Average Shale Research Articles

The role of effective thickness of the Asmari Formation zones on oil production

This paper investigates the role of the effective thickness of the Asmari reservoir formation zones on oil production in one of the Iranian carbonate oil fields. Effective thickness is a term that includes the total gross thickness of rocks by lithofacies for a selected wellbore. The lithology of the Asmari Formation in the studied area consists of dolomite, sandstone, lime, dolomitic-lime, sandstone-shale, and shale limestone dolomites. Based on the existing well-logs, the average shale volume, the effective arithmetic means of porosity in the gross intervals, and average water saturation or hydrocarbon-bearing increments of the studied field is calculated from well-logs. The depth interval of 2214 to 2296, in wellbore #A shows 9.6% average shale volume, 27.2% average water saturation, and 20.9% average porosity. The depth interval of 2213 to 2280, in wellbore #B, shows 6% average shale volume, 21.25% average water saturation, and 28.5% average porosity. Based on our petrophysical assessments we divide the Asmari reservoir in the studied field into eight zones. Zone 1 is made of carbonate (calcareous and dolomitic), zones 2 to 5 are mainly sandstone, zones 7 and 8 are calcareous and shale and zone 6 is a mixture of all the above-mentioned rocks. Among these eight zones, there are two main hydrocarbon productive zones. The numerical calculation of in situ oil volume showed that zone two contains 65% of oil volume in this reservoir. This zone with more than 80% of sand has the highest net hydrocarbon column.

Three-Dimensional Modelling of Desorbed Gas Volume and Comparison to Gas Production Rate in the Montney Plays, Western Canadian Sedimentary Basin

Shale reservoir has been focused among unconventional resources since the first extraction of free and adsorbed gas from the low-permeable Barnett Shale via horizontal drilling and hydraulic fracturing. In the beginning of production, free gas was rapidly recovered through an artificial fracture system, and then, desorbed gas followed at the final stage due to a decrease of reservoir pressure. This desorbed gas volume commonly occupies 10 to 40% of total gas production in shale gas play although it shows wide variety in cumulative gas volume and production time. The largest gas production in Canada is recovered from either tight sandstone or shale reservoirs. The Montney play in Western Canadian Sedimentary Basin (WCSB) has produced up to 80% of Canadian natural gas production. The desorbed gas production from this play has been reported up to 10% of total produced gas. The distribution and productivity of the desorbed gas have not been fully studied. Therefore, we focus to understand the distribution of the desorbed gas volume of eastern, middle, and northwestern areas in the Montney play. The desorbed gas volume within these areas was estimated from the relationship among canister, illite, and shale volumes in core samples and well logs. The average shale volume fraction in eastern area is 0.38 v / v , the average illite mineral volume fraction is 0.25 v / v , and the average desorbed gas volume refers to 8.52 scf/ton. In middle area, calculated volume represents 0.34 v / v , 0.216 v / v , and 8.15 scf/ton as listed above. The northwestern area also shows 0.65 v / v , 0.4 v / v , and 9.78 scf/ton, respectively. 3D models of each area indicated relatively rich and lack parts of desorbed gas volume. These estimated desorbed gas volume and gas production history were compared in order to understand when and how the desorbed gas would affect to gas production. It shows strong positive relationship, gradually increasing correlation to the later stage (from 24-44 months to 36-44 months) of gas production in the entire areas. This result implies that the estimation of later stage gas productivity is able from the estimated volume of desorbed gas, and also, the total gas production can be forecast in shale gas reservoir. Northwestern area in Montney play preserves relatively abundant desorbed gas volume, which will be dominant after 24 months of production.

Elemental composition, environment of deposition of the lower Carboniferous Emma Fiord formation oil shale in Arctic Canada

