Carbon isotopic compositions of individual terpenoids in heavy oils from Karamay oilfield

The carbon isotopic compositions of individual terpenoids in the heavy oils from the Karamay oilfield were determined by using the method of enrichmen t of terpanes with molecular sieve 13X and GC-IRMS technique. The terpanes, selectively enriched from the biodegraded oils with molecular sieve 13X, c an meet the demand of GC-IRMS analysis. The carbon isotopic compositions of the hopanoids (delta C-13 - 31.7 parts per thousand- - 37.8 parts per thou sand) infer that their main source is probably non-methanotrophic bacteria, and that the depositional environment of source rocks is a strongly reduct ive, rapidly depositional, and closed-semi-closed saline lagoon.