A Study On Reservoir Patterns Of Mesozoic Strata Within Oil Source Lithotogic Hydrocarbon Reservoir Of Yuqia Depression In North Qaidam

Yuqia area is located in the middle of Margin of Qaidam Basin. On the basis ofreserch about the Jurassic source rock, reservoir and the cap rock of it. It is concludedthat the source rock is mainly consist in the middle–lower Jurassic stratum, and it hasthe characteristics of big thickness and high abundance of organic matter. The betterreservoir of Yuqia region is mainly distributed in the middle–fine sandstone formationof braided river face and braided river delta face. The caprock is contributed withareal-cap and isolated-cap; By the research of burial history and fluid inclusion，Thereis two times of uplift and one time of reservoir formation in the hisrory of the Yuqiaarea. In general, Yuqia–Hongshan fault sag mainly form reservoir–cap combinationwith the features of lower–generation and upper–reservoir, self–source andself–reservoir. Besides, reservoir is relatively thin, abundant, scattered and complex.1. Research of Source RockThe source rock is mainly consist in the middle–lower Jurassic stratum, and ithas the characteristics of large scale，thin thickness, rich organic and high quality ofsource rock. There are three types of source rocks in Yuqia region: shale, coal,carbonaceous mudstone, in which quality of origin of petroleum of mudstone ispreferable, coal and carbonaceous mudstone are poor and very poor.2. Research of ReservoirThe mailly reservoir physical property is ultra-low porosity and ultra-lowpermeability.The better reservoir is coarse fine sandstone by face of braided fluvial and braided—delta.The diagenetic stage period is early B-middle A.3. Caprock EvaluationThe mudstone as caprock is dense，and has low permeability, porosity, butdeveloped micro-cracks and corrosion phenomena. Has a good cover for oil sealingability, poor sealing capacity for natural gas.4. Burial History Researchthe area has twice big uplift and denudation in middle cretaceous and middle latepliocene by Yanshan movement and Xishan movement. The denudation result showsthat is1080m of the Pliocene，and is410m of the cretaceous.5. Hydrocarbon accumulation periodThe results of reservoir fluid inclusions homogenization temperature and that ofmicrosurgery infrared spectrum analysis are very anastomosis, confirmed that there isa hydrocarbon class of fluid migration in the two study blocks at the Mesozoic Theresult determined period of accumulation is only once and it occurred at the time ofthe previous late Pliocene (±3Ma).6. Factors Controlling Oil Accumulation and Oil and Gas Pool-Forming ModelsLithologic and lithologic-fault hydrocarbon reservoir is the mainly type of thisarea. The source-reservoir-cap assemblage of Yuqia area has two models， they areSelf-generation&Self-reserving lower intervals generation and upper intervalreserving. The effective source rocks and fracture distribution volume is the vitalcontrolling factors of hydrocarbon accumulation.