Abstract:

The key factors that influence sealing capacity of fault include fault activity, shale smearing factor, lithologic juxtaposition on both sides of fault, and relation between pressure on fault plane and shale stratum ratio. Taking these four key influential factors as appraisal parameters and integrating with tectonic evolution of the basin, the vertical and lateral sealing capacities and sealing history of the faults in Gas fault depression in Qaidam basin are studied. It is shown that the sealing capacities of faults vary largely in time and space in western Qaidam basin and have played different roles in hydrocarbon migration and accumulation. When acting as migration pathways of hydrocarbon, the faults would interconnect source rocks and traps and controlled the horizons and times of vertical migration and accumulation of hydrocarbons, such as the Ⅶ and Ⅺ faults. When acting as barrier beds, they would control the formation of traps for hydrocarbon accumulation, such as Wunan fault. Reactivation of faults would destruct oil and gas reservoirs, leading to the redistribution of oil and gas, such as the faults in Youshashan and Nanyishan areas.

Key words: Qaidam basin, Gas fault depression, fault sealing capacities, sealing history of fault, hydrocarbon migration and accumulation