塔里木盆地塔北地区奥陶系碳酸盐岩油气成因与运移

It is rich of hydrocarbons in the Ordovician carbonate reservoirs Tarim basin. The Ordovician hydrocarbon 3P reserves in this area are estimated to be 10 billion tons by late 2003. However, the area has undergone multiple tectonic movements, resulting in complex hydrocarbon accumulation, which leaves some geologic problems unsolved and restricts the development of theories and exploration practice even though in recent years, the exploration has achieved a major breakthrough. Specifically, the problems includes: the "source-to-trap" relationship based on the discovered reservoirs is not clear; at present, the exploration deployment is mainly based on the results of reservoir prediction, and the risk of exploration remains high. The project focused on the process of "source-to-trap" considering the heterogeneity of carbonate reservoirs, and provides guide for the hydrocarbon exploration of the Ordovician reservoirs in the Tabei area. Firstly, build the identifying model of hydrocarbon origin according to the study of the hydrocarbon sources; then, determine the hydrocarbon accumulation periods by the means of generation, expulsion forward modeling of source rocks and fluid inclusion inversion ; followed that, investigate the process and mechanisms of secondary hydrocarbon migration integrating the hydrocarbon properties and geochemical characteristics with reservoir quality, fault, fluid potential, hydrocarbon property, well production and methyl diamantane property; and finally, build the model of hydrocarbon generation, migration and accumulation of Ordovician carbonate reservoirs in the Tabei area, based on the previous study of hydrocarbon origin, accumulation periods, migration direction and pathways.

塔里木盆地塔北地区奥陶系碳酸盐岩油气资源丰富，截止到2013年底，发现三级油气储量近10亿吨，勘探潜力巨大。然而，由于该地区油气成藏条件复杂，具有多期成藏和调整改造的特点，近几年虽然勘探取得了重大突破，但依然存在一些地质难题制约理论及实践的再发展。具体表现在：目前所发现的油气田“源-位”关系不清，勘探主要依据储层预测结果来部署，勘探风险较高。本项目针对碳酸盐岩非均质性的特点，加强“源-圈闭”的过程研究，对指导塔北地区奥陶系油气的勘探有重要的意义。首先通过油气来源的研究，建立油气成因的判识模版；然后根据烃源岩生、排烃量正演法和流体包裹体反演法综合确定油气成藏期次；接下来通过对储层物性、断裂、流体势、油气性质、产能变化、甲基金刚烷指标等参数的分析，采用地质和地化相结合综合研究二次运移。最后，根据油气来源、成藏期次和运移方向和路径的研究结果，建立塔北地区奥陶系碳酸盐岩地层的油气生成和运聚模式。

塔里木盆地塔北地区奥陶系碳酸盐岩油气资源丰富。然而，目前所发现的油气田“源-位”关系不清，勘探风险较高。本项目通过加强“源-圈闭”的过程研究，对指导塔北地区奥陶系油气的勘探有重要的意义。本项目通过对油气来源、成藏期次和油气运移的综合研究，建立了塔北地区奥陶系碳酸盐岩地层的油气生成和运聚模式。结果表明：中上奥陶统低丰度已排烃碳酸盐岩烃源岩主要分布在一间房组， Tmax大都＞460℃（对应Ro=1.1%)。依据生烃动力学分析，干酪根的转化率达到了80%以上。因此，现今观察到的已排烃烃源岩氢指数大都＜400 mg/g TOC，在干酪根未成熟前的原始氢指数可高达900mg/g。高成熟阶段源岩的TOC恢复系数可达2.5-3.5倍，恢复后的原始TOC超过1%。有机孔隙的形成是使得已排烃层段孔隙度高于未排烃层段的主要原因。油源对比和含氮化合物咔唑总量综合分析表明已排烃中-上奥陶统低丰度源岩对研究区油贡献。在塔北地区西部的英买力地区，油气沿着南西向北东方向运移；在中部的哈拉哈塘地区，油气沿H13井区向附近运移；在西部的轮南地区，油气从东向西运移。原油密度、咔唑类含氮化合物含量在英买力地区从南西向北东，在哈拉哈塘地区从H13井区向附近，在轮南地区从东向西逐渐增大，天然气干燥系数和气油比参数逐渐减小。基于此，建立了中-上奥陶统高、低丰度混源，长、短距离运移共存的油气运聚模式。研究成果为塔里木盆地海相碳酸盐岩油气勘探提供了新的思路。