Volatile organic sulfur compounds (VOSC) are found in petroleum natural gas and condensates at trace levels. The abundance and δ³⁴S values of VOSC were proposed as a proxy for thermal processes such as oil and gas generation during thermal maturation, thermochemical and microbial sulfate reduction, migration and expulsion. The understanding of VOSC formation and degradation mechanisms is needed to refine the use of δ³⁴S values of VOSC as proxies for thermal processes over geological timescales in the subsurface. We therefore conducted pyrolysis experiments at 360 °C for 4, 12 and 72 h using pentane and H₂S or pentanethiol as model compounds to study the formation and degradation pathways of VOSC and associated variations in δ³⁴S values. The main products of these experiments are C₁-C₄ alkanes along with a variety of thiols and thiophenes, the most dominant VOSC formed. Most thiols were in equilibrium with H₂S after 4 h based on their δ³⁴S values. Thiophenes were first ³⁴S depleted relative to H₂S and only reached equilibrium at the 72 h experiment. The products and ³⁴S fractionations in the pyrolysis experiment of pentanethiol at 360 °C and 12 h were similar to those of the experiment with H₂S and pentane at the same conditions. This similarity suggests that pentanethiol is an intermediate product in the formation of aromatic VOSC during pyrolysis of pentane and H₂S. Benzo- and dibenzothiophenes (BTs and DBTs) were formed in the liquid phase and their ³⁴S depleted values relative to H₂S indicated that they had not reached equilibrium. Ab-initio calculations of the thermodynamic properties of thiols, thiolanes, thiophenes BTs and DBTs were used to explain the relative abundance of products in the system and predict their abundance and S isotopic signature at reservoir conditions. The thermodynamic data suggests that at equilibrium, only small quantities of thiols and even smaller quantities of thiolanes can exist under our experimental conditions. Unlike thiols, the free energy of formation of thiophenes, BTs and DBTs is negative under these conditions indicating that the formation of these compounds is thermodynamically favored. The result suggests that the δ³⁴S values of thiols are controlled by a very rapid equilibrium isotopic effect (EIE). On the other hand, aromatic sulfur compounds can preserve the δ³⁴S value of the kinetic isotopic effect (KIE) associated with their formation for longer. However, under typical petroleum reservoir conditions, the formation of aromatic VOSC in the gas phase from short alkanes (<C₅) and H₂S is not thermodynamically preferred and thus their presence is expected to be either as kinetic products or due to influx and charge from a different source where the reactions were thermodynamically favorable. Thus, the abundance and Δ³⁴S between H₂S and VOSC can be used as a new approach to evaluate charge history within sulfur containing reservoirs.

石油天然气和冷凝物中的微量有机硫化合物（VOSC）含量极低。的丰度和δ ^34个VOSC的价值观，提出了作为热成熟过程中的热处理过程中，如石油和气体产生的代理，热化学和微生物硫酸盐还原，迁移和驱逐。需要的VOSC形成和降解机制的认识来细化使用δ的³⁴ VOSC第值作为代理用于通过在地下地质时间尺度的热过程。因此，我们在360℃下进行热解实验为使用戊烷和H 4，第12和72小时₂在δS或戊硫醇作为模型化合物，研究VOSC的形成和降解途径和相关联的变化³⁴S值。这些实验的主要产物是C ₁ -C ₄烷烃以及各种硫醇和噻吩，形成的最主要的VOSC。最硫醇均用H平衡₂基于它们δS4中小时后³⁴价值观。噻吩首先比H ₂ S减少³⁴ S ，仅在72 h实验达到平衡。戊硫醇在360°C和12 h的热解实验中的产物和³⁴ S的分馏与H ₂的实验相似S和戊烷在相同条件下。这种相似性表明戊烷硫醇是戊烷和H ₂ S热解过程中芳族VOSC形成的中间产物。苯并噻吩和二苯并噻吩（BTs和DBTs）在液相中形成，相对于H ₂ S ，它们的³⁴ S损耗值表明他们尚未达到平衡。从头开始硫醇，噻吩，噻吩BT和DBT的热力学性质的计算用于解释系统中产品的相对丰度，并预测其在储层条件下的丰度和S同位素特征。热力学数据表明，在我们的实验条件下，在平衡状态下只能存在少量硫醇，甚至更少量的硫烷。与硫醇不同，在这些条件下，噻吩，BT和DBT的形成自由能为负，表明这些化合物的形成在热力学上是有利的。结果表明，δ ³⁴硫醇的S值在通过非常快速平衡同位素效应（EIE）控制。在另一方面，芳族硫化合物可以保留δ ³⁴与其形成相关的动力学同位素效应（KIE）的S值时间更长。但是，在典型的石油储层条件下，在热力学上，由短链烷烃（<C ₅）和H ₂ S形成的芳族VOSC并不是热力学优选的，因此，它们的存在可能是动力学产物，也可能是由于流入和电荷来自反应热力学上有利的其他来源。因此，丰度和Δ ³⁴ ħS之间₂ S和VOSC可以用作一种新的方法来评估含硫储层内充电历史。