Search Results (23)

The transition zone between a shallow-water delta and tidal flat is characterized by a high degree of mixed siliciclastic–carbonate sedimentation. There are frequent lateral and vertical variations in sandstone, dolostone, limestone, and mixed siliciclastic–carbonate rock (MSR); however, their influence on reservoir quality remains uncertain. Member B of the Asmari Formation (Asmari B) in Iraq’s C Oilfield was deposited in a remnant ocean basin formed by the closure of the Neo-Tethys Ocean. During the Oligocene–Miocene, frequent exposure of the Arabian Shield provided intermittent sediment sources to the study area. Under shallow water and relatively arid conditions, widespread mixed sedimentation of siliciclastic sand and dolomitic components occurred. Taking Asmari B as a case study, this research employs core and thin-section observations, trace element analyses, and quantitative mineralogical interpretations of logging data to investigate the characteristics of mixed sedimentation and to evaluate its impact on reservoir quality. Four key aspects were identified: (1) Four main types of mixed lithofacies developed in Member B of the Asmari Formation, namely sandstone-bearing dolomite, dolomitic sandstone, dolostone-bearing sand, and sandy dolostone. These lithofacies were deposited in the transition zone between distributary channels and intertidal zone with different water depths. As the terrigenous input decreased, the water depth for sand-bearing facies increased. In particular, sandy dolostone was predominantly formed in subtidal settings under the influence of storm events. (2) MSRs are categorized based on the proportion of the minor component into high and low mixing degrees. Based on mineral compositions interpreted from well logging data, the mixing degree of MSRs was characterized by the thickness ratio, using the thickness of high- and low-mixing-degree MSRs relative to the total thickness of the formation. The MSRs mainly developed in the B1, B2, B3-1, B3-2, and B4 sublayers, where moderate provenance supply facilitated the high mixing of terrigenous clastic and carbonate components. (3) The pore and throat patterns of MSR reservoirs change with the mixing degree index. When the dolomite content in sandstone exceeds 25%, the pore–throat structure changes significantly. A small amount of sand in dolostone has little effect on the pore and throat. Sandy dolostone exhibits the poorest reservoir quality. (4) Mixed sandstone reservoirs are distributed on both sides of the distributary channels and mouth bar. The dolostone-bearing sand reservoirs are distributed in the transition zone between the sandy flat and dolomite flat. Sandy dolostone is mainly thin and isolated due to the influence of storm events. This study provides guidance for understanding the development patterns of MSR reservoirs under similar geological settings, facilitating the next step of oil and gas exploration in these special reservoirs. Full article

The assessment of grain size and sediment output is crucial for analyzing the pace of sediment erosion, engineering dams and reservoirs, anticipating the impact of climate change and human activities on river systems, and comprehending the presence of trace and heavy metal pathogens and micropollutants. In July 2024, 16 samples of bed sediments were collected from the mainstream of Wadi Fatima and its tributaries in the Makkah region of Saudi Arabia to identify the depositional environments and the hydrodynamic conditions using Passega diagram, Linear Discriminate Function (LDF) and bivariate plots. The results indicate that the sediments being studied exhibit polymodal properties in both the upstream and midstream regions of the main channel of Wadi Fatima. However, in the downstream region, the samples show trimodal properties. Regarding tributaries, the WFT1, WFT2, and WFT4 sediments exhibit polymodal properties, except for WFT3, which is bimodal. Folk’s classification system categorizes the samples into four distinct classes/facies: gravel, sandy gravel, gravely sand, and sand, with respective proportions of 13%, 62%, 6%, and 19%. The sediments found in Wadi Fatima contain a range of graphic mean (M_Z) values, from −3.34 (indicating medium gravel) to 2.48 (indicating fine sand). On average, the M_Z value is −0.79, which shows extremely fine gravel. The standard deviation (sorting (σi)) values of the samples analyzed from Wadi Fatima vary between 0.71 (moderately sorted) and 3.44 (very poorly sorted), with an average of 2.00 (very poorly sorted). The data exhibits a range of skewness (Sk) values, ranging from −0.41 (showing a very coarse Sk) to 0.82 (representing a indicating a very fine Sk). On average, the data shows a Sk value of −0.02, indicating a symmetrical distribution. The kurtosis (K) values span from 0.51 (indicating a very platykurtic distribution) to 2.65 (indicating a very leptokurtic distribution), with an average of 0.95 (indicating a mesokurtic distribution). Full article

