Search Results (328)

The aim of the study is to assess the effect of diagenesis on the reservoir properties of Carboniferous sandstones in Western Pomerania (NW Poland). The research focuses on Mississippian (Łobżonka Shale, Gozd Arkose, and Drzewiany Sandstone formations) and Pennsylvanian (Wolin, Rega, and Dziwna formations) rocks. A comparative analysis of the sandstones in the individual formations was carried out. The sandstone samples taken from 13 deep boreholes were studied petrographically (using a polarizing microscope, cathodoluminescence, and a scanning electron microscope), and petrophysical features were measured. The Carboniferous sandstones are represented mainly by quartz arenites ranging from very fine- to medium-grained and arkosic and lithic arenites from fine- to coarse-grained. The main diagenetic processes that affected the porosity and permeability of quartz arenites were compaction and cementation. Compaction reduced the primary porosity by an average of about 60% and cementation by about 40% in the Pennsylvanian sandstones. Primary porosity of arkosic and lithic arenites was affected mainly by compaction, cementation, and dissolution. Arkosic arenites have lost an average of 80% of their primary porosity as a result of mechanical compaction. The porosity of these sandstones increased due to the dissolution of mainly feldspar grains and the formation of secondary porosity. Among the Mississippian sandstones, quartz arenites of the Łobżonka Shale Formation exhibit unfavorable reservoir properties (porosity approx. 1%, impermeable). The volcaniclastic arkosic and lithic arenites of the Gozd Arkose Formation have poor reservoir qualities (porosity usually around 5%, mostly impermeable). The quartz arenites of the Drzewiany Sandstone Formation show the best reservoir properties (porosity of about 18%, permeability up to 1000 mD). The Pennsylvanian sandstones, quartz arenites of the Wolin and Rega formations, are characterized by good reservoir qualities (porosity approx. 10%, permeability up to 200 mD), while the Dziwna Formation sandstones show worse properties (porosity approx. 10%, often impermeable). Full article

The northern part of the Naomugeng Sag in the Erlian Basin shows favorable sandstone-type uranium mineralization in the lower member of the Saihan Formation. The sandstone thickness ranges from 39.67 to 140.36 m, with an average sand content ratio of 76.33%, indicating broad prospecting potential. This study focuses on samples from uranium ore holes and uranium-mineralized holes in the area, conducting grain-size analysis of uranium-bearing sandstones, heavy mineral assemblage analysis, and detrital zircon U-Pb dating to systematically investigate provenance characteristics. The results indicate that the uranium-bearing sandstones in the lower member of the Saihan Formation were primarily transported by rolling and suspension, characteristic of braided river channel deposits. The heavy mineral assemblage is dominated by zircon + limonite + garnet + ilmenite, suggesting that the sedimentary provenance is mainly composed of intermediate-acid magmatic rocks with minor metamorphic components. Detrital zircon U-Pb ages are mainly concentrated in the ranges of 294–217 Ma (Early Permian to Late Triassic), 146–112 Ma (Middle Jurassic to Early Cretaceous), 434–304 Ma (Late Carboniferous to Early Permian), and 495–445 Ma (Middle–Late Ordovician to Early Silurian). Combined with comparisons of the ages of surrounding rock masses, the provenance of the uranium-bearing sandstones is mainly derived from intermediate-acid granites of the Early Permian–Late Triassic and Middle Jurassic–Early Cretaceous periods in the southern part of the Sonid Uplift, with minor contributions from metamorphic and volcanic rock fragments. The average zircon uranium content is 520.53 ppm, with a Th/U ratio of 0.73, indicating that the provenance not only supplied detrital materials but also provided uranium-rich rock bodies that contributed essential metallogenic materials for uranium mineralization. This study offers critical insights for regional prospecting and exploration deployment. Full article

Infrared spectroscopic analysis of palygorskite clay from the Dashkovskoye and Borshchevskoye deposits yielded key insights into the sedimentation conditions prevailing in the study area. In this paper, the composition, structure, and adsorption properties of smectite–palygorskite clays from the Steshevian sub-stage of the Lower Carboniferous (Russia) are investigated. The study applied X-ray diffraction, infrared spectroscopy, scanning electron microscopy, assessment of cation exchange capacity by adsorption of [Cu(trien)²⁺], assessment of Cs sorption, and particle size analysis. It is demonstrated that the Al–palygorskite of the Dashkovskoye deposit was formed by sedimentation from suspended matter in a shallow-water basin in the Steshevian sub-age, despite a different genesis (chemogenic in the case of the palygorskites, clastic/redeposited in the case of the smectites). The palygorskites of the Borschovskoye deposit have a complex terrigenous genesis and were formed from redeposited chemogenic Al–palygorskites transported into the basin from the surrounding region of the Dashkovskoye deposit. With increasing depth of the basin in the Steshevian sub-age, the volume of incoming palygorskite material decreases, and the proportion of smectite material increases. The Fe–palygorskites entered the Borschovskoye deposit due to the redeposition of sediments from soils upstream of water flows. All the studied clays have considerable adsorption properties (32–49 mg-eq/100 g) and can be used in various industries. Full article

