Identification and formation of sulfur-containing steroids in sulfur-rich heavy oils in the Jinxian Sag, Bohai Bay Basin, North China

Abstract

High abundant sulfur-containing steroids were identified and detected in saturate hydrocarbon fractions of heavy oil with a high sulfur content in the Jinxian Sag, Bohai Bay Basin, North China. These sulfur-containing steroids were structurally merged into the D-ring of steroid nucleus with thiophene ring and/or combined into the C-22 in the side-chain. Based on the previous reports of sulfur-containing steroids with methylthio-teroids and intra-molecular form, four formation mechanisms of sulfur-containing steroids and diagenetic pathway of steroids under S-rich conditions were proposed in this paper according to the double bond positions in the sterene compounds. Hydrogenation and sulfurization both occurred in the diagenetic processes of olefinic bond in the side-chain of steroids: abiogenic chemical hydrogenation of H2S and HS− leads to the formation of regular steranes; a successful sulfurization process leads to the formation of the side-chain sulfur-containing steroids whereas unsuccessful cyclization and/or sulfurization result in the generation of short-chain steranes. This kind of mechanism of hydrogenation/sulfurization of side-chain olefinic bond provides a potential genesis clue for the occurrence of high abundance of short-chain steranes (higher than the common regular steroids, phytane and n-alkanes) in S-rich heavy oils and source rocks in the Jinxian Sag, Bohai Bay Basin, North China.