塔中地区原油含硫化合物类型与TSR成因关系

Relationships Between Sulfur-containing Compound Types in Crude Oil and Causes of Thermochemical Sulphate Reduction in Tazhong Area

塔中奥陶系原油中检测到噻吩、四氢噻吩(Tetrahydrothiophenes,TIs)、苯并噻吩(Denzothiophenes,BTs)、二苯并噻吩(Dibenzothiophenes,DBTs)及硫代金刚烷(Thiaadamantanes,TAs)等多种含硫化合物,这些化合物的含量及其单体硫同位素值存在较大差异。分析认为,这些差异可能与热化学硫酸盐还原反应作用(Thermochemical Sulfate Reduction,TSR)对原油的改造有关。未经历TSR改造的原油样品,其四氢噻吩及硫代金刚烷化合物含量均较低;但是,受过TSR改造的原油样品,随着TSR程度的增高,其二苯并噻吩类化合物的含量也随增高,表明TSR过程中可能生成了二苯并噻吩类化合物。另外,通过对比未经历TSR的寒武系原油样品和经受强烈TSR改造的寒武系凝析油样品的硫同位素值及硫代金刚烷总浓度等数据,证明TSR也改变了原油硫同位素值。在TSR强烈改造的原油样品中,DBTs和硫代金刚烷单体化合物的硫同位素值在36‰~40‰;而在TSR改造较弱和未改造的奥陶系原油中,DBTs主要来自于烃源岩裂解,其硫同位素值相对较低(约20‰),与寒武系干酪根的硫同位素值接近。研究认为,塔里木盆地奥陶系原油主要来自寒武系烃源岩,而储层中一些有机硫同位素较高的原油主要为TSR改造所致。

Various sulfur-containing compounds,such as thiophene,tetrahydrothiophene,benzothiophene dibenzothiophene,and thioadamantane,were detected in crude oil extracted from the Ordovician reservoirs in the Tazhong Area.These compounds differ in their contents and isotopic values for single-atom sulfur.The analysis results show that modifications of crude oil by thermochemical sulphate reduction(TSR) may be the cause of the differences.There is less tetrahydrothiophenes and thioadamantanes in the crude oil not modified by TSR.As crude oil is increasingly modified by TSR,the total dibenzothiophene(DBT) concentration increases.This indicates that DBTs are probably formed during TSR.Meanwhile,non-TSR-modified crude oil samples were compared to highly TSR-modified condensate oil samples from Cambrian reservoirs for their sulfur isotopic values and total thioadamantane concentrations.It was found that TSR can also change the sulfur isotopic values of crude oil.The DBTs and thioadamantanes in the highly TSR-modified crude oil samples have sulfur isotopic values of from36‰to 40‰.In contrast,the DBTs in slightly TSR-modified and non-TSR-modified crude oil from Ordovician reservoirs are mainly from cracking of source rocks;thus,their sulfur isotopic values are relatively low(~20‰) near that of kerogen in the Cambrian reservoirs.Thus,it is believed that the crude oil extracted from the Ordovician reservoirs in the Tarim Basin is mainly from Cambrian source rocks and the crude oil with higher organic sulfur isotopic values is mostly caused by TSR modification.