As a tectonically stable and extensively superimposed basin situated in the North China Craton, the Ordos Basin hosts abundant reserves of oil, natural gas, and coal within its Paleozoic strata, rendering it a focal area in energy-related geological research. The basin’s evolutionary history provides a comprehensive record of key geological transitions—from an Early Paleozoic carbonate platform to Late Paleozoic marine–continental transitional deposits and ultimately to continental clastic sedimentation—largely governed by the regional tectonic dynamics associated with the North China Plate. This study presents a systematic review of the sedimentary and tectonic evolution of the Paleozoic sequence in the basin. Findings indicate that during the Early Paleozoic, the basin developed under a passive continental margin setting, characterized by widespread epicontinental marine carbonate deposition. By the Late Ordovician, subduction of the Qinqi Ocean triggered the Caledonian orogeny, resulting in regional uplift across the basin, widespread erosion, and a significant hiatus in Middle to Late Ordovician sedimentation, which facilitated the formation of paleo-weathered crust karst reservoirs. In the Late Paleozoic, the basin evolved into an intracratonic depression. From the Late Carboniferous to the Early Permian, the Hercynian tectonic event influenced the transformation from isolated rift basins to a broad epicontinental sea, leading to the deposition of critical coal-bearing strata within marine–continental transitional facies. Starting in the Middle Permian, the closure of surrounding oceanic domains induced widespread tectonic uplift, shifting the depositional environment to a terrestrial fluvial-lacustrine system and marking the termination of marine sedimentation in the region. Based on the comprehensive research findings, this study underscores that the superposition, inheritance, and interaction of multiple tectonic events are the primary controls on the paleogeographic architecture and sedimentary. Full article

Bottom-water coning is a core challenge in the development of high-temperature, high-pressure, high-permeability, and fractured bottom water reservoirs. Taking the Carboniferous reservoir in Xinjiang as the research object, this work uses numerical simulation to optimize key parameters of artificial barriers, water drainage, and nitrogen injection technologies. The results show that an artificial barrier with a 30-m radius and intervention at 60% water cut placed at the reservoir top reduces water coning height by over 40%; water drainage starting after the third production year delays water cut rise by more than 2000 days; and nitrogen injection in the eighth production year at 65 MPa cuts water coning height by 30% to 40%. This work proposes a full-life-cycle phased synergy strategy, integrating early artificial barrier water blocking, mid-term intelligent water drainage pressure reduction, and late nitrogen injection oil stabilization. This work provides a direct and feasible technical paradigm for the efficient development of similar high-temperature, high-pressure, and fractured bottom water reservoirs worldwide. Full article

This article presents a comprehensive study of the nitrogen-radon thermal mineral waters of the Jety-Oguz area, located in the southeastern part of the Issyk-Kul intermountain artesian basin (Northern Tien Shan). Based on new data from chemical and isotopic (δ¹⁸O, δD) analyses of natural waters (lake, river, and mineral) and the chemical composition of the water-bearing rocks, we identify the formation mechanisms of mineral waters with diverse composition, total dissolved solids (TDS), and temperature. Three main genetic types have been identified: (1) saline, high-TDS (up to 12.8 g/L) chloride sodium-calcium thermal waters (up to 32 °C). These waters are of meteoric origin and circulate within Middle Carboniferous carbonate rocks, acquiring their unique composition at depths of up to 3.0 km, where reservoir temperatures reach ~105 °C; (2) chloride-sulfate sodium-calcium waters (0.5 g/L, fresh, 22 °C), formed in alluvial deposits within the zone of active water exchange; and (3) low-TDS (1.8 g/L, brackish) waters of mixed composition, resulting from the mixing of a deep fluid with infiltrating meteoric waters. Isotopic data confirm a meteoric origin for all studied waters, including the high-TDS thermal types. The chemical composition diversity is attributed to several processes: mixing between the deep, high-TDS fluid and low-TDS infiltration waters, intense dissolution of evaporite rocks, and water–rock interaction. These findings are crucial for understanding the genesis of mineral waters in the Tien Shan intermountain basins and provide a scientific basis for their sustainable balneological exploitation. Full article

