Cenozoic giant coal-bearing basin belt discovered in China's sea and its adjacent areas

Sea area is an important area of oil and gas exploration in China.It has been found that China's sea area mainly consists of coal type oil and gas,and the exploration of coal-bearing series source rocks has become an important part of oil and gas exploration there.Through years of comprehensive geological research in China's sea area,it has been revealed that it has undergone multiple occurrences of tectonic opening and closing movements in varying degrees in the Paleogene,forming 26 Cenozoic sedimentary basins of various types,such as active continental margin,passive continental margin,transitional continental margin and drift rift basins.In the present study,it is observed for the first time that coal type source rocks are mainly developed in 14 continental margin basins in China's sea area,revealing that a very large C-shaped coal-bearing basin group developed there in the Cenozoic.Next,based on the coupling analysis of paleoclimate,paleobotany,paleogeography and paleostructure,it is observed that there are five coal-forming periods in China's sea area,namely the Paleocene,Eocene,early Oligocene,late Oligocene and Miocene-Pliocene,and the coal-forming age is gradually new from north to south.It is also found that the coal seams in the sea area are mainly developed in three coal-forming environments in Cenozoic,namely delta,fan delta and tidal flat-lagoon.The coal seams developed in different environments are characterized by thin thickness,many layers and poor stability.However,the coal-bearing series source rocks in China's sea area have a wide distribution range,very high thickness and large amount,thus forming a material basis for the formation of rich coal type oil and gas.

Sedimentology and Paleoenvironmental Characteristics of Fine-grained Sediments in Coal-bearing Strata in the Eastern Ordos Basin:A Case Study of the Exploratory Well in the Zizhou Area

The continuously collected cores from the Permo-Carboniferous coal-bearing strata of the eastern Ordos Basin are essential for studying the hydrocarbon potential in this region.This study adopted sedimentological and geochemical methods to analyze the sedimentary environment,material composition,and geochemical characteristics of the coal-bearing strata.The differences in depositional and paleoclimatic conditions were compared;and the factors influencing the organic matter content of fine-grained sediments were explored.The depositional environment of the Benxi and Jinci formations was lagoon to tidal flat with weakly reduced waters with low salinity and dry-hot paleoclimatic conditions;while that of the Taiyuan Formation was a carbonate platform and shallow water delta front,where the water was highly reductive.The xerothermic climate alternated with the warm and humid climate.The period of maximum transgression in the Permo-Carboniferous has the highest water salinity.The Shanxi Formation was deposited in a shallow water delta front with a brackish and fresh water environment and alternative weak reductiveness.And the paleoclimate condition is dry-hot.The TOC content in fine-grained samples was averaging 1.52%.The main controlling mechanism of organic matter in this area was the input conditions according to the analysis on input and preservation of organic matter.

Geochemical Characteristics and Sedimentary Control of Pinghu Formation(Eocene)Coal-bearing Source Rocks in Xihu Depression,East China Sea Basin

Coal-bearing source rocks of the Pinghu Formation in the Xihu Depression comprise an important material basis of oil and gas resources in the East China Sea Basin.Based on drilling core observation results combined with the analysis and test results of macerals,trace/rare earth elements,and rock pyrolysis,the geochemical characteristics and sedimentary control of coal-bearing source rocks formation are discussed in a high-frequency sequence framework.The results indicate that the macerals composition of the coal-bearing source rocks of the Eocene Pinghu Formation in the Xihu Depression is dominated by vitrinite,with low-medium abundance of exinite and almost no inertinite.The coals and carbonaceous mudstones display higher amounts of total organic carbon(TOC)(14.90%-65.10%),S1+S2(39.24-136.52 mg/g),and IH(191-310 HC/g TOC)respectively,as compared to the mudstones.Organic matter is plotted in typeⅢkerogens and partially in typeⅡ;it is mainly in the low maturity stage.The trace elements results imply that the samples were deposited in a weakly reducing to weakly oxidizing environment and were occasionally affected by seawater.The coal-bearing source rocks were deposited in a relatively oxygen-containing environment.The coal-bearing source rocks development is jointly controlled by the coal accumulation environment,the water conditions affected by ocean currents in offshore basins in China,oxidation-reduction cycles of aqueous media and paleoclimate evolution in a high-frequency sequence framework.

