利用定量荧光技术表征厚层源岩层系的油气运聚机制——以渤海湾盆地廊固凹陷沙河街组四段为例

厚层源岩层系由于存在非均质性及烃源岩有效排烃厚度影响,其油气运聚机制不明确,这直接影响着盆地油气资源量的评价和成藏模式的建立。定量荧光分析包括颗粒定量荧光（QGF）、萃取液定量荧光（QGF-E）和全息扫描荧光（TSF）等一系列技术,可精确反映地层在地质历史时期和现今的含油气饱和度、油气成熟度以及运移路径等重要信息,且具有快速简便、经济高效的特点。通过利用定量荧光技术和盆地模拟技术,对廊固凹陷沙河街组四段厚层源岩层系内的油气运移特征和充注历史开展了分析,重建了油气从源岩层系到储层的运聚过程。研究结果表明,廊固凹陷沙河街组四段厚层源岩层系内夹层砂体的QGF指数普遍大于4.0、QGF-E强度部分大于40、QGF与QGF-E的最大荧光强度波长（λ_max）具有较大差异,指示砂体中曾存在过古油层并在后期发生贫化、转移,砂体在油气运移中具有"中转站"的作用。定量荧光的差异响应表明,砂体在不同深度段的中转能力具有差异;当砂体的颗粒越粗、砂地比越接近0.25、厚度越大时,砂体的运聚效率越高,中转能力越大。烃源岩的生烃热演化史、砂层的定量荧光光谱特征以及断层的活动历史表明,中转砂体内存在2期幕式油气中转运聚过程。其中,第1期发生在沙河街组三段沉积末期-东营组沉积早期（35~30 Ma）,砂体内以中质油气-轻质油气充注为主,油气在沙河街组一段沉积末期-东营组沉积早期随着断层开启而向上高效运移,在东营组沉积末期生烃停止后,砂体内的油气饱和度降低;第2期发生在明化镇组沉积期至今（5~0 Ma）,砂体内以大量凝析油气充注为主,由于断层趋于封闭,砂体内的油气以稳态渗流方式向上运移,并在保存条件变好的情况下得以在潜山储层中成藏。

Applying quantitative fluorescence techniques to characterize mechanism of hydrocarbon migration and accumulation in thick source strata: a case study of Member 4 of Shahejie Formation,Langgu sag in Bohai Bay Basin

Due to the influence of heterogeneity and effective hydrocarbon expulsion thickness, the mechanism of hydrocarbon migration in thick source strata is still not clear, directly affecting the evaluation of petroleum resources quantity and the establishment of hydrocarbon accumulation model in the basin. The quantitative fluorescence analysis includes a series of techniques including quantitative grain fluorescence (QGF), quantitative grain fluorescence on extract (QGF-E), and total scanning fluorescence (TSF), which can accurately provide such important information as hydrocarbon saturation, maturity and migration path during the past and present geological periods in a fast, simple, economical and efficient way. Using the quantitative fluorescence technique and basin simulation technique, this paper analyzes the hydrocarbon migration characteristics and charging history in the thick source strata of Member 4 of Shahejie Formation in Langgu sag, and also reconstructs the hydrocarbon migration and accumulation process from thick source strata to reservoirs. The results show that the QGF index of sandstone interlayers in thick source strata is generally greater than 4.0, the QGF-E intensity is partially greater than 40, and the λ_max of QGF and QGF-E are quite different. It is indicated that paleo-oil layers once existed in the sand body were diluted and transferred in the later stage; the sand body played the role of "transfer station" during hydrocarbon migration and accumulation. The difference in quantitative fluorescence response indicates that the transit capacity of sand body varies at different depths. The coarser the lithology of sand body is, the more closely the sand ratio approaches to 0.25; the thicker the sand body is, the higher the migration efficiency is, and the larger the transit capacity is. The hydrocarbon generation and thermal evolution histories of source rocks, quantitative fluorescence spectra of sand strata and fault activity histories demonstrate that there are two episodic hydrocarbon transport and accumulation processes in the "transfer station". The first stage is from the end stage of Member 3 of Shahejie Formation to the early stage of Dongying Formation (35-30 Ma). The sand body was mainly filled with medium-light oil and gas. With the opening of faults, oil and gas migrated upward efficiently from the end stage of Member 1 of Shahejie Formation to the early stage of Dongying Formation. When hydrocarbon generation ceased at the end stage of Dongying Formation, the oil and gas saturation in the sand body was decreased. The second stage is from the sedimentary period of Minghuazhen Formation to the present (5-0 Ma). The sand body is mainly charged with a large amount of condensate oil and gas. Since the faults tend to be closed, the oil and gas in the sand body migrate upward by steady seepage; till the formation of better preservation conditions, oil and gas can be accumulated in the buried hill reservoir.