Distribution and modes of occurrence of U and Th in oil shale
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The concentrations and modes of occurrence of U and Th in 23 oil shale samples from China were studied.The concentrations of U and Th were determined by inductively coupled plasma-mass spectrometry.The occurrence of U and Th in Huadian and Luozigou oil shale was investigated using six-step sequential chemical extract method.The concentrations of U in oil shale are within 10×10-6 and average of 3.92×10-6.The concentrations of Th in oil shale are within 20×10-6 and average of 10.51×10-6.The abundances of U and Th in oil shale are slightly higher than in crust and close to sedimentary rocks.The experimental results of floating and sinking roughly equal that of the sequential chemical extraction in U and Th.The U and Th in oil shale are mainly existed in minerals.Cite
With the aim of better understanding of geochemistry of marine oil shale, 25 samples from the Shengli River area were studied.The concentrations of Sr, U, Rb, Pb, and Th were 1.22 to 3.66 times higher compared to the average concentrations in the crust (Clarke values), while the concentrations of other elements were slightly higher/lower compared to the respective Clarke values.Trace elements including U, Pb and Th are important from the environmental point of view.The elements in the Shengli River oil shale may be divided into three groups according to their modes of occurrence, i.e. group A, B, and C. Group A exhibits a relatively high affinity with organic matter.Group B has weakly positive or slightly negative correlation coefficients with ash yield, while Group C shows high positive correlation coefficients with ash yield and possibly has an inorganic affinity.Elements related to terrigenous origin in the oil shale seams in the Shengli River oil shale have originated from two sources: the Nadi Kangri Formation felsic volcanic rocks and the Suowa Formation limestone.
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Systematic sampling and geochemical analysis of the oil shale member of Dingqinghu Formation show that SiO2are low, K2O /Na2O ratios are relatively high, Al2O3+ Fe2O3are in the range of 6. 43% ~ 10. 28%, and Al2O3/( Na2O + K2O) values are between 1. 7 and 4. 91, indicating that the oil shale contains mafic components and more stable components. Chemical indexes of alteration( CIA) are between 65 and 85, and Th /U ratios are concentrated in the range of 0. 97 ~ 3. 38, suggesting that the provenances of oil shale had experienced relatively moderate weathering and were in a warm and humid climate environment. Sr /Ba ratios are between 0. 45 and 0. 82,V /( V + Ni) ratios are between 0. 46 and 0. 68, and Th /U ratios have an average of 0. 59, indicating that the oil shale was formed in a fresh water and anoxic lacustrine environment. Warm and humid climatic conditions,abundant biological sources, fresh water and anoxic environment were important for the formation of Lunpola oil shale.
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Abstract Gases that are evolved, as eastern oil shale is heat- ed from 150°C to 900°C, have been monitored by mass spectrometry. Profiles of gas evolution as a function of retort temperature are reported for CO2, CO, Ch4 H8 C3HS, and H2S. Over the temperature range associated with oil production, less H2, is produced at increased heating rates. The Sunbury Shale (Mississippian age) and the Cleveland Member of the Ohio Shale (Devonian age) have very similar gas evolution profiles over this temperature range to within the experimental precision of ± 5 ±. Hydrogen and methane evolution profiles of eastern oil shales are qualitatively intermediate between those of coal and western oil shale. The low carbonate content of eastern shales makes it possible to observe char gasification by the water liberated from mineral matter. In the case of western shales, the reaction is masked by mineral carbonate decomposition. The comparison of the rate that specific gases are evolved from eastern shale, western shale, and Western Kentucky coal gives some additional insight into the similarities and differences that these fuel resources exhibit.
Retort
Oil shale gas
Shale oil extraction
Devonian
Carbonate minerals
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The Shengli River-Changshe Mountain oil shale zone represents the potentially largest marine oil shale resource in China.With the aim to have better knowledge of the distribution of trace elements in oil shale, and their behaviour during oil shale combustion and gasification, 28 raw Changliang Mountain oil shale and marl samples, 19 oil shale combustion residue samples and 23 samples of minerals isolated from Changliang Mountain oil shale are studied for trace element content.The oil shale samples from the Changshe Mountain area are characterized by high ash yield (54.69-86.75%)and total organic carbon (TOC) content (2.20-13.44%).The contents of Se, Mo, Cd, As, B, and Ni in raw oil shale samples are 3.78 to 28.44 times their upper continental crust values.The enrichment of an element in oil shale seams may be a function of that association and the origin of oil shale fractions.Some trace elements in the Changshe Mountain oil shale show susceptibility to release into the atmosphere, including about 93% Ba, Be, Co, Cr, Nb, and Sc.The behaviour and migration of trace elements during oil shale combustion strongly depend on their mode of occurrence in the rock.Based on Pearson's coefficients of correlation between elements, as well as cluster and isolated mineral analyses, the main modes of occurrence of trace elements in marine oil shale are distinguished: 1) clay mineral affined -B, Ba, Be, Cr, Cs, Ga, Hf, Li, Nb, Rb, Sc, Sn, Ta, Th, V, W, Zr, REEs; 2) organic affined -As, Mo, Se; 3) Fe-bearing mineral affined -Bi, Co, Cu, Ni, Pb, U; 4) calcite affined -Cd, Sr and 5) fossil affined -Cd, Zn.
