Formation environment and hydrocarbon potential of the Paleogene Enping Formation coal measures in the ZhuⅠDepression of northern South China Sea

The coal-measure source rock in the Chinese sea area plays a significant role as a hydrocarbon source rock,with its genetic environment,development and distribution,and hydrocarbon generation potential serving as essential factors for the exploration of coal-type oil and gas fields.This study focuses on the coal-measure source rock of the Paleogene Enping Formation in the ZhuⅠDepression,located in the northern South China Sea.The main geological insights obtained are as follows.The coal measures of the Enping Formation are developed in a warm and wet tropical-subtropical climate.The development environment of the coal-measure source rock in the Enping Formation includes the braided river delta upper plain peat swamp,characterized by dry forest swamp coal facies with relatively thick coal seams and a small number of layers.The braided river delta lower plain swamp-interdistributary bay of braided river delta front represents a forest edge-wetland herbaceous swamp coal facies with numerous layers of thin coal seams and poor stability.The shore swamp corresponds to an open water swamp coal facies with multiple layers of thin coal seams and poor stability.The organic matter abundance in the braided river delta upper plain is the highest,followed by the braided river delta lower plain-braided river delta front,and the shore-shallow lake.The organic matter type is predominantly typeⅡ1.Thermal evolution analysis suggests that the organic matter has progressed into a substantial oil generation stage.The hydrocarbon generation potential of the coal-measure source rock in the Enping Formation is the highest in the braided river delta upper plain,followed by the braided river delta lower plain-braided river delta front and the shore-shallow lake.Overall,this study proposes three organic facies in the coal-measure source rock of the Enping Formation:upper-plain swamp-dry forest swamp facies,lower plain-interdistributary bay-forest-herbaceous swamp facies,and lake swamp-herbaceous swamp facies.

The Development Characteristics and Distribution Predictions of the Paleogene Coal-measure Source Rock in the Qiongdongnan Basin,Northern South China Sea

There are known to be enormous Cenozoic coal-type oil and gas resources located in the basins of the South China Sea,among which the Paleogene coal-measure source rock are one of the main source rock.In order to more effectively analyze the distribution laws of coal-measure source rock in marginal sea basins and guide coal-type oil and gas explorations,the Oligocene coal-measure source rock in the Qiongdongnan Basin were selected as examples in order to systematically analyze the types,development characteristics,control factors,and distribution prediction methods of coalmeasure source rock in marginal sea basins.The Qiongdongnan Basin is located in the northern region of the South China Sea.Previous explorations of the area have determined that the Oligocene coal-measure source rock in the Qiongdongnan Basin have typical"binary structures",which include coal seams and terrigenous marine mudstone.Among those,the terrigenous marine mudstone has been found to greatly expand the scope of the coal-measure source rock.In addition,the coal seams which have been exposed by drilling have been observed to have the characteristics of thin single layer thickness,many layers,and poor stability.Meanwhile,the terrigenous marine mudstone has the characteristics of large thickness and wide distribution.The development of coal-measure source rock is known to be controlled by many factors,such as paleoclimate and paleobotany condition,paleo-structure and topography,paleo-geography,rise and fall of base level,and so on.In accordance with the comprehensive analyses of various control factors of coal-measure source rock,and the changes in water body energy in sedimentary environments,a genetic model of the"energy belt"for the development and distribution of coal-measure source rock was proposed.Also,the development and distribution characteristics of coalmeasure source rock in different types of energy belts were clarified.Then,based on the development and distribution characteristics of coal-measure source rock and their controlling factors,prediction methods of the distribution ranges of coal-measure source rock were proposed from both qualitative and(semi-)quantitative aspects.That is to say,a method for(semi-)quantitative predictions of the distribution ranges of coal-bearing intervals based on model wave impedance inversion and neural network wave impedance inversion,along with a method for(semi-)quantitative predictions of the distribution ranges of terrigenous marine mudstone based on topographical slopes,were introduced in this study.

