页岩油岩心样品洗油实验效率对比分析

doi:10.19657/j.geoscience.1000-8527.2022.049

摘要/Abstract

摘要：

页岩储层中的裂缝和微纳米级孔隙是页岩油的主要赋存空间。岩心样品高效无损洗油是页岩孔隙结构表征和页岩油赋存研究的关键,但是目前的实验方案并不统一。通过调研总结常用的洗油方法,针对现行广泛使用的浸泡抽提法、快速萃取法以及气驱+索氏抽提法对大港油田沧东凹陷孔二段页岩(块样,1 cm×1 cm×1 cm)进行洗油测试,利用Rock-Eval 热解仪和气相色谱仪对洗油前后的样品以及萃取出的可溶有机质进行了实验效果对比和三种方法之间的优劣性分析。研究结果表明,随着实验时间的延长萃取物中重烃含量逐渐增加,且低孔低渗的页岩岩心在常温常压下难以达到理想的洗油效果。升温和增压可以提高洗油效率,但长时间的高温作用会使部分重烃和吸附组分裂解,当裂解的速度大于轻烃组分被萃取的速度时,S₁值会出现随着洗油时间上升的现象;合适的压力条件可以有效促进洗油速率,但如果条件控制不好会造成样品破碎或者内部孔隙被破坏。建议在洗油过程中采用较低的压力、常温或者稍微加温以加快实验速度,驱替法和抽提法结合会有更好的效果。

关键词: 页岩, 孔隙, 岩心洗油, 索氏抽提, 洗油效率

Abstract:

Fractures and micro-/nano-scale pores in shale reservoirs are the main occurrence space of shale oil. Efficient and non-destructive washing oil of core samples is the key to the characterization of shale pore structure and shale oil occurrence, yet there is no unified scheme currently. In this study, we investigated and summarized the common “washing oil” schemes, and selected Soxhlet extraction, rapid extraction and gas flooding + Soxhlet extraction to compare their effects on shale block samples (1 cm×1 cm×1 cm) from the Kongdian Formation (Ek₂, 2^nd member) in the Cangdong depression. Rock-eval pyrolysis instrument and gas chromatograph were used to compare the experimental results and the pros and cons of the three methods, by analyzing the samples before and after washing oil and the extracted soluble organic matter. The results show that the heavy hydrocarbon components in the extract increase gradually with time. It is difficult for low-porosity/-permeability shale cores to achieve ideal washing oil effect under room temperature and pressure. Heating and pressurization can improve experimental efficiency, but heavy hydrocarbons and adsorbed components would partially break down into light hydrocarbons due to prolonged high temperatures, and the S₁ value would rise when the rate of decomposition is higher than that of extraction. Appropriate pressure conditions can effectively promote the washing oil rate, but the samples or its pore structures may be destroyed under the unstable pressure. We suggested to use lower pressure, room temperature or slightly higher temperature in washing oil to speed up the process, which would produce better results when combining the displacement and extraction methods.

Key words: shale, pore, washing oil experiment for core, Soxhlet extraction, washing oil efficiency

中图分类号:

P618.1
TE34

王志昊, 赵建华, 蒲秀刚, 刘可禹, 李俊乾, 程斌. 页岩油岩心样品洗油实验效率对比分析[J]. 现代地质, 2022, 36(05): 1304-1312.

WANG Zhihao, ZHAO Jianhua, PU Xiugang, LIU Keyu, LI Junqian, CHENG Bin. Comparison of Washing Oil Experiment of Core Samples from Shale Oil Reservoir[J]. Geoscience, 2022, 36(05): 1304-1312.

图/表 8

图1 平行块样的取样图

Fig.1 Sampling diagram of parallel block samples

图2 CO2气驱+索氏抽提法洗油步骤(修改自文献[16])

Fig.2 Flow diagram of CO2 dissolved gas drive+ Soxhlet extractor(modified after ref. [16])

图3 浸泡抽提法热解参数随时间变化趋势 (图中首个点为原始样品的热解值,最后一个点为粉末样品经72 h索氏抽提后的热解值)

Fig.3 Variation trend of pyrolysis parameters over time(by soaking method)

图4 快速萃取法热解参数随时间变化趋势 (图中首个点为原始样品的热解值,最后一个点为粉末样品经72 h索氏抽提后的热解值)

Fig. 4 Variation trend of pyrolysis parameters over time (by accelerated solvent extraction method)

图5 不同洗油时间的全烃气相色谱图 (a) 粉末抽提物;(b)块样洗油0~12 h抽提物;(c) 块样洗油12~24 h抽提物

Fig.5 Total hydrocarbon gas chromatograms at different experimental time

图6 页岩油微观赋存状态图(改自文献[37]) (a) 烃类吸附模式;(b)孔隙内油赋存

Fig. 6 Microscopic occurrence state map of shale oil(modified after ref. [37])

图7 CO2气驱+索氏抽提法热解参数随时间变化趋势(首个点和最后点分别代表洗油的“起点”和“终点”)

Fig.7 Variation trend of pyrolysis parameters over time (by CO2 dissolved gas drive+Soxhlet extractor method)

表1 三种实验方案效果对比

Table 1 Comparison of effects for three experimental programs

实验方案	S₁洗油效率/%	优点	缺点
浸泡抽提法	93	状态稳定,过程可控	耗时长,洗油效率较低
快速萃取法	94	耗时短,可快速达到较为理想的洗油效果	高温高压下样品内部变化不可控,S₁和S₂会出现反复上升下降的趋势,延长洗油时间,成本高
CO₂气驱+ 索氏抽提法	98	结合驱替和抽提的优点,具有最理想的洗油效果	较高的压力会加剧S₂值波动的现象

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