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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

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.

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]

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]

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.

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.)

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]

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]

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]

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]

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]

Though Yaoundé zone is characterized by abundant rains, access to safe drinking water becomes a difficult activity, because of climate change and pollution caused by human activities. Lineament zones on the earth’s surface are important elements in understanding the dynamics of the subsurface fluid flow. However, good exposures of these features are always lacking in some areas around Yaoundé, characterized by thick alteration. During field surveys these conditions, in many cases, hinder the proper characterization of such features. Therefore, an approach that identifies the regional lineaments on remote-sensing images (Landsat Thematic Mapper and shaded digital terrain models), with its large scale synoptic coverage, could be promising. This paper aims to the structural organization of lineament network in the crystalline basement of Yaoundé from remote sensing data and characterize them by statistical and geostatistical techniques. The results were validated on the basis of the geological maps, the hydrogeological maps and the outcrop data. Statistical analysis of the lineaments network shows a distribution along the N0–10, N20–30, N40–60 and N140–150. The correlation between the productivity of high yield wells and the closest lineament confirms that these lineaments are surface traces of regional discontinuities and act as main groundwater flow paths.

For a long time, the north-western part of the East European Craton, specifically the East Baltic region (EBR), was considered an aseismic territory. Historical earthquakes did take place in the EBR, but they occurred rarely and could not always be associated with tectonic conditions. The attitude towards seismicity of the region began to change after the Osmussaar earthquake on 25 October 1976 (M=4.7) and especially after the Kaliningrad earthquakes on 21 September 2004 (Mw = 5.0; Mw = 5.2). In this study, the seismicity of the EBR was generalized over 13 years after the Kaliningrad earthquakes on the basis of Scandinavian and our own data. In several cases focal mechanisms were solved for weak earthquakes. The study showed a tendency of seismic activity to decrease from northwest to southeast, a predominant concentration of earthquakes sources in the East Baltic coastal zone, and the activation of Ladoga-Bothnia, Vyborg, Olaine-Inčukalns, Võrtsjärv zones. The main problems are associated with a rare seismic network, high level of ambient seismic noise, and a large number of man-made sources. [ABSTRACT FROM AUTHOR]

Exhumed faults hosting hydrothermal systems provide direct insight into relationships between faulting and fluid flow, which in turn are valuable for making hydrogeological predictions in blind settings. The Grimsel Breccia Fault (Aar massif, Central Swiss Alps) is a late Neogene, exhumed dextral strike-slip fault with a maximum displacement of 25-45 m, and is associated with both fossil and active hydrothermal circulation. We mapped the fault system and modelled it in three dimensions, using the distinctive hydrothermal mineralisation as well as active thermal fluid discharge (the highest elevation documented in the Alps) to reveal the structural controls on fluid pathway extent and morphology. With progressive uplift and cooling, brittle deformation inherited the mylonitic shear zone network at Grimsel Pass; preconditioning fault geometry into segmented brittle reactivations of ductile shear zones and brittle inter-shear zone linkages. We describe 'pipe'-like, vertically oriented fluid pathways: (1) within brittle fault linkage zones and (2) through along-strike-restricted segments of formerly ductile shear zones reactivated by brittle deformation. In both cases, low-permeability mylonitic shear zones that escaped brittle reactivation provide important hydraulic seals. These observations show that fluid flow along brittle fault planes is not planar, but rather highly channelised into sub-vertical flow domains, with important implications for the exploration and exploitation of geothermal energy. [ABSTRACT FROM AUTHOR]

Though Yaoundé zone is characterized by abundant rains, access to safe drinking water becomes a difficult activity, because of climate change and pollution caused by human activities. Lineament zones on the earth’s surface are important elements in understanding the dynamics of the subsurface fluid flow. However, good exposures of these features are always lacking in some areas around Yaoundé, characterized by thick alteration. During field surveys these conditions, in many cases, hinder the proper characterization of such features. Therefore, an approach that identifies the regional lineaments on remote-sensing images (Landsat Thematic Mapper and shaded digital terrain models), with its large scale synoptic coverage, could be promising. This paper aims to the structural organization of lineament network in the crystalline basement of Yaoundé from remote sensing data and characterize them by statistical and geostatistical techniques. The results were validated on the basis of the geological maps, the hydrogeological maps and the outcrop data. Statistical analysis of the lineaments network shows a distribution along the N0–10, N20–30, N40–60 and N140–150. The correlation between the productivity of high yield wells and the closest lineament confirms that these lineaments are surface traces of regional discontinuities and act as main groundwater flow paths. [ABSTRACT FROM AUTHOR]

