海相含膏盐岩层系烃源岩发育特征与生烃潜力评价

Since a significant breakthrough on the exploration has been achieved in the gypsum- and salt-bearing strata of the Middle Triassic Leikoupo Formation in the Sichuan Basin recently, the applicants intend to focus on the oil and gas reservoirs of this stratum combining with the development characteristics of source rocks in oil and gas breakthrough zone beneath salt in the Ordovician strata in the Ordos Basin and the Cambrian strata in the Tazhong area of the Tarim Basin, and in gypsum- and salt-bearing strata in the Permian and Mississipi-Louisiana basins in America, in oder to clarify the depositional environment and the hydrocarbon precursor types of source rokcs in marine gypsumand salt-bearing strata, reveal the paleosedimentary environment and biological assemblages controlling the formation of marine gypsum- and salt-bearing rocks, and build the development model of the effective source rocks. The applicants also intend to simulate the hydrocarbon generation processes under the participation of gypsum- and salt-bearing rocks by independently developed high-temperature and high-pressure apparatus, probe into the hydrocarbon generation potential of source rocks under the participation of gypsum-salt rocks and the impact of gypsum-salt rocks on the thermal cracking of reservoir bitumen in the paleo-oil resrvoirs, reveal the hydrocarbon generation regime under the participation of gypsum-salt rocks, and build the geochemical identification index system for hydrocarbons generated by organic matter under the participation of gypsum-salt rocks. Moreover, the applicants intend to figure out the geochemical characteristics of hydrocarbon products generated from the gypsum- and salt-bearing source rocks and oil-gas-source correlation based on the analysis of typical oil and gas reservoirs in marine gypsum- and salt-bearing strata, ascertain the coupling relationship between the oil and gas oxidation modification and reservoir dissolution by TSR (thermochemical sulfate reduction), and figure out the role of gypsum-salt rocks in the oil and gas accumulation combining with the tectonic evolution and source-reservoir-cap assemblage correlation.

本项目以最新勘探取得重要突破的四川盆地雷口坡组含膏盐岩层系油气藏为重点，结合鄂尔多斯盆地奥陶系盐下、塔里木盆地塔中寒武系盐下油气突破区带以及美国二叠盆地和密西西比-路易斯安那盆地含膏盐岩层系烃源岩发育特征，阐明海相含膏盐岩层系烃源岩发育沉积环境、成烃母质类型，明确控制海相含膏盐岩形成的古沉积环境与生物组合，建立其有效烃源岩发育模式。通过自主研制的高温高压装置模拟有机质在含膏盐岩参与下生烃过程，探索膏盐岩参与下烃源岩生烃潜力以及膏盐岩对古油藏储层沥青热裂解的影响，揭示膏盐岩参与下有机质成烃机制，建立膏盐岩参与下有机质生成烃类的地球化学鉴别指标体系。通过典型海相含膏盐岩层系油气藏解剖，明确含膏盐岩烃源岩成烃产物地球化学特征与油气源对比，查明TSR对油气氧化改造与储层溶蚀的耦合关系，结合构造演化和生储盖配置关系，明确膏盐岩在油气成藏的中作用。

受多种因素控制，膏盐岩层系在全球多个含油气盆地内广泛发育。这些发育膏盐岩的含油气盆地中蕴藏着丰富的石油资源。前人关于膏盐岩与油气藏关系的研究主要集中在膏盐岩作为优质盖层的油气保存作用。但目前的勘探发现表明，与膏盐岩层系有关的油气源对比指标存在明显变化，暗示膏盐岩层系可能会影响烃源岩的形成和生烃过程。但是，这些与膏盐岩有关的烃源岩的发育环境及生烃潜力，研究的相对较少。此外，在膏盐岩存在条件下形成油气藏的识别，成为直接影响判定该类型资源潜力的关键。为了解决海相含膏盐岩层系烃源岩的烃源特征及生烃潜力评价的问题，本项目综合利用岩相古地理、烃源岩油气地球化学等知识，通过岩相古地理编图、有机质热解生烃实验、同位素地球化学分析、色谱-质谱联用、显微有机岩石学分析技术，分析了塔里木盆地、鄂尔多斯盆地以及四川盆地等典型的含膏盐岩层系烃源岩的成烃生物组合特征，恢复了膏盐参与下烃源岩形成的的岩相古地理环境。利用美国二叠盆地海相优质烃源岩开展了膏盐岩影响下的生烃模拟实验，以查明该类型烃源岩的生烃潜力，并通过典型油气藏解剖建立了油气成藏模式。研究表明，塔里木盆地寒武系含膏盐岩烃源岩中的发育有大量的成烃生物，成烃生物可以分为浮游藻与底栖藻两大类，这两类成烃生物在显微学上具有显著特征，并且其碳同位素组成差别较大，即同期浮游藻的碳同位素组成较重（>-30‰），而底栖藻的碳同位素组成较轻（<-34‰）（PDB）。生烃模拟实验结果表明，随着膏盐岩含量的增加，烃源岩生气率大幅增加，从不含膏盐岩时的60mg/g TOC增加到当膏盐岩含量为1%时的184mg/g TOC，同时，烷烃气的碳同位素组成特征符合热解气的特点，但随着膏盐岩含量的增加，烃类气体的干燥系数逐渐变小，而碳同位素组成逐渐变重。液态烃的FT-ICR MS 分析结果表明，膏盐岩含量的增加，会造成含1个双键的含N化合物的增加，而含N和含S化合物的降低。通过典型油气藏解剖建立了该类型油气成藏模式，为未来油气勘探提供了理论支撑。