The Carboniferous coal seams in Northeast Kazakhstan remain insufficiently investigated, with a lack of comprehensive mineralogical and geochemical assessments necessary to understand the geological processes controlling coal quality. This study examines 15 coal samples from the Karagandy Coal Formation (KCF) at the Saradyr and Bogatyr mines using proximate and ultimate analyses, FTIR, XRD, SEM–EDS, ED-XRF, and ICP-OES, providing the first detailed comparison of mineralogical and geochemical characteristics—including depositional signals and inorganic constituent distribution—between these mines within the KCF. The coals exhibit an average ash yield of 24.1% on a dry basis, volatile matter of 21.6% on a dry and ash-free basis, and low moisture content of 1.1% (air-dry), with low sulfur levels of 0.7% in whole coal across both mines. Mineralogical composition is dominated by quartz and clay minerals, with minor pyrite, apatite, chalcopyrite, and rutile. Major oxides in the coal ash average 68.2% SiO₂ and 19.5% Al₂O₃, followed by Fe₂O₃, K₂O, and TiO₂ (3–12.1%). Among the 24 identified trace elements, Sm is the most abundant at 6.3 ppm with slight enrichment (CC = 2.8), Lu remains at normal levels (CC < 1), and most other elements are depleted (CC < 0.5). The Al₂O₃/TiO₂ ratios (3.8–10.8) indicate contributions from intermediate to mafic parent materials. The detrital mineralogy, parting compositions, and elevated ash content indicate significant accommodation space development during or shortly after peat accumulation, likely within a vegetated alluvial plain depression. These findings provide new insights into the depositional environment and coal-forming processes of the KCF and contribute to regional assessments of coal quality and resource potential. Full article

During the course of the Carboniferous to Permian, large parts of eastern Laurentia and northern Gondwana were affected by the Variscan Orogeny accompanying the assembly of Pangea. Here, we concentrate on the Appalachian belt of eastern Laurentia and the Mauritanide of western Gondwana. Owing to the irregular shapes of the craton margins, the collision between Laurentia and the West African Craton provides several conjugate promontories and embayments alongside both cratons. Among others, the coupled pair formed by the African Reguibat promontory and its counterpart in North America, the Pennsylvania embayment, is the principal subject of this study. The western movement of the Reguibat Shield had initially imprinted the West African belts but finally also affected the Appalachians. Acting as a “hallmark”, it produced two specific lobes (stacks of nappes) on both sides of the promontory. The southern NW-SW lobe (Akjoujt nappes) is long known. However, the northern lobe of the “Adrar Souttouf Massif” has not been identified previously, owing to being partially covered and also to its N-S alignment instead of an expected symmetrical SW-NE direction. Furthermore, the Adrar Souttouf Massif is partially covered by allochthonous terranes (Western Thrust Belt, TB, or Appalachians). This new discovery supports a classical impingement model for the deformation of the North American and African belts by westward displacement of the Reguibat Shield. Full article

The Hongche Fault Zone in the Junggar Basin exhibits significant spatiotemporal variations in the relationship between fault systems and hydrocarbon accumulation across different structural belts. Two key factors contribute to this phenomenon: frequent tectonic activities and well-developed Paleozoic fault systems. To date, no detailed studies have been conducted on the fault systems in the Paleozoic strata of the Hongche Fault Zone. In this study, the fault systems in the Paleozoic strata of the Hongche Fault Zone were systematically sorted out for the first time. Furthermore, the controlling effects of active faults in different geological periods on hydrocarbon charging were clarified. Firstly, basing on the 3D seismic and well-log data, the structural framework and fault activity, fault systems, source-contacting faults were characterized. Vertically, the Hongche Fault Zone experienced three major thrusting episodes followed by one weak extensional subsidence Stage, forming four principal tectonic layers: Permian (Thrusting Episode I), Triassic (Thrusting Episode II), Jurassic (Thrusting Episode III), and Cretaceous–Quaternary (Post-Thrusting Subsidence). Laterally, six fault systems are identified: Middle Permian (Stage I), Late Triassic (Stage II), Jurassic (Stage III), post-Cretaceous (Stage IV), as well as composite systems from Middle Permian–Jurassic (Stages I–III) and Late Triassic–Jurassic (Stages II–III). These reveal multi-stage, multi-directional composite structural characteristics in the study area. According to the oil–source correlation, the Carboniferous reservoir is primarily sourced by Permian Fengcheng Formation source rocks in the Shawan Sag. Hydrocarbon migration tracing shows that oil migrates along faults, progressively charging from depression zones to thrust belts and uplifted areas. In this process, fault systems exert hierarchical controls on accumulation: Stage I faults dominate trap formation, Stages II and III faults regulate hydrocarbon migration, accumulation, and adjustment, while Stage IV faults influence hydrocarbon conduction in Mesozoic–Cenozoic reservoirs. By clarifying the fault-controlled hydrocarbon accumulation mechanisms in the Hongche Fault Zone, this study provides theoretical guidance for two key aspects of the Carboniferous reservoirs in the study area: the optimization of favorable exploration zones and the development of reserves. Full article

