Conglomeratic Sandstone Research Articles

Facies variations in gravelly cyclic steps deposited from turbidity currents: Miocene fan delta front deposits compared with a modern active fan delta, central Japan

AbstractGravelly cyclic steps formed by turbidity currents have recently been widely recognised in the geological record. However, the comparison between modern and ancient gravelly cyclic steps remains challenging. In this study, the facies variations of gravelly cyclic steps deposited from turbidity currents in an outcrop of Miocene fan delta front deposits in central Japan are compared with the geomorphic evolution of analogous cyclic steps on the active fan delta front in modern geological systems. These cyclic steps share common characteristics in setting, grain size and dimensions, allowing direct comparison between ancient and modern examples. Repeat bathymetric surveys of the modern Kurobe River fan delta have revealed various types of upslope migrating bedforms interpreted as cyclic steps. Most of these are short‐lived due to erosion of thalwegs by powerful surge‐type turbidity currents triggered by slope failures or burial of thalwegs by deposition, possibly from river‐fed hyperpycnal flows. Such erosion and burial events occur annually on the fan delta front, resulting in compensational cycles. Sedimentary facies of the Miocene fan delta front deposits include conglomerate with a gently upslope dipping erosional base, backset‐stratified sandstone and foreset‐stratified sandstone, which are interpreted as deposits of hydraulic jumps in high‐density turbidity currents in scours on the stoss sides of cyclic steps. Parallel‐stratified conglomerate sandstone is an additional component. Although previous facies models of gravelly cyclic steps have focussed on deposits on stoss sides, a comparison of modern and ancient examples suggests that facies on the lee sides could be parallel‐stratified conglomerate sandstone and undulating bedforms, reflecting supercritical flow conditions. The present study also suggests that hyperpycnal and surge‐type high‐density turbidity currents may deposit different types of facies and play different roles in the construction and destruction of cyclic steps. The present study has significant implications for facies models of gravelly cyclic steps.

Characterization of Pore Structure and Two-Phase Seepage Pattern in Sandstone Conglomerate Based on CT Scanning

Characterization of Pore Structure and Two-Phase Seepage Pattern in Sandstone Conglomerate Based on CT Scanning

Investigating the causes of permeability anisotropy in heterogeneous conglomeratic sandstone using multiscale digital rock

Heterogeneous conglomeratic sandstone exhibits anisotropic physical properties, rendering a comprehensive analysis of its physical processes challenging with experimental measurements. Digital rock technology provides a visual and intuitive analysis of the microphysical processes in rocks, thereby aiding in scientific inquiry. Nevertheless, the multiscale characteristics of conglomeratic sandstone cannot be fully captured by a single-scale digital rock, thus limiting its ability to characterize the pore structure. Our work introduces a proposed workflow that uses multiscale digital rock fusion to investigate permeability anisotropy in heterogeneous rock. We use a cycle-consistent generative adversarial network to fuse computed tomography scan data of different resolutions, creating a large-scale and high-precision digital rock that comprehensively represents the conglomeratic sandstone pore structure. Subsequently, the digital rock is partitioned into multiple blocks, and the permeability of each block is simulated using a pore network. Finally, the total permeability of the sample is calculated by conducting an upscaling numerical simulation using the Darcy-Stokes equation. This process facilitates the analysis of the pore structure in conglomeratic sandstone and provides a step-by-step solution for permeability. From a multiscale perspective, this approach reveals that the anisotropy of permeability in conglomeratic sandstone stems from the layered distribution of grain sizes and differences in grain arrangement across different directions.

Agrogeological and mineralogical characteristics of the soil from experimental fields of the Institute of Agriculture-Kyustendil, Bulgaria

