Alteration of solid bitumen by hydrothermal heating and thermochemical sulfate reduction in the Ediacaran and Cambrian dolomite reservoirs in the Central Sichuan Basin, SW China
Alteration of solid bitumen by hydrothermal heating and thermochemical sulfate reduction in the Ediacaran and Cambrian dolomite reservoirs in the Central Sichuan Basin, SW China
复制标题
川中埃迪卡拉系和寒武系白云岩储层水热加热和热化学硫酸盐还原对固体沥青的改造
DOI：
10.1016/j.precamres.2018.12.014
复制
发表时间：
2019
影响因子：
3.8
通讯作者：
Jiang Mengya
中科院分区：
文献类型：
--
作者：
Zhang Pengwei;Liu Guangdi;Cai Chunfang;Li Meijun;Chen Ruiqian;Gao Ping;Xu Chenlu;Wan Weichao;Zhang Yiying;Jiang Mengya
储集岩中的固体沥青是由沥青或液态烃经各种蚀变作用形成的异地有机质。利用岩相学、显微测温、化学和同位素等资料，在四川盆地中部埃迪卡拉纪灯影组和寒武纪龙王庙组中识别出两种类型的蚀变固体沥青。热液蚀变沥青（1型）与充填的鞍状白云岩和石英有关，其中某些流体包裹体的均一温度比灯影组最高埋藏温度高10 °C以上。它具有各种各向异性纹理，具有显著高的双反射率值（Rbmax-Rbmin，%），在3.89%和9.21%之间。此外，热液蚀变导致13 C-富集的1型沥青相比，正常成熟的沥青来自同一来源。另一方面，热化学硫酸盐还原（TSR）蚀变沥青（2型）的S/C原子比高达约0.06。2型沥青的δ 34 S值与碳酸盐岩伴生硫酸盐的δ 34 S值接近，与同一储层中TSR衍生的H2S的δ 34 S值相似。灯影组2型沥青的S/C原子比与δ 13 C值之间存在较强的负相关性，这可能是TSR过程中贫13 C的乙烷乙烷醚掺入沥青中的程度增加的结果。这一解释与剩余的乙烷随着TSR的进行而变得同位素更重的事实是一致的。此外，TSR反应性硫酸盐主要来源于热液硫酸盐，如重晶石。这主要表现在热液重晶石被富34 S的黄铁矿所取代，以及重晶石与同一地层中的2型沥青（或TSR衍生的H2S）之间δ 34 S值的微小差异。我们认为埃迪卡拉纪和寒武纪油气藏中的TSR可能是由热液活动引发的。
Solid bitumen in reservoir rocks is an allochthonous organic matter formed from bitumen or liquid hydrocarbons by various alteration processes. In this study, two types of altered solid bitumen have been identified in both the Ediacaran Dengying and Cambrian Longwangmiao formations in the Central Sichuan Basin using petrographic, microthermometric, chemical, and isotopic data. The hydrothermally altered bitumen (type 1) is associated with the pore-filling saddle dolomite and quartz in which homogenization temperatures of some fluid inclusions are more than 10 °C higher than the maximum burial temperature of the Dengying Formation. It has various anisotropic textures with significantly high bireflectance values (Rbmax− Rbmin, %) between 3.89% and 9.21%. Moreover, the hydrothermal alteration led to13C-enrichment in the type 1 bitumen compared to the normally matured bitumen derived from the same source. On the other hand, the thermochemical sulfate reduction (TSR)-altered bitumen (type 2) has S/C atomic ratios of up to approximately 0.06. The δ34S values of type 2 bitumen are close to those of the carbonate-associated sulfate and similar to the TSR-derived H2S in the same reservoirs. A strong negative correlation exists between S/C atomic ratios and δ13C values in the type 2 bitumen in the Dengying Formation, which is interpreted as a result of an increasing incorporation of the13C-depleted ethanethiol into the bitumen during TSR. This interpretation is consistent with the fact that the remaining ethane became isotopically heavier as TSR proceeded. In addition, the reactive sulfate for TSR was primarily derived from the hydrothermal sulfate, such as barite. This is evidenced by the replacement of hydrothermal barite by the34S-enriched pyrite and the small differences in δ34S value between the barite and the type 2 bitumen (or the TSR-derived H2S) in the same strata. We suggest that TSR in the Ediacaran and Cambrian hydrocarbon reservoirs was probably initiated by hydrothermal activity.