Tight sandstone gas constitutes a strategically significant resource in the exploration of unconventional hydrocarbon systems. Current understanding of the geochemical composition and genesis of tight sandstone gas in the Daning–Jixian Block, southeastern Ordos Basin, is insufficient, which hampers a comprehensive assessment of its resource potential. This study is the first to systematically investigate the geochemical characteristics and genetic origin of high-maturity tight sandstone gas in the southeastern Ordos Basin’s Daning–Jixian Block. Gas specimens were systematically acquired from multiple stratigraphic units within the reservoir interval and subjected to compositional and carbon–hydrogen isotope analysis. Compared with other gas fields in the Ordos Basin, the Daning–Jixian Block has higher average methane concentration, and notably lower ethane and propane concentrations; its average δ¹³C₁ and δ²H-CH₄ is heavier, while δ¹³C₂ and δ¹³C₃ are lighter. Based on the δ¹³C₁-δ²H-CH₄ diagram, all gas samples from the block and other basin gas fields fall into the geothermal, hydrothermal and crystalline gas domain, indicating gas genesis associated with over-mature organic matter interacting with external hydrogen. Milkov genetic diagram analysis reveals that the natural gas consists of primarily early-stage kerogen-cracking gas, with a minor contribution from crude oil-derived gas originating from Carboniferous–Permian source rocks. Notably, samples from Daning–Jixian exhibit a unique δ¹³C₁ > δ¹³C₂ reversal, attributed to mixing effects between gas from highly mature kerogen and gas from secondary cracking of crude oil. Consequently, ethane carbon isotopes alone are insufficient for definitive genetic classification. These findings provide a new geochemical interpretation framework for analogous high-maturity tight gas reservoirs. Full article

Archaeognatha is phylogenetically positioned as the basal lineage relative to all extant insect orders and comprises approximately 600 described species. The internal phylogenetic relationships and divergence times within this ancient order have long been a subject of scientific debate. In this study, we assembled 14 mitochondrial genomes from species within the genera Pedetontus and Pedetontinus to clarify the phylogenetic relationship and estimate divergence times within Archaeognatha. Phylogenetic analyses revealed that both Machilidae and Machilinae are paraphyletic; Pedetontinus included in this analysis formed a well-supported monophyletic clade, whereas the sampled Pedetontus species were not recovered as a monophyletic clade. Divergence time estimates indicate that Archaeognatha originated during the Late Carboniferous (301.15 Mya, 95% HPD: 298.88–303.67 Mya), with subsequent diversification spanning from the Mesozoic era to the present. The adaptive radiation of epiphytic bryophytes and potential coevolutionary interactions between plants and insects are proposed to have significantly contributed to the diversification of Archaeognatha. Based on multiple lines of evidence, we propose that the current morphological criteria for species delineation within Pedetontus (Pd.) require revision to better reflect its evolutionary history. In the branch-site model analysis, when Pd. silvestrii—collected from temperate regions—was designated as the foreground branch, two positively selected sites were detected at the 66th position of the Cytb and the 34th position of ATP6. When Pd. hainanensis and Pd. bawanglingensis—collected from tropical regions—were used as the foreground branches, six positively selected sites were identified at the 622nd position of Cytb, the 499th position of ATP6, and the 623rd, 873rd, 1106th, and 1141st positions of COI. Full article

The Khanbogd-Erdene region in southern Mongolia is a globally important copper–polymetallic metallogenic province, hosting large to super-large deposits, such as Oyu Tolgoi and Tsagaan Suvarga. The area experiences frequent tectonic–magmatic activity, particularly Late Paleozoic subduction-related magmatism, which controls the occurrence of large-scale copper–polymetallic mineralization. This study focuses on the Late Paleozoic granitic intrusive rocks in the Khanbogd-Erdene region of southern Mongolia. Using LA-ICP-MS and SHRIMP dating techniques, precise zircon U–Pb ages were obtained for 10 samples. A total of 209 zircon grains from these 10 intrusive rocks were analyzed, with most cathodoluminescence (CL) images of zircon grains showing distinct oscillatory zoning. Th/U ratios ranging from 0.11 to 2.92 indicate they are magmatic. The younger group of granitic rocks yielded ages between 260.2 ± 1.2 Ma and 286.6 ± 0.9 Ma, indicating an Early Permian geological age. The other seven samples yielded older ages between 315.9 ± 1.8 Ma and 340.9 ± 0.9 Ma, indicating a Carboniferous geological age. These large-scale Carboniferous to Early Permian intrusive rocks in the Khanbogd-Erdene region are products of tectonic–magmatic activity during specific stages of crustal evolution. The findings provide reliable chronological data for regional tectonic–magmatic activity and offer new evidence for constraining the timing of the Variscan orogeny in southern Mongolia. Full article

