Basin Basement Research Articles

Structure of the basement of the near-Laptev part of the Eurasian basin according to geological and geophysical data

The near-Laptev part of the Eurasian basin is the area of transition from modern spreading to intraplate rifting. We propose an approach to the construction of a 3D model of the basement of the Laptev Sea part of the Eurasian basin based on the linkage of all currently available geological and geophysical data. The structure of the acoustic basement of the Eurasian basin is characterized by alternating troughs and highs in cross-section. The sparse seismic data do not allow us to directly trace the strike of these structures, but they can be correlated with the linearity established by gravity and magnetic data and related to the sequential opening of the basin. For the Laptev Sea part of the Eurasian basin, where linearity is no longer traceable from magnetic data, we propose a method of determining the strike of the basement structures on the basis of seismic stratigraphic analysis. The new 3D model of the acoustic basement in the studied area provided the basis for the tectonic scheme of the entire Eurasian basin. The model reflects the main stages of basin development: continental rifting up to 56 Ma, normal spreading 56–45 Ma, ultra-slow spreading 45–34 Ma, ultra-ultra-slow spreading 34–20 Ma. The southern part of the study area is overlain by a sedimentary cover with an age of 20 Ma and younger, which is associated with the cessation of spreading here no later than 20 Ma.

Constrained simultaneous recovery of the depth to basement and lateral susceptibility variation

AbstractThe basin environment is a widely studied subject in both geology and geophysics for its economic significance in energy and mineral explorations. However, the estimation of the basement depth is often a challenging task given the complexity of the basement relief and lateral physical property change. Previous works simplify the problem by only inverting for the depth to the basement, and more recent studies have suggested the need to incorporate the variation of physical properties to improve basement structure imaging. In this study, we develop an inversion method with the associated workflow to simultaneously recover both the depth to a magnetic basement and a laterally varying magnetic susceptibility in the basement rock. To achieve this, we employ a set of constraints on the inverse problem. Particularly, both the recovered susceptibility and basement depth models are bounded below a possible maximum value, and the depth model is guided by a few depth points obtained from the resistivity models that are obtained from the one‐dimensional blocky inversions of magnetotelluric (MT) data. In addition, we apply the fuzzy C‐means (FCM) clustering to the susceptibility model during the inversion and use the inverted cluster centers to differentiate for different geological units in the basement. To show the effectiveness of our work, we compare the existing approaches and our method using two test inversions on one synthetic model resembling the basin–basement environment before demonstrating our method on a field data example with magnetic data collected by the U.S. Geological Survey (USGS) over the Illinois Basin. Our results show improved recovery in both basement relief and susceptibility in the basement rock, and inversion with field data is able to identify three different susceptibility zones in basement rock below the Illinois Basin.

Lithospheric structure of the Paraná, Chaco-Paraná, and Pantanal basins: Insights from ambient noise and earthquake-based surface wave tomography

To investigate the lithospheric seismic structure of southern South America beneath the Paraná, Chaco-Paraná, and Pantanal basins, we measure two distinct sets of dispersion curves of Rayleigh waves: the first corresponds to 25,986 phase velocity dispersion curves in the period range 5–50 s, extracted from cross-correlation of the ambient noise between pairs of stations and thus sensitive mainly to crustal structure; the second set is derived from group velocities extracted from earthquake recordings, resulting in 33,888 dispersion curves with periods ranging from 8 to 200 s, allowing us to probe deeper Earth structure. From these data sets, we derive two independent S-wave velocity models following a two-step inversion procedure, resulting in a crustal and a lithospheric mantle model with depths extending up to 50 and 200 km, respectively. Features imaged in our crustal model include low velocity anomalies in agreement with the surface position of the major sedimentary basins and high velocity anomalies within fold-thrust provinces and the basement of the Pantanal basin. In the uppermost mantle, we identify high velocities in the region of the Paraná basin, São Francisco and Amazonian cratons, and Luiz Alves block, and a low velocity feature beneath the Pantanal basin, which suggests a potentially thinner lithosphere under the basin. We also illuminate a strong velocity gradient boundary between the eastern border of the Pantanal basin with the Paraná basin, from crustal to lithospheric mantle depths, which seems to delineate the western and southern borders of the Paraná basin, coinciding with the Western Paraná Suture. Additionally, we construct a Moho depth proxy map for the study area, which has an overall good agreement with previous results, except for a thicker crust beneath the southern Chaco-Paraná basin. This area, together with a thicker crust counterpart in the Paraná basin, has a remarkable correlation with the position of a volcanic layer related to the Paraná Magmatic Province, which leads us to suggest that magmatic processes played an important role in the south Chaco-Paraná basin as well.