Alteration in greisen-type granites develops through the progressive replacement of feldspars by potassic micas. Under the name ‘greisen’, quartz–muscovite assemblages display differences and include a variety of facies with variable relative proportions of quartz and muscovite. In principle, feldspar conversion to muscovite is written usually considering constant aluminium, and should result in a modal proportion of six quartz plus one muscovite. In Beauvoir greisens, which result from albite-rich granite, the relative proportion of quartz–muscovite is in favour of muscovite. Such a balance results from a reaction that implies imputs of potassium and aluminium, thus different from the classic one. The Q’-F’ diagram provides a graphical solution for discriminating between reaction paths. A representative series of greisen data from the literature is compared in this diagram: Beauvoir B1 unit, Cligga Head, Cinovec, Panasqueira, Zhengchong, and Hoggar. Full article

The Upper Miocene–Pliocene Kampungbaru Formation crops out in the easternmost part of the Lower Kutai Basin, Indonesia. The sedimentological analysis of seven outcrops was carried out, and a total of twenty-five samples from these outcrops was analyzed for bulk geochemistry, organic petrography, and bulk and clay mineralogy to assess the effect of the climate and depositional environment on organic matter enrichment. The Kampungbaru Formation consists of interbedded sandstone, siltstone, claystone, and thick coal beds, which were classified into eleven lithofacies. Subsequently, seven facies associations were identified, namely the fluvial-dominated distributary channel, sheet-like sandstone, tide-influenced distributary channel, mouth bar, crevasse splay, delta plain, and delta front. The coal facies generally have a high amount of total organic carbon (TOC, 5.1–16.9; avg. 10.11 wt.%), and non-coal layers range from 0.03 to 4.22 wt.% (avg. 1.54 wt.%). The dominant maceral is vitrinite, while liptinite occurs only rarely in the samples. Organic matter is inferred to have originated from terrestrial plants growing in mangrove swamps. Identified clay minerals include varying proportions of kaolinite, illite, chlorite, and mixed layer illite/smectite (I/S). Kaolinite, which commonly constitutes up to 30% of the clay volume, indicates intensive chemical weathering during a warm and humid climate. In accordance with the Köppen climate classification, the paleoclimate during the deposition of the Kampungbaru Formation is classified as type Af, which is a tropical rainforest. Tropical climate was favorable for the growth of higher plants and deposition of organic matter under anoxic conditions and led to higher amounts of TOC in the Kampungbaru Formation. Full article

Magmatic–hydrothermal breccia pipes are widespread in numerous major porphyry and epithermal gold deposits globally, representing significant repositories of metal resources and serving as potential indicators for exploration targeting. More than ten breccia pipes occur in the Central Taihangshan District (CTD) of the North China Craton. Some of these breccia pipes host gold mineralization and are proposed to be related to the adjacent lode gold mineralization. However, the lack of detailed geological constraints make this hypothesis ambiguous. To address this, the present study conducted comprehensive field observations, drill core logging, an in situ sulfur isotope analysis of pyrite, and the ⁴⁰Ar/³⁹Ar dating of adularia along a 1400 m section of the Tietangdong breccia pipe at Yixingzhai. Three distinct breccia facies were identified at Tietangdong, exhibiting variable proportions across the entire section, including a massive skarn breccia; polymictic, skarn matrix-supported breccia; and polymictic, intrusive rock cement chaotic breccia. Furthermore, adularia ⁴⁰Ar/³⁹Ar dating indicates a syn-/post-gold mineralization age of 136 ± 1.5 Ma, coinciding with the age of post-breccia felsite dike. The deepest sampled pyrite displays δ³⁴S values of ~2.7‰, strongly indicating a magmatic–hydrothermal signature. These results, when combined with the geological, geochronological, and isotopic studies on the adjacent lode gold mineralization, further suggest a close genetic relationship between the breccia pipes and the lode Au mineralization, paving the way for their utilization as effective indicators for gold targeting within the CTD. Full article

