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The Study On Geochemistry Characteristics Of Hydrocarbon Source Rocks And Natural Gas In The Middle Section Of Western Sichuan Depression

Posted on:2009-11-10Degree:MasterType:Thesis
Country:ChinaCandidate:J ChenFull Text:PDF
GTID:2120360242493173Subject:Mineral prospecting and exploration
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This paper is a part of the study on petroleum accumulation geochronology and fluid evolution in Western Sichuan Depression. Through researching into hydrocarbon source rocks and natural gas's geochemistry characteristic, it's highly advantageous to probe oil-gas accumulation and direct hydrocarbon exploration in the middle of western Sichuan depression.The western Sichuan depression is a deep depression of Terrestrial Basin in west of Sichuan basin since Late Triassic and a foreland basin in the Longmenshan Nappe structure belt. The field of terrestrial clastic rock in western Sichuan depression has a very complicated oil-gas distribution and many gas reservoirs.The formation of Xujiahe in the middle of western Sichuan depression is emphatically researched in this paper. As a result of complicated evolution, the hydrocarbon source rocks generate abundant natural gas. So they may provide necessary gas source condition to the gas reservoir in Xujiahe formation.According to the research of predecessor, objective to recognize more comprehensively discuss source rocks characteristics of Xujiahe Fm, we do abundant studies on them by organic carbon, specular reflectance, kerogen types and so on, especially the characteristic on the 4th and 2th members of Xujiahe Fm. Based on research, we found the source rocks were high-content organic carbon and high maturity. The organic matter is dominated by III type, including less II type, and is the mixing source input, mainly from terrigenous higher plants.According to the gas-source correlation by the analysis of natural gas component ,light hydrocarbon fingerprint and carbon isotope characteristics, we found gas source is relatively complicated in each layers of the western Sichuan depression. The source type of organic matter mainly belongs to III-type kerogens. II -type kerogens are partial. Natural-gas hydrocarbon origin is coal-formed gas. The natural gas was characterized with dry gas, with a dry coefficient between 0.95 and 0.98, containing much low non-hydrocarbon components, and its composition migration and fractionation were significant. Theδ13C1 value (methane carbon isotopic ratio) was mostly from -36‰to -32‰. According to the data, the traditional interpretation might consider that the gas could reach mature stage.The natural gas on the 2th member of Xujiahe Fm was self-generating and self-preserving that may be from the contributions of the source rocks of T3t+m member of Xujiahe Fm. The natural gas on the 4th member of Xujiahe Fm was also self-generating and self-preserving. There may be some natural gas crossflow layer migrate to the layer where has fault development. The natural gas of lower submember was mainly from the 3th member of Xujiahe Fm. The natural gas of Jurassic depression in the west of Sichuan was from the source rocks on lower 5th and 4th members of Xujiahe Fm in Upper Triassic reservoirs of western Sichuan basin.
Keywords/Search Tags:Western Sichuan Depression, Hydrocarbon source rock, Organic geochemistry, Light hydrocarbon, Gas-source Correlation
PDF Full Text Request
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