The sedimentary succession of 51-m consisting of a thin coal seam (1 m) and oil shale with a marlstone and carbonate-mudstone matrix of the Lower Carboniferous (Viséan) Emma Fiord Formation located on the Grinnell Peninsula, Devon Island, Arctic Canada was examined. The techniques used include reflected light microscopy, and instrumental neutron activation analysis (INAA) for elemental concentration, and inductively coupled plasma emission spectrometry (ICPES) for boron concentration.The coal and oil shale was deposited in a lacustrine, freshwater environment. Due to the climatic variation, two types of oil shale were developed based on the amount of precipitation. One with carbonate-mudstone matrix, with high calcite (75%) and low TOC (1.14–1.87%) content. The other a marlstone-dominated matrix with high aluminosilicate (64%) and TOC (16.4–53.6%) content.Oil shale from Emma Fiord experienced a slow rate of sedimentation and terrestrial flux as determined using Th/K/ Na/K, ratios Mn/Ca ratio to Ca respectively, and compared to the oil shale of Carboniferous age deposited in a lacustrine environment with a regular rate of recharge/discharge. The redox conditions for the Emma Fiord oil shale indicate anoxic to dysoxic conditions based on the variation of Cr and V + Ni.Thorium and U systematics indicate that U is more concentrated in oil shale with marlstone matrix and is associated with clay minerals and organic matter (OM), similar to the Carboniferous oil shale from the Big Marsh. The authigenic U is associated with TOC content and is higher for oil shale with the marlstone matrix.The variation of U with TOC indicates both paleo-productivity and preservation and is higher for oil shale with the marlstone matrix.The concentration of rare earth elements (REEs) is 95% due to the presence of light rare earth elements (LREEs) in both oil shale with marlstone and carbonate-mudstone matrices.The REES were normalized to the post-Archean average shale (PAAS). The high volatile bituminous coal at the base of the oil shale sections displays a flat, featureless pattern. The oil shale with a carbonate matrix decreases slightly from light rare earth elements (LREEs) to heavy rare earth elements (HREES). In contrast, the REEs concentration for oil shale with the marlstone matrix decreases more sharply from the LREEs (La-Eu) to HREEs (Tb-Lu). It displays a weak negative Eu anomaly typical of the upper continental crust.

Evaluation of heavy metal contamination levels in river sediments and their risk to human health in urban areas: A case study in the Matanza-Riachuelo Basin, Argentina

Anthropogenic contamination of Cd, Cr, Cu, Ni, Pb and Zn in riverbed sediments of the Pampean area (Matanza-Riachuelo Basin, MRB), Argentina, was evaluated using various indices: Geo-accumulation Index (Igeo), Contamination Factor (Cf), Metal Pollution Index (MPI), Pollution Load Index (PLI) and Contamination Degree (Cdeg). A database based on previous samplings of heavy metal concentrations at different sites in the Upper, Middle and Lower MRB was used. The Igeo and Cf values are calculated using selected local background (Pristine Pampean loess, LZB), and global average shale values (ASTW). Paired Igeo and Cf results with LZB and ASTW fall in dissimilar classes, especially in respect of Cd. In turn, MPI, PLI and Cdeg show similar results, as they do not have the same degree of confidence as Igeo and Cf. The Upper Basin, mainly rural, shows the following profile of sediment contamination: Cd > Ni > Cu ≫ Pb > Zn > Cr. The Middle Basin, which is at the periphery of a very industrialised and urban area, displays the following contamination profile for both Igeo and Cf: Cu > Pb > Zn > Ni > Cd > Cr. Conversely, in the Lower Basin, where land-use is urban/industrial, the levels of metal contamination are higher and appear in this order: Cr > Pb > Cu > Zn > Ni > Cd. Cadmium, Cu, Ni and Zn have shown no significant oral and/or dermal HQ nor carcinogenic risk but the potential risk posed by Cr and Pb must be taken into account. Maximum and mean values of Cr total carcinogenic risk (TCR) as well as Ni TCR also point to a health risk to children in the Lower Basin Area. All the data analysed confirm that industrial and urban growth without land-use planning, and a poor environmental legislation until the beginning of the 21st century, have not provided the necessary framework for sustainable development in the MRB.

Source and risk assessment of heavy metals and microplastics in bivalves and coastal sediments of the Northern Persian Gulf, Hormogzan Province

The objectives of the current study are to investigate the concentration, biological risks, chemical speciation, and mobility of of heavy metals and also the determination of their distribution, physicochemical characteristics, and abundance of microplastics in coastal sediments and edible bivalves in the Persian Gulf, the coastal area of Hormozgan Province. Sampling points were selected considering the location of industrial, urban and Hara forest protected areas. In November 2017, a total of 18 sediment samples from coastal sediments (top 0–10 cm) and the most consumed bivalve species in the region were collected from two stations, Lengeh and Bandar Abbas Ports. The average concentration of heavy metals (except for Ni and Cd) in the sediments were lower than their average shale and the upper continental crust. Enrichment factors revealed significant enrichment of Ni, Mn, Cr, Cd and As. The fractionation of heavy metals using the Community Bureau of Reference (BCR) sequential extraction scheme indicated the high bioavailability of Zn, As, Mn, and Co. In general, the highest concentration of Mo, Cd, Pb, Zn, Cr, Cu, Mn, Hg, and Sb was detected in areas with frequent human activities including Shahid Rajaee Port, Shahid Bahonar Port, and Tavanir station. Shahid Rajaee and Shahid Bahonar Ports are the most important ports on the coast of Hormozgan province. The Risk Assessment Code calculated for the study elements indicates that As, Co, Zn, and Cu pose a moderate environmental risk a threat to the aquatic biota. Health risks of most heavy metals arising from bivalves consumption were safe, except for As which is associated with the high target cancer risk values. With reference to the type of microplastics found, they were mainly fibeours with lengths ranging between 100 and 250 μm in sediments and bivalves. Most of the microfibers found in the sediments were made of polyethylene terephthalate (PET) and polypropylene (PP), and the fibers found in the bivalves were made of PP.

