Generation and accumulation of Quaternary shallow gas in eastern Qaidam Basin, NW China

1INTRODUCTION SHALLOW(MOSTLYBIOGENIC)GASACCOUNTSFOROVER20%OFTHEWORLD’SDISCOVEREDGASRESERVES(RICEAND CLAYPOOL,1981;CLAYPOOLANDKAPLAN,1974),AND REPRESENTSONEOFTHEUNCONVENTIONALENERGYSOURCES THATINCREASINGLYATTRACTTHEATTENTIONOFPETROLEUMGEOL OGISTS.NUMEROUS…     

A study on the geochemical characteristics of natural gas and gas sources in the Bozhong sag

Natural gas is composed largely of hydrocarbon gas, especially wet gas in the Bozhong sag. The carbon isotopic composition shows that the gas is of organic origin. The carbon isotopic values of ethane indicate that the natural gas is dominated by mixed gas with minor coal-generated gas and oil-type gas. A gas-source correlation study showed that the source rocks of natural gas are those of the Lower Dongying Formation, the Shahejie Formation and the pre-Tertiary. The natural gas is characterized by multi-source and continuous generation in the study area, indicating that gas exploration potential is good in the Bozhong sag.     

Heavy metals contamination and assessment in gas station dust of Xi’an,a mega-city of China

The dust samples from 30 gas stations located in Xi’an are analyzed for Mn, Ni, Co, Cr, Cu, Cd, Pb and Zn by using atomic absorption spectrometry. The concentration, spatial distribution, source and the contamination levels provide scientific basis for urban planning and environmental renovation in Xi’an. The results indicate that the mean values of Ni, Cr, Co, Cu, Pb, Zn and Cd in the dust are 1.15, 1.19, 8.13, 3.94, 4.42, 5.09 and 15.62 times higher than the corresponding background values of Shaanxi soil, respectively. The high concentration of heavy metals is located in the inner and second ring road of Xi’an, China. Furthermore, the contents of metals in the south are higher than in the north. In addition, the concentrations of the gas station dust metals in the west are higher than in the east, particularly in the southwest. Three main sources of heavy metals of gas station dusts are identified in Xi’an. Mn and Ni mainly originate from a natural source; Cr, Cu, Pb, Cr and Zn mainly originate from traffic flow; and Co is mainly from industrial sources. The results of the potential ecological risk assessment indicate that the potential ecological risk index (RI) of Co is moderate; Cd is very high ecological risk, and the other analyzed metals belong to low ecological risk. The mean RI value of eight heavy metals in the gas station dusts from Xi’an is considerable ecological risk.     

The oil and gas contents of the Lower Jurassic and Achimovka reservoirs of the Nyurol’ka megadepression

The paper describes Lower Jurassic (horizons J₁6 and J₁5) and Achimovka (Neocomian clinoforms) reservoirs in the area of the Nyurol’ka megadepression and its framing (42,000 km²). The total thicknesses of seven Achimovka sedimentary cycles are mapped. The thermal history of the Togur and Bazhenov parental sediments in the sections of 39 deep wells is reconstructed by paleotemperature modeling. The geotemperature criterion is used to identify paleosources of oil generation, starting from the Jurassic. The distribution of the relative density of the resources of the generated Togur and Bazhenov oils is estimated and shown on sketch maps. The Lower Jurassic reservoir is divided into zones depending on the distribution of the relative density of the Togur oil resources, and the Achimovka reservoir, of the Bazhenov oil resources. The priority oil search zones are proposed.     

