Abstract:

Shacan-2 well is a high yield oil well in the Tarim Basin,the reser-voir is Ordovician limestone.The author studied the biodegradation pro-ducts(25-nor-hopanes)in the oil,the pyrolysis product of the asphaltenefrom this well,and the extracts of Ordovician limestone core in Lunnan-1well.The author considered that the crude oil in Shacan-2 well is a mixtureformed by two accumulations.The crude oil accumulated at the first timeunderwent serious biodegradation,but the rest did not.