The research aims to examine the distribution of porosity and the combined heat and moisture movement while grains are being dried. This research concerns the porosity and flow of soybeans with different particle size ratios and the drying of soybeans with varying particle temperatures. Due to the similarity in shape between soybeans and balls, this article adopts a ball shape to study the heat and moisture transfer of soybean particles, which can also be used for the study of grains with similar shapes, such as mung beans and red beans. Random models of soybeans with varying proportions were created using modeling software Edem and UG. UDF programming was added to the preprocessing software Fluent to analyze the porosity, airstream allocation, and the interaction of temperature and moisture transfer in packed beds with various cylinder-to-particle size ratios and particle temperatures. A packed bed of soybeans was created, and the study examined the impact of cylinder-to-particle size ratios of 4.44, 5.6, and 6.25 on porosity. The results show that the radial porosity in the packed bed displays a fluctuating profile, with partial porosity increasing as the cylinder-to-particle size ratio increases. Increasing the ratio of cylinder size to particle size exacerbated the tortuosity of the flow paths within the packed bed. Simultaneously, the particle temperature increases, leading to a rise in the instantaneous heat transfer during the drying process, strengthening the ratio of moisture transfer within the packed bed. The method effectively models during convective heat and mass transfer in the liquid facies, as well as thermal and mass spread in the solid facies. The results of this study have been validated on physical models. The air temperature of 273 K is considered during the simulation process Full article

Taking the Zhongqiu 1 Gas Field in the Tarim Basin as an example, the heterogeneity of large-scale mono-block gas fields and their primary controlling factors have been analyzed. Based on drilling core data, well log data, scanning electron microscopy, thin-section analysis, and mercury injection experiments, combining sedimentological interpretation, research on the reservoir characteristics and variability was carried out. The results showed that: (1) The lithologic characteristics showed obvious variations among wells in the Zhongqiu 1 gas field. Specifically, the main lithology developed in the Zhongqiu 1 well is feldspar lithic sandstone, while the remaining wells predominantly consist of lithic feldspar sandstone. These differences in rock composition maturity reveal that a higher proportion of stable mineral components leads to poorer reservoir properties; (2) the main factors controlling oil and gas productivity include the variations in petrology, mineralogy, and diagenetic process characteristics. The high content of unstable mineral components and constructive diagenesis could increase reservoir porosity together. (3) Sedimentary facies of the Bashijiqike Formation in the Zhongqiu 1 Gas Field played a dominant role in the reservoir distribution. The division of sedimentary facies zones reflects variations in material composition and grain size, serving as the main material basis for reservoirs. Differences in mineral composition reflect the sedimentary environment of the reservoir. Additionally, mineral composition indicates the relationship between diagenetic processes and reservoir evolution. The high feldspar content in well ZQ1 corresponded to relatively favorable reservoir properties. The dominant feldspar type was plagioclase, suggesting that early-stage chemical weathering had undergone significant alteration. The above conclusions provided a microscopic perspective to explain the differences in oil and gas production capacity of large delta-front gas fields, serving as a geological basis for the exploration and exploitation of similar fields. Full article

Many input parameters in reservoir modeling cannot be uniquely determined due to the incompleteness of data and the heterogeneity of the reservoir. Sedimentary facies modeling is a crucial part of reservoir modeling. The facies proportion is an important parameter affecting the modeling results, because that proportion directly determines the net gross ratio, reserves and sandbody connectivity. An uncertainty evaluation method based on Bayesian transformation is proposed to reduce the uncertainty of the facies proportion. According to the existing data and geological knowledge, the most probable value of the facies ratio and the prior distribution of uncertainty are estimated. The prior distribution of the facies proportion is divided into several intervals, and the proportions contained in each interval are used in facies modeling. Then, spatial resampling is carried out for each realization to obtain the likelihood estimation of the facies proportion. Finally, the posterior distribution of the facies ratio is achieved based on Bayesian transformation. The case study shows that the uncertainty interval of sandstone proportion in the study area has been reduced from [0.31, 0.59] to [0.35, 0.55], with a range reduction of 29%, indicating that the updated posterior distribution reduces the uncertainty of reservoir lithofacies proportion, thereby reducing the uncertainty of modeling results. Full article

A reservoir is the space and gathering place of underground oil and gas reservoirs. Lithofacies proportion is the key parameter of a reservoir. Due to the heterogeneity of geological bodies, the multi-solution of seismic data and the limited and uneven distribution of logging data, it is unclear how to determine the lithofacies proportion in the study area directly from the available data. The mean is a way to make a quick estimate, but the mean cannot quantify the uncertainty of the lithofacies proportion using the available data. In this paper, a new method for quantifying uncertainty and determining the value of the three levels of the facies proportion is proposed. Taking sandstone proportion as an example, a normality test was carried out to verify the applicability of the sandstone proportion data to this method, and then the mean and variance of samples were calculated. Based on the confidence interval theory, the uncertainty of the mean value and the range of sandstone proportion were determined, that is, the optimistic value and the pessimistic value of the sandstone proportion. The results show that this method provides a new reference for quantifying values for the three levels of the uncertainty, and it uses the petrographic proportion as an example to provide the data basis for subsequent modeling and reservoir research. Full article