Signals of combined chromium–cadmium isotopes in basin waters of the Early Cambrian – Results from the Maoshi and Zhijin sections, Yangtze Platform, South China

The combination of authigenic chromium and cadmium stable isotopes in marine sedimentary archives enables reconstruction of the redox conditions and levels of primary productivity in past oceans and basins. The Ediacaran to Cambrian Nanhua Basin (Yangtze Platform, South China) and its sedimentary sequences have been studied intensively in the past with respect to investigating the effects of post-Snowball Earth glaciations on the oxygenation of Earth's atmosphere, and intimately related, on the consequences of climate changes on the evolution of the ocean environment and of life during the Precambrian-Cambrian transition. Following recent propositions of using cadmium isotopes as a novel proxy for reconstructing the extent of primary productivity in paleooceans, we here present results from a combined cadmium (Cd)‑chromium (Cr) isotope study on metalliferous black shale, black shale and phosphorite sediments deposited during the Early Cambrian Niutitang Formation at the Maoshi and Zhijin sections. Results point toward strongly oxidized and highly productive surface water layers in the Nanhua Basin during this period. The samples have strongly positively fractionated δ114Cd and δ53Cr values up to +0.6‰ and + 1.4‰, respectively, similar to such values from carbonaceous sediments in modern oceans. The association of Cd with sulfides in the sediments, together with high Cd/TOC ratios particularly in the metalliferous black shales, implies a sulfide-controlled enrichment of Cd under restricted euxinic conditions. The lower Cd/TOC values in phosphorites and barren black shales and negatively fractionated δ114Cd values down to −0.33‰ point to less effective precipitation of Cd under more suboxic conditions as likely prevailing in an open shallow shelf. The Cr content in the sediments is mostly close to average shale, and the δ53Cr values are little fractionated in the 0–0.2‰ range, corroborated by flat shale-like rare earth element + yttrium (REE + Y) patterns. However, some metal-rich shale samples have clearly authigenic Cr isotope signatures with up to +1.4‰ δ53Cr, and the authigenic Cr component in the phosphorite samples is around 1‰ δ53Cr, indicating oxic surface waters. The latter sediments also depict seawater-like, middle REE enriched REE + Y patterns with distinct negative Ce and positive Y anomalies indicative of an oxygenated surface water layer, and with positive Eu anomalies which they likely received during phosphatogenesis in the euxinic bottom water environment. In accord with previous studies reporting on extreme trace metal enrichments (Mo, Ni, V, Hg, etc.) in these Early Cambrian sediments, our Cd and Cr isotope signatures favor a scenario of a strongly stratified basin in which high primary productivity thrived in an oxidized surface water layer, potentially as a result of increased nutrient supply from a strongly weathering continental hinterland in the aftermath of the last Snowball Earth glaciations in the Ediacaran.

Reservoir Characterization of the Early Cretaceous Sarmord and Garagu Formations from Atrush-1 and Mangesh-1 Wells, Kurdistan Region, Iraq

Petrophysical properties of the Early Cretaceous Sarmord and Garagu formations from the Atrush and Sarsang Blocks in the Kurdistan Region are studied. These formations are generally composed of limestones and dolomitic limestones interbedded with thin to medium layers of yellowish-gray marl (calcareous mudstone). The current study shows that the average shale volume in the Sarmord and Garage formations is between 16% and 20%. In Atrush-1 Well, the average porosity ratio of the Sarmord and Garagu formations is fair to good (15% and 11%, respectively). However, in Mangesh-1 Well, the porosity value is poor; it is around 4% on average. Generally, most of the hydrocarbons that have been observed within the pore spaces are residual oil type in Atrush-1 Well and movable hydrocarbon type in Mangesh-1 Well. In Atrush-1 Well, out of 362 m thickness of both formations, only 180 m is considered to be a pay zone; whereas, the pay zone is just around 8.0 m thick out of 347 m of the total thickness. According to the calculated porosity values, the Garagu and Sarmord formations are not considered as good reservoirs in the studied wells, with the exception of Atrush-1 Well where the Sarmord Formation has fair potential reservoir characteristics.