A possible shale gas prospect? First results of the organic composition and thermal maturity of the Carboniferous Namoi Formation,northern NSW,Australia

The Namoi Formation in the Werrie Syncline, north and west of Tamworth, is part of the well-preserved Devonian–Carboniferous fore arc in the New England Fold Belt. The formation is between 640–914 m thick and consists of dominant olive-green mudstones with lenses of sandstone and oolitic limestone. To assess shale gas prospectivity, we analysed five outcrop samples from the Namoi Formation in the Keepit area. Well-preserved aliphatic and aromatic hydrocarbon fractions do not show evidence of weathering or biodegradation. n-Alkanes in all samples have a unimodal distribution maximising at C₂₆ to C₂₈. Little odd-to-even n-alkane carbon number predominance and relatively low Pr/n-C₁₇ and Ph/n-C₁₈ ratios are consistent with a high thermal maturity. Based on the distribution of alkylnaphthalenes and alkylphenanthrenes, the Namoi Formation is in the gas window. Calibration of the methylphenanthrene index and ratio with vitrinite reflectance suggests a calculated reflectance around 2.1%, which given a normal geothermal gradient is equivalent to a maximum temperature of 205°C for the deepest burial of the formation. There is a dominance of parent polycyclic aromatic hydrocarbons (PAH) over alkylated PAHs, supporting a high thermal maturity. Some samples contain biomarkers suggestive of a marine depositional environment, including the C₃₀ sterane index and the C₃₁/C₃₀ hopane ratio. The Namoi Formation is a prospective shale-gas source, as it has been buried sufficiently to be well within the gas window. Where it is exposed at the surface gas will have been lost, but elsewhere it will be buried beneath other sediments and may still retain gas. Key exploration uncertainties include information on organic richness, lateral variation in thermal maturity, mineralogy, and porosity–permeability relationships.     

Comparison of Fenton,ultraviolet–Fenton and ultrasonic–Fenton processes on organics and colour removal from pre-treated natural gas produced water

Produced water (PW) from natural gas field, characterized with high organic contents, has brought high environmental concerns world widely. Fenton and enhanced Fenton technologies were considered as the potential methods to degrade the organic contaminates in the PW, but with very limited data or reference. Here, we examined the optimum conditions of Fenton on organics and colour removal from natural gas PW after coagulation pre-treatment. Simultaneously, the optimal Fenton process integrated with ultraviolet (UV) and ultrasonic (US) irradiation were applied to enhance pollutants removal efficiencies. The optimal Fenton conditions were found at 60 min with molar ratios of 6:1 and 25:1 for H₂O₂/COD and H₂O₂/Fe²⁺, respectively and the initial pH of 3. Among these the three treatment processes, chemical oxygen demand (COD), total organic carbon, 5-day biological oxygen demand (BOD₅), and colour removal efficiencies were highest during UV–Fenton (82, 73, 68, and 95%,) followed by US–Fenton (79, 70, 66, and 95%) and Fenton treatment (70, 58, 51, and 92%), respectively. High biodegradability (BOD₅/COD) was also observed after UV–Fenton process (0.76) than the others (both 0.73). The current study showed a satisfactory carbon and colour removal efficiencies from PW using different Fenton processes; however, there still is a need for final polishing such as biological treatment or low cost constructed wetland before discharge. This study can be a good reference for engineering application PW treatment.     

Pyrite characteristics and shale gas significance of the Niutitang Formation in Cengong area,Guizhou ProvinceSCIEI北大核心CSCD

黄铁矿特征研究可为页岩沉积环境恢复与页岩气富集保存规律预测提供依据。以贵州岑巩地区岑页1井牛蹄塘组为研究对象,基于岩心、薄片、扫描电镜及微量元素、硫同位素地球化学,确定牛蹄塘组页岩沉积环境及页岩气富集地质条件。研究表明,牛蹄塘组页岩黄铁矿发育为草莓状、自形-半自形及他形(主要为胶状他形)三种形态,不同形态的黄铁矿形成于不同沉积环境,草莓状黄铁矿形成于缺氧还原环境,自形-半自形黄铁矿形成于贫氧环境,胶状他形黄铁矿指示沉积过程有热液活动的参与。测试井牛蹄塘组整体处于较开放的沉积水体,上段为含氧-贫氧环境,硫同位素整体变轻且发生负漂;中段为较缺氧环境,硫同位素跨度大且发生正漂;下段为还原性更强的沉积环境,硫同位素小幅度负漂。黄铁矿含量与有机质富集密切相关,与黄铁矿有关的孔隙为页岩气吸附、保存及运移提供载体,且草莓状黄铁矿指示的缺氧硫化环境更利于有机质保存。研究工作系统梳理了黄铁矿对牛蹄塘组页岩沉积环境及储层页岩气富集的指示作用,为页岩气勘探提供指示。     