Four main and two secondary feeding provinces with minerals and soil forming material are determined: Bistritsa River feeding province, Struma River feeding province, Struma Diorite Formation feeding province and Neogene Conglomerate Sandstone feeding province. Montmorillonite from the clay minerals, quartz, magnetite, and chlorite shales are determined as the most important agricultural minerals for the studied soils. Quartz has property of creating electrical energy under the influence of external factors such as pressure, shock, heat, friction, chemical reactions, etc. make it a prime suspect as a source of energy and electrical impulses in soil, which are very important for cation exchange between soil and plant roots and for converting some substances into others, incl. of inorganic chemical compounds in organic. Quartz determines the basic granular composition of the soil and determines the moisture absorption, plasticity, moisture performance, etc. It helps maintain constant temperature and acidity of the soils. Magnetite associates with carbonates and quartz and by this way marks secondary mineralization due to adsorption processes in the soil and speaks of the participation of magnetite in cation exchange processes in the soil. The mineral magnetite is also related to the microbial composition of the soil. Chlorite shale as well as Montmorillonite can, under certain conditions, release chlorine and thus, together with the released sodium described above, NaCl salt is formed, which is the mineral halite or otherwise table salt, which salinized the soil and leads to damage to agricultural production, worsens the quality and storage life of the fruit and finally leads to the death of the plants and economic loses. In these cases it is needed to use gypsum agricultural mineral fertilizer for neutralization of the salt and its drainage.

THE COMPARATIVE DEPOSITIONAL HETEROGENEITY OF MANCHHAR FORMATION (SIWALIK GROUP), SOUTHERN INDUS BASIN, PAKISTAN

Present study is carried out for detailed description, distribution and interpretation of lithofacies and textural analysis of Manchhar Formation from Gaj River, Manchhar Lake and Lal Bagh Sections of Southern Indus Basin Pakistan. Four different clastic lithofacies are identified during present study, which are conglomeratic sandstone (Gt), shale (Fm), fine to coarse grain flat bedded sandstone (Sh) and fine to coarse grain trough cross-bedded sandstone (St). These Facies suggest that Manchhar Formation is deposited in the Beach to shallow agitated water and fluvial system. Twenty-nine (29) unconsolidated loose and friable sandstone samples were selected for textural analysis. Grain-size parameters such as mean, median, standard deviation, Skewness and Kurtosis were used for transport history, mode and hydrodynamic energy condition to recognize the depositional environment. Stewart Diagram shows deltaic/wave water process takes active role under the influence of wave process. Linear discriminant functions analysis show that the fluvial environment of deposition dominates and influences shallows water and beach environment. Passega diagram reveals that transport mode was rolling and suspension by the tractive current that shows the fluvio-deltaic to deltaic wave with the influence of wave depositional environment of Miocene-Pliocene (Neogene) Manchhar Formation.

Experimental study of the effects of a multistage pore-throat structure on the seepage characteristics of sandstones in the Beibuwan Basin: Insights into the flooding mode

To investigate the relationship between grain sizes, seepage capacity, and oil-displacement efficiency in the Liushagang Formation of the Beibuwan Basin, this study identifies the multistage pore-throat structure as a crucial factor through a comparison of oil displacement in microscopic pore-throat experiments. The two-phase flow evaluation method based on the Li–Horne model is utilized to effectively characterize and quantify the seepage characteristics of different reservoirs, closely relating them to the distribution of microscopic pores and throats. It is observed that conglomerate sandstones at different stages exhibit significant heterogeneity and noticeable differences in seepage capacity, highlighting the crucial role played by certain large pore throats in determining seepage capacity and oil displacement efficiency. Furthermore, it was found that the displacement effects of conglomeratic sandstones with strong heterogeneity were inferior to those of conventional homogeneous sandstone, as evidenced by multiple displacement experiments conducted on core samples with varying granularities and flooding systems. Subsequently, core-based experiments on associated gas flooding after water flooding were conducted to address the challenge of achieving satisfactory results in a single displacement mode for reservoirs with significant heterogeneity. The results indicate that the oil recovery rates for associated gas flooding after water flooding increased by 7.3%–16.4% compared with water flooding alone at a gas–oil ratio of approximately 7000 m3/m3. Therefore, considering the advantages of gas flooding in terms of seepage capacity, oil exchange ratio, and the potential for two-phase production, gas flooding is recommended as an energy supplement mode for homogeneous reservoirs in the presence of sufficient gas source and appropriate tectonic angle. On the other hand, associated gas flooding after water flooding is suggested to achieve a more favorable development effect compared to a single mode of energy supplementation for strongly heterogeneous sandstone reservoirs.