Types of Organic Fades and Source Rock Assessment of the Coal-Measure Mudstone in the Turpan-Hami Basin

This paper discusses the enviromental characteristics of carbonaceous mudstone and mudstone (coal-measure mudstone in short) of the Early and Middle Jurassic in the Turpan-Hami basin, which were formed in swamps. Through the organic facies study of the coal-measure mudstone in this area, the authors clarify that the flowing-water swamp is the most advanced organic facies belt. Furthermore, according to the practical materials of coal-measure mudstone in the area and with the evaluation criteria of lacustrine mudstone in the past, the authors have established the integrated symbol systems from the abundance of organic matter and the type of organic matter, which can be used in the source rock evaluation of the coal-measure mudstone.

Resource types, formation, distribution and prospects of coal-measure gas

Coal-measure gas is the natural gas generated by coal, carbonaceous shale, and dark shale in coal-measure strata. It includes resources of continuous-type coalbed methane (CBM), shale gas and tight gas reservoirs, and trap-type coal-bearing gas reservoirs. Huge in resources, it is an important gas source in the natural gas industry. The formation and distribution characteristics of coal-measure gas in San Juan, Surat, West Siberia and Ordos basins are introduced in this paper. By reviewing the progress of exploration and development of coal-measure gas around the world, the coal-measure gas is confirmed as an important strategic option for gas supply. This understanding is mainly manifested in three aspects. First, globally, the Eurasian east-west coal-accumulation belt and North American north-south coal-accumulation belt are two major coal-accumulation areas in the world, and the Late Carboniferous–Permian, Jurassic and end of Late Cretaceous–Neogene are 3 main coal-accumulation periods. Second, continuous-type and trap-type are two main accumulation modes of coal-measure gas;it is proposed that the area with gas generation intensity of greater than 10×10^8 m^3/km^2 is essential for the formation of large coal-measure gas field, and the CBM generated by medium- to high-rank coal is usually enriched in syncline, while CBM generated by low-rank coal is likely to accumulate when the source rock and caprock are in good configuration. Third, it is predicted that coal-measure gas around the world has huge remaining resources, coal-measure gas outside source is concentrated in Central Asia-Russia, the United States, Canada and other countries/regions, while CBM inside source is largely concentrated in 12 countries. The production of coal-measure gas in China is expected to exceed 1000×10^8 m^3 by 2030, including (500–550)×10^8 m^3 conventional coal-measure gas,(400–450)×10^8 m^3 coal-measure tight gas, and (150–200)×10^8 m^3 CBM.

Research on the Occurrence of Titanium in Coal-Measure Kaoline in Songyi, Hubei

Using X-ray diffraction (XRD) analysis and an electron-probe microanalyser (EPMA), this research found that the main independent mineral of titanium (Ti) in the kaoline of Songyi is anatase. The granularity of anatase is from 0.5 μm to 1.5 μm, and some exceed 10 μm. This research provides important scientific evidence for the exploitation of the coal-measure kaoline in the South China.

The contribution of bacteria to organic matter in coal-measure source rocks

On the basis of GC–MS analysis, a suite of nine coal-measure source rocks(Ro 0.51%–0.63%) from the southern margin of Junggar basin was found to contain many biomarkers for bacterially-generated hydrocarbons:hopane, sesquiterpene, C_(23)+ monomethyl alkanes(even carbon predominance), and C_(24)+ alkyl cyclohexane.Rock–eval and microscope analysis indicate that vitrinite(especially desmocollinite and homocollinite) plays a significant role in the generation of hydrocarbons in coalmeasure source rocks. Vitrinite performs this role by absorbing ultramicroscopic organic matter, generally in the form of resins or bacterial plastids. C_(23)+ monomethyl alkanes(even carbon predominance) and C_(24)+ alkyl cyclohexane series compounds are derived from bacterial metabolites of higher plants. The ultramicro organic matter adsorbed by vitrinite source rocks in the study area is probably ultramicro bacterial plastids. Because the organic matter of higher plants with low hydrogen content has been transformed into organic matter rich in hydrogen by bacteria, the hydrocarbon generation capacity of source rocks is greatly improved. In other words, in coal-measure source rocks, bacteria play an important role in hydrocarbon generation.

