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Shale oil reservoir has different fabric facies (lamellar, thin lamellar, massive, etc.) rock based on lamina development degree and longitudinal superposition relationship of different lithology. Laboratory tests show that the spontaneous imbibition recovery rate of shale with different fabric facies is different, and the difference of pore structure is the main reason. In this paper, spontaneous imbibition experiment of shale based on nuclear magnetic resonance (NMR) technology is carried out. The difference of pore structure of shale with different fabric facies and its influence on imbibition are comprehensively compared, and the imbibition transport mechanism of shale oil in pores with different sizes is studied.
The cores used in this study are two kinds of fabric facies rock from continental shale oil reservoirs in China, which are lamellar (single lamina thickness 1mm-1cm) and massive (single lamina thickness > 50 cm). Firstly, the samples were tested by scanning electron microscopy (SEM), high-pressure mercury intrusion and low-temperature nitrogen adsorption (LTNA). It is difficult to characterize nano-micropores in high-pressure mercury intrusion test. However, the pore size distribution of shale can be characterized by LTNA and NMR. With the help of NMR and high precision electronic balance, the slick water spontaneous imbibition experiment of shale core was carried out. The imbibition recovery of shale oil in different pore sizes was calculated according to the measured NMR T2 spectrum and core weight variation.
SEM showed that the development degree of inorganic pore: lamellar > Massive, organic matter content and organic pore development degree: massive > lamellar. The average pore size of lamellar shale (20.30nm) is larger than that of massive shale (9.96nm) by LTNA test. The pore size distribution of lamellar shale (69.00% mesopores, 30.11% macropores, 0.89% micropores) is different from that of massive shale (83.26% mesoporous, 15.37% macroporous, 1.37% microporous). The experimental results show that the imbibition recovery rate of lamellar shale (25.60%) is significantly higher than that of massive shale (17.74%). Compared with the shale oil recovery rate in the pore of massive shale, the rate of micropores in lamellar shale is higher (37.12% vs. 6.63%), the rate of mesopore is higher (35.24% vs. 14.80%), and the rate of macropore is lower (2.65% vs. 34.63%). The difference in shale oil recovery of micropores is due to the difference in micro-wettability, that caused by the rich inorganic micropores in lamellar shale and organic micropores in massive shale. The low recovery rate of macropores in lamellar shale is due to the fact that the large pores mainly act as migration channels during spontaneous imbibition, and most of the oil is retained in the large pores after the imbibition process is balanced.
The major contribution is to gain insight on the pore structure difference of shale with different fabric facies, and hence reveal the cause of the imbibition recovery difference among different fabric facies shale. The outcomes are of great interest for the field operators to optimize the designs of well stimulation best for their reservoirs.
| Participation | Online |
|---|---|
| Country | China |
| MDPI Energies Student Poster Award | No, do not submit my presenation for the student posters award. |
| Time Block Preference | Time Block A (09:00-12:00 CET) |
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