The Magmatic Activity And Its Effects On The Oil And Gas Formation In Southwest Erdos Basin

There are different occurrences and properties of Mesozoic magmatite in southwestErdos Basin, and Triassic magmatic activity is strong and wide which is the main componentof Longmen concealed rock. Cretaceous magmatite mainly includes Angou–Erxianzi rock,Tongcheng rock and the late intrusive body of Longmen concealed rock. The magmatismthermal effect of Triassic and early Cretaceous obviously affects on the hydrocarbon sourcerocks and the formation of oil and gas. The metamorphism occurred in the JixianSysterm–Shanxi Group hydrocarbon source rock of Longmen concealed rock influenced byTriassic magmatic activity (Ro reached to3.4%). Ro of the Yanchang Group hydrocarbonsource rock reached to3.2%influenced by magmatic activity in the end of Cretaceous.Yanchang Group is the highest intrusive position of Longmen concealed rock which has noeffect on Jurassic coal beds. The research shows that the influence range of magmaticintrusion is very small (approximately70m) through the organic geochemistry, rock pyrolysisanalysis and mineralogy analysis of Jixian Systerm hydrocarbon source rock with Tongchengrock instrusion.There are three types of the thermal evolution process of hydrocarbon generation insouthwest Erdos Basin.(1) The thermal evolution process of hydrocarbon generation in lowtemperature in the edge of the basin: due to in the denudation area for a long time, thehydrocarbon source rock is in the low maturity stage and the hydrocarbon generation processis simple which has no thermal evolution conditions of natural gas formation andreservoir-forming conditions;(2) The magmatic thermal evolution of hydrocarbon generationin Longmen upheaval zone: the magmatic activity in Middle Triassic and Late Cretaceousrespectively makes the Paleozoic,the Strata of before and Yanchang Group of hydrocarbonsource rocks occur metamorphism to dry gas;(3) The normal buried hydrocarbon generationprocess without magmatic activity in basin: the hydrocarbon generation process is controlledby normal burial thermal evolution process without affecting by the magmatic activity. Thethermal evolution extent of the hydrocarbon source rocks of Jixian Systerm, Ordovician andPermian reached to maturity stage in Middle Triassic and formed liquid hydrocarbon.To LateCretaceous, the buried thermal evolution reached to the postmature stage which is a dry gasgeneration stage. The Triassic hydrocarbon source rocks reached to the main stage of largeliquid hydrocarbon generation in Late Cretaceous.