Sedimentary sequence and evolutionary characteristics of the rift system of Neoproterozoic Nanhua System and Doushantuo Formation: A case study from the northeastern margin of Sichuan Basin

Neoproterozoic strata are widely developed in the Upper Yangtze region of South China, among which the Sinian Dengying Formation has been discovered with numerous large gas fields in the Sichuan Basin, and hence they have become an essential domain for natural gas exploration and development. The early‐to‐middle Neoproterozoic Nanhua System and Doushantuo Formation are characterized by rifting deposits in the northeastern margin of Sichuan Basin, but their depositional succession and sequence architectures are still unclear, which has largely restricted our understanding of the resource potential of these strata. In this paper, based on the outcrops of the Neoproterozoic Nanhua System and Doushantuo Formation in the northeastern margin of Sichuan Basin, we describe the stratigraphic distribution and sedimentary evolutionary characteristics, and establish the regional stratigraphic framework, sedimentary cycle and evolutionary sequence of the Nanhua System and Doushantuo Formation. The results show that the lithology of the Nanhua System and Doushantuo Formation is primarily composed of conglomerate, conglomeratic sandstone, medium‐fine sandstone, siltstone, mudstone, shale and tillite; a variety of sedimentary facies including alluvial fan, river, delta, coastal shore, shelf, basin and tillite were developed; five third‐order sequences could be identified, representing multiple cycles of marine transgression and regression. The climate during the deposition of the Nanhua System and Doushantuo Formation underwent from a warm and humid pre‐glacial period through cold and arid multiple glacial periods to a warm and humid interglacial period, which consequently formed a sedimentary sequence of alluvial fan and fluvial delta to tillite during the early period, shelf basin to tillite during the middle period and slope basin to delta facies during the late period. In terms of a plan view, the depositional pattern is composed of alluvial fans and deltas at the proximal part of the rift, deep‐water shelf to slope at the middle part of the rift and slope to basin facies at the central part of the rift. Finally, we propose that large‐scale distribution of high‐quality source rocks developed in the interglacial Datangpo and Doushantuo formations, while fluvial‐deltaic reservoirs occurred in the Gucheng, Nantuo and Doushantuo formations, thus showing favourable resource potential and exploration prospects within the Sichuan Basin.

Sedimentology and stratigraphy of silicified fossil trunks bearing Missão Velha Formation (late jurassic-early cretaceous), Araripe Basin, Northeastern Brazil: Paleoclimatic implications

The paper focuses on the sedimentological, stratigraphic, and climatic implications of silicified fossil trunks found in the Missão Velha Formation (MVF) of the Araripe Basin in Northeastern Brazil. The rich fossiliferous plant assemblages in the MVF are primarily dominated by conifers, specifically a group known as Agathoxylon, and are associated with coarse sandstone and conglomerate fluvial beds. The MVF represents a late Jurassic-early Cretaceous formation deposited during the Early Rift phase of the basin. Silicified fossil trunks and woods from the MVF have been known since 1863, and previous studies have discussed their morphology, internal structure, and paleogeographic implications. Taphonomically, these macrofossils have been interpreted as hypautochthonous, meaning they originated from their growth sites. However, some authors have suggested an allochthonous origin for these fossils. Despite their significance, the sedimentological and stratigraphic characteristics of these fossil associations have received limited attention in previous research. We have collected the fosil trunks exclusively in the MVF, and they are restricted to the upper parts above an internal unconformity. Two main taphofacies were identified: T1 comprises coarse-to medium-sandstones, locally conglomeratic, with planar and trough cross-stratifications, with abundant fossil wood and trunks, and T2 defined as well-stratified pebbly conglomerates, with horizontal to cross bedding, with larger common fossil wood and trunks fragments. T1 taphofacies occur in most of the cross-stratified sandstones of the upper part of the MVF, T2 taphofacies (larger wood logs) are primarily concentrated in a coarse sandstone to conglomeratic bed strata at the top of the MVF. The preservation of the trunks is characterized by uncompressed fragments with poorly rounded edges. The cell walls are preserved by permineralization, with the spaces filled by silica, indicating short transport and rapid burial. The silicified fossil woods are found in foresets of planar and trough cross-stratifications, associated with coarse-grained to conglomeratic sandstones. These sandstones are highly abundant, sometimes forming anomalous concentrations, such as in the Grota Funda outcrop. The dimensions of the fossil trunks range from 5 cm up to 2 m in length, with some exceptionally large trunks measuring approximately 1.70 × 1.40 m. The investigated trunks exhibit various orientations, with some concordant and others dissenting from the surrounding strata. However, the majority of the fossil trunks do not show a preferential orientation. Orientation analysis of more than twenty logs suggests a predominant south paleocurrent direction trend, likely resulting from monsoon storms originating from a source area to the north. The assemblages were likely formed through putrefaction processes and late fragmentation, followed by size-selection through fluvial transport. The relatively short transport distance is indicated by the preserved edges, lack of preferential position, and the size of the trunks. Consequently, it is inferred that the trunks originated within the basin itself rather than being transported from the basement area, supporting their hypautochthonous character. The MVF and the associated plant remains bear resemblance to deposits of similar age in other Northeast Brazilian basins, such as the Recôncavo-Tucano-Jatobá, Sergipe-Alagoas, and Camamu-Almada basins, as well as the Gabon Basin in Western Africa. Evidence from the trunk taphofacies, stratigraphy and sedimentology of the MVF is consistent with a warm, seasonal, hot, and humid climate, indicative of a monsoon climate similar to other conifer forests in Gondwana during the Mesozoic era.

Volcanoclastic and epiclastic diagenesis of sandstones associated with volcano-sedimentary deposits from the upper Jurassic, Lower cretaceous, Paraná Basin, southern Brazil

The opening of South Atlantic Ocean produced an immense volume of lava that covered an active aeolian system during Lower Cretaceous. The contact of Botucatu Formation sandstones with the Serra Geral volcanic flows generated a variety of volcano-sedimentary features and deposits. During volcanism, the temperature contrast between lava and wet or water-saturated sediments formed volcanoclastic features and related sedimentary deposits. In moments of magmatic quiescence, epiclastic deposits were generated due to the return of sedimentation. Volcanoclastic deposits include volcanic breccias with sandy matrix, and epiclastic deposits include conglomerates and conglomeratic sandstones with intraclasts. Quantitative petrography of the sandy matrix samples of these deposits was analyzed, in order to discuss the paragenesis of volcano-sedimentary interactions. Regular burial diagenetic processes were discussed for epiclastic sandstones and contact diagenesis processes for volcanoclastic sandstones. The original composition of volcanoclastic and epiclastic sandstones is heterogeneous. However, the main difference between them is the presence of textural fluidization indicators found in the volcanoclastic sandstones, along the lava-sediment interface. These textural characteristics indicate that the unconsolidated sediments were probably wet or saturated in water during the interaction with the volcanic flow. Epiclastic sandstones have infiltrated clays and neoformed smectites as their main diagenetic constituent due to alteration of available volcanic lithoclasts. For volcanoclastic sandstones, the formation of opal, chalcedony and megaquartz cements through burial is unlikely, due to the intergranular volume occupied by these cements, indicating near-surface early diagenetic conditions. Therefore, the mechanisms of dissolution and repreciptation of the siliceous fluids, incorporated in the system, formed mainly the chalcedony cementation. Furthermore, zeolite cementation, which occurs along the lava-sediment contact, is another important indicator of contact diagenesis for volcanoclastic sandstones. During telodiagenesis, the formation of secondary porosity by dissolution of volcanic lithoclasts and detrital K-feldspar grains was of great importance in volcanoclastic and epiclastic sandstones.

Sedimentology, stratigraphy and glacial genetic model of the coromandel phosphate deposit, Vazante group, central Minas Gerais state, Brazil