Geochemical discrimination of the altered volcanic tuff from sediments in the Lunpola Basin, central Tibetan Plateau

AbstractVolcanic tuffs are important in determining the stratigraphic age of sedimentary sequences, which is closely related to the tectonic, sedimentological, geomorphological, palaeoclimatic, and palaeo-ecological evolution of the sequences. However, it may be difficult practically to identify tuffs in stratigraphic sections, especially when they are altered after deposition. In this study, a series of petrographic, mineralogical, and geochemical analyses was deployed in the tuff layers cropping out in the Lunpola Basin of the central Tibetan Plateau, which is a crucial site for studying the dynamics and processes of the Cenozoic uplift of the Tibetan Plateau and its environmental impacts. In these pyroclastic layers, authigenic analcime is the main volcanic glass alteration product. The analcime-bearing samples are Na-enriched, in contrast to the K-abundant magmatic rocks in the central Tibetan Plateau. The distribution patterns of the rare earth elements (REEs) of the bulk analcime-bearing samples are similar to those of the magmatic rocks but different from those of the analcime-poor sediments and analogues of well-mixed upper continental material (e.g. the upper continental crust and post-Archaean Australian average shales). The distinct distributions of Na and REEs among analcime-bearing samples, analcime-poor sediments, and volcanic rocks reveal that analcime formed both from alteration of volcanic material and from mixing processes with non-volcanic sediments. It is proposed, therefore, that the discrimination plot of Na2O/Al2O3-(La/Yb)Nmay be used to distinguish the analcime-related pyroclastic rocks from the basin sedimentary sequence, and thus it may provide a means of discriminating between various volcanic material and of supporting age dating by tephrochronology in the central Tibetan Plateau.

Assessment the Seasonal Variability and Enrichment of Toxic Trace Metals Pollution in Sediments of Damietta Branch, Nile River, Egypt

This work appraises the extent of toxic trace metals and seasonal pollution degree in Damietta branch sediments of the River Nile of Egypt. The toxic trace metals Fe, Mn, Cd, Co, Cu, Ni, Pb, and Zn were analysed in sediments from six sites during the summer and winter seasons. The metal concentrations and organic matter were determined using inductively-coupled-plasma mass spectrometry and loss-on-ignition, respectively. Multivariate statistical methods were used in order to allocate the possible metals sources and their relationships in sediments. The seasonal mean sequence of toxic trace metals was: Fe > Mn > Zn > Pb > Cu > Ni > Co > Cd. The mean Cd, Pb, and Zn values exceeded the sediment quality guidelines and average shale and they represent severe potential toxicity for aquatic organisms. Cu and Co were enriched during winter. The geo-accumulation index stipulated that metal pollution degree in the sequence of: Pb > Zn > Cd > Co > Cu > Mn > Ni > Fe. The highest metal pollution index reported in winter in sites S4/S5 and during summer in sites S4–S6. Different agricultural, wastewater discharge, fisheries, and industrial activities, as well as the effect of dilution/concentration during summer/winter seasons, are the main factors that contributed to metal accumulations in Damietta branch sediments. Continuous monitoring and evaluation of toxic trace metal concentrations of the Damietta sediments and similar localities worldwide can help to protect the ecosystem from harmful metal contaminations.

Geochemistry and pollution status of surface sediments of Loktak Lake, Manipur, India

