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Natural Gas Reservoir Formation Mechanism Of Ordovician And Its Relation With Tectonic Evolution In Ordos Basin

Posted on:2004-09-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:G Y HuFull Text:PDF
GTID:1100360092996253Subject:Structural geology
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The essential elements and process of gas reservoir formation of Ordovician in Ordos basin have been annalysed systematicly and scientificly by means of the theory and method of organic geochemistry and tectonic geology in this dissertation.The several advanced techniques,such as gas generation thermal simulation, on-line individual gas compounds carbon isotope determination(PY-GC-C-IR-MS), the analysis technique of light hydrocarbons and biomarkers in natural gas, gas migration simulation and gas carbon isotope determination in fluid inclusions, have been applied to focuse on the study of the gas generation mechanism of souce rock, correlation between gas and source rock, reservoir formation history, migration direction, charging road in detail. Some conclusions have been made in the following.That the value of TOC is 0.2% may be regarded the low evaluation value of marine carbonate souce rock at the stage of high to over mature. According to the content of bitumen in source rock and reservoir, gas generation quantity, the maximum absorption gas quantity and geology analogy. Good source rock is developed in the slope belt of platform in the southwest part and middle-east part of Ordos basin. The gas generation of low mature source rocks has been simulated in the open system and close system respectively.The models of primary cracking gas (gas from kerogen) and secondary cracking gas (gas from oil) have been established. The Ro value of primary cracking gas generation peak is ranged from 1.0% to 1.5%. The Ro value of secondary gas generation peak is ranged from 1.5% to 2.5%. The quantity of primary cracking gas is up to 21 percentage of total gas generated. The quantity of secondary cracking gas is up to 79 percentage of the total gas generated.The comprehensive correlation between gas and source rock shows that natural gas in the north, west and south part of the center gas fields mainly come from Lower Paleozoic source rock, The attribution ratio of Lower Paleozoic source rock is up to 60-70%. In the other part, natural gas is mainly from Upper Paleozoic souce rock, its attribution ratio is up to 70%.Author pay more attention to the carbon isotope values of gas in fluidinclusions.The methods of pyrolysis and vaccum ball grinding have been used to obtain carbon dioxide, methane and other gases.Then, the carbon isotope values of these gases have been identified by GC-C-IR-MS. Because carbon oxide generated during pyrolysis process affected the carbon isotope value of methane by pyrolysis, authors concluded that the method of vacuum ball grinding is better than that of pyrolysis.The carbon isotope values of carbon dioxide, methane, ethane and propane of fluid inclusions of calcite samples in center field of Ordos basin have been determined.The results show that the values of 8 13Ci is distributed between -26.73% and -43.60%.The values of 13C2 are from -22.53%~-25.80%o and the values of 8 13Cs are from -22.53%o~-25.80%o. The characteristics of gas from fluid inclusion show that these gas are generated from coal and is very different from gas in gas fields. Authors speculate the times of gas filling reservoir are two at least. At early time, it is probably coal type gas.The analysis results of hydrocarbon generating history, paleotemperature history, the homogenization temperature distribution of fluid inclusions and individual fluid inclusion compounds show that the natural gas charging times in the center gas field is two. The first is at the age of late Triassic. At that time, natural gas migrated from the east to the west and from the south to the north. The center of basin is the accumulation target of gas migration and accumulation. At the age of early Cretaceous, the natural gas generated in the MiZhi depression migrated to the west and the north. At the ages of gas generation peak, anormally high pressures exsisted. With the help of this kind of pressure, natural gas generated from coal in the TaiYuan formation can be migrated to the Ordovician wethered crust reservoir accrossing micro-fiss...
Keywords/Search Tags:Ordos Basin, Ordovician, Central Gas Field, Natural Gas, Reservoir Model, Tectonic Revolution
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