The Coromandel sedimentary phosphate deposit is inserted at the external zone of the Brasília Fold Belt geological context, more specifically in the Retiro Formation, basal unit of the Vazante Group. Compared to the world-class Rocinha Formation deposits, widely studied due to high economic interest, the Coromandel Deposit is the one that most lacks studies focused on the main rocks description, faciological characterization and proposal of a plausible metallogenetic model according to the depositional environments. Thus, from the detailed field description of outcrops, geological cartography, microscopic petrography and X-ray diffraction and fluorescence analysis, it was possible to contribute to a better understanding of the deposit. The Retiro Formation is characterized by a glaciogenic facies association that comprises polymictic diamictite, conglomeratic sandstone, fine whitish arkosean, massive and laminated siltstone, besides phosphate facies, including phosphate siltstone, laminated phosphorite and brecciated phosphorite. The phosphatic facies occur in straight relation to the glaciogenic sediments and not rare directly over diamictite, which matrix can be phosphated as well. These rocks P2O5 contents range from 2% to 34% and the succession suggest an establishment of a glaciotransitional environment responsible to constrain favorable alkalinity, temperature and oxi-reduction conditions to directly chemical precipitation of fluorapatite in a mechanism analogue as the cap dolomites, supporting an idea of “cap phosphorites”. The phosphate source is related to the glacial sedimentary supply of continental origin (granite, carbonatite and other alkaline bearing rocks). In addition, the input of cold water, as result of ice melting episodes, became a limiting development factor for phosphorus metabolizing organism which improves the P2O5 system enrichment. For the unique genetic conditions, this phosphatic deposit has been called as the Coromandel Deposit Type.

Stressing environmental conditions in the “petrified forest” from the Mata Sequence in the Triassic context of the Paraná Basin

This study deals with the Piscina Outcrop, a Rhaetic reddish conglomeratic sandstone containing silicified logs which corresponds to the Mata Sequence in the southernmost Brazilian Paraná Basin. We performed ground-penetrating radar (GPR) analysis and the results ratified previous sequence stratigraphy analysis indicating that these deposits correspond to architectural elements exclusively related with the filling processes of fluvial channels. The erosive unconformity identified at the boundary between the Mata Sequence and the underlying rock packages could represent a considerable depositional hiatus. The integration of the GPR results with sedimentological and paleovertebrate data from a nearby outcrop at slightly lower topographic level indicated that the layer with the fossil woods is superimposed through an erosive unconformity to the stratigraphic levels corresponding to the Hyperodapedon Assemblage Zone of Carnian age from the basal portion of the Candelária Sequence. The wood assemblage was composed exclusively of araucarian coniferous stems identified as Agathoxylon (cf. Agathoxylon). The wood growth patterns were mainly characterized by woods showing indistinct growth rings, with latewood mostly restricted to one cell in each ring, suggesting weak seasonality and short-term, periodic droughts. Rare specimens with absent growth rings were also present. Oscillations in growth ring width and the common occurrence of false rings were likely linked to plant exposure to climatic instability. Anatomical evidence pointed to active biochemical responses to intense and extensive biological attack of fungi and arthropods. The dominant presence of carbon in the elemental composition of a dark substance filling many tracheid lumens suggested a very likely affinity with polyphenol remnants in biochemical barriers. The set of wood signatures seems to be linked to regional stressing conditions rather than to the paleolatitudinal location when compared to other key South American basins during the Rhaetic. An allochthonous taphocoenosis is the most likely taphonomic interpretation for this wood assemblage. The logs were probably incorporated into the stream through the collapse of riparian areas and buried in the fluvial channel by high-energy flows after biotic and abiotic decay processes during lifetime and secondarily through exposition before entombment in a river channel.

The characteristics and genetic mechanisms of the Upper Permian Shangwuerhe clastic reservoir in the eastern Junggar Basin, Northwest China

In this paper, the lithology, pore type, throat structure, and physical characteristics of the sandstone and conglomerate reservoirs of the Upper Permian Shangwuerhe Formation in the Fukang Sag of the Junggar Basin were analyzed through rock cast thin section, scanning electron microscopy, fluid inclusions, piezometric mercury, and porosity–permeability analysis. In addition, the reservoir densification mechanism and the genesis of deep effective reservoirs were discussed. The results show that the reservoir is dominated by lithic sandstone (or lithic sandstone conglomerate). The lithic fragments primarily comprise tuffaceous volcanic rocks, supported by grains and cemented by clay, carbonate, authigenic quartz, and laumontite. The reservoir properties are characterized by extra-low porosity and permeability, and the pore type is dominated by inter- and intragrain dissolved pores of lithic fragments, feldspar, and quartz. The pore connectivity is poor due to poorly sorted extra-fine throat channels. The tightness of the reservoir.is due to the strong cementation of calcite, chlorite, montmorillonite, illite-montmorillonite mixed layer, authigenic quartz, and laumontite. Furthermore, the large amount of Ca2+ released by the hydration of tuff rock debris and intermediate–basic volcanic rock debris and the CO2-rich thermal fluid from the deep layers cause the development of several calcites. The formation of several montmorillonites is mainly related to the alteration of filled volcanic ash, and the hydration of volcanic tuff material primarily causes the development of laumontite cementation. The dissolution of feldspar and various volcanic lithic fragments by acidic fluids triggers the physical improvement of the reservoir in the local section.