Trace element
Shale oil extraction
Oil shale gas
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Located in North Qiangtang Basin in the northern part of the Shengli River-Changshe Mountain oil shale belt(currently the largest marine oil shale belt in China), the Changshe Mountain oil shale section mainly consists of oil shale, micrite limestone, black shale and marl. In order to determine the content of total organic matter, organic matter type, thermal maturity and sedimentary environment of the source rocks along the Changshe Mountain oil shale section, the authors collected twenty samples for multiple organic geochemistry tests. The results show that the oil shale has the best hydrocarbon generation potential, followed by the black shale and micrite limestone. The total organic carbon(TOC) content varies from 0.41% to 9.49%, with an average of 4.02%, and the oil shale samples have the highest values(ranging from 4.53% to 9.49%), with an average of 7.74%. Chloroform bitumen A varies from 0.0252% to 0.3403%, and the average value of the oil shale sample is 0.27%, indicating moderate to good source rocks. The kerogen types assessed from organic element composition and organic petrography data show that there is mainly typeⅡ 1 kerogen, with small amounts of type Ⅱ 2 and Ⅲ kerogen. The distribution of Ro ranges from 1.08% to 1.43%, with an average of 1.27%, demonstrating a mature to overmature stage of the organic matter, with the Ro gradually becoming higher along the oil shale section. The source rocks along the Changshe Mountain oil shale section were deposited in a reductive and high-saline water environment, and the organic source material was mainly low-grade hydrobios.
Petroleum geochemistry
Organic geochemistry
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Oil shale will be the important complementary and alternative energy in future.Xiamaling oil shale in Yanshan region,which is one of the oldest marine oil shale in China,has been selected to non-isothermally simulate hydrocarbons generation process using rapid heating protocol in open system.The result shows that most of the thermal pyrolysis occurred within the temperature range of 440-480 ℃.The kinetics parameters were thus calculated according to the Parallel principle in kinetics.The values of the activation energy were in the range of 170-290 kJ/mol,mean value is 240 kJ/mol,which is higher than lacustrine oil shale(Fushun oil shale and Maoming oil shale) and similar to the Lower Paleozoic marine(Ordovician Kukersite oil shale in Estonia and Ordovician marl in Pingliang,Gansu).Hydrocarbon generation was calculated with the kinetics parameters by heating method(about 2℃/d) of ICP technologies.The main generation temperature of Xiamaling oil shale,which ranges within 275-325℃,is higher than lacustrine oil shale(265-305℃) and comparable with Paleozoic marine ones.That shows the Xiamaling oil shale could have similar pyrolysis characteristics and same generation mechanism with the Lower Paleozoic marine,which might be related to simple biological species composition.
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Paleogene
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Organic geochemistry
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A detailed study of the upper Ordovician Wufeng shale and lower Silurian Longmaxi shale in northwestern Guizhou province of the upper Yangtze block was conducted on the basis of systematic analyses of a series of experimental measurements on core samples. Trace element ratios V/Cr, U/Th, and V/(V + Ni) reveal that variable paleoredox conditions existed during the deposition of the shale and the degree of anoxia decreased upward. The shale has high thermal maturity with an average Ro value of 3.38% (ranging from 2.94 to 3.65%) and high amounts of organic matter with an average total organic carbon (TOC) content of 2.02% (ranging from 0.36 to 6.73%), the type of which is sapropelic (I) to humic–sapropelic (II1). This indicates that the shale is good gas-producing shale in terms of geochemistry. The mineralogy of the shale is composed of 44.7% quartz and 32.6% clay minerals on average. The shale is characterized by low porosity ranging from 0.6 to 4.4% (averaging 1.8%) and low permeability varying from 0.0066 × 10–3 to 0.1098 × 10–3 μm2 (averaging 0.0378 × 10–3 μm2). The correlations of porosity with the TOC content, quartz content, and clay mineral content demonstrate that the shale interval rich in quartz and organic matter has higher porosity than the clay-rich interval. The gas adsorption capacity increases with the increasing of the TOC content, indicating that organic matter is responsible for adsorbing gas in this shale. Comprehensive analyses through experimental data show that the studied Wufeng–Longmaxi shale succession, especially the lower section, holds the potential for shale gas exploration and development because of TOC enrichment, high thermal maturity, good fracability, and potentially large gas content.
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Located in the middle‐western area of China, Ordos Basin is a large continental basin with vast petroleum resources. Oil shale of Chang 7 oil layer from Triassic Yanchang Formation represents the typical lacustrine oil shale in China. Oil shale samples were collected from Chang 7 oil layer to study the characteristics of elements geochemistry. The rare earth elements (REEs) concentration of oil shale samples varies from 138.51 to 206.36 μg/g with an average of 162.64 μg/g, close to the average REEs content of the North American shale Composite and slightly higher than the upper continental crust. The chondrite‐normalized and North American shale composite‐normalized REEs distribution patterns explain that oil shale samples, together with silty mudstone samples, may have been derived from a similar terrigenous source. The oil shale deposited mainly in early diagenetic stage B period and the paleoclimate condition was warm and humid with moderate chemical weathering. The whole sedimentary rate of oil shale was low. The source rocks of oil shale were mainly from the felsic rocks and deposited in the continental island arc tectonic setting. The total REE of oil shale samples show positive correlations with Al, Si, K, and ash yield concentration and negative correlations with oil yield, Fe, P, and total sulfur concentration, illustrating that REEs concentration in clay minerals is more than that in organic matter. In addition, the light REEs and heavy REEs are both present in clay minerals and controlled by land‐derived detritus.
Detritus
Terrigenous sediment
Felsic
Tight oil
Petroleum geochemistry
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