Fracture evaluation of the plutonic basement in the Upper Magdalena Basin: Implications for the development of naturally fractured reservoirs in the Northern Andes

Plutonic rocks typically have negligible matrix porosity and permeability. However, fractures and mineral alterations create storage space and flow pathways that turn plutonic rocks into fluid reservoirs. Despite significant hydrocarbon discoveries, naturally fractured reservoirs in plutonic rocks have been poorly studied. In most Colombian basins, the crystalline basement has undergone multiple deformational events and is thrust over the Cretaceous to Cenozoic source and reservoir rocks of the conventional petroleum system. This structural configuration is ideal for the migration of oil into a fractured basement. A multiscale fracture analysis, including field, petrographical and petrophysical techniques was conducted on the Permian and Jurassic plutonic basement of Upper Magdalena Basin in order to understand the controls on brittle deformation, the development of fracture networks and their potential to form hydrocarbon reservoirs. The results indicate that protolith textures and structures, including magmatic and mylonitic foliation, favours fracturing. Dykes exhibit higher fracture density (7–48 fractures/m), porosity (mean = 0.4%) and permeability (mean = 125,818.75 mD) than the host rock (2–25 fractures/m; 0.23%; 12,066.09 mD). Intersection zones from regional faults, are characterized by the highest fracture and lineament intensity. Our results suggest that dyke swarms and interacting damage zones can significantly enhance the reservoir quality of plutonic rocks by providing storage in fractures and fluid pathways to the host rock.

Impact and implications of hydrothermal fluids migration in the Frolov hydrocarbon province in West Siberia

Both the prolific source rocks of the Bazhenov Formation and the reservoir-prone units of the Abalak Formation cover most of the West Siberian region. Hydrothermal fluids circulation has been suggested to affect hydrocarbon potential and reservoir properties at some localities of this vast hydrocarbon province. However, integrated studies are currently lacking. Here we present an extensive multidisciplinary study combining regional studies with core logging properties and sample analyses (i.e. geochemistry, petrography, organic geochemistry) to reveal processes related to the hydrothermal activity that affected both formations. We also focus on the factors and implications for secondary unconventional reservoir formation within the deposits from the Kamennaya summit of the Frolov oil and gas region. Three boreholes corresponding to type sections located in different parts of the study area (elevated, transitional and deep) were investigated. The elevated and transitional parts of the basin are adjacent to the weakened contact zones of a granite massif. These tectonic discontinuities acted as conductors for hydrothermal fluids circulation on the area. Lithological and stable isotope studies revealed the presence of intensive hydrothermal secondary alterations in various types in rocks, including massive metasomatic carbonatization, sulfatization, sulfide mineralization and leaching processes. This hydrothermal fluid activity resulted in reservoir formation within siliceous radiolarite layers, while in the deep part of the basin potential reservoirs were completely healed. Organic matter maturity varies in different parts of the basin. We identify several mechanisms related to the various hydrothermal processes that influenced rocks composition, structure and organic matter maturity: (1) A weakened zone located on the periphery of the granite massif in the basin basement is characterized by extensive fault damage zones facilitating the migration of high temperature fluids along deposits during post-sedimentation stages; (2) The thickness, mineral composition of the rocks overlying the basement control fault attenuation and fluid workflow; (3) The fluids composition, their acidity/alkalinity, prompted various changes in rock structure, especially in secondary porosity formation. The identification of various hydrothermal processes and their influence on pore space allowed to determine the approach for the spatial distribution prediction of unconventional reservoirs in the studied formations, and subsequently improve the efficiency and effectivity of the exploration process not only at the Kamennaya summit, but also on the other similar West Siberian basin areas.