Sedimentation control over the oil and gas contents in the cretaceous deposits of the Russkoe–Chaselka Mega-Arch (West Siberian oil and gas basin)

Most of the hydrocarbon resources of the Russkoe–Chaselka Mega-Arch are related to the Pokur Formation reservoirs. They are generally composed of alluvial sandstones and shales. Due to their genesis the Pokur reservoirs have a complex structure and a localized spread within ancient alluvial plains. The performed integrated interpretation of the well and 3D seismic data made it possible to estimate new perspective fields and to geometrize the oil and gas deposits.     

“Source-Diagenesis-Accumulation” enrichment and accumulation regularity of marine shale gas in southern China

After the breakthrough of shale gas exploration and development in the Ordovician Wufeng Formation (Fm.) and Silurian Longmaxi Fm. of Chongqing Jiaoshiba area, Changning-Weiyuan area, etc. in Sichuan basin, a series of discovery and breakthrough were obtained by China Geological Survey in the Cambrian Niutitang Fm. and Sinian Doushantuo Fm. shale of the areas with complicated structure outside Sichuan basin. Based on the understanding of the law of shale gas enrichment in Longmaxi Fm. in the basin, this paper puts forward three elements of the formation and enrichment of shale gas, which are the “Source”, the “Diagenesis” and the “Accumulation”, after deeply studying the law shale gas enrichment and accumulation in Sinian-Cambrian reservoir of the complex structure area outside the basin. The “Source” means the sedimentary environment and petrological characteristics of organic shale. The “Diagenesis” means the basin tectonic subsidence and hydrocarbon generation and expulsion process of organic matter. The “Accumulation” means the tectonic uplift and shale gas preservation. It is proposed that the Sinian-Cambrian and Ordovician-Silurian black shale series in the middle and upper Yangtze region of southern China were both formed in the deep-water shelf environment of rift trough and foreland basin respectively. The dessert intervals were formed in the strong reduction environment under transgressive system tract. The shale lithology belongs to calcium-siliceous and charcoal-siliceous respectively. Based on the summary of structural evolution in Yangtze area, the correlation of structural burial depth with shale diagenesis and the coupling evolution of organic matter with pore structure are discussed. Combining with structural styles, the preservation conditions of shale gas are discussed. Five types of shale gas reservoir control models are further described. Two types of future exploration directions, which are reverse fault syncline and paleo-uplift margin in complex structural area outside the basin, are proposed.     

Effects of gas pricing reform on China’s price level and total output

Natural gas plays an important role in the mitigation of climate change, yet its development is constrained by the current natural gas pricing mechanism in China. In the context of the natural gas pricing reform, this paper analyzes the potential effects on price level and total output. Through the input–output model, some conclusions are drawn as follows: (1) The gas pricing reform has relatively great impact on the products’ price of the sectors that have large gas consumption, such as industrial sectors and some service sectors, and on the total output of the gas production and supply sectors and the petroleum and natural gas extraction sectors, whereas the reform has relatively small impact on other industries; (2) effects of gas pricing reform on urban and rural residents are dissymmetrical, with larger effects on urban residents and (3) the reform has relatively small impacts on both various price indices and total output levels; thus, the government can realize the promotion of gas pricing reform nationwide at a cost of relatively small increase in general price level and little lose of total output.