Synthesis of TiO₂/Al-MCM-41 Composites with Coal-Measure Kaolin and Performance in Its Photocatalysis

TiO2/Al-MCM-41 composites with various titania content were prepared by loading titania into the mesopores of Al-MCM-41 mesoporous molecular sieve from coal-measure kaolin as silicon and aluminum source via general sol-gel method and incipient wetness impregnation method. TiO2/Al-MCM-41 composites were characterized by XRD, FT-IR and SEM, and the photocatalytic degradation of methyl orange solution under visible light irradiation. The results showed that the titania crystalline phase was anatase, and the particles size of TiO2 increase with TiO2 content. The photocatalytic degradation rates of all samples prepared by sol-gel method and incipient wetness impregnation have been become stable by visible light irradiation for 150 min, and the highest degradation rate was 83.7% and 76% respectively.

Effect of Surfactant/Silica and Hydrothermal Time on the Specific Surface Area of Mesoporous Materials from Coal-Measure Kaolin

Mesoporous materials with the highest surface area were synthesized by hydrothermal treatment from coal-measure kaolin using cetyltrimethylammonium bromide（CTAB）as template.The effect of several factors on surface area of products also had been discussed.The products were characterized by FT- IR,HRTEM and N 2 adsorption and desorption isotherm plot methods.There was typical structure as Si-O,Si- OH and Si-O-Si of mesoporous materials in the framework of synthesized materials;the pore size distributions of the products showed a sharp peak at 3.82 nm.The effect of hydrothermal treatment time and the amount of template on the specific surface area of mesoporous materials was important,when the Surf/Si=0.135,and hydrothermal time=12 h,and the surface area of the product reached up to 1 070 m2/g,which was higher than other products.

On the Paleogene coal-measure distribution over the China sea area

The Paleogene coal accumulation basins of China are part of the global Tertiary coal-accumulated zone of the Pacific Rim located in the eastern coastal provinces and areas. Although the coal-bearing basins of the China Sea area are faults and depressed basins, they come up in groups. The overall structures are suitable for the development of coal-bearing deposition. The continuity of basin groups are good, and the coal-bearing depositions are thick. For example, the coal-bearing deposi- tion is more than a kilometer thick at the Qiongdongnan Basin and Xihu Sag in the East China Sea, which the continental Pa- leogene coal basins cannot reach. Research shows that the coal accumulation basins in the sea area consist of many sags. There are two types of coal accumulation sags： half-graben sag and graben sag. In terms of water depth, coal accumulation sags can also be classified as deep-water half-graben sag and shallow-water half-graben sag; the graben sag is the deep-water sag. There are two distinct coal-accumulated zones in the basin： gentle slope and steep slope, with the gentle slope being the dominant one. The marshes of the supratidal zone and intertidal zone in a tidal flat system is favorable for the coal accumulation process widely taking place. There are two types of peat accumulation： autochthonous accumulation and allochthonous accumulation. Because of tectonic activities in the basins, allochthonous accumulations may be the more important form of coal-forming ac- tivities in the sea area. The very thick coal-bearing deposition in the sea area provides a rich material base for the assemblage of coal-related gas. Also, as a result of the deep burial depth, the degree of coal metamorphism is relatively high, so the coal-bearing strata become good hydrocarbon source rocks.

Water-bearing characteristics and their effects on the nanopores of overmature coal-measure shales in the Wuxiang area of the Qinshui Basin, north China