Surface sediments (n = 29) from Loktak Lake, the largest freshwater lake in northeastern India, were studied for geochemistry, mineralogy and the heavy metal pollution of the lake sediments was assessed. The XRD spectra of bulk sediments showed the dominance of quartz and clay fractions showed the dominance of illite and chlorite. The major oxides consist dominantly of SiO2, Al2O3 and FeO with low concentrations of K2O, Na2O and CaO. The depletion of CaO, Na2O and K2O compared to upper continental crust, post-Archean average shale and North-American shale composite indicated moderate to strong weathering, recycling of the source rock and their removal during transportation. The chemical index of alteration values (76.86–84.98) also suggested moderate to extreme chemical weathering of the Loktak Lake catchment lithologies. The mean concentrations (in mg/kg) of Zn (117 ± 23.45), Co (34 ± 13.67), Fe (7 ± 1.38 wt%), Cu (67 ± 12.87), Cr (282 ± 45.25) and Ni (194 ± 30.12) are about 2–4 times higher than that of the upper continental crust, except for Mn (425 ± 168.99 mg/kg) and Pb (17 ± 7.47 mg/kg). The heavy metal concentrations follow the trend of Fe > Mn > Cr > Ni > Zn > Cu > Co > Pb. The assessment of heavy metal pollution using enrichment factor, geo-accumulation index and modified degree of contamination suggested non-contamination to moderate contamination of sediments. According to sediment quality guidelines, the sediment-dwelling biota could be affected by the higher concentrations of Ni and Cr. The mean-effect range median-quotient suggests medium–high to high potential of the effects of heavy metal pollution. The uniformly higher concentration of heavy metals in general and Ni and Cr, in particular, indicated the dominance of natural (ophiolitic) sources with no or little, if any, anthropogenic influence.

Assessment of element concentrations in surface sediment samples from Sığacık Bay (eastern Aegean)

Concentrations of Al, Fe, As, Co, Cr, Cu, Mn, Ni, Pb, Zn, Hg, and organic carbon, and grain size distribution were investigated in the surface sediments of 7 sampling stations in the Sığacık Bay (western Anatolia) in December 2016. At all of the sampling stations, the concentrations of Pb, Ni, Cr, and As were higher than the average shale values. The highest concentrations of Pb, Cu, Zn, As, and Hg were found at stations near Doğanbey Cape. The possible sources of pollution were evaluated using several parameters: the enrichment factor (Ef), contamination factor (Cf), and contamination degree (Cd). The Ef values ranged between 0.12 and 7.61 in the bay. The high Ef (>1.5) values of Pb, Cu, Ni, Co, and As were assessed to explain the influence of anthropogenic sources. Additionally, the Cf values ranged from 0.46 to 5.61, while the Cd values ranged from 11.69 to 20.45 in the study area. The Cd of the Cr and As ranged between moderate and considerable, and the highest Cd was measured at stations near Doğanbey Cape. Additionally, the pollution degrees were assessed using sediment quality guidelines (SQGs), the threshold effect level (TEL), the probable effect level (PEL), the effects range low (ERL), and the effects range median (ERM). It was demonstrated that the sediments were generally heavily polluted with Cr and Ni, and moderately with Pb and Cu, according to the numerical SQGs. The concentrations of Pb, Cr, Cu, Zn, and Ni were above the TEL, while Cr and Ni were also higher than the PEL levels for all of the samples.

Optimal Selection of Shale Gas Processing and NGL Recovery Plant from Multiperiod Simulation

The advent of unconventional oil and gas has resulted in a plethora of shale gas production, and it has been predicted to increase from 1 in 2000 to 40% in 2035 of the total US domestic gas produced. Since shale gas is both industrially economical and environmentally clean compared to oil or coal as a resource, many studies are focused on developing technologies to monetize shale gas. However, one of the key challenges in utilizing shale gas is its varied flow rate and uncertain compositional behavior. The flow rate of a shale gas well dwindles over a period of time, and the composition differs from well to well in the same shale play. This provides a challenge in designing a plant of optimum capacity for shale gas processing and natural gas liquids (NGL) recovery. In this study, the periodic variation in feed flow rate is addressed while designing shale gas processing and NGL recovery plant. Different shale gas flow rates as obtained from average shale gas rate declination curve of a shale play over the period of well life is used for the design of five different plants with varied capacities. The corresponding economics of different plants are compared to find optimal plant capacity. The base case scenario is further improved through incorporation of heat integration and optimization of individual units of the process using pinch and sensitivity analyses, respectively. Economic analysis of the optimum plant size is also performed with a constant feed flow rate over its entire life. From the economic analysis of various period studies, it is observed that the optimum plant design with highest ROI percentage has more than minimum ROI requirement both with declining and constant flow rate case, implying that the proposed processing plant is economically viable to implement. Finally, environmental impact of the base case and improved design is also discussed.

