松辽盆地北部白垩系青山口组不同赋存状态页岩油特征

Characteristics of shale oil in different occurrence states of the Cretaceous Qingshankou Formation in the northern Songliao basin

通过对松辽盆地北部青山口组15个湖相页岩样品进行岩石矿物学、有机地球化学和储集空间特征分析,综合运用XRD、热解、分步热解、分步抽提和分步核磁测试等实验方法,以表征青山口组不同赋存状态页岩油含量、组成和分布特征,进一步探讨了滞留烃含量评价、生产潜力以及勘探制约因素与建议。此次研究得到以下认识:(1)青山口组矿物组成较为均一,岩性主要为黏土质页岩,但以伊利石为主的黏土矿物特征有利于储层的压裂。有机质分布较为均一,TOC平均值为2.41%。含油性好,油质轻、饱和烃含量和含油饱和度指数(OSI)高。(2)页岩油的赋存状态被定义为在冷抽提和索氏抽提条件下从不同粒度中提取的游离油、游离-吸附油和吸附油。游离油主要以轻质组分为主,吸附油的重质组分增多,较大孔隙以游离油为主,吸附油绝大部分分布在较小孔隙中。游离油与吸附油化学组成的变化,也揭示了石油排出微运移过程中的组分分馏效应,运移后的石油具有更高的饱和烃+芳烃含量、更小的分子量和更低的Pr/n-C17、Ph/n-C18值,指示更大的流动可能。(3)青山口组油质相对优越,但相对较高的黏土矿物含量是研究层段生产需要关注的制约因素。页岩油微运移后指示更大的生产可能,在该区未来一段时间勘探过程中可以尝试寻找油气运移汇聚区。

The petromineralogy, organic geochemical, and reservoir pore space characteristics of 15 lacustrine shale samples from the Qingshankou Formation in the Songliao basin were studied. The experimental methods of XRD, pyrolysis, stepwise pyrolysis, stepwise extraction and stepwise NMR testing were comprehensively applied to characterize the content, composition and distribution characteristics of shale oil in different occurrence states of the Qingshankou Formation. The evaluation of retained hydrocarbon content, production potential, exploration constraints factors and suggestions are further discussed. The following conclusions can be obtained from this study:(1) The mineral composition of the Qingshankou Formation is relatively homogeneous, mainly shale with high clay content, and the clay mineral characteristics dominated by illite are favorable for reservoir fracturing. The rich distribution of organic matter is relatively uniform, and the average TOC is 2.41%. It has good petroleum bearing property with light oil quality, high saturated hydrocarbon content and oil saturation index.(2) The occurrence state of shale oil is defined as free oil, free-adsorbed oil and adsorbed oil extracted from different particle sizes under the conditions of cold extraction and Soxhlet extraction. The free oil is mainly composed of light components, while the heavy components are higher in the adsorbed oil. The larger pores are mainly composed of free oil, and most of the adsorbed oil is distributed in the smaller pores. The change in chemical composition of free oil and adsorbed oil also reveals the component fractionation effect in the process of oil micro-migration. The oil after oil discharge and migration has higher saturated hydrocarbon+aromatic hydrocarbon content, smaller molecular weight and lower Pr/n-C17and Ph/n-C18values, indicating greater flow possibility.(3) The oil quality of the Qingshankou Formation is relatively superior, but the relatively high clay mineral content is the restrictive factor that needs to be paid attention to in production. The micro-migration of shale oil indicates a greater possibility of production. In the exploration process of this area in future, we can try to find oil migration and accumulation areas.