The Heuningnes Catchment in the Republic of South Africa was used as a case study in this research to describe the application of saltwater fraction/quantification and hydrogeochemistry methods to evaluate the extent of saline intrusion in the coastal aquifers. The argument of the research is that the presence of seawater incursion may be conclusively determined by combining the examination of the major ions, seawater fraction, stable isotopes of water, bromide, and geochemical modeling. Using stable isotopes of oxygen (¹⁸O) and deuterium (²H), major ions chemistry, seawater composition, and geochemical modeling, the genesis of salinity and mixing of different water masses were examined. Twenty-nine (29) samples of groundwater were examined. All samples showed water facies of the Na-Cl type, indicating a seawater-related origin. The significance of mixing in coastal aquifers under natural conditions was shown by the hydrogeochemical characteristics of key ions derived from ionic ratios, which demonstrated substantial adherence to mixing lines among endmembers for freshwater as well as saltwater (seawater). The quantification of seawater contribution in groundwater percentages varied from 0.01 to 43%, with three samples having concentrations of seawater above 50%. It was clear from the hydrogeochemical analysis and determination of the proportion of saltwater that the seawater intrusion impacted the coastal fresh groundwater. In addition, the chloride concentration in the groundwater ranged from 81.5 to 26,557.5 mg/L, with the corresponding δ¹⁸O values ranging from −5.5‰ to −0.9‰, which suggested that freshwater and saltwater were mixing. The Br⁻/Cl⁻ ratios showed that evaporation had played a part in elevating groundwater salinity as well. Since saturation indices were below zero, the mineral dissolution could also contribute to the salinization of groundwater. Further proof of seawater incursion in the investigated catchment was supplied by geochemical modeling and bromide. Even though such tools were not verified in multiple coastal aquifers for widespread generalization, the study offered a scientifically significant understanding of the application of such tools on seawater intrusion in coastal aquifers and has useful recommendations for the aquifer setting of similar environments. Full article

Reducing uncertainty in 3D carbonate rock type distribution is a critical factor that profoundly impacts field development for hydrocarbon or carbon capture and storage (CCS) projects. Miocene carbonate reservoirs in the Central Luconia offshore region are economically important global gas reservoirs. The nature of these carbonate rocks can be visually distinct in the core and the multiscale reservoir heterogeneity might vary in scale from the 100-m scale to the sub-millimeter scale. This work presents a series of steps workflow to obtain spatial information about the organization scheme of carbonate rock types, and capture the most important petrophysical and sedimentary controls on rock property distribution in the E11 field, a carbonate buildup, located in Central Luconia Province, offshore Malaysia. The spatial data were generated from a supervised neural Kohonen algorithm. The rock types predicted with this workflow were propagated using IPSOM probabilized self-organizing maps SOM. This tool is used for classifying multivariate data samples according to “patterns” or multivariate responses. The workflow includes several steps: A Step 1—Core data description, B Step 2—Thin section description, C Step 3—Well log interpretation, and D Step 4—IPSOM probabilized self-organizing maps for facies prediction SOM. The depth plots of the predicted rock type showed close correspondence to the core-based rock types in terms of the stratigraphic organization of tight and reservoir layers, proportions, and juxtaposition. This result is sufficient to merit the application of the rock type logs into a future porosity model of the E11 field, and to understand the lateral and vertical distribution of tight and reservoir rock types of distribution. The results can be used to build a future realistic digital twin of the subsurface, and in digital geological modeling. Full article

In this study, sulphate efflorescent minerals covering the surface of the Donnoe and Dachnoe fields of the Mutnovsky volcano are described. The minerals were precipitated on the argillic facies as the result of water–rock interaction and fumarole emission. A chemical composition of Ca, Ba, (NH₄)⁺, Na-Fe³⁺, (NH₄)⁺-Al, (NH₄)⁺-Fe³⁺, Na-Al, K-Al, and K-Fe³⁺ sulphates was reported. Elements such as Sr, Mg, Co, Ni, Ti and P were found as isomorphic impurities. Ammonia species were concentrated around fumaroles. The mineral assemblage described herein is unique in relation to other geological settings and reflects the process of low-temperature mineral formation associated with volcanism. The thermal water contains cations such as H, Na, K, NH₄, Ca, Mg, Fe²⁺, Fe³⁺, and Al in different proportions with pH ranging from 2.4 to 6.5 and the dominance of acidic waters. The gas condensate bears such cations as (NH₄)⁺, Ca, and Mg and has a pH of ~5. Thus, the rest of the main cations are derived from the leaching of the host rocks. Among the identified phases, the alunite-supergroup minerals are more prone to isomorphism. The Ti, Co, and Ni impurities mark the unique geochemistry of thermal water at the Mutnovsky volcano. We postulate that the chemical composition of alunite-supergroup minerals reflects the types of hydrothermal occurrences and contains important information on the geochemistry of the hydrothermal process. Full article

