Occurrence and Origins of Thiols in Deep Strata Crude Oils, Tarim Basin, China

Thiols (or mercaptans) in crude oils have been considered to be associated with thermochemical sulfate reduction (TSR). However, the molecular composition and the formation mechanism of thiols in crude oils are not clear. This study provides the molecular composition of thiols in several deep strata condensate oils (condensates) from the Tarim Basin. Selective Michael addition products of thiols were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and comprehensive two-dimensional gas chromatography–MS (GC × GC MS). The carbon numbers and double bond equivalents of the thiols ranged between 4–20 and 0–10, respectively. Abundant diamondoidthiols found in two condensates were from high-temperature reservoirs. Various thiol compounds with multiple heteroatoms (S2, S3, S1O1, S1O2, and S2O1 class species) were detected in two other condensates, and low reservoir temperature made it possible to prevent the depletion of the multiple-heteroatom thiols. The pronounced 34...