Gao Jian, Li Shaojie, Li Huan, Cao Zicheng, Li Huili, Geng Feng, Han Jun, Huang Cheng
Petroleum Exploration and Production Research Institute, SINOPEC, Beijing, 102206, China.
SINOPEC Key Laboratory of Geology and Resources in Deep Stratum, Beijing, 102206, China.
Sci Rep. 2025 Jan 12;15(1):1759. doi: 10.1038/s41598-025-85485-2.
Deep oil reservoirs are becoming increasingly significant fields of hydrocarbon exploration in recent decades. Hydrothermal fluid flow is deemed as a potentially crucial factor affecting the occurrence of deep oil reservoirs, such as enhancing porosity/permeability of reservoirs, accelerating oil generation and thermal cracking, and modifying organic properties of crude oils. Understanding the interplay between hydrothermal fluids and crude oils would provide useful constraints for reconstructing hydrocarbon accumulation processes and predicting the distribution patterns of crude oils. Voluminous crude oils have been discovered in the deeply buried Ordovician carbonate reservoirs within the Shunbei area of the northern Tarim Basin. Previous studies revealed that the Early Permian Tarim Large Igneous Province (LIP) has affected the Shunbei area, whereas it is still debated whether the LIP-related hydrothermal infiltration affected hydrocarbons within the Ordovician reservoirs. To resolve this puzzle, this study was designed to unravel the potential thermal impact of hydrothermal infiltration on hydrocarbons according to molecular and stable carbon isotopic compositions of oils and associated natural gases, reflectance analysis of solid bitumen, and fluid inclusion thermometry. The studied crude oils are characterized by uniform organic indicators of paraffin, terpanes, steranes, and light hydrocarbons, implying that crude oils are derived from the same source rock. Genetic binary diagrams, such as dibenzothiophene/phenanthrene (DBT/P) vs. Pr/Ph (pristane/phytane), Pr/n-C alkane vs. Ph/n-C alkane, CR/Chopane vs. C/Ctricyclic terpane (TT), and C/C TT vs. C/C TT, indicate that marine shales deposited in a reducing-weakly oxidized environment are major source rocks. Natural gases are associated with oil reservoirs and are mainly generated via the decomposition of kerogen and crude oil. Solid bitumen with abnormally high reflectance values (2.17-2.20%) occurred in the studied area, suggesting their formation temperatures were 252-254 °C. The abnormally high temperatures may be caused by hydrothermal infiltration related to the Tarim LIP. Hydrothermal infiltration is supported by the presence of high contents of CO (30-48%) with enriched δC ratios (between - 2.5‰ and - 2.3‰), enriched n-alkane δC ratios, and incongruent temperatures estimated by multiple indicators, such as light hydrocarbon compositions, homogenization temperatures of fluid inclusions, and bitumen reflectance. Outcomes of this study support the interpretation that hydrothermal infiltration indeed occurred and may have facilitated hydrocarbon generation in the Shunbei area, and possibly elsewhere in the cratonic regions of the northern Tarim Basin.
近几十年来，深层油藏正日益成为油气勘探的重要领域。热液流体流动被认为是影响深层油藏形成的一个潜在关键因素，例如提高储层的孔隙度/渗透率、加速石油生成和热裂解，以及改变原油的有机性质。了解热液流体与原油之间的相互作用，将为重建油气成藏过程和预测原油分布模式提供有用的限制条件。在塔里木盆地北部顺北地区深埋的奥陶系碳酸盐岩储层中发现了大量原油。先前的研究表明，早二叠世塔里木大火成岩省（LIP）对顺北地区产生了影响，然而，与LIP相关的热液渗透是否影响了奥陶系储层中的油气，仍存在争议。为了解决这一难题，本研究旨在根据原油和伴生天然气的分子和稳定碳同位素组成、固体沥青的反射率分析以及流体包裹体测温，揭示热液渗透对油气的潜在热影响。所研究的原油具有石蜡、萜烷、甾烷和轻烃等均匀的有机指标特征，这意味着原油来源于同一烃源岩。遗传二元图，如二苯并噻吩/菲（DBT/P）与姥鲛烷/植烷（Pr/Ph）、姥鲛烷/正构烷烃与植烷/正构烷烃、蒈烷/藿烷与三环萜烷（TT）的C/C、以及三环萜烷的C/C与三环萜烷的C/C，表明沉积于还原-弱氧化环境的海相页岩是主要烃源岩。天然气与油藏伴生，主要通过干酪根和原油的分解生成。研究区出现了反射率值异常高（2.17-2.20%）的固体沥青，这表明其形成温度为252-254℃。异常高温可能是由与塔里木LIP相关的热液渗透引起的。热液渗透得到了高含量CO（30-48%）、δC比率富集（-2.5‰至-2.3‰之间）、正构烷烃δC比率富集以及由多种指标（如轻烃组成、流体包裹体均一温度和沥青反射率）估算出的不一致温度的支持。本研究结果支持了热液渗透确实发生且可能促进了顺北地区油气生成的解释，并且可能在塔里木盆地北部克拉通地区的其他地方也有促进作用。