In this study,a group of overmature coal-measure shale core samples was collected in situ from an exploration well located in the Wuxiang area of the Qinshui Basin,north China.The pore water contents(CPW)of the shales under as-received conditions,equilibrium water contents(CEW)of the shales under moisture equilibrium conditions(relative humidity:100%),and nanopore structures of the shales under both as-received and dried conditions were measured.The results indicate that the CPW values of these shales are much lower than their CEW values,which implies that the bulk pore systems of these shales have low water-bearing extents.In addition,approximately half of the total pore volumes and surface areas of the as-received shales are occupied by pore water,and the effects of pore water on shale nanopores with various pore types and widths are different.The average water-occupied percentages(PW)are 59.16%−81.99%and 42.53%−43.44%for the non-micropores and micropores,respectively,and are 83.54%−97.69%and 19.57%−26.42%for the inorganic-matter hosted(IM)and organic-matter hosted(OM)pores,respectively.The pore water in shales not only significantly reduces the storage of shale gas by occupying many pore spaces,but also causes the shale gas,especially the absorbed gas,to be mostly stored in the OM pores;meanwhile,the IM pores mainly store free gas.Therefore,the water-bearing characteristics and their effects on the pore structures and gas-bearing properties of coal-measure shales should be noted for the evaluation and exploration of shale gas in the Qinshui Basin.

Gas Generation from Coal and Coal-Measure Mudstone Source Rocks of the Xujiahe Formation in the Western Sichuan Depression,Sichuan Basin

The Triassic and Jurassic tight sandstone gas in the western Sichuan depression,Sichuan Basin has attracted much attention in recent years,and the Upper Triassic coal-bearing Xujiahe Formation is believed to be the major source rock.However,there are relatively few studies on the carbon isotopic heterogeneity of methane generated from coal-measure source rocks and the origin of the natural gases in Xinchang Gas Field is still controversial.In this study,one coal-measure mudstone sample and one coal sample of the Xujiahe Formation in western Sichuan Basin were selected for gold tube pyrolysis experiment to determine their gas generation characteristics.Geological extrapolation of gas generation and methane carbon isotope fractionation parameters reveals that the main gas generation stage of Xujiahe Formation ranges from Late Jurassic to Cretaceous in the Xinchang Gas Field.The natural gas in the 5th member of Xujiahe Formation in Xinchang Gas Field is mainly derived from the 5th member of Xujiahe Formation itself,i.e.,self-generation and self-reservoir,however,the gas in the Jurassic gas pools is mainly derived from the source rocks of the 3rd member of Xujiahe Formation rather than the 5th member of Xujiahe Formation.

River-Delta Systems:A Significant Deposition Location of Global Coal-Measure Source Rocks

Natural gas is providing a larger proportion of primary energy, and will soon surpass oil to become the most important fossil fuel. There are various genetic types of natural gas of which the type that pyrolysed or cracked from humic kerogen accounts for 70% of presently discovered global natural gas reserves. The parent material of humic kerogen is higher multi-cellular plants. Investigations of offshore basins in China, Russia, Indonesia, Bangladesh, Australia, Egypt and Namibia show that river-delta systems contain the major sources of coal-type gas. Sand and mud carried by rivers form deltas at river mouths and fertile soil of these deltas encourages the long-term growth of higher plants. Autochthonous higher plants and allochthonous terrigenous phytoclasts contribute to the formation of coal, carbargilite and dark mudstone, which are potential parent materials of natural gas and the basis of coal-type gas generation.

Classification and origin of natural gases from Lishui Sag,the East China Sea Basin

Natural gases discovered up to now in Lishui Sag,the East China Sea Basin,differ greatly in gaseous compositions,of which hydrocarbon gases amount to 2%―94%while non-hydrocarbon gases are dominated by CO2.Their hydrocarbon gases,without exception,contain less than 90%of methane and over 10%of C2 + heavier hydrocarbons,indicating a wet gas.Carbon isotopic analyses on these hydrocarbon gases showed thatδ13C 1 ,δ13C 2 andδ13C 3 are basically lighter than-44‰,-29‰and-26‰, respectively.The difference in carbon isotopic values between methane and ethane is great,suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation.δ13C CO2 values of nonhydrocarbon gases are all heavier than-10‰,indicating a typical abiogenic gas.The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit,consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter.Moreover, δ13C 1 values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit whileδ13C 2 andδ13C 3 values of the former are over 9‰heavier than those of the latter.Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag,where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter,therefore,natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks.