The terrestrial gravity data are inverted for the top of the Paleoproterozoic basement and, independently, for the top of the Ediacaran using seismic horizons from the PolandSPAN™ seismic survey and well tops as input depth measurements. The depth to the Ediacaran modelling was additionally extended to cover the Łysogóry Block and northern Małopolska Block. The results are visualised as isobath maps for the top of the Paleoproterozoic basement and top of the Ediacaran and an isopach map for the Ediacaran, supplemented with qualitative structural interpretation based on gravity and magnetic data. The results of modelling show a smooth crystalline basement slope within the TTZ with the top of the Paleoproterozoic basement uniformly descending south-westwards by 10–14 km. The thickness of the Ediacaran in SE Poland increases in the same direction to more than 10 km within the TTZ. Such a crustal architecture, in combination with the earlier documented Moho elevation of 4–6 km, reveals significant thinning of the Paleoproterozoic crust within the TTZ to form a crustal necking zone due to the Ediacaran rifting. A smooth geometry of the top of basement along with the lack of basement-rooted faults suggests a ductile mode of crustal thinning during rifting of Rodinia. Moreover, the development of the NW–SE-oriented rift, a precursor of the Tornquist Ocean, was associated with rifting in a NE–SW direction parallel to the Orsha-Volyn Rift. [ABSTRACT FROM AUTHOR]