Systematics of Trace Elements in Sediments from the North-Western Caucasus Mud Volcanoes

Comparison of trace element distribution in bulk samples from the North-Western Caucasus mud volcanoes with PAAS (average Australian post-Archean shale) showed their depletion in many elements. The contents of most elements in sediments of the mud volcanoes are comparable with those of the Middle Maikopian clay. Compared to the Upper Maikopian clay, most of the studied samples have much higher concentrations of Mo, Sr, Y, Nb and Ba, whereas contents of many other elements, in contrast, are lower. The rare earth elements (REE) distribution in bulk sediment samples is similar to that of PAAS. On the La/Sc–Th/Co diagram, the compositions of most bulk samples of the North-Western Caucasus mud volcanoes fall in the field typical of disintegration products of felsic rocks. This is confirmed by their localization in the Cr/Th–Th/Sc and Sc–Th/Sc diagrams. The comparison of the distribution of data points of sediments of mud volcanoes of the North-Western Caucasus, the Junggar Basin, and the Andaman Islands on the La/Sc–Th/Co and Cr/Th–Th/Sc diagrams shows that the latter have a large contribution of geochemically immature components, possibly the disintegration products of mafic igneous rocks. The data points of sediments ejected from the North-Western Caucasus mud volcanoes on the La/Sc–Th/Co and Cr/Th–Th/Sc diagrams show the wider compositional range than those of other two regions (mixing “felsic” and “mafic” components in the proportions ~100 : 1 to 50 : 50). In general, the comparison of trace element distribution in sediments from mud volcanoes of the North-Western Caucasus, the Junggar Basin and the Andaman Islands suggests the geochemical heterogeneity of these sediments not only in different geodynamic regions, but also within mentioned mud volcanic provinces, thus indicating a heterogeneous composition of their sources.

Provenance and paleo-weathering of Paleoproterozoic siliciclastic sedimentary rocks of Bijawar Group, Sonrai Basin, Uttar Pradesh, India: using a geochemical approach

Shales and sandstones of the Paleoproterozoic Bijawar Group (India) have been studied to decipher their paleo-weathering conditions and provenance based on geochemistry. Shale samples are composed of k-feldspars, mica, quartz, and fine iron-oxides, whereas sandstones are composed of quartz and k-feldspars. The predominant positive correlation of K2O vs TiO2, Na2O vs Al2O3, and K2O vs Al2O3 indicates that the elements are associated with detrital phases. Trace elements Sc, Rb, Ba,Th, Y, and Zr show a strong positive correlation with Al2O3 and K2O which indicates that the absolute abundances of these elements are controlled mainly by illite. A negative correlation of trace elements Ni, Cu, Co with Al2O3, and K2O represents their presence in iron oxides like magnetite, ilmenite, and hematite. Multi-element Post-Archaean Australian Average Shale (PAAS) normalized spider diagrams show enrichment of V, Pb, Zr, Y, Hf, Th, Rb, and depletion of Ni, Sr, Ba, Nb, U. The depletion of Sr indicates the least enrichment of plagioclase and the same is also supported by negative Eu-anomaly of the samples, though weak. The chondrite normalized rare earth element (REE) plots show a slightly light-REE (LREE) enriched and flat heavy-REE (HREE) pattern with weak negative Eu anomaly. The overall, high values of LaN/SmN (avg. 10.49), CeN/YbN (avg.0.37), LaN/YbN (avg. 34.28) and low values of GdN/YbN (avg. 1.82) and TiO2 (0.27–1.82, average 0.92 < PAAS) in most of the samples, show a relationship with the felsic source rocks. The index of compositional variability (ICV) of the samples is < 0.84 which indicates no enrichment of primary minerals. The chemical index of alteration (CIA) of present samples varies from 48.60 to 81.69, indicating low to moderate intensity of chemical weathering of the source. The plot between SiO2 and Al2O3 + K2O + Na2O depicts that majority of the samples belong to the environment from humid to semi-humid and have attained a high chemical maturity. The high SiO2/Al2O3 values (1.36–20.79) in studied samples indicate relatively high sediment maturity due to the extreme sorting of sediments in a stable cratonic regime. A stable cratonic regime, with a low upliftment rate that has allowed strong chemical weathering of protoliths, is further indicated by low CaO, Na2O, and Sr contents of the studied samples. The overall geochemical characteristics of the present samples—high SiO2, Al2O3 and K2O and low TiO2, MgO, Na2O, and CaO contents—suggest a felsic provenance. The felsic nature of the source rocks is also supported by the trace element ratios like (La/Lu)N (7.72–76.89), La/Sc (1.50–7.40), La/Co (0.39–11.48), Th/Co (0.80–15.90), and Cr/Th (0.08–5.10). Since the Bijawar Group is sited over the Bundelkhand Granite Gneiss Complex (BGGC), it is, therefore, plausible that the main source components of Bijawar Group siliciclastic rocks are the BGGC felsic rocks.