The Strategy on Radioactive Waste Management of Lithuania (Radioaktyviųjų… 2008) envisages evaluating the possibilities of disposal of spent nuclear fuel and long-lived radioactive waste from operation and decommissioning of Ignalina NPP in a deep geological repository. The crystalline basement and sedimentary cover of south-eastern Lithuania was selected for the current model case studies due to availability of geological and hydrogeological data from previous explorations. Groundwater flow, radionuclide (iodine-129 as mobile and long-lived one) transport and heat transfer, modelling using computer code FEFLOW was performed. The model domain of south-eastern Lithuania comprises Protero-zoic-Archaean aquifer with overlaying aquifers system of sedimentary cover. The upward groundwater flow through defected canister located in tectonically damaged zone was conservatively generated. The main results of calculations are following: in case of upward groundwater flow, the maximum activity concentration of 129I in groundwater of the tectonic fracture zone above defected canister will not exceed 10−4 Bq/l; the maximum temperature in the tectonic fracture will obtain about 30-35°C and will not impact on the radionuclide transport. Location of model domain in south-eastern Lithuania does not mean any reference to the site for deep geological repository. The results show that doses obtained by human via drinking water should be below the dose constraint (0.2 mSv /year). Santrauka Radioaktyviųjų atliekų tvarkymo strategija numato galimybę panaudotą branduolinį kurą ir kitas ilgaamžes radioak- tyviąsias atliekas, susidariusias eksploatuojant Ignalinos AE ir susidarysiančias ją demontuojant, galutinai patalpinti giliai geologinėse formacijose. Dėl didelio geologinės bei hidrogeologinės informacijos kiekio šiame darbe nagrinėti tik Pietryčių Lietuvos kristalinis pamatas bei jį dengiantys nuosėdinių uolienų sluoksniai. Radionuklidų bei šilumos sklaidai kristalinio pamato uolienose vertinti naudota kompiuterinė programa FEFLOW 5.0. Pasirinkta konteinerio defekto scenarijus, taikant skaičiavimus, atliktus LEI ekspertų. Modelis apima archėjaus ir proterozojaus vandeningąjį sluoksnį bei nuosėdinėje dangoje slūgsančius vandeninguosius kompleksus. Modeliuotas požeminio vandens srautas, kylantis per tektoniškai pažeistą zoną, kurioje palaidotas PBK konteineris. Iš pagrindinių modeliavimo rezultatų nustatyta, kad ilgaamžio ir mažai sorbuojamo radionuklido 129I sklaidos intensyvumas mažai priklauso nuo geologinės aplinkos savybių, o šilumos sklaida neturi įtakos radionuklidų sklaidai. Žmogaus gaunama dozė, skaičiavimų duomenimis, nesieks ribinės vertės (0,2 mSv/metai). Reikšminiai žodžiai: panaudotas branduolinis kuras, geologinis atliekynas, kristalinis pamatas, požeminis vanduo, baigtiniai elementai