Deposition of sandstone (early Cambrian) above the Great Unconformity in the Sino-Korean Block, Gondwana: Control of antecedent topography

The global transition between the Precambrian and Phanerozoic eons in concert with rise in eustatic sea-level caused an important change in paleoenvironments, represented by sedimentary records above the Great Unconformity. In the Sino-Korean Block, Gondwana, the unconformity has been recognized by a boundary between various basement rocks and the overlying distinctive suite of sandstone (including conglomerate, conglomeratic sandstone, and mudstone) of the early Cambrian age. A plate tectonic reconstruction of the Cambrian-Ordovician succession in the northeast Asian continent reveals that the sandstone deposited largely in the eastern part of the platform (North China Platform), including the Taebaeksan and Pyeongnam basins. In the western part of the platform, the basal sandstone is correlated to basal carbonate rocks of middle Cambrian age, forming a time-transgressive or diachronous unconformity. The disparity in sedimentary facies of the basal deposits overlying the Great Unconformity was primarily due to antecedent topography of the bounding continent: in the eastern platform, the drainage area comprised high-relief Precambrian massifs, whereas in the western part, it comprised low-relief massifs. During the initial stage of sea-level rise, the eastern part of the platform formed progressively open shoreface and foreshore environments with localized embayments in which relatively coarse-grained gravelly sandstone deposited in fan-delta and tide-dominated environments. In the western platform, however, the supply of siliciclastic sediments was limited and the sandstone formed a relatively narrow linear belt of delta and distributary mouth bars and foreshore deposits. In the rest of the platform farther west, accommodation created by subsequent sea-level rise was filled with carbonate sediments. This study demonstrates that antecedent topography of the unsubmerged drainage area played a major role for the deposition of sandstone in the initial transgression stage, forming the Great Unconformity.

Epithermal Vanadium Mineralization in Sonia Sandstone of Marwar Supergroup, India

Abstract Present study of vanadium mineralization in the Sonia sandstone of Jodhpur Group shows first hydrothermal activity in the Sonia sandstone of Marwar Supergroup. The Sonia sandstone served as a host for the mineralizing solutions. The vanadium mineralization occurred in sandstone- gritty sandstone-conglomerate along faults. Field relationship and petrological study suggests that mineralization is filled by epithermal solutions and provide a better understanding of the timing and nature of the alteration processes. Though the source of the vanadium is not well constrained, but is possibly from the partial melting of banded gneissic complex-II (Sirohi Group), the source (crustal) melt had assimilated material from the rocks of Sirohi Group in significant amount. Deposition of tuffs at top of Sonia Formation (Chhoti Khatu) and emplacement of last stage Malani dykes suggest that the last phase of Malani magmatism generated heat for the partial melting of banded gneissic complex-II (Sirohi Group). The occurrence of vanadium in sandstone–gritty sandstone–conglomerate from Sonia Formation of Marwar Supergroup has opened a new chapter to explore uranium which generally occurs after vanadium mineralization in conglomeratic sedimentation.

Research on Proppant Optimization and Field Test of Ultra-Deep Tight Conglomerate Sandstone Reservoir

Efficient development of deep tight reservoirs in the southern margin of the Junggar Basin requires stimulation technology, and effective propped hydraulic fractures are the key to successful stimulation. To optimize the proppant selected for reservoir stimulation, the important parameters of proppant selection were determined through the proppant conductivity evaluation experimental study and field test, considering the influences of high temperature and high closure pressure. The results show that closure pressure, temperature, and sand concentration have a great influence on the conductivity of the proppant pack. The conductivity of the proppant pack decreases by about 10% at high temperatures, which is because the high temperature will rupture more proppant and thus reduce proppant pack permeability. In the long term, the Scenario B placement pattern can maintain high conductivity, and the long-term conductivity is increased by 6–26% compared with the Scenario C placement pattern. Furthermore, increasing the proppant placement concentration is conducive to the long-term conductivity of the fracture. During the operation of the test well, the treatment pressure was stable, and the fractures were effectively propped. No proppant flowing back occurred in the test production after the fracturing treatment, which achieved the purpose of the evaluation well, provided support for the large-scale development of subsequent development wells, and ensured orderly development.