Arctic Continental Margin Sediments as Possible Fe and Mn Sources to Seawater as Sea Ice Retreats: Insights From the Eurasian Margin

AbstractContinental margins are hot spots for iron (Fe) and manganese (Mn) cycling. In the Arctic Ocean, these depositional systems are experiencing rapid changes that could significantly impact biogeochemical cycling. In this study, we investigate whether continental margin sediments north of Svalbard represent a source or sink of Fe and Mn to the water column and how climate change might alter these biogeochemical cycles. Our results highlight that sediments on the Yermak Plateau and Sofia Basin exhibit accumulations of Fe and Mn phases compared to average shale. Conversely, sediments from the Barents Sea slope exhibit lower enrichments of Fe and Mn compared to average shale, with the exception of enriched, near‐surface sediment layers. Pore waters from these slope sites provide evidence for Fe and Mn reduction and diffusion of Fe and Mn into near surface sediments, which are susceptible to physical or biogeochemical remobilization. These regional patterns are best explained by the spatial distribution of sea ice coverage and labile organic carbon fluxes to the seafloor. As sea ice continues to retreat and the Yermak Plateau becomes seasonally ice‐free, productivity is expected to increase, which would increase the flux of carbon to the sediments, thereby increasing oxidant demand, and the reduction of Fe and Mn mineral phases. Our results suggest that as sea ice continues to retreat, the Yermak Plateau and other Arctic continental margins could become sources of Fe and Mn to Arctic bottom waters.

Geochemical fractionation of trace elements in the coral reef sediments of the Lakshadweep Archipelago, Indian Ocean

Geochemical fractionation of seven trace elements (Cr, Mn, Fe, Cu, Zn, Cd, and Pb) was investigated in the surficial coral reef sediments of three inhabited islands (Kavaratti, Kadmat, and Agatti) belonging to the Lakshadweep Archipelago. The observations indicated that the metals showed their highest contents in the residual fraction of geological origin. The extent of risk, bioavailability, and contamination of trace elements was assessed by risk assessment codes and contamination factors. Based on the results, medium potential adverse effects were observed in the sediments of Kavaratti and Agatti. The concentration of Cd in the exchangeable and carbonate-bound fractions was above its global average shale value in the sediments of Kavaratti and Agatti, suggesting its high mobility and bioavailability and thus an environmental threat to the coral reef ecosystem.

Petrophysical Analysis to Determine Reservoir and Source Rocks in Berau Basin, West Papua Waters

Berau Basin is assessed to have same potential in clastic sediments with Mesozoic and Paleozoic ages, where reservoirs and source rocks are similar to productive areas of hydrocarbons in Northwest Shield Australia. This study aims to identify the hydrocarbon prospect zones and potential rocks zones using petrophysical parameters, such as shale volume, porosity, water saturation and permeability. Petrophysical analysis of reservoir and source rock are carried out on three wells located in the Berau Basin, namely DI-1, DI-2 and DI-3 in Kembelangan and Tipuma Formation. Qualitative analysis shows that there are 4 reservoir rock zones and 4 source rock zones from thorough analysis of these three wells. Based on quantitative analysis of DI-1 well, it has an average shale volume (Vsh) 9.253%, effective porosity (PHIE) 20.68%, water saturation (Sw) 93.3% and permeability (k) 55.69 mD. DI-2 well’s average shale volume, effective porosity, water saturation and permeability values are 29.16%, 2.97%, 67.9% and 0.05 mD, respectively. In DI-3 well, average shale volume, effective porosity, water saturation and permeability values are 6.205%, 19.36%, 80.2% and 242.05 mD, respectively. From the reservoir zone of these three wells in Kembelangan Formation, there are no show any hydrocarbon prospect.

Dissolution pores in shale and their influence on reservoir quality in Damintun Depression, Bohai Bay Basin, East China: Insights from SEM images, N2 adsorption and fluid-rock interaction experiments

