Characteristics Of Coal-measures Source Rocks And The Identification Marks Of Their Coal Gases In The Mesozoic And Paleozoic Erathern Of Gubei Buried Hill, Zhanhua Sag

Besides the investigation of tectonic and sedimentation feature, as well as thedevelopment of coal measures of Gubei buried hill, Zhanhua Sag, what were mainlyinvolved in this dissertation are as follows: i) the origin-classification of natural gasesin Gubei area, confirming that there exist coal gases in this area and providing theresearch objects for the identification marks and the source of the coal gases; ii)comparison of hydrocarbon-generating conditions of the Mesozoic and PaleozoicErathem coal-measures source rocks after the analysis of conventional geochemicalcharacteristics of them; iii) research of dynamic geochemical characteristics,hydrocarbon generating potential, and the differences of light hydrocarbons of thethermal simulated gases of the two coal-measures source rocks through the physicaland dynamic simulation experiments on hydrocarbon generation; iv) selection ofparameters or indexes for effectively differentiating the Mesozoic and PaleozoicErathem coal gases according to the geochemical analysis of the adsorbedhydrocarbons of coal-measures source rocks and the heavy hydrocarbons of naturalgases; v) establishment of the identification marks of the Mesozoic and PaleozoicErathem coal gases and determination of the source of coal gases in Gubei buried hill,Zhanhua Sag; vi) prediction of the favorable exploration targets based on thecomplete analysis of the hydrocarbon generation potential of the two coal-measuressource rocks and the controlling factors of the formation of coal gas pool.The main conclusions or viewpoints from this dissertation are as below:1) According to the sedimentary facies and lithology, Taiyuan formation ofCarboniferous System, Shanxi formation of Permian System and Fangzi formation ofJurassic System are the main strata of coal measures and coal-measures source rocksbecause of their thick and stable coal beds and dark mudstones. 2) Based on the analytical results of the composition, stable carbon isotope andlight hydrocarbon of the natural gases, it is concluded that the natural gases in theOrdovician System and the fourth part of Shahejie formation (Es4) are petroliferousgases (the natural gas in Es4 of Well Yi 115 is probably mixed with coal gas), thenatural gases in the Carboniferous-Permian System (C-P) of Well Gubeigu 1, Yi 155,Bo 930 are coal gases, and the natural gases in the Ordovician-Permian System ofWell Bo 93, Yi 132, Gubeigu 2 are mixed gases of coal gas and petroliferous gas.3) Analytical results of conventional geochemistry show that the organic matterabundance and type of the C-P source rock are better than that of Mesozoic Erathem(Mz). In addition, according to the biomarker characteristics, the distribution of Mzsource rock's regular steranes ofααα-C27 (20R),ααα-C28(20R) andααα-C29(20R) islike reverse character"L", and that of C-P is like character"V"; the gammaceranecontent in terpane series compounds of Mz source rock is very low, and that of C-P ismedium; these characteristics indicate that the organic matter and sedimentaryenvironment of C-P source rock for hydrocarbon generation are more favorable thanthat of Mz source rock. So, in general, the C-P source rock has an advantage over theMz source rock in static conditions for hydrocarbon generation.4) Hydrocarbon-generation physical simulation results show that the gasgeneration processes of the two coal-measure source rocks are almost the same, butthe total hydrocarbon yield of C-P source rock is higher than that of Mz source rock.It is also found that, at the same simulation temperature spots, the heptane value andiso-heptane value of C-P source rock are higher than that of Mz source rock.Meanwhile, the simulation gas of Mz source rock has more cyclanes (N) and there aremore chain-alkanes (I+P) in that of C-P source rock, reflecting on an obviousdifference between C-P and Mz source rocks in the C6N/(I+P)－C7N/(I+P) chart.5) Hydrocarbon-generation and carbon isotope dynamic experiments'resultsshow that, in the process of simulation, the general law of carbon isotope evolvementand the connection of methane conversion with carbon isotope of the two sourcerocks'simulated gases are similar, but in general, the Carboniferous System coal hasthe highest gas-generation potential because of its largest yield of methane or C2-C5.Meanwhile, there are several differences between the two source rocks on activationenergy of hydrocarbon generation, gas production mode, evolvement of methane,ethane and propane isotopes with Ro, in which the evolvement of methane isotope ofMz coal and mudstone appears as"two sub-process"and that of CarboniferousSystem coal and mudstone appears as"three sub-process". It is also found that the relationship plate of methane and ethane carbon isotope between accumulative gasand instantaneous gas can approximately differentiate the continuous generated gasand secondary generated gas; the evolvement of carbon isotope of methane in gaspool is generally between that of instantaneous gas and accumulative gas. Accordingto the research of hydrocarbon generation and burial history of source rocks, thehydrocarbon accumulation in Gubei buried hill mainly occurred in four periods,which were middle-late Triassic Period, middle Cretaceous Period, late PaleogenePeriod and Neogene-Quaternary Period. Based on the relationship of methane'saccumulated yield and carbon isotope, the coal gas in Well Gubeigu 1 was mainlygenerated from C-P source rock.6) Some characteristics of acidolysis hydrocarbon can be better used todistinguish the two source rocks, including light hydrocarbon fingerprint, heptanevalue and iso-heptane value, related chart of C₆N/(I+P)－C₇N/(I+P), Mangoparameters of K1 and K2. Meanwhile, there are also differences on the characteristicsof thermal released hydrocarbons of the two source rocks, such as light hydrocarbonfingerprint, heptane value and iso-heptane value, naphthenic parameter of CA2. Inaddition, the heavy hydrocarbon's biomarker is the most effective characteristic todistinguish the coal gases with different origin.7) Based on the geochemical characteristics of biomarker, physical simulationgas, dynamic simulation gas, acidolysis hydrocarbon, thermal released hydrocarbon ofcoal-measure source rocks, as well as the heavy hydrocarbon of natural gas, theidentification marks of Mesozoic and Paleozoic Erathem coal gases were determined,including the sterane and terpane chromatogram of heavy hydrocarbon, lighthydrocarbon's heptane value and iso-heptane value, relationship of C₆N/(I+P) andC₇N/(I+P), Mango parameters of K1 and K2, characteristics of fingerprint, as well asthe stable carbon isotope of the gas (more details of the identification marks areshown in Chapter eight). It is indicated that these parameters or plates should beintegrated in application.8) Using the identification marks, the source of coal gases in Gubei buried hillwas determined. It was concluded that the coal gas in Well Gubeigu 1 was generatedfrom the C-P source rock, coal gas in Well Bo 930 was from the Mz source rock, andthe coal gas in Well Yi 155 was mainly from the C-P, subordinately from the Mzcoal-measure source rock.9) Comprehensive analysis shows that the C-P coal-measure source rock is themain source of the coal gas in Gubei buried hill; the controlling factors of the formation of coal gas pool are characterized by hydrocarbon generation in late period,hydrocarbon accumulation controlled by tectonic feature and hydrocarbon enrichmentin the Permian System sandstone. According to the research mentioned above, thethree favorable targets for the exploration of coal gas pool in Gubei buried hill wereproposed.