Dual Control of Depositional Facies on Uranium Mineralization in Coal-bearing Series： Examples from the Tuanyushan Area of the Northern Qaidam Basin, NW China

The uranium deposits in the Tuanyushan area of northern Qaidam Basin commonly occur in coal-bearing series. To decipher the U-enrichment mechanism and controlling factors in this area, a database of 72 drill cores, including 56 well-logs and 3 sampling wells, was examined for sedimentology and geochemistry in relation to uranium concentrations. The results show that coal-bearing series can influence uranium mineralization from two aspects, i.e., spatial distribution and dynamic control. Five types of uranium-bearing rocks are recognized, mainly occurring in the braided river and braided delta sedimentary facies, among which sandstones near the coals are the most important. The lithological associations of sandstone-type uranium deposits can be classified into three subtypes, termed as U-coal type, coal-U-coal type, and coal-U type, respectively. The coal and fine siliciclastic rocks in the coal- bearing series confined the U-rich fluid flow and uranium accumulation in the sandstone near them. Thus, the coal-bearing series can provide good accommodations for uranium mineralization. Coals and organic matters in the coal-bearing series may have served as reducing agents and absorbing barriers. Methane is deemed to be the main acidolysis hydrocarbon in the U-bearing beds, which shows a positive correlation with U-content in the sandstones in the coal-bearing series. Additionally, the 613C in the carbonate cements of the U-bearing sandstones indicates that the organic matters, associated with the coal around the sandstones, were involved in the carbonation, one important component of alteration in the Tuanyushan area. Recognition of the dual control of coal-bearing series on the uranium mineralization is significant for the development of coal circular economy, environmental protection during coal utilization and the security of national rare metal resources.

Distribution of Selected Critical Elements in the Carboniferous Coal-bearing Series of the Upper Silesian and Lublin Coal Basins(Poland)

The distribution of selected critical elements in the sedimentary rocks of the Carboniferous coal-bearing series within the Polish Coal Basins is presented.Critical elements such as Be,Mg,Si,P,Sc,V,Co,Y,Nb,In,Sb,La,Ce,Hf,Ta,W,Bi were analysed using inductively-coupled plasma mass spectrometry(ICP/MS).Concentrations of elements such as Sb,Bi,In and,to a slightly lesser extent,Nb,as well as Sc,show average concentrations higher than those from the upper continental crust.The average concentrations of elements like Hf,Mg,P,Y,La,and Ce are slightly lower than in the upper continental crust.Other elements,such as Be,Co,Si,Ta,W and V have average concentrations that are similar,but slightly enriched or slightly depleted,relative to the upper continental crust.The research showed enrichment of some critical elements in the analysed samples,but not high enough that extraction would be economically viable.Statistical methods,which include correlation coefficients between elements and cluster analysis,reveal a strong positive correlation between elements like Be,Bi,Nb,Sc,Ta,W and V.Very high,almost total,positive correlation is also noted between La and Ce.

A New Understanding on South China Permian Coal-bearing Strata and Coal Accumulation Regularity

The Longtan Formation was originally thought to belong to the Late Permian, but this study reveals that the lower part of this formation belongs to the Middle Permian. The study proposes the corresponding chro-nostratigraphic boundary and new schemes for the correlation of geological sections. Based on these schemes a new understanding on the accumulation regularity of Permian coal measures in South China is reached.

Identification methods of coal-bearing source rocks for Yacheng Formation in the western deepwater area of South China Sea

Owing to the fact that the coal-beds are with the characteristics of multi-beds, thin single-bed, rapid lateral changes and deep burial, coal-bearing source rocks are difficult to be identified and predicted, especially in the lower exploration deepwater area. In this paper, a new integrative process utilizing geology and geophysics is proposed for better predicting the distribution of coal-bearing source rocks. Coal-beds were identified by the logging responses of“three higher, three lower, and one expand”and carbargilite were recognized by the characteristics of“four higher and one lower”. Based on the above logical decision, coal-beds and carbargilite can be distinguished automatically by cluster analysis of logging curves in verticality. Within the constraints of well-seismic calibration, the coal-beds group also can be detected in horizontality by the integrated representation of“negative phase, higher Q, lower impedance and lower frequency”within the seismic data. However, the distribution of coal-bearing source rocks utilizing geophysical methodology may do not conform to the geological rules of coal accumulation. And then the main geological controlling factors of coal accumulation are comprehensively analyzed as follows：（1） Paleotopography and tectonic subsidence determine the planar range of terrestrial-marine transitional facies markedly;（2） The relative sea level changes affect the accommodation space and shoreline migration, and limit the vertical range of coal-beds. More specifically, the relationship between the accommodation creation rate and the peat accumulation rate is a fundamental control on coal accumulation. The thickest and most widespread coals form where those two factors reached a state of balance;（3） The supply of autochthonous clasts and the distance between deposition places and paleovegetation accumulated area are the critical factor to form abundant coal, which means that if deposition area is close to paleouplift, there would be sufficient organic matters to form abundant source rocks. The results show that the integrated methods can significantly improve prediction accuracy of coal-bearing source rocks, which is suitable for early exploration of western deepwater area of South China Sea.

Gas-in-place and its influence factors of the upper Paleozoic coal-bearing shale in the Qinshui Basin, China

Coal-bearing shale shows great potential for unconventional gas resources in China, while its exploration and development have been challenging for a long time. Gas-in-place (GIP) is critical to shale gas evaluation, but the major factors controlling the GIP content of coal-bearing shale remain unclear. To address this issue, the coal-bearing shales of the upper Carboniferous-lower Permian Taiyuan and Shanxi formations in the Zuoquan Block, Qinshui Basin, China, were collected for GIP measurements and an integrated investigation, including organic geochemistry, inorganic mineral compositions, and pore characterizations, was carried out. Our results show that the GIP content of the studied shales displays relatively low values and wide variations, which range from 0.30 to 2.28 m^(3)/t. The GIP is dominated by desorbed gas and residual gas. Total organic carbon (TOC) contents of the studied shales vary from 0.92% to 16.91%, and inorganic minerals are dominated by clays that mainly consist of illite/smectite mixed layer (I/S) and kaolinite. Inorganic pores have been widely observed in the studied shales, while the organic matter-hosted pores are rarely found using SEM observations. Total porosity of the studied shales is primarily contributed by clay minerals, followed by organic matter and quartz. Weak positive relationships between the GIP content and pore structure parameters imply that the adsorption of methane to nanopores is relatively weak, which may be attributed to the hydrophilicity of clay-hosted pores. Moreover, hydrophobic organic pores are not well developed. Positive correlations between the GIP contents and contents of TOC, clays, and the I/S indicate that major factors influencing the GIP contents of the coal-bearing shales are clays (especially I/S) and TOC content. In summary, these findings would be very helpful to reveal the enrichment mechanism of coal-bearing shale gas and provide a scientific basis for the exploration and development of coal-bearing shale gas.

Insights into lithium adsorption by coal-bearing strata kaolinite

The sharp increase in the demand for lithium(Li)for high-energy-storage battery materials due to its high specific energy and low negative chemical potential render Li a geopolitically significant resource.It is urgent to develop a low-cost,efficient method to improve lithium extraction.Herein,Li ion(Li+)adsorption in coal-bearing strata kaolinite(CSK)was studied.The effects of pre-activation acid leaching(meta-kaolinite/H2SO4,MK-HS)and dimethyl sulfoxide intercalation(coal-bearing strata kaolinite/dimethyl sulfoxide,CSK-DMSO)on the Li+adsorption capacity were studied under the same adsorption conditions.The results indicated that the adsorption was completed in 60 min under alkaline conditions(pH=8.5),a high solution concentration(400 mg/L),and a low dosage(1 g/100 mL);and the comprehensive adsorption capacity is MK-HS>CSK-DMSO>CSK.Furthermore,the DMSO intercalation caused the interlayer spacing of the CSK to increase,which provided more space for Li+to enter and increase the adsorption capacity.After thermal pre-activation and acid leaching,structural failure and lattice collapse resulted in the presence of more micropores in the MK-HS,which resulted in a 10-fold increase in its specific surface area and caused coordination bond changes(Al(VI)to Al(IV))and leaching of aluminum(Al)from the lattice.It is proposed that these structural changes greatly improve the activity of CSK so that Li+cannot only adsorb onto the surface and between the layers but can also enter the lattice defects,which results in the MK-HS having the best adsorption performance.Combined with the adsorption kinetics analysis,the adsorption methods of CSK and two modified materials include physical adsorption and chemical adsorption.In this study,the adsorption capacity of CSK and its modified products to Li were explored,providing a new option for the reuse of CSK and the extraction of Li.

Piston mechanism of interaction of non-linear geomechanical and physicochemical gas exchange and mass transfer processes in coal-bearing rocks

The article focuses on a theoretical and experimental framework for the quantification of interaction between nonlinear geomechnical and physicochemical processes in high-stress coal-bearing rock mass during mining under high seismic risk due to large-scale blasting and earthquakes,as well as because of structural and temperature effects.The tests were aimed to examine and study comprehensively the piston mechanism of gas exchange and mass transfer processes,revealed recently at the Institute of Mining,SB RAS,as well as to explain the fact that the earthquake-induced low-velocity(quasi-meter range)pendulum waves(velocity to 1 m/s and frequency of 0.5–5 Hz)could stimulate an increase in the gas content in coal mines.In order to perform laboratory investigation at the Institute of Mining SB RAS,special-purpose stand for analyzing gas exchange and mass transfer processes in coal-bearing geomaterials under various thermodynamic conditions(P,V,T)and gas composition was constructed in cooperation with the Institute of Semiconductors Physics SB RAS.Matching of air flow rate with compression pressures allowed to obtain relations showing that air flow rate increases at the uncertain time interval under the increasing of the compression pressure.The same measurements was carried out with another gases such as Hydrogen H_(2),Helium He,methane CH_(4),carbon dioxide CO_(2) and carbon oxide CO.The laboratory tests aimed to detailed investigation of the previously revealed“piston mechanism”of gas exchange and mass transfer processes in the coal specimens and their quantitative description in terms of theory of the pendulum waves were carried in the first time.Consequently,there are some arguments for the testing of the opportunity of quantitative description of the“piston mechanism”related to gas exchange and mass transfer processes in the scale of coal mines.It is relevant when pendulum waves induced by powerful earthquakes and technical blasting reaches the mine.

A NEW TYPE OF DISTRIBUTARY CHANNEL DEPOSITS IN COAL-BEARING STRATA OF NAYONG AREA, GUIZHOU PROVINCE

Considerable progresses in the sedimentologic studies of the anastomosing river models have been made in recent years. There are now many modern and ancient examples such as those described by Smith, Rust et al. Flores et al. But all examples are found in the alluvial plains and the intermontane basins. None is known reporting about the upper delta plain environment. However, this type of distributary channels

DEPOSITS OF TIDAL SAND RIDGES IN THE COAL-BEARING STRATA OF MAYI DISTRICT, PANXIAN COUNTY, GUIZHOU PROVINCE

Tidal sand ridges are large-scale linear bottom configurations in a good many tidal seas. The modern tidal sand ridges in Jianggang area, the northern part of Jiangsu Province, China, have attracted the attention of geological circles because of the radial form and large scale. Berg, Brenner and Davies have reported that linear sand bodies of this kind were recognized within the Mesozoic strata of western America, but we have not seen any reports about the discovery of this kind of sediment from the ancient lithofacies analyses of China, especially in coal-bearing strata. Based on the study of sedimentary facies, this note describes the deposits of tidal sand ridges in the coal-bearing strata of China.

Coalfield structure and structural controls on coal in China

The occurrence of coal-bearing strata in a variety of coal-bearing basins of China is characterized by late tectonic deformation and remarkable spatial and geochronologic differences.The main controlling factors,which determine the tectonic framework of coalfields,include the geodynamic environment,tectonic evolution,deep structures,tectonic stress,and lithologic combination of the coal measures.The Chinese continent has experienced multi-stage tectonic movements since the Late Paleozoic.The spatial and temporal heterogeneity of its continental tectonic evolution,the complexity of its basement properties,and its stratigraphic configurations control the tectonic framework of its coalfields’present complex and orderly patterns.The concept of coal occurrence structural units is proposed in this paper and is defined as the structural zoning of coal occurrence.China’s coalfields are divided into five coal occurrence structural areas,and the structural characteristics of the coalfields in five main coal occurrence areas throughout the country are summarized.Based on the analysis of the relationship between the structure characteristics and occurrence of coal in these coalfields,the coal-controlling structures are divided into six groups:extensional structural styles,compressional structural styles,shearing and rotational structural styles,inverted structural styles,sliding structural styles,and syn-depositional structural styles.In addition,the distribution of coal-controlling structural styles is briefly summarized in this paper.

Cyclic Characteristics of the Physical Properties of Key Strata in CBM Systems Controlled by Sequence Stratigraphy—An Example from the Gujiao Block

Multiple coal seams and interbedded rock assemblages formed in vertical progression due to the influence of multiple stages of sea level transgressions.Based on mercury injection experiment,low temperature liquid nitrogen experiment,porosity and permeability experiment and breakthrough pressure experiment,the vertical variation characteristics of coal-bearing strata in Gujiao block are explained in detail.The results of the mercury injection and low temperature liquid nitrogen experiments show that the pore structure characteristics fluctuate with increasing depth in the strata,with fewer micropores followed by transition pores.The BET specific surface area and average pore diameter of the Shanxi Formation are generally larger than those of the Taiyuan Formation.Due to the continuous cyclic sequence stratigraphy changes,the porosity,permeability,breakthrough pressure and breakthrough time of the samples show a certain cyclicity.Within the same sequence,the porosity is larger,and the permeability is smaller near the maximum flooding surface.Although the permeability of the sandstone samples is higher,the porosity is lower,and the breakthrough pressure and breakthrough times are greater.The strata in the study area formed in an oxidized environment that was affected by freshwater,and the pore structure of different lithologies is quite different.After the formation of sandstone,the intergranular pores generally underwent filling with secondary quartz,clay minerals and organic matter,resulting in low porosity and permeability.

Genesis of Coal Metamorphism of Late PalaeozoicCoals in the South of North China——A Further Approach to the Effects of ThermalGroundwater on Coal Metamorphism

The close relationship between the genesis of coal metamorphism and the evolution of the regional tectonic framework is expounded on the basis of an analysis of the geological factors causing the metamorphic zonation of the Late Palaeozoic coals in southern North China; in terms of the mechanism for the formation of palaeogeothermal anomalies, the effects of thermal groundwater on coal metamorphism is highlighted and a geological model for thermal groundwater metamorphism of coal established; with the concept of the palaeogeotherm-coal metamorphism system, the genesis of coal metamorphism is analysed according to the distribution pattern of three geological factors: heat source, heat-carrier and channel, and heat-collector.

蒙古国含煤盆地的地质背景(英文)

Mongolia is located within the Central Asian Orogenic Belt.The belt is consist of numerous tectonic blocks or terranes,which resulted from collisions during the Early Paleozoic(Caledonian orogeny),Late Paleozoic(Hercynian orogeny) and partly in Early Mesozoic(Indosinian orogeny)(Seng r et al.,1993;Heubeck,2001;Badarch et al.,2003).These collisions had a profound effect on the coal-bearing sedimentary basins in Carboniferous,Permian,Jurassic and Cretaceous periods of Mongolia.A total of more than 200 coal occurrences and deposits are known,of which about 70 have been explored.

