Comparison of Washing Oil Experiment of Core Samples from Shale Oil Reservoir

doi:10.19657/j.geoscience.1000-8527.2022.049

Abstract

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

CLC Number:

P618.1
TE34

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.

Figures/Tables 8

Fig.1 Sampling diagram of parallel block samples

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

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

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

Fig.5 Total hydrocarbon gas chromatograms at different experimental time

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

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

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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