The evolution of the sedimentary environment in the Early Carboniferous Dawuba Formation of the Qiannan Depression significantly controlled the distribution of low-total organic carbon (TOC) sediments. In this study, the core samples were analyzed by thin section microscopy, field emission-scanning electron microscopy, pyrite morphology, X-ray diffraction, and geochemical analysis (TOC, sulfur, organic petrography, and major and trace elements). The formation is vertically divided into two members from bottom to top: Member 1 (average TOC = 1.15%) and Member 2 (average TOC = 0.88%). Depositional environment parameters indicate that Member 1 was in a suboxic-oxic transition environment, with weak detrital influx, and moderate paleoproductivity (more developed algae). Member 2 evolved into a stable oxic environment, with significantly enhanced detrital influx and reduced paleoproductivity. The correlations between multiple geochemical proxies (paleoredox, paleoproductivity, and terrestrial detrital influx) and TOC content indicate that high productivity in Member 1 was the main driver of organic matter accumulation, but the suboxic-oxic environment limited preservation efficiency (1.00% < TOC < 2.00%). Member 2, deposited during sea-level fall, experienced long-term oxic conditions and low productivity due to shallower water. Nevertheless, the partial reduction in the exposure time of organic matter within the oxic water column-driven by rapid detrital accumulation-represents a critical mechanism favoring organic-poor sediments (TOC < 1.00%). In conclusion, the development of low-TOC sediments in the Dawuba Formation reflects a transition from a relatively deep to shallow water column, where the synergistic effects of redox conditions, paleoproductivity, and terrigenous detrital influx controlled the distribution and enrichment of organic matter. Full article

The carbonate reservoir of the NT oilfield in the Precaspian Basin is a fracture-pore type with an extremely complex fracture network, comprising both high-angle structural fractures and abundant low-angle bedding-parallel fractures. Both fracture types significantly impact waterflood development, making effective prediction and characterization of the complex fracture network crucial for optimizing waterflooding and development plans. Using core, imaging logging, conventional logging, seismic, and production performance data, we predicted the distribution of high-angle structural and low-angle bedding-parallel fractures. A discrete fracture network (DFN) was constructed by grouping fractures based on strike and dip angles, and the influences of fractures with different dip angles on the initial production of individual wells and production decline rates were analyzed. Results show that high-angle fracture distribution is effectively predicted by combining imaging logging data with seismic volumes processed via ant-tracking technology, while low-angle fractures are well predicted using conventional logging, imaging logging, and seismic data processed by dip deviation. High-angle fractures are predominantly developed near and parallel to faults; low-angle fractures are mainly distributed in fold limbs. Fractures were grouped into northeast, southeast, southwest, northwest high-angle fractures, and low-angle fractures. Fracture modeling indicates a reservoir fracture porosity of 0~0.27% and permeability of 10~100 mD. With increasing fracture density, single-well initial productivity and production decline rates are higher in high-angle fracture zones than in low-angle fracture zones. Low-angle fractures contribute to ~56.45% of high-angle fractures’ production and affect production decline at ~82.5% of high-angle fractures’ level. This method is significant for predicting and modeling complex fracture networks in other reservoirs. Full article

Structures resembling iron-related bacteria (IRB) have been found in the Mississippian limestones that form part of the carbonate platform in the Moravo-Silesian Basin that surrounds the Upper Silesian Block, an eastern margin of the Brunovistulicum. Microfacial, petrological, and geochemical analyses were used to determine the bacteria-like structures that are present in narrow zones unrelated to bedding. We present here the morphology and chemistry of the studied microstructures showing their similarities to IRB from the present-day Sphaerotilus-Leptothrix group, the Galionella group, and the Mariprofundus ferrooxydans species. We suggest that bacterial growth occurred in the originally empty micropores of microfossil skeletons and shells, between bioclasts or in secondary voids formed during the selective dissolution of micrite or smaller sparite crystals. Hydrothermal solutions, associated probably with the post-Variscan magmatism in this area, provided iron compounds for the growth of the IRB. Full article