塔中原油超高二苯并噻吩硫特征及其控制因素

塔中相当部分原油具有高丰度芳香硫——二苯并噻吩(DBTs)特征,其在原油中的绝对丰度高达26 859μg/g,在芳烃中的相对丰度高达58.2%,主要分布在塔中I号构造带下奥陶统、塔中4(TZ4)和塔中1-6(TZ1-6)井区。采用综合地球化学研究途径,对该区原油的高DBTs特征及其主控因素进行初步探讨。分析表明,研究区母源岩较强地控制DBTs的丰度,纯泥岩、页岩中DBTs丰度不高,灰岩、云岩等烃源岩DBTs丰度偏高或超高;观察到在正常油窗范围内,烃源岩和相关原油随成熟度增加DBTs丰度增加,而塔中型高-过熟原油中DBTs丰度有先增加后减小的趋势,表明热成熟作用对该化合物有较强的控制作用;发现生物降解、水洗可使原油中DBTs丰度降低,但对塔中原油中DBTs影响较小;观测到塔中相当部分原油的DBTs含量与硫酸盐热化学还原作用——TSR的作用产物H2S、硫醇、长链烷基四氢噻烷有一定正相关性。对比研究认为,有多种因素控制塔中原油中DBTs丰度与分布,热成熟作用、TSR是导致塔中下奥陶统部分原油高DBTs特征的重要原因,前者可能是主要因素,特殊母源岩因素相对较少,尽管尚不能排除。TZ4井区等石炭系高DBTs原油主要来自深部地层,与下奥陶统抑或更深层高DBTS原油的混入有关。本研究对于该区深层油气勘探具有重要意义。

Geochemical Characteristics and Affecting Factors of the Unusually High Dibenzothiophenes Oils in the Tazhong Uplift

Unusually high dibenzothiophenes(DBTs) oils were detected in the Tazhong Uplift,Tarim Basin,with the maximum absolute abundance up to 26,859 μg/g and relative abundance among the aromatic hydrocarbons recognizable up to 58.2%.The oil is usually situated in the Lower Ordovician in the No.1 Fault Belt and the TZ4 and TZ1-6 well-blocks.An integrated geochemical approach was utilized in characterizing the oils.The results show that the type of source rock has an significant controlling on the distribution and abundance of DBTs.Normal DBTs were detected in pure dark mudstones and shales,whereas super high DBTs were observed in the source rocks with high content of sulphate.An increasing trend of the DBTs content was observed for the source rock and the related oils within normal oil window in the Dongying Depression.However,in the case of the Tazhong oils with high thermal maturity,there is an increasing and then decreasing trend with a breakpoint around 5,500 m,suggesting strong controlling of thermal evolution.It was also observed that biodegradation and water-washing have an effect on DBTs in a varying degree,with an decreasing trend of DBTs concentration with increasing biodegradation.But it is unlikely that this kind of secondary alteration is one of the reasons responsible for the abnormal oils in the Tazhong region.It was detected that there is a positive relation between DBTs,H2S content(in associated gas),mercaptan and long chain alkyl-thiolanes in the high DBTs oils,which is recognized as productions of TSR.We believe there are several factors having an effect on the DBTs in the Tazhong oils.Thermal chemical alteration and TSR are suggested to be the essential factors responsible for the high DBTs in partial Lower Ordovician oils,and little possibility of a kind of special source rocks have caused the abnormal oils,although it could not be excluded at present.As to the oils in the Carboniferous in the TZ4 well-block etc,we suggest that mixing of later charged deep oils with high DBT concentrations with earlier oils in situ is the most likely mechanism responsible for the abnormal DBT concentrations.