Origin of the unusually high dibenzothiophene oils in Tazhong-4 Oilfield of Tarim Basin and its implication in deep petroleum exploration
Origin of the unusually high dibenzothiophene oils in Tazhong-4 Oilfield of Tarim Basin and its implication in deep petroleum exploration
复制标题
塔里木盆地塔中4油田二苯并噻吩异常高油成因及其深层石油勘探意义
DOI：
10.1016/j.orggeochem.2012.04.008
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发表时间：
2012-07-01
影响因子：
3
通讯作者：
Zhang, Haizu
中科院分区：
文献类型：
--
作者：
Li, Sumei;Shi, Quan;Zhang, Haizu
塔里木盆地塔中隆起塔中4油田原油中二苯并噻吩（DBT）含量异常高。采用正离子电喷雾电离傅里叶变换离子回旋共振质谱法（FT-ICR MS）与常规地球化学方法相结合，揭示了富集机理。在3种热成熟度较高的下奥陶统油中发现了大量的硫醚类、硫醇类、噻吩类和苯并噻吩类S-1物质，其DBE值相对较低（0-8），可能是储层中热化学硫酸盐还原（TSR）的产物。油伴生气体中硫化物和硫化氢的存在也支持了TSR的发生。三种油的DBE = 9 S-1（主要相当于C-0-C-35 dbt）浓度明显低于其同系物，这可能是TSR改变了三种油，表明TSR与dbt之间不存在正相关关系。塔中4组原油的硫化合物与下奥陶统大部分原油的硫化合物特征非常相似，主要表现为高浓度的dbt， DBE = 9 S-1，只有少量的硫化合物，DBE = 0-8，热稳定性较低，表明只有一小部分硫化合物来自TSR。在大多数下奥陶统油中，导致DBT浓度异常高的是热成熟度，而不是TSR。本文认为塔中4油田异常高DBT油是由下奥陶统晚期（甚至更深）充注的原油混合而成，而高DBT丰度是由早期欠成熟的原油混合而成的。本文的混合实验和前人的相关研究结果支持了这一观点，同时也支持了塔中4油田丰富的自生黄铁矿热液成因。根据FT-ICR MS结果，我们认为塔中隆起发生了TSR。然而，在大多数油中检测到正常的硫化合物，并且在气态烃中未观察到δ (C2H6)-C-13- δ (C4H10)-C-13的增加，这表明目前和/或最近仅对油进行了轻微的TSR改变。推测下奥陶统油中异常的硫化合物也可能是深层石油混合作用的结果，这可能意味着下奥陶统的含油气层位更深，即寒武系，具有较高的含油气潜力。该研究对该区进一步进行深部油气勘探具有重要意义。(C) 2012 Elsevier Ltd.版权所有。
Unusually high dibenzothiophene (DBT) concentrations are present in the oils from the Tazhong-4 Oilfield in the Tazhong Uplift, Tarim Basin. Positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used in combination with conventional geochemical approaches to unravel the enrichment mechanisms. Significant amounts of S-1 species with relatively low DBE values (0-8), i.e., sulfur ethers, mercaptans, thiophenes and benzothiophenes, were detected in three Lower Ordovician oils with high thermal maturity, which were suggested to be the products of thermochemical sulfate reduction (TSR) in the reservoir. The occurrence of TSR was also supported by the coexistence of thiadiamondoids and abundant H2S in the gases associated with the oils. Obviously low concentrations of the DBE = 9 S-1 species (mainly equivalent to C-0-C-35 DBTs) compared to its homologues were observed for the three oils which were probably altered by TSR, indicating that no positive relationship existed between TSR and DBTs in this study. The sulfur compounds in the Tazhong-4 oils are quite similar to those in the majority of Lower Ordovician oils characterized by high concentrations of DBTs and dominant DBE = 9 S-1 species with only small amounts of sulfur compounds with low thermal stability (DBE = 0-8), suggesting only a small proportion of sulfur compounds were derived from TSR. It is thermal maturity rather than TSR that has caused the unusually high DBT concentrations in most of the Lower Ordovician oils. We suggest that the unusually high DBT oils in the Tazhong-4 Oilfield are caused by oil mixing from the later charged Lower Ordovician (or perhaps even deeper), with high DBT abundances from the earlier less mature oils, which was supported by our oil mixing experiments and previous relevant investigations as well as abundant authigenic pyrite of hydrothermal origin. We believe that TSR should have occurred in the Tazhong Uplift based on our FT-ICR MS results. However, normal sulfur compounds were detected in most oils and no increase of delta(C2H6)-C-13-delta(C4H10)-C-13 was observed for the gas hydrocarbons, suggesting only a slight alteration of the oils by TSR currently and/or recently. We suspect that the abnormal sulfur compounds in the Lower Ordovician oils might also be a result of deep oil mixing, which might imply a deeper petroliferous horizon, i.e., Cambrian, with a high petroleum potential. This study is important to further deep petroleum exploration in the area. (C) 2012 Elsevier Ltd. All rights reserved.