Well-Logging-Based Lithology Classification Using Machine Learning Methods for High-Quality Reservoir Identification: A Case Study of Baikouquan Formation in Mahu Area of Junggar Basin, NW China

The identification of underground formation lithology is fundamental in reservoir characterization during petroleum exploration. With the increasing availability and diversity of well-logging data, automated interpretation of well-logging data is in great demand for more efficient and reliable decision making for geologists and geophysicists. This study benchmarked the performances of an array of machine learning models, from linear and nonlinear individual classifiers to ensemble methods, on the task of lithology identification. Cross-validation and Bayesian optimization were utilized to optimize the hyperparameters of different models and performances were evaluated based on the metrics of accuracy—the area under the receiver operating characteristic curve (AUC), precision, recall, and F1-score. The dataset of the study consists of well-logging data acquired from the Baikouquan formation in the Mahu Sag of the Junggar Basin, China, including 4156 labeled data points with 9 well-logging variables. Results exhibit that ensemble methods (XGBoost and RF) outperform the other two categories of machine learning methods by a material margin. Within the ensemble methods, XGBoost has the best performance, achieving an overall accuracy of 0.882 and AUC of 0.947 in classifying mudstone, sandstone, and sandy conglomerate. Among the three lithology classes, sandy conglomerate, as in the potential reservoirs in the study area, can be best distinguished with accuracy of 97%, precision of 0.888, and recall of 0.969, suggesting the XGBoost model as a strong candidate machine learning model for more efficient and accurate lithology identification and reservoir quantification for geologists.

Petrography and Heavy Mineral Studies of Lokoja Formation along Mount Patti North Central Nigeria: Implication for provenance Studies

The Southern Bida basin consists of the Lokoja, Patti, and Agbaja formations. This study focuses on the Lokoja formation and samples gotten were used for petrography and heavy mineral analysis. Results of all analytical techniques employed in the study are presented here. A critical assessment of each set of results and their integration aided the proper interpretation and useful discussion. This study focuses on the Southern Bida Basin, specifically the Lokoja Formation because the exposures of Patti are poorly exposed. Outcrop samples were obtained from the exposed sections of the study area in Kabawa and Robinson street respectively. Different features were observed, such as the thickness of the exposure, the nature of the lithology, color, and sedimentary structures. The dominant lithologies in the area include sandstone and ironstone. The sandy facies are generally arkosic characterized by poorly sorted very fine to conglomeratic sandstone sequence. Laboratory investigations of samples included petrography and heavy mineral analysis. Sandstone samples were collected from the study area. Each sample was divided into two parts: the first part for petrographic studies and the second part for heavy mineral analysis.

Integrating Petrography With Core-Log-Well Test Data For Low Permeability Sandstone Reservoir Characterization: Preliminary Recommendation For Production Optimization

Integrating petrographic core information into combined core petrophysics, log, and well test data for understanding facies and environmental deposition in rock characterization has proved itself useful to improving quality and reliability of the required conclusions. This integrated approach has specifically shown its use in the cases of complex reservoirs such ones characterized as low-permeability sandstone reservoirs. It is in this spirit that this paper demonstrates how this virtually cost efficient analysis provides preliminary recommendations for the exploitation of such reservoirs. As case study, two types of producing reservoirs (Bekasap, Bangko, Pematang, and Tanjung Formations) have been taken in 2009. The first type is strongly controlled by depositional environment. It is found in the upper part of Bekasap and Bangko formations (1900 - 2300 ft-ss), deposited in estuarine system, and made of very fine to fine grained sand with low to moderate bioturbation. This mostly feldspathic and lithic greywackes have permeability of up to 200 mD. The second type is strongly dominated by diagenesis process and is mainly found in the Upper Pematang and Tanjung Formations (6200 - 7400 ft-ss). This reservoir type is characterized by its coarse-grained and conglomeratic sandstones resulted from fan- elta and braided channel depositional system. Diagenetic events such as compaction, recrystallization of matrix into microcrystalline clay minerals, precipitation of authigenic minerals in pore system are also well identified from the performed petrographic analysis. This is dominated by sublitharenite and litharenite sandstones exhibit horizontal permeability of up to several dozens mD. The two producing reservoir types have undergone carefully planned exploitation and stimulation operations, and the horizontal drilling and fracturing