     

Effects of gas pricing reform on China’s price level and total output

Natural gas plays an important role in the mitigation of climate change, yet its development is constrained by the current natural gas pricing mechanism in China. In the context of the natural gas pricing reform, this paper analyzes the potential effects on price level and total output. Through the input–output model, some conclusions are drawn as follows: (1) The gas pricing reform has relatively great impact on the products’ price of the sectors that have large gas consumption, such as industrial sectors and some service sectors, and on the total output of the gas production and supply sectors and the petroleum and natural gas extraction sectors, whereas the reform has relatively small impact on other industries; (2) effects of gas pricing reform on urban and rural residents are dissymmetrical, with larger effects on urban residents and (3) the reform has relatively small impacts on both various price indices and total output levels; thus, the government can realize the promotion of gas pricing reform nationwide at a cost of relatively small increase in general price level and little lose of total output.     

Mercury as an indicator of modern ore-forming gas—hydrothermal systems,Kamchatka

New data are discussed on the distribution of mercury in the host volcanosedimentary and igneous rocks, hydrothermal—metasomatic rocks, and all types of modern newly formed materials (hydrothermal clays, argillized soil—pyroclastic beds, siliceous and limonite—hematite covers, bottom sediments, salt ‘sweat-outs’ of various compositions, etc.) typical of the supergene zone of geothermal deposits. By the example of the Nizhne-Koshelevskii (vapor-dominated) and Pauzhetka (water-type) geothermal deposits and thermal fields of the Koshelevskii volcanic massif and Kambal’nyi volcanic range (southern Kamchatka), the role of mercury was illustrated as an indicator element of the temperature, phase state, and dynamics of hydrothermal systems; intensity of rock argillization; and relative age (maturity) of geothermal deposits and thermal anomalies.     

Evolution of oil and gas generation in the Earth’s history and petroleum prediction in sedimentary basins

Oil and gas generation is a basic problem of geology and natural sciences, which is associated with energy resources as well as with the origination of life on the Earth. The evolution of hydrocarbons is controlled by the evolution of the biosphere and is an issue of phylogeny. Organic matter (OM) buried in sediments since the Early Precambrian consists mostly of phytoplankton, the main carrier of lipids producing hydrocarbons. Organic matter accumulates in marine sediments according to the law of periodicity. Middle Paleozoic fossilized OM is largely composed of zooplankton. Zooplanktonic OM, classified as sapropelites, had interfered with the process of oil and gas generation since its origin, e.g., tentaculites of the Domanik formation increased oil content. The inception of low-lipid macrophytes gave rise to introduction of humic OM into water bodies and formation of mixed-type OM. The larger the humic component in OM, the higher its gas potential. However, instead of replacing oil generation, enhanced gas generation had come on the scene since the Mesozoic, and their scales were approximately equal. The actual oil/gas ratio in sedimentary basins depends both on phylogenetic factors and on the evolution of each separate basin.     

Mineralogy and Mode of Occurrence of Gold, Silver and Bismuth of the Caijiaying Lead-Zine-Silver Deposit, Hebei Province

The deposit under study is a hydrothermal filling-metasomatic vein type lead-zinc-silver deposit, in whichgold and silver can be recovered as by-products. These metals mainly occur as microgranular native gold,electrum, stephanite, acanthite, pyraragyrite, freibergite, and native silver. Gold minerals tend to be associatedwith galenobismutite, native bismuth and unnamed Bi_2Te. They are either enclosed in pyrite, marmatite,iron-bearing sphalerite and galens or fill the microfissures of these minerals. Silver minerals usually occur incleavages or fissures of galena, marmatite and pyrite, but are not associated with gold and bismuth minerals.Gold and silver mineralizations occurred later than lead and zinc, while the silver mineralization was precededby that of gold.     

Steppe landscapes of the Ural–Volga region in response to oil and gas production: Evaluation and minimization of direct geoecological aftereffects

This paper reports on the geoecological state of landscapes of oil and gas fields in the Ural–Volga steppe zone. Large-scale direct disturbances and impacts with dramatic aftereffects have been revealed on the basis of field research using the geographic information system (GIS) and data from remote sensing of the Earth. It has been shown that the current land-use pattern in oil and gas production areas is in need of professional control to protect and recover the landscapes in the steppe zone.

     

Formation Conditions and Distribution Regularities of Oil—gas Pools in Tertiary Volcanic Rocks in Western Huimin Depression,Shandong Province

The formation conditions and distribution regularities of oil-gas pools in volcanic rocks in western Huimin Depression have been studied in terms of geolgic,sesmic and well logging information,This paper discusses the types and lithofacies,development and distribution of Tertiary volcanic rocks in the area.The results demonstrate that volcanic activity occurred mainly during the period from the Sha-4 stage to the Guantao episode,i.e.,before the oil-generating period(before the end of the Guantao episode and the Minghuazhen episode).The activity did not destroy oil and gas formation and accumulation,but was favourable for the concentration of organic matter and its conversion to hydrocarbons;besides,volcanic rocks can serve as reservoir rocks and cap rocks,playing a role very similar to that of a syndepositional anticline,The volcanic rocks are distributed near the margins of the oil-generating depression;there are many secondary interstices in the rocks,which are connected with each other.These are the leading conditions for the formation of oil-generating period and their self-sealing or good combination with other cap rocks are important factors for forming volcanic rock-hosted oil and gas pools.The oil-gas pools associated with volcanic rocks in western Huimin are mainly distributed around the deep oil-generating depression,in the central up lift or the high structural levels on the margins of the depression.In particular,the sites where several faults cross are usually locatons where hith-yielding oil-gas pools in volcanic rocks are concentrated.     

Geological and geochemical characteristics of the Middle–Lower Jurassic shales in the Kuqa Depression,Tarim Basin: an evaluation of shale gas resources

Middle–Lower Jurassic terrigenous shales constitute a set of significant hydrocarbon source rocks in the Kuqa Depression of the Tarim Basin. Until recently, however, most investigations regarding this set of hydrocarbon source rocks have mainly focused on conventional oil and gas reservoirs, and little research has been conducted on the formation conditions of shale gases. This research, which is based on core samples from nine wells in the Kuqa Depression, investigated the geological, geochemical, mineralogical and porosity characteristics of the shales, analysed the geological and geochemical conditions for the formation of shale gases, and evaluated the shale gas resource potential. The results show that the distribution of the Middle–Lower Jurassic shales is broad, with thicknesses reaching up to 300–500 km. The total organic carbon (TOC) content is relatively high, ranging from 0.2 to 13.5 wt% with a mean of 2.7 wt%. The remaining hydrocarbon generative potential is between 0.1 and 22.34 mg/g, with a large range of variation and a mean value of 3.98 mg/g. It is dominated by type III kerogen with the presence of minor type II₁ kerogen. The vitrinite reflectance values range from 0.517 to 1.572%, indicating the shales are in a mature or highly mature stage. The shales are mainly composed of quartz (19–76%), clay (18–68%) and plagioclase (1–10%) with mean contents of 50.36 wt%, 41.42 wt%, and 3.37 wt%, respectively. The pore spaces are completely dominated by primary porosity, secondary porosity and microfractures. The porosity is less than 10% and is mainly between 0.5 and 4%, and the permeability is generally less than 0.1 mD. These results classify the shale as a low-porosity and ultra-low-permeability reservoir. The porosity has no obvious correlation with the brittle or clay mineral contents, but it is significantly positively correlated with the TOC content. The maximum adsorbed gas content is between 0.82 and 8.52 m³/t with a mean of 3.37 m³/t. In general, the shale gas adsorption content increases with increasing the TOC content, especially when the TOC content is greater than 1.0%. The volumetric method, used to calculate the geological resources of the Middle–Lower Jurassic shales in the Kuqa Depression, shows that the geological resources of the Middle and Lower Jurassic shales reach 667.681 and 988.115 × 10⁹ m³, respectively with good conditions for the formation of shale gas and good prospects for shale gas exploration.     