Shale pore characterization is crucial for understanding the mechanism of shale hydrocarbon accumulation and its effective exploitation. X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), pore extraction, nitrogen (N2) adsorption, and fluid-rock interaction experiments were used to study the shale pore structure of the fourth member of the Paleogene Shahejie Formation in the Damintun Depression, East China. The Damintun shale included three types of pores: organic matter pores, mineral matrix pores, and microfractures. The dissolution pores were mainly developed between and inside the matrix minerals, such as calcite, dolomite, and feldspar. The average shale visible dissolution porosity determined using SEM was 1.12%. N2 adsorption analysis revealed that the less than 20 nm pores were the main reservoir space in the Damintun shale. Fluid-rock interaction experiments indicated that the degrees of dissolution of the calcite and dolomite were similar and stronger than those of the K-feldspar and plagioclase. The shale with a high content of carbonate minerals (calcite and dolomite) exhibited more intense dissolution. The degree of dissolution pores development was positively correlated with total organic carbon (TOC) and carbonate mineral (calcite and dolomite) contents. The average contribution of the dissolution porosity to the total porosity of the shale was 18.20%. However, the contribution of the dissolution pores increased with increasing pore size only when the average pore diameter was larger than 12 nm. This may be due to the fact that small pores (diameter <12 nm) are more easily to be filled by re-precipitated minerals. The total porosity and the contribution of the dissolution pores were positively correlated with the dissolution porosity, revealing that dissolution pores are an important factor affecting the quality of shale reservoirs.

Arsenic in marine sediments: how robust a redox proxy?

Arsenic (As) is reputed to be a redox-sensitive element but has not been fully explored yet as a proxy in marine sediments and sedimentary rocks, compared to extensively examined elements such as molybdenum (Mo) and uranium (U). Here the behavior of As is compared to that of Mo and U in a number of paleo-environmental situations that have been studied before and are, therefore, rather well constrained. The results indicate that attention must be paid to the reference values used to normalize sedimentary As content in geochemical studies. The most-commonly used references (namely the Post-Archean Australian Shale and average upper crust of Earth, to be opposed to the Average Shale) tend to overestimate slightly As enrichments as shown by As enrichment factors being quasi systematically larger than 1, whatever the geological setting. The results also show that As enrichments are less straightforward compared to those of Mo and U, when using these elements as redox proxies. In addition, the depositional milieus that endured the most hydrologically-restricted and/or reducing (euxinic) conditions are not those with the highest As enrichments. Thus, arsenic shows a redox-sensitive behavior but is not adequate as a redox proxy. However As enrichments are correlated with Mo enrichments in two distinct types of situations: settings impacted 1) by particulate iron shuttling processes and, 2) by diagenetic fluid circulation (cold seeps). In both cases, the Mo-As correlation is induced by the strong relationship between these trace metals and reactive iron: Fe conveys both As and Mo to the sediment where they are trapped. Thus arsenic has a promising potential to allow recognition of past depositional environments associated with iron shuttling and (cold) seep circulations. Lastly, high-TOC, high-Mo, low-As situations point out possible occurrences of sulfurized organic matter in sediments. High Mo concentrations indicate reducing, sulfidic conditions prone to organic-matter accumulation (high TOC values), but low As concentrations indicate that reactive iron was a limiting factor, preventing As capture. Under such conditions, free H2S was not associating with iron and could react with organic matter, causing its sulfurization.

Evaluation of trace elements concentration in surface sediments of Parishan International Wetland (Fars Province, SW Iran) by using geochemical and sedimentological analysis

This study investigated the concentration of trace metals in surface sediments of Parishan Lake. Parishan Lake is one of the biggest freshwater lakes in the Middle East, situated in Kazerun area (Fars Province, Iran). This preliminary study concerns the mineralogy, enrichment level, and trace elements source identification in surface sediment of this lake. The geochemical Enrichment Factor (EF) and Geo-accumulation index (Igeo) and sedimentological approaches were applied to characterize the contamination by heavy metals, comparing with Average Shale. Multivariate statistical analysis was also used to identify probable studied elements sources in collected samples. The XRD and microscopic analysis show that main mineral of surface sediments is aragonite with small amounts quartz and nepheline. Chemical analysis of sediments showed that the mean concentrations of As, Cd, Cr, Cu, Ni, Pb, Zn, and Sr were 1.88, 27.2, 32.4, 18.6, 8.1, 38.4, and 3934.9 mg/kg, respectively, and average concentrations of Cd, Cu, and Sr exceeded the corresponding values of upper continental crust (UCC) values. The outcomes of this study indicate that geochemical indices (EF and Igeo) revealed an extremely high enrichment for Sr, whereas other elements had minimal enrichment. The levels of potential ecological risk index (RI) for studied trace elements in all sampling locations were 41.13 and 23.76, lower than baseline value (150), signifying that ecological risks displayed by those elements in sediments were moderate. The multivariate statistical analysis indicated that Sr had a geogenic source (natural source), while As and Cd came probably from Industrial source (chemical fertilizers), Ni and Cr were likely derived from vehicle emissions, particularly agricultural machinery, and Pb originated from exhaust and non-exhaust traffic emissions.