Formation of C15 Sesquiterpanes as a Result of Thermolysis of Asphaltenes, Resins, and Acids from Weakly Transformed Oil of the Anastasievsko-Troitskoe Field (Horizon IV)

Abstract

Asphaltenes, resins, and acids from immature oil were subjected to thermolysis, and the distribution patterns of hydrocarbon biomarkers (HC biomarkers) C₁₅ sesquiterpanes were then studied. It was shown that both the original oil and the thermolysis products of high-molecular-weight hydrocarbon (HC) precursors of the oil contain all seven isomers of C₁₅ sesquiterpanes, which usually occur in mature oils, but the relative distributions of C₁₅ sesquiterpane isomers are different. The relative content of 1,2,3,7,7-pentamethylbicyclo[4,4,0]decane (drimane) in the thermolysis products of high-molecular-weight petroleum hydrocarbon precursors is significantly higher than in the original immature crude oil. This means that drimane, like normal alkanes, is released from high-molecular-weight precursors under more severe conditions. The relative content of drimane in oil may perhaps be indicative of the maturity of the oil.