Abstract:

Well Tashen-1 is so far the deepest well in China.The well is designed to target at the large-scale build-up traps located at the edge of the Cambrian carbonate platform in the east of Akekule uplift,Tarim Basin. The stratigraphic succession from the Ordovician to the Cambrian has been built based on the drilling results of the well.It has been confirmed that quality reservoirs exist in the ultra-deep build-up.The types of reservoir space are various including intercrystalline pores,intercrystalline dissolved pores,non-structure-selective dis-solved vugs,and reticular fractures.As the burial depth increases,the reservoirs become more favorable and dis-solved vugs are better developed.It is preliminarily suggested that corrosion of the organic acid fluids discharged from hydrocarbon generation of source rocks be the main factor for the formation of reservoir space and that ultra deep(>7000 m) build-ups are characterized by multiple hydrocarbon accumulation.What is worth mentioning is that the liquid hydrocarbons observed on the cores and the fluorescence thin-sections may lead us to a re-un-derstanding of the lower limits of"oil-generating window"in different regions (or basins).It is also safe to con-clude that the geological fruits gained from Well Tashen-1 can be used effectively in guiding the exploration for ultra deep hydrocarbons in the Tarim Basin.

Key words: dissolution, oil-generating window, build-up, multiple-period hydrocarbon accumulation, Tashen-1 well, Tarim Basin