Hydrocarbon accumulation characteristics in basement reservoirs and exploration targets of deep basement reservoirs in onshore China

Based on the global basement reservoir database and the dissection of basement reservoirs in China, the characteristics of hydrocarbon accumulation in basement reservoirs are analyzed, and the favorable conditions for hydrocarbon accumulation in deep basement reservoirs are investigated to highlight the exploration targets. The discovered basement reservoirs worldwide are mainly buried in the Archean and Precambrian granitic and metamorphic formations with depths less than 4 500 m, and the relatively large reservoirs have been found in rift, back-arc and foreland basins in tectonic active zones of the Meso-Cenozoic plates. The hydrocarbon accumulation in basement reservoirs exhibits the characteristics in three aspects. First, the porous-fractured reservoirs with low porosity and ultra-low permeability are dominant, where extensive hydrocarbon accumulation occurred during the weathering denudation and later tectonic reworking of the basin basement. High resistance to compaction allows the physical properties of these highly heterogeneous reservoirs to be independent of the buried depth. Second, the hydrocarbons were sourced from the formations outside the basement. The source-reservoir assemblages are divided into contacted source rock-basement and separated source rock-basement patterns. Third, the abnormal high pressure in the source rock and the normal–low pressure in the basement reservoirs cause a large pressure difference between the source rock and the reservoirs, which is conducive to the pumping effect of hydrocarbons in the deep basement. The deep basement prospects are mainly evaluated by the factors such as tectonic activity of basement, source-reservoir combination, development of large deep faults (especially strike-slip faults), and regional seals. The Precambrian crystalline basements at the margin of the intracontinental rifts in cratonic basins, as well as the Paleozoic folded basements and the Meso-Cenozoic fault-block basements adjacent to the hydrocarbon generation depressions, have favorable conditions for hydrocarbon accumulation, and thus they are considered as the main targets for future exploration of deep basement reservoirs.

Plume‐Modified Lithosphere Mantle Controlled the Cenozoic Sediment Thickness in the Tarim Basin

AbstractThe Cenozoic sediments are very thick in the southwest Tarim Basin and very thin in the northwest, but what controls these variations is unclear. Here, we use two‐dimensional thermo‐mechanical models to investigate how the lateral variations in rheological strength and depletion density of cratonic lithosphere mantle affect the cratonic basin deformation. Model results show that the basin basement uplift occurs above either the region with crustal thickening or high depletion in the mantle. A model with a stronger and density‐depleted northern half of cratonic lithosphere mantle in the context of compression matches the differential Cenozoic subsidence and deformation observed in the Tarim Basin well. We propose that a Permian plume led to the lateral heterogeneity of the lithosphere mantle under the Tarim craton, and the modified lithosphere mantle characteristics caused the differential Cenozoic sediment thickness in the Tarim Basin.

ТЕКТОНИЧЕСКОЕ СТРОЕНИЕ И ИСТОРИЯ ГЕОЛОГИЧЕСКОГО РАЗВИТИЯ ЗЕЯ-БУРЕИНСКОГО ОСАДОЧНОГО БАССЕЙНА ПО РЕЗУЛЬТАТАМ КОМПЛЕКСНОЙ ИНТЕРПРЕТАЦИИ МАТЕРИАЛОВ БУРЕНИЯ И СЕЙСМОРАЗВЕДКИ