The strategy of radioactive waste management of Lithuania provides for evaluating the possibilities of disposal of spent nuclear fuel and long‐lived radioactive waste originated from Ignalina NPP in deep geological formations. The initial studies performed in Lithuania during 2001–2004 focused on screening of all potentially prospective geological formations as host formations. Since most information is available on crystalline basement, this formation was selected for the model case studies. Taking into account the assumptions (canister defect scenario proposed by Swedish experts and evaluated by LEI experts), groundwater flow and radionuclide (iodine‐129 as mobile and long‐lived one) transport modelling using computer code FEFLOW was performed according to geosphere conditions and parameters characteristic of the southern part of Lithuania (0,8×0,6×0,52 km far‐field block). The upward groundwater flow through defected canister located in tectonically damaged zone was simulated. The main results of calculations are the following: in the case of upward groundwater flow, the maximum I‐129 volumetric activity in single tectonic fracture above defected canister will not exceed 1 Bq/1, and in the active water exchange zone, it is close to 10−2 Bq/l. These figures show that doses obtained by human recipient via aquatic pathway should be below the dose constraint (0,2 mSv/y). More complicated scenarios and assumptions should be investigated in future studies. Požeminio vandens tėkmių ir radionuklidų pernašos kristaliniame pamate modeliavimas feflow kodu Santrauka Pagal radioaktyviųjų atliekų tvarkymo strategiją Lietuvoje yra numatoma galimybė panaudotą branduolinį kurą ir ilgaamžes radioaktyviąsias atliekas, susidarančias Ignalinos AE, laidoti giliose geologinėse formacijose. Pradiniai tyrimai 2001−2004 metais buvo skirti atrinkti šiam tikslui tinkamiausias geologines formacijas. Modeliui sudaryti pasirinktas labiausiai ištirtas kristalinis pamatas. Požeminio vandens srauto ir radionuklido (itin mobilaus ir ilgaamžio jodo-129) pernašos modelis buvo sudarytas kompiuterine programa FEFLOW, laikantis esminės prielaidos (Švedijos ekspertų pasiūlytas bei Lietuvos energetikos instituto specialistų apskaičiuotas konteinerio defekto scenarijus) bei pagal Pietų Lietuvai būdingas geologines sąlygas ir vyraujančius parametrus (0,8×0,6×0,52 km tolimojo lauko blokas). Darbo metu buvo modeliuotas požeminio vandens srautas, kylantis per tektoniškai suardytą zoną, kurioje yra patalpintas pažeistas konteineris. Pagrindiniai skaičiavimų rezultatai: didžiausias 129I tūrinis aktyvumas, kai požeminio vandens srautas, kylantis tektoniškai suardytoje zonoje šalia konteinerio, nesieks 1 Bq/l, aktyvioje vandens apytakos zonoje − iki 10−2 Bq/l. Rezultatai rodo, kad žmogaus gaunama dozė, jei jis gertų požeminį vandenį, neturėtų siekti ribinės dozės (0,2 mSv/m). Modeliavimo darbai, remiantis sudėtingesnėmis prielaidomis bei geologinėmis sąlygomis, bus atliekami ateityje. Reikšminiai žodžiai: panaudotas branduolinis kuras, geologinė saugykla, kristalinis pamatas, požeminis vanduo, skaitmeninis modeliavimas, baigtiniai elementai. Моделирование потоков подземных вод и переноса радионуклидов в кристаллическом фундаменте компьютерным кодом feflow Резюме Стратегия обращения с радиоактивными отходами Литвы в качестве одной из альтернатив предусматривает оценку возможностей захоронения отработанного ядерного топлива и долгоживущих радиоактивных отходов в глубоких геологических формациях. Начальная оценка пригодности всех потенциальных геологических формаций для захоронения отработанного ядерного топлива произведена в Литве в течение 2001–2004 гг. Из-за большого объема существующей разносторонней информации кристаллический фундамент был отобран в первую очередь для моделирования потоков подземных вод и переноса радионуклидов. Принимая во внимание главные предпосылки нормального развития (предложенный шведскими экспертами и оцененный экспертами LEI сценарий дефектного канистра с отработанным ядерным топливом) и подобранные параметры, характерные для кристаллического фундамента и вышележащей толщи осадочных пород Южной части Литвы (0,8×0,6×0,52-километровый блок дальнего поля), моделировался перенос радионуклидов (йода-129 как мобильного и долгоживущего радионуклида) с потоком подземных вод, используя компьютерный код FEFLOW. Через дефектный канистр, гипотетически расположенный в тектонически нарушенной зоне, средствами моделирования был воссоздан восходящий поток подземных вод. Главные результаты численного моделирования для очень консервативного случая таковы: при восходящем потоке подземных вод максимум активности I-129 в воде тектонически нарушенной зоны рядом с дефектным канистром не будет превышать 1 Бк/л, а в зоне активного водообмена он близок к 10−2 Бк/л. Результаты показывают, что получаемые человеком через питьевую воду дозы должны быть меньше ограниченной дозы (0,2 мЗ /год). Ключевые слова: отработанное ядерное топливо, геологическое хранилище, кристаллический фундамент, подземные воды, численное моделирование, конечные элементы. Firstd Published Online: 14 Oct 2010

The delineation of pollution plumes generated by household waste landfills is not easy, particularly in the case of discontinuous or intricately extending water tables, such as those developed in a fractured crystalline bedrock context. In Ouagadougou (Burkina Faso), there are many uncontrolled landfills throughout the urban area. The water table, generally located between 3 and 10 m deep, is likely to be contaminated by the leachate from these landfills. More than 1000 measurements of spontaneous potential (self-potential), referenced by GPS, have been carried out on a landfill and its immediate surroundings to the south of the urban area. The geostatistical processing by analysis of variograms and correlograms highlights an adapted prospecting technique and reliable cartography. The response seems to be mainly due to the electrochemical component with hot spots within the landfill and a plume heading towards the North-East. The distribution of the spontaneous potential seems to be controlled, not by the topography of the site, but by the fracturing of the mother rock of dominant direction 15° N, and by the mother rock/saprolite contact. Thus, the plume does not flow to the market gardening just below the landfill but rather to a residential area where monitoring of the quality of the borehole water is required. [ABSTRACT FROM AUTHOR]