Tectonic Developmental Feature And Its Control For Hydrocarbon Accumulation In Northern Margin Of Qaidam Basin

The northern margin of Qaidam Basin is a distribution area of the Jurassic petroleum system, and hydrocarbon resources are abundant. Since Mesozoic era and Cainozoic era, the tectonic movements with different properties and multi-stage effect have not only led to complex tectonic deformation but also controlled a series of processes such as the distribution and evolution of hydrocarbon source rocks, the formation of the combination of source-reservoir-cap, the formation and distribution of traps, the accumulation and transformation of oil gas. Through summarizing the previous research, with perspective of the large north margin of Qaidam for the first time and on the basis of seismic, drilling, logging and geologic investigation materials, this paper further fulfills the characteristics of tectonic development and evolution, identifies the control effect of structure on hydrocarbon accumulation, and proposes new favorable pre-exploration fields through using multi-disciplinary land multi-methods which include tectonics, sedimentation, sequence stratigraphy, organic geochemistry, geophysical exploration and others.1. The Qiangtang block, the Lhasa block, the Himalayan block and the Indian plate drift northward and combine with the Eurasian continent, which are the main power sources of formation and evolution of the northern margin of Qaidam Basin. The migration direction and speed of the Tarim plate and the North China plate affect the force manner and stress intensity of the northern margin of Qaidam Basin. The direction and intensity of strike-slip events of Arkin fault and the intensity of extrusion stress of the South Qilian Mountains control the property and intensity of tectonic deformation of the northern margin of Qaidam Basin.2. The northern margin of Qaidam Basin has experienced Early Jurassic fault basin, Middle Jurassic fault-depression composite basin, Late Jurassic - Early Cretaceous depression basin and Tertiary depression basin since Early Jurassic. The late Yanshan tectonic movement and the late Himalayan tectonic movement are the periods of formation, transformation and stereotypes for the structure and tectonic framework of the north Qaidam Basin.3. The north of Qaidam Basin deforms intensively and develops numerous fractures and folds which are abundant in type. These structures are characterized by polystage activity in aspect of time, diversity in aspect of the genesis and style, and obvious stratification, zonation and segmentation in the space.4. The types of prototype basin and the basin structure control the depositional systems and sedimentary facies; the strength of tectonic movement and the degree of development of fracture in late Yanshan control the properties of Mesozoic and Cenozoic reservoir. The property and structure of prototype basin, the period and intensity of tectonic movements control the distribution of Middle and lower Jurassic's hydrocarbon source rock, the thermal evolution of organic matter and the period of hydrocarbon generation and expulsion; two-period tectonic movements forms the universal law for two-period reservoir-forming. The fault structure is the main thoroughfare for hydrocarbon migration. The intensity of Late Himalayan tectonic movement controls the reservoir degree of post-preservation; fault sealing controls the enrichment of oil and gas reservoirs.5. Jurassic petroleum system of Delingha depression, the deep gas in the margin of Yibei depression and Carboniferous have a certain exploration potential, they are three important new areas for the pre-exploration of oil and gas.