The latest geological and geophysical information on the Zeya-Bureya sedimentary basin (Russia, Far East) is summarized. Based on drilling data from corehole and deep wells, 2D and 3D CDPM seismic data, taking into account the integrated interpretation of gravity and magnetic survey data, geological survey materials, a map was constructed on the surface of the pre-Mesozoic basement of the sedimentary basin, as well as structural maps on the top of the Cretaceous formations. The maps reflect a series of rift grabens and uplifts identified by the authors on seismic time sections during their reinterpretation. The method of constructing maps is given. A geological map of sediments overlying the pre-Mesozoic basement of the Zeya-Bureya sedimentary basin and a tectonic map of the sedimentary cover were constructed. During the tectonic zoning of the sedimentary cover, the classification of tectonic elements was adopted, which is widely used in the tectonic zoning of oil and gas regions, proposed by V.D. Nalivkin and updated at INGG SB RAS. As a result of tectonic zoning in the basin, the Inner Region and the Outer Belt were identified, and the tectonic elements complicating them were characterized. A characteristic feature of the Outer Belt is the presence of large intermediate structures - monoclines, mega- and mesomonoclines. On the contrary, the Inner region of the basin is characterized by the presence of a large negative structure, complicated by smaller positive and negative elements. The main stages of the formation and development of the sedimentary cover of the Zeya-Bureya sedimentary basin are identified and described: rifting, early syneclise, late syneclise and neotectonic.

Crustal architecture of the Dharwar craton and Southern Granulite Terrane, Southern India, from the analysis of gravity-magnetic data

The potential field (gravity & magnetic) data, along with results of available seismic and magnetotelluric studies over the Southern India Shield comprising the Dharwar craton (DC), Southern Granulite Terrane (SGT) and southern part of the Eastern Granulite Mobile Belt (EGMB), were synthesized. The study attempts to elucidate the geometry and continuity of greenstone belts/shear zones, isostatic condition and deeper crustal architecture. We observed a characteristic elevation-gravity relationship for each of the tectonic domains. The greenstone belts of the DC are characterized by N-S to NW-SE trending positive residual gravity anomalies and continue beneath the Cuddapah sediments. The basement of the Cuddapah basin is characterized by NW-SE trending greenstone belts with low-density intrusive rocks. The gravity anomaly suggests occurrence of a high-density rock unit occurs at mid-crustal depth beneath the ‘Closepet granite’ and ‘Chitradurga schist belt’. The potential field signatures of the DC and SGT are distinctly different. The Cauvery Shear Zone is characterized by positive residual gravity and magnetic anomalies with ∼E-W to ENE-WSW trend that continues further east under sediment covers of the east coast. The residual gravity signatures and horizontal gravity gradient signatures suggest that the orogenic systems encompassing the Cauvery Shear Zone and the eastern part of the EGMB may be a part of a common structural belt or tectonic regime associated with the assembly of the Gondwana supercontinent. The potential field modelling reveals the presence of a thick, high-density material resting over the base of the crust in the entire stretch of the east-coast of India.

CANVAS: An Adjoint Waveform Tomography Model of California and Nevada

AbstractWe present the California‐Nevada Adjoint Simulations (CANVAS) model, an adjoint waveform tomography model of the crust and uppermost mantle of the states of California and Nevada. We used WUS256 (Rodgers et al., 2022, https://doi.org/10.1029/2022jb024549) as the starting model and iteratively decreased the minimum period of CANVAS from 30 to 12 s. CANVAS was iterated in two distinct stages: the first stage with source mechanisms from the Global Centroid Moment Tensor (GCMT) catalog and the second stage with inverted moment tensors (MT) using the CANV_WUS model (Doody et al., 2023, https://doi.org/10.1029/2023jb026463). We show that updating the MTs with 3D Green's functions improved waveform fits and azimuthal coverage of windowed data used to calculate the gradients. As for the model itself, we improved waveform fits over WUS256, particularly in the dispersed surface waves. CANVAS resolved tectonic features seen in other models and accurately defined the depth to basement of major basins, including the Central Valley and the Ventura Basin. We propose CANVAS as a starting model for crustal tomography models on smaller scales.

Analysis of the Hydrodynamic Properties of the Fissure Aquifers of the Black Volta Catchment in Ivory Coast

The present study aims to analyze the productivity of aquifers in the Ivorian part of the Black Volta basin. It proposed to characterize the intrinsic hydrodynamic parameters of the productivity and to know the influence of these on the productivity of the drillings. The hydraulic parameters of the catchment structures and the pumping test sheets were used to determine the hydrodynamic properties through a methodological approach integrating Cooper Jacob's empirical formulas and automated calculations using the Pumping Interpretation Assistance Tool (OUAIP). A standardized principal component analysis (ACPN) was used to analyze the correlation of the different parameters. The results obtained range over several orders of magnitude. The values of the specific flow oscillate between 0. 01 and 4.87m²/h while the transmissivity varies between 1.25E-07 and 7.34E-03 m².s-1. As for the critical flow, it is between 0.869 and 26.6 m3/h. These values indicate that the aquifers generally have low specific flow rates, but fairly good transmissivity. The Normalized Principal Component Analysis (ACPN) allowed to highlight the different productivity factors of the aquifers in the region: water level variation, and hydraulic role of fractures. It also showed the influence of the depth of the drilling on productivity. These results contribute to the knowledge of the structure and hydrodynamic functioning of the aquifers of the basin basement. They show the structural links between hydrodynamics and aquifer productivity.

LATE PALEOZOIC – MESOZOIC TECTONIC EVOLUTION AND PROSPECTS OF HYDROCARBON EXPLORATION IN THE ALAKOL SEDIMENTARY BASIN (KAZAKHSTAN)

Based on the analysis of stratigraphic, lithofacies, and geological and geophysical data, consideration is being given to the main stages in the formation of the basement and cover structures of the Alakol sedimentary basin. For this region, there was developed the substantiation of a scheme of tectonic zoning and there were proposed structural characteristics of faults and lithofacies features of the section. Evidence was found of a complex, multi-stage tectonic evolution. There were discovered potentially promising stratigraphic oil and gas complexes of the Late Paleozoic and Mesozoic. The deep-seated structure of the region is illustrated by a geological and geophysical section, spatially coincident with the "Turkestan" seismic profile. Based on the lithological and paleogeographic reconstructions, there were identified four major tectonic boundaries: Cambrian-Ordovician, Devonian-Carboniferous, Permian-Early Triassic, and Middle Triassic-Cretaceous. The correlation of the stratigraphic range of the hydrocarbon potential of the Alakol basin has been carried out. The criteria for forecasting hydrocarbon accumulations were substantiated.

STRATIGRAPHY AND LITHOLOGY OF THE PALEOZOIC DEPOSITS IN THE TASBULAK GRABEN, SHU-SARYSU BASIN

Despite of more than 40-year history of prospecting work, the degree of geological and geophysical knowledge of the Shu-Sarysu basin is still very low. Current comprehensive study is based on the geological, geophysical, well and geochemical data from published literature and reports of the state institutions. The Shu-Sarysu sedimentary basin evolved at the western margin of the Kazakhstan microcontinental plate in the beginning of Devonian. Subduction of oceanic crust under the microcontinent raised to magmatic and volcanic processes in the south and east territories of the basin. Afterwards, throughout the late Paleozoic, these areas became a source of the clastic sediments of the basin. Territory of the Shu-Sarysu basin was uplifted in the Triassic and Jurassic. This confirmed by the absence or very thin sediments of the Cretaceous and Tertiary in the territory of the basin. The basement of the Shu-Sarysu basin is represented by the Precambrian and partially the Lower Paleozoic formations. They are dislocated, metamorphosed, and intruded by intrusions of various compositions and ages.The lithology and stratigraphy of the Paleozoic sediments in the north and west parts of the Shu-Sarysu basin are have the similar construction. This statement well confirmed by the well data from the parametric and prospecting wells drilled within the Tasbulak and Kokpansor grabens. Based on this data, the next lithological-stratigraphic layers are established within the Paleozoic sediments of the Tasbulak graben: carbonate-terrigenous-halogen Upper Devonian; terrigenous-carbonate Lower Carboniferous; continental terrigenous of the Middle-Upper Carboniferous, terrigenous-halogenous of the Lower Permian and terrigenous-carbonate of the Upper Permian.

Доюрское основание Терско-Каспийского прогиба в связи с проблемой глубинной нефти и формировании ее скоплений

Актуальность работы. В последние десятилетия в практике геологоразведочных работ на нефть и газ отмечаются негативные тенденции, связанные неблагоприятным соотношением между добычей УВ-сырья и приростом запасов нефти и газа. Это связано не только со снижением объемов ГРР на нефть и газ, но и устареванием теоретико-методологических основ поисков и разведки нефти и газа базировавшихся в основном на осадочно-миграционной и антиклинальной теориях. Экспериментальными данными и результатами сверхглубокого бурения в ряде регионов мира доказана возможность нахождения месторождений УВ на глубинах до 9-11 км. В этой связи определенные перспективы нефтегазоносности исследуемого и других нефтегазоносных регионов можно связывать с фундаментом и нижними горизонтами осадочного чехла. Цель работы. Исследование взаимосвязей между разломно-блоковой структурой фундамента, строением осадочного чехла, процессов нефтегазообразования и формирования скоплений углеводородов. Методы исследований. Для решения поставленной задачи были использованы фондовые материалы и опубликованные литературные источники, произведен комплексный анализ и обобщение геолого-геофизической информации (МОВЗ, МОВ ОГТ, КМПВ, бурение скважин и т.д.) по доюрскому основанию и осадочному чехлу. Результаты исследований. Освещена история развития взглядов о разломно-блоковом строении фундамента и нижнего структурного этажа осадочного чехла и нефтегазоносности Восточного Предкавказья. Описаны результаты, полученные различными методами – сейсморазведкой МОВ ОГТ, КМПВ, МОВЗ, повторным нивелированием и др. Установлена взаимосвязь разломной тектоники, процессов глубинного нефтегазообразования и формирования многопластовых месторождений в пределах ТКП. Отмечается, что разломно-блоковая структура земной коры сыграла активную роль в формированиии сложного складчато-блокового строения западной части ТКП, путей миграции флюидных потоков и характера размещения УВ-скоплений. В практическом отношении предполагая формирование скоплений УВ в результате вертикальной миграции флюидов можно прогнозировать нефтегазоносность практически всех слоев осадочного чехла вплоть до пермо-триасовых отложений включительно, при наличии благоприятных структурно-тектонических, литолого-фациальных и других условий. Relevance. In recent decades, in the practice of geological exploration for oil and gas, there have been negative trends associated with an unfavorable ratio between the extraction of hydrocarbon raw materials and the increase in oil and gas reserves. As is known, for the stable development of oil and gas production, it is necessary that the pace of development of exploration ahead of the pace of hydrocarbon production. The above trends are associated not only with a decrease in the volume of exploration for oil and gas, but also with the obsolescence of the theoretical and methodological foundations of oil and gas prospecting and exploration, based mainly on sedimentary-migration and anticlinal theories. At present, experimental data and results of ultra-deep drilling in a number of regions of the world have proved the possibility of finding hydrocarbon deposits at depths of up to 9-11 km. In this regard, certain prospects for the oil and gas potential of the studied and other oil and gas regions can be associated with the basement and lower horizons of the sedimentary cover. Aim. Study the relationship between the fault-block structure of the basement, the structure of the sedimentary cover, the processes of oil and gas formation and the formation of hydrocarbon accumulations. Methods. To solve the problem, stock materials and published literature sources were used, a comprehensive analysis and generalization of geological and geophysical information (methods of the deep seismic sounding, CDP, seismic refraction, well drilling, etc.) was carried out on the pre-Jurassic basement and sedimentary cover. Results. The history of the development of views on the fault-block structure of the basement and the lower structural stage of the sedimentary cover and the oil and gas potential of the Eastern Ciscaucasia is covered. The results obtained by various methods are described - seismic exploration of the CDP, refraction correlation, deep seismic sounding, re-leveling, etc. The relationship between fault tectonics, processes of deep oil and gas formation and the formation of multilayer deposits within the Tereк-Caspian basin is established.

Modelling geochemical indices from hyperspectral drill core data from the Eucla Basin basement

Whole rock geochemical analysis of drill core is crucial for rock classification and understanding the evolution of a geological province. This becomes even more important when access to fresh rock samples is hindered by considerable overburden, such as in the case of the basement to the Eucla Basin sediments in Australia. A partial least squares (PLS) regression method was trialled to model geochemical indices, commonly applied for classification of igneous rocks, from hyperspectral visible-near infrared (VNIR; 350 to 1200 nm), shortwave infrared (SWIR; 1200 to 2500 nm) and thermal infrared (TIR; 6000 to 14,500 nm) reflectance spectra of three drill cores intersecting the basement of the Eucla Basin. Modelling of the Mg# (Mg/Mg + Fe) achieved a high correlation between the calculated and predicted values (i.e. R2 > 0.9) at an RMSE of about 10 %. The 2200 to 2400 nm wavelength region of the SWIR was key in modelling the Mg#, with amphibole and chlorite-related absorption features overlapping with the most important input bands in the PLS model. Modelling of the silicon, calcium, iron, magnesium index (SCFM; SiO2/(SiO2 + CaO + FeO + MgO)) required the TIR wavelength range, where diagnostic spectral signatures of silicates are located. PLS-based modelling of the SCFM achieved even a high correlation (i.e. R2 > 0.8) when the model was developed for one drill core but applied to another drill core that intersects the same lithologies. The third geochemical index trialled was the aluminium saturation index (ASI; Al2O3/(Na2O + K2O + CaO), producing high correlation between calculated and predicted ASI when using either, the VNIR-SWIR and the TIR wavelength ranges as input. Our study demonstrates how PLS regression can utilise hyperspectral data to determine geochemical indices, without the cost of full geochemical analysis of every sample in a wide array of rock types. The higher spatial resolution of the modelled geochemistry and the extrapolation of the modelling results to intervals that haven't been sampled for geochemistry supports stratigraphic correlation between drill cores. Furthermore, the combined analysis of geochemical and hyperspectrally-derived mineralogy helps mapping the intensity of weathering of basement as well as mineralogical and physicochemical gradients potentially related to hydrothermal systems.

Convective Versus Conductive Heat Flow in The Central Alberta Part Of The Western Canada Sedimentary Basin

Alberta, Canada, T6H 5X2. A detailed study of the hydrogeological and geothermal regimes in the Phanerozoic sequence of the Western Canada Sedimentary Basin was carried out for the Swan Hills and Cold Lake areas in central Alberta. The study was based on the examination, processing and interpretation of information from 6276 wells distributed over a total area of 39,500 km². The information processed refers to stratigraphic picks, chemistry of formation waters, drill stem tests and bottom hole temperatures. As a result, every stratigraphic unit is defined in terms of geometry and lithology, and characterized by appropriate hydraulic and thermal parameters. A sequence of eight major aquifer groups separated by eight aquitards and two aquicludes was identified. The fluid flow in the Paleozoic aquifers is mainly horizontal and regional in nature, being driven by the difference in hydraulic potential between the high areas in the foothills and the lowland areas in the prairies. The fluid flow in the Cretaceous aquifers is of regional to intermediate type, with a significant downward component. The fluid flow in the aquitards is vertical. The very low permeability of the strata is reflected in flow velocities on the order of magnitude of 1 cm/a and less. Dimensional analysis of heat transport processes in each hydrostratigraphic unit shows that convective heat transfer is negligible with respect to conductive heat transfer. The respective values of the Peclet number for heat flow in porous media areas are less than 10-2. In the Swan Hills and Cold Lakes areas the flow of the terrestrial heat flux from the crystalline Precambrian basement of the sedimentary basin to the atmosphere is controlled by the geometry and the changes in the thermal properties of the formations in the basin. The geothermal gradients for individual layers vary from 17 mK/m for sandstone units to 42 mK/m for shales. The integral geothermal gradient of the entire sedimentary column varies between 22 mK/m and 36 mK/m. The areal distribution of the integral geothermal gradient shows a strong correlation with stratigraphy and lithology.