Seismotectonic investigations of the Chulmakan fault,southern Yakutia,to assess the seismic hazard for the East Siberia–Pacific Ocean oil and power of Siberia gas pipelines

Based on the analysis of space images and maps, the data of laser scanning, trenching, and field geophysical and seismotectonic studies in southern Yakutia, the Chulmakan seismogenic fault is mapped and characterized. The structure and parameters of seismogenic deformations of this fault, which crosses the Power of Siberia gas pipeline, are determined. A preliminary estimate of the Chulmakan seismodislocation age is given, as well as the magnitude of the corresponding paleoearthquake. The level of potential seismic hazard at the site where the Chulmakan Fault crosses the East Siberia–Pacific Ocean oil pipeline and Power of Siberia gas pipeline is determined.     

Geochemistry of О, Н, C,S, and Sr isotopes in the water and sediments of the Aral basin

The paper presents original authors' data on the O, H, C, S, and Sr isotopic composition of water and sediments from the basins into which the Aral Sea split after its catastrophic shoaling: Chernyshev Bay (CB), the basin of the Great Aral in the north, Lake Tshchebas (LT), and Minor Sea (MS). The data indicate that the δ¹⁸О, δD, δ¹³C, and δ³⁴S of the water correlate with the mineralization (S) of the basins (as of 2014): for CB, S = 135.6‰, δ¹⁸О = 4.8 ± 0.1‰, δD = 5 ± 2‰, δ¹³C (dissolved inorganic carbon, DIC) = 3.5 ± 0.1‰, δ³⁴S = 14.5‰; for LT, S = 83.8‰, δ¹⁸О = 2.0 ± 0.1‰, δD =–13.5 ± 1.5‰, δ¹³C = 2.0 ± 0.1‰, δ³⁴S = 14.2‰; and for MS, S = 9.2‰, δ¹⁸О =–2.0 ± 0.1‰, δD =–29 ± 1‰, δ¹³C =–0.5 ± 0.5‰, δ³⁴S = 13.1‰. The oxygen and hydrogen isotopic composition of the groundwaters are similar to those in MS and principally different from the artesian waters fed by atmospheric precipitation. The mineralization, δ¹³С, and δ³⁴S of the groundwaters broadly vary, reflecting interaction with the host rocks. The average δ¹³С values of the shell and detrital carbonates sampled at the modern dried off zones of the basins are similar: 0.8 ± 0.8‰ for CB, 0.8 ± 1.4‰ for LT, and –0.4 ± 0.3‰ for MS. The oxygen isotopic composition of the carbonates varies much more broadly, and the average values are as follows: 34.2 ± 0.2‰ for CB, 32.0 ± 2.2‰ for LT, and 28.2 ± 0.9‰ for MS. These values correlate with the δ¹⁸O of the water of the corresponding basins. The carbonate cement of the Late Eocene sandstone of the Chengan Formation, which makes up the wave-cut terrace at CB, has anomalously low δ¹³С up to –38.5‰, suggesting origin near a submarine methane seep. The δ³⁴S of the mirabilite and gypsum (11.0 to 16.6‰) from the bottom sediments and young dried off zone also decrease from CB to MS in response to increasing content of sulfates brought by the Syr-Darya River (δ³⁴S = 9.1 to 9.9‰) and weakening sulfate reduction. The ⁸⁷Sr/⁸⁶Sr ratio in the water and carbonates of the Aral basins do not differ, within the analytical error, and is 0.70914 ± 0.00003 on average. This value indicate that the dominant Sr source of the Aral Sea is Mesozoic–Cenozoic carbonate rocks. The Rb–Sr systems of the silicate component of the bottom silt (which is likely dominated by eolian sediments) of MS and LT plot on the Т = 160 ± 5 Ma, I₀ = 0.7091 ± 0.0001, pseudochron. The Rb–Sr systems of CB are less ordered, and the silt is likely a mixture of eolian and alluvial sediments.