Controlling factors for large gas field formation in thrust belt of Kuqa coal derived hydrocarbon foreland basin

Kuqa depression is a foreland basin developedwith Mesozoic-Triassic-Jurassic coal-bearing formation. Theresearch results of the coal-derived hydrocarbon forelandbasins in Kuqa depression indicated that the coal-bearingformation can be the rich sources for generating gas becauseof their thickness and rich source rocks with gas-generatingpredominant kerogen. Although the foreland thrust beltmainly acting in compression is very complicated, integrallarge structural traps can be formed. Moreover, the thrustbelt can act as the passage for communication with deepsource rocks. The high quality gypsolish and gypseous mud-stone cap rock developed in the upper formation is the keyfor the formation of the large gas field. The late formation ofreservoirs in the large gas fields depended on the hydrocar-bon-generating history controlled by the foreland basin andthe developing process of foreland thrust belt.

Geological constraints of giant and medium-sized gas fields in Kuqa Depression

There is a gas-rich and well-charged petroleumsystem in the Kuqa Depression where Triassic and Jurassicsource rocks play important roles. Distributed in an area ofmore than 10000 km and with a thickness of up to 1000 m,they are composed of dark mudstones, carbonaceous mud-stones and coal seams containing 6%, 40% and 90% of TOC,respectively, and are mainly the humic organic matter. Ashigh-quality regional cap rocks, the Neogene and Eogenegypsum rocks and gypseous mudstones matched well withthe underlying Neogene and Cretaceous-Eogene sandstones.They have formed the most favorable reservoir-seal assem-blages in the Kuqa Depression. Also the Jurassic sandstonesand mudstones formed another favorable reservoir-seal as-semblage. The traps are shaped late in the fold-thrust belt,mainly fixed in the Tertiary-Quaternary, where ten structurestyles have been distinguished. These traps spread as a zonein N-S, are scattered like a segmental line in W-E and showtier-styled vertically. The best traps are gypsum-salt coveredfault-bend anticlines related to the passive roof duplex. Thispetroleum system is characterized by late accumulation. Inthe early Himalayan Movement, mainly gas condensate andoil accumulated and were distributed in the outer circularregion of the kitchen; whereas in the middle and late Hima-layan the gas accumulations mainly formed and were dis-tributed in the inner circular region near the kitchen. Theoverpressure of gas pools is common and is formed by sealcapacity of thick gypsum layers, extensive tectonic compres-sion and large uplift. The well-preserved anticline traps un-derlying the high-quality regional cap rocks of the Tertiarygypsum rocks and gypseous mudstones are the main targetsfor the discovery of giant and medium-sized gas fields. Aboveconclusions are important for the petroleum geology theoryand the exploration of the fold-thrust belt in foreland basinsin central and western China.

Formation mechanism of carbonate cemented zones adjacent to the top overpressured surface in the central Junggar Basin,NW China

Carbonate cemented zones are normally adjacent to the top overpressured surface in the central Junggar Basin,NW China.Stable carbon and oxygen isotopic compositions and petrological investigations of carbonate cements in the carbonate cemented zones indicate that:(1) carbonate cements are composed dominantly of ferrocalcite,ferroan dolomite,and ankerite;(2) carbonate cements are formed under a high temperature circumstance in the subsurface,and organic fluid migration has an important effect on the formation of them;and(3) carbon and oxygen ions in the carbonate cements migrate from the underlying overpressured system.This suggests that the occurrence of carbonate cemented zones in this region results from multiple phases of organic fluid expulsion out of the overpressure compartment through geological time.This study provides a plausible mechanism of the formation of carbonate cemented zones adjacent to the top overpressured surface in the clastic sedimentary basins,and has an important implication for understanding the internal correlation between the formation of carbonate cemented zones adjacent to top overpressured surface and geofluids expulsion out of overpressured system.