Abstract

Summary It is well known that oil content ( pyrolysis S1 or soluble EOM ) in a shale is under-estimated due to light hydrocarbon loss during measurement procedure, and the restoration of such loss is a great challenge while estimating shale oil resources and determining mobility. In this paper, the light hydrocarbon losses of fresh shale cores from Qingshankou Formation of northern Songliao Basin and their produced oils were compared. The results show that under ambient conditions, the hydrocarbon losses of pyrolysis S1 and crude oils overall increase with shale maturity (Ro) and oil API gravity. However, a shale with greater maturity (e.g. Ro>1.6%) tends to have better seal capacity and the hydrocarbon loss may be much lower than expected. Compared with their produced oils, shales tend to lose more light hydrocarbons. The cause of such difference is that S1 yields of a shale are composed of more light hydrocarbons and less heavy ends as indicated by gas chromatography analysis. It is suggested that restoring light hydrocarbon loss based only on oil density as proposed by previous studies will significantly under-estimated shale oil resources and more controlling factors should be considered.

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