Shale oil is an unconventional oil resource that needs to be developed and utilized urgently. However, the Chang 7 shale in the Ordos Basin, as the most typical continental source rock in China, is limited by the study of organic matter (OM) enrichment factors in continental lacustrine facies, and there are still controversies about the controlling factors, which limit the progress of oil and gas exploration. This paper aims to reconstruct the paleoenvironment of Chang 7 shale in the southern margin of Ordos Basin and reveal the controlling factors of organic rich shale by organic and elemental analysis, X-ray diffraction (XRD) analysis, thin section observation, and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) analysis. The results show that during the deposition period of Chang 7 shale, the climate was warm and humid, the lake water has strong reducing, low salinity and rapid depth changes. Total organic carbon (TOC) is positively correlated with salinity and hydrothermal action and inversely proportional to terrigenous input. The high productivity, low consumption and low dilution result in high enrichment of shale OM in the southern margin of Ordos Basin. Full article

Efficient identification of groundwater contamination is a major issue in the context of groundwater use and protection. This study used a new approach of multi-hydrochemical indicators, including the Cl-Br mass ratio, the hydrochemical facies, and the concentrations of nitrate, phosphate, organic contaminants, and Pb in groundwater to identify groundwater contamination in the Pearl River Delta (PRD) where there is large scale urbanization. In addition, the main factors resulting in groundwater contamination in the PRD were also discussed by using socioeconomic data and principal component analysis. Approximately 60% of groundwater sites in the PRD were identified to be contaminated according to the above six indicators. Contaminated groundwaters commonly occur in porous and fissured aquifers but rarely in karst aquifers. Groundwater contamination in porous aquifers is positively correlated with the urbanization level. Similarly, in fissured aquifers, the proportions of contaminated groundwater in urbanized and peri-urban areas were approximately two times that in non-urbanized areas. Groundwater contamination in the PRD was mainly attributed to the infiltration of wastewater from township-village enterprises on a regional scale. In addition, livestock waste was also an important source of groundwater contamination in the PRD. Therefore, in the future, the supervision of the wastewater discharge of township-village enterprises and the waste discharge of livestock should be strengthened to protect against groundwater contamination in the PRD. Full article

The basement of eastern Mexico comprises Grenvillian-age granulite-facies metamorphic rocks. The Oaxacan Complex represents the largest outcrop belt of this basement in Mexico. In this work, southwestern Oaxacan Complex garnets are studied from a petrographical, geochemical, and geothermobarometrical perspective for the first time. The studied garnets display different grain sizes nucleated in a polyphase evolution. The almandine end member proportion is similar in all of the studied lithotypes. The highest pyrope concentrations are found in Qz Fsp paragenesis and ultramafic rocks and the lowest pyrope concentrations are found in amphibolite. The highest grossular and spessartine concentrations are found in the amphibolite lithotype. Southwestern Oaxacan Complex garnets from paraderivate samples are more enriched in Rb, Ba, Pb, Ni, and Zn than those from orthoderivate samples enriched in Ti and V. This fact is related to the nature of the protoliths and the mineral phases that fractionate the same minor and trace elements. Garnets from para- and orthoderivate samples display 0.02–1.1 Eu/Eu* anomalies. This fact indicates that almost all of the garnets formed while the plagioclase was stable, and it does not rule out the interpretation that some garnets were peritectic. The pressure obtained using a Grt-Opx-Pl-Qz geobarometer in the southwestern Oaxacan Complex is higher than the pressure obtained in the northern part of the Complex, and it is consistent with the pressure obtained in the Grenvillian-age granulites of the Novillo Gneiss from northeastern Mexico. Geothermobarometric studies reveal different P-T features at the study site, so different structural levels of the orogen are inferred. Full article