Basement and lithospheric structure of the central Ganga Basin between the Bundelkhand craton and the Sharda Deep by magnetotellurics

The geological and tectonic fabric of the Indian plate in the Ganga Basin is masked by alluvial sediments. Geophysical exploration of the basin for hydrocarbons yielded information on the presence of transverse basement ridges and Cenozoic as well as some pre-collision stratigraphy of the basin. However, the depth of the basement especially in the northern part of the basin and the nature of the underlying crust and mantle lithosphere is largely unknown. We have carried out a magnetotelluric (MT) study along a 300-km-long profile between the Bundelkhand craton (BC) and the Sharda Deep (at the Himalayan foothills) across the central Ganga Basin to delineate the basement and the lithospheric structure. The electrical resistivity image obtained by 2-D inversion of broadband MT data reveals significant lateral heterogeneity in the subsurface structure along the profile. The model yields a super-thick sedimentary basin in the Sharda Deep consisting of multiple stages of basin formation, including a Proterozoic paleo-rift, and a highly heterogeneous lithospheric structure of the Indian plate north of the BC. The model consists of two major upper mantle conductors connected to the conductors within the lower crust. It is surmised that enhanced conductivity could be due to the presence of fluids and the upper mantle conductors are feeding to the crustal conductors. However, an in-depth analysis of the genesis of these conductors would require other independent geophysical information which is not available at present. This is the first reporting of such a heterogeneous nature of the Indian continental lithosphere beneath the Ganga Basin at a regional scale. Our model further supports the presence of the electrical Moho in the BC and, together with earlier published MT results along another profile, suggests that the BC extends much farther north than its presently known northern limit.

Digital estimation of the gravitational effect of the crystalline basement of the Yevlakh-Agjabadi basin (Middle-Kura depression, Azerbaijan)

Digital estimation of the gravitational effect of the crystalline basement of the Yevlakh-Agjabadi basin (Middle-Kura depression, Azerbaijan)

А conceptual model for the formation of oil and gas accumulation zone within the Paleozoic basement of the southeastern West Siberian basin

In modern conditions of high demand for oil reserves in the Russian Federation, the most important region for its production remains the West Siberian oil and gas basin with target objects in well studied and developed Jurassic and Cretaceous sediments. The high degree of depletion of oil reserves at traditional sites and low exploration of complex and unconventional oil accumulations contribute to intensification of prospecting activities in Achimov, Bazhenov and Tyumen deposits, as well as those in deeper and less studied Lower Jurassic, Triassic and Paleozoic deposits located in the basement of sedimentary cover. The issue of oil and gas content of the pre-Jurassic complex of the West Siberian oil and gas basin has been debated for many years by experts, who highly appreciate the potential of identifying new large-scale oil and gas accumulations in such sediments. A series of recent discoveries in the Tomsk region (Urman-Archinsk group) confirms the importance of selecting such an exploration area. A review of existing ideas about the prospects of oil and gas content in the Paleozoic basement of the southeastern part of the West Siberian basin, along with an analysis of the identified conditions of hydrocarbon accumulation formation, allowed to propose a conceptual model that can be used as a basis for prediction when searching for accumulations in the pre-Jurassic complex.

Dolomitization in the Upper Paleozoic succession of the north-Ostaninsk field, Nyurolsk Basin, Western Siberia: Implications for hydrocarbon exploration

Paleozoic rocks in Western Siberia may contain significant hydrocarbon resources. However, effective methods for their exploration are poorly constrained. This study provides new insights into the causes of reservoir formation using the upper part of the Paleozoic succession of the North-Ostaninsk field in the Nyurolsk Basin as a case study. The carbonate rocks have been affected by dolomitization. Four dolomite generations have been identified: Floating in the matrix (D1), fracture-filling (D2.1), stylolite-associated (D2.2), partly replacive (D3) and, pervasive (D4). The last one replaces biogenic limestone in the upper part of the Paleozoic succession and coincides with the presence of a reservoir in the field. A systematic analysis petrographic, fluid inclusion, and carbon and oxygen isotope investigations suggest that the origin of dolomite is from the downward infiltration of meteoric water with higher Mg2+ and Fe2+ derived from the alteration of tuffaceous materials. The results, along with values of the magnetic field anomaly, reveal the relationship between dolomitization and the distribution of the oil and gas reserves in this Paleozoic succession within the basement of the West Siberian Basin. This new insight may be used to predict similar accumulations in poorly explored territories.