深层油气的来源和演化：单体化合物和硫碳同位素限定

Deep and super-deep reservoirs (>4500m) become key targets for petroleum exploration in China. However, it is unclear about the sources, destruction and even “death“ of the deep buried petroleum. Oil and gas and source rocks from the Cambrian and Ordovician in the Tarim Basin will be chosen for case studies, carbon and sulfur isotopic compositions will be analyzed on whole oil and kerogen,individual compounds, and a series of hydrous pyrolysis simulation experiments will be carried out. The purposes are, 1) to determine controlling conditions under which deep oil and solid bitumen can be correlated with the potential source rocks using organic sulfur and carbon isotope compositions, to find multi-proxies to determine the sources of oils and gas in the Tarim basin; 2) to check if diamandoids are generated during oil thermal maturation and to develop a new proxy to reflect the cracking degrees; 3) to confirm whether and how diamondoids and thiadiamondoids are generated during TSR, and if and why TSR has effects on diamondoids-related maturity proxies ; and to develop new proxies to determine maturities and degrees of oxidization-destruction of deep petroleum; 4) to determine factors to control cracking, destruction and even death of liquid hydrocarbons by comparing different basins and different areas of the same basin and to establish a synthetic model to predict deep oil and gas distribution, and thus to establish methods for correlation of source rocks with oil and gas generated and charged during multi-generations, and summarize a law for preservation and destruction of oils in deep to super-deep reservoirs, which are characteristic of basins in western China.

>4500m的深层-超深层油气已成为了我国勘探的重点。但是，对于深层油气的来源、破坏甚至“死亡”的机理还认识不清。本研究拟以塔里木盆地寒武-奥陶系油气藏和烃源岩为研究对象，测试油、干酪根和单体化合物硫碳同位素组成，结合实验模拟，1)研究硫碳同位素用于深层油气与烃源岩对比的适用条件，建立多指标对比方法，查明塔里木盆地下古生界油气的来源；2)查明热成熟作用是否生成了新的金刚烷，开发新的地球化学指标来计算深层油裂解程度 3)验证TSR是否同时生成了金刚烷和硫代金刚烷，影响了金刚烷成熟度参数，阐明其成因；开发新的地球化学指标来计算深层油气成熟度和氧化-破坏程度；4)比较不同盆地、不同地区油气裂解、氧化-破坏程度，确定控制因素，建立预测深层油气分布的综合模式；从而建立具有我国特色的、多期成藏的油气与源岩对比的方法和深层油气保存和破坏理论。

阐明有机硫同位素组成可以很好地用于阐明二叠纪-三叠纪过渡时期、泥盆纪晚期弗拉阶–法门阶过渡时期生物灭绝原因，以及Sturtian冰期刚消融后（660Ma）超重黄铁矿形成。发现萨尔干组和良里塔格组δ34SOS值<10‰；而下寒武统玉尔吐斯组烃源岩以15—22‰为主； 揭示上奥陶统与缓坡相玉尔吐斯组有机质C27-C29甾烷分布类似，均为“V”型，而盆地相玉尔吐斯组则为反“L”分布；查明萨尔干组δ13COM值变化较小，集中在-30‰，玉尔吐斯组δ13COM值变化大，前者明显重于后者。提出全组分和单体化合物硫同位素、碳同位素和芳基类异戊二烯烷烃分布，是确定塔里木盆地下古生界原油的油源有效指标；在包括巴楚-麦盖提斜坡等构造带中，发现仅顺北7、顺北7x1和中古29井（靠近阿瓦提凹陷）原油可能具有奥陶系烃源岩的贡献。发现顺北4号断裂带发生了TSR，对没有被TSR改造的天然气，利用其碳、氢和单体化合物硫同位素组成，确定了塔河、顺北天然气为干酪根降解气、原油裂解气及次生生物气等多种成因，但均来自寒武系烃源岩。实验揭示了水会促进原油裂解生成金刚烷并导致改变了金刚烷成熟度参数，修正了原油裂解程度参数EOGC = 1.2402 × EOC-28.952 (EOC计算式来自Dahl等2003）；实验首次证实了原油TSR新生成了金刚烷和硫代金刚烷等化合物。利用上述新建立的EOGC计算式，对塔北和顺北等地区原油进行裂解程度计算。结果显示，塔中和顺北地区受TSR改造原油的EOGC值为45.40～98.25%，明显高于所有其他非TSR原油。在非TSR改造原油中，塔中原油的EOGC值分别高于塔北和顺北原油。发现塔中奥陶系储层现今温度高于塔北地区，但原油EOGC值却低，认为较高的加热速率和高温(>120℃)下较短的持续时间是塔北和顺北地区原油EOGC值低于塔中地区的原因。提出塔北和顺北轻油可以保存到>200C和埋深达9500m。在综合世界不同盆地原油分布与温度和埋深关系基础上，认为温度、TSR和压力是主控因素，建立了全球通用的控制原油稳定性和裂解作用的模式。意义：扩展了有机硫同位素的应用范围、扩大了液态烃死亡界线和油气勘探范围，修正了部分石油地质学内容，指导了油气勘探。