INTEGRAÇÃO DE DADOS AEROGAMAESPECTROMÉTRICOS E ELETROMAGNÉTICOS TERRESTRES EM REGIÃO DE OCORRÊNCIAS DE COBRE NO EXTREMO NOROESTE DA BACIA DO CAMAQUÃ, SUL DO BRASIL

Nas diferentes fases de campanhas prospectivas de minerais metálicos como o cobre, a geofísica atua como ferramenta de apoio tanto no reconhecimento de novos alvos exploratórios, quanto na ampliação de jazidas conhecidas, devido à obtenção de contrastes de propriedades físicas entre as mineralizações e as rochas hospedeiras. O presente estudo apresenta os resultados da fase de reconhecimento pela aerogamaespectrometria seguidos de detalhamento de alvos potenciais de cobre pelo método eletromagnético indutivo terrestre em área contemplada pelas ocorrências denominadas Victor Teixeira e Capão Grande, localizadas no interior do município de Caçapava do Sul, Rio Grande do Sul, Brasil. A ocorrência Victor Teixeira está inserida em rochas metamórficas do Escudo Sul-Riograndense, enquanto a de Capão Grande tem como encaixante os litotipos vulcanossedimentares da Bacia do Camaquã. A mineralização aflorante de ambas as ocorrências compreende disseminações de carbonatos dominantemente em fraturas. Os dados radiométricos aéreos possibilitaram a definição de áreas enriquecidas em potássio associadas a produtos de alteração hidrotermal como guias indiretos para a localização de alvos de cobre. A correlação desse guia potássico com concentrações elevadas de tório também constituiu indicativo promissor. Os dados de condutividade aparente obtidos ao longo dos alvos aeroradiométricos possibilitaram sugerir a presença de sulfetos de cobre em áreas condutivas nos xistos do embasamento metamórfico e nos arenitos arcosianos conglomeráticos da Bacia do Camaquã.

The NW Amazonian Craton in Guainía and Vaupés departments, Colombia: Transition between orogenic to anorogenic environments during the Paleo-Mesoproterozoic

In order to improve our understanding of the NW-Amazonian Craton evolution, we present new petrographic, geochemical and geochronological analyses of 27 samples from the geotectonic Rio Negro-Juruena Province in eastern Colombia (Guainía and Vaupés departments). New LA-ICP-MS zircon U-Pb ages suggest that the oldest known rocks in Colombia are metamorphic rocks (migmatitic gneisses) with ages between ~ 1850 and ~ 1800 Ma, and gneisses and granitoids with ages between ~ 1800–1720 Ma which form part of the Mitú Complex, interpreted as the result of Statherian collisional and orogenic events (Querari Orogeny). Detrital zircons in low-grade meta-sedimentary sequences of the Tunuí Group (sandstones, conglomeratic sandstones and mudstones), that crop out over almost the entire basement, indicate older than ~ 1770 Ma source rocks. Intrusions of different suites of granitic rocks with syn- to post-collisional affinities suggest a termination of the collisional events between ~ 1600–1500 Ma which had affected the whole region, occasionally metasomatically overprinting parts of the Tunuí meta-sedimentary sequence. The recognizable metamorphic and magmatic-processes finish with ~ 1400–1340 Ma anorogenic granites without signs of tectonic deformation, resembling anorogenic granites in the Western Amazonian Craton in Brazil and the Parguaza Batholith in Venezuela. This study allows us to conclude that the basement records the collision of a continental arc (Rio Negro-Juruena Province) against the NW-Amazonian Craton (Ventuari-Tapajos Province) and its subsequent transition to anorogenic conditions in a continental rift setting long before the actual stable craton conditions.