Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

How Ultrasonic-Assisted CO2 EOR to Unlock Oils From Unconventional Reservoirs?

Version 1 : Received: 2 August 2021 / Approved: 3 August 2021 / Online: 3 August 2021 (11:25:12 CEST)

A peer-reviewed article of this Preprint also exists.

Wang, H.; Tian, L.; Zhang, K.; Liu, Z.; Huang, C.; Jiang, L.; Chai, X. How Is Ultrasonic-Assisted CO2 EOR to Unlock Oils from Unconventional Reservoirs? Sustainability 2021, 13, 10010. Wang, H.; Tian, L.; Zhang, K.; Liu, Z.; Huang, C.; Jiang, L.; Chai, X. How Is Ultrasonic-Assisted CO2 EOR to Unlock Oils from Unconventional Reservoirs? Sustainability 2021, 13, 10010.

Journal reference: Sustainability 2021, 13, 10010
DOI: 10.3390/su131810010

Abstract

CO2 enhanced oil recovery (EOR) has been proven its capability to explore the unconventional tight oil reservoirs and potential for geological carbon storage. Meanwhile, the extremely low permeability pores exaggerate the difficulty CO2 EOR and geological storage processing in the actual field. This paper initiates the ultrasonic-assisted approach to facilitate the oil-gas miscibility development and finally contribute to unlock more tight oils. First, the physical properties of crude oil with and without ultrasonic treatments were experimentally analysed through gas chromatography (GC), Fourier-transform infrared spectroscopy (FTIR) and viscometer. Second, the oil-gas minimum miscibility pressures (MMPs) were measured from the slim-tube test and the miscibility developments with and without ultrasonic treatments were interpreted from the mixing-cell method. Third, the nuclear-magnetic resonance (NMR) assisted coreflood tests were conducted to physically model the recovery process in porous media and directly obtain the recovery factor. Basically, the ultrasonic treatment (40KHz and 200W for 8 hours) was found to substantially change the oil properties, with viscosity (at 60°C) reduced from 4.1 to 2.8mPa·s, contents of resin and asphaltene decreased from 27.94% and 6.03% to 14.2% and 3.79%, respectively. The FTIR spectrum shows the unsaturated C-H bond, C-O bond and C≡C bond in macromolecules were broken from ultrasonic, which caused the macromolecules (e.g., resin and asphaltenes) to be decomposed into smaller carbon-number molecules. Accordingly, the MMP was determined to be reduced from 15.8 to 14.9MPa from the slim-tube test and the oil recovery factor increased by over 10%. This study reveals the mechanisms of ultrasonic-assisted CO2 miscible EOR in producing tight oils.

Keywords

Ultrasonic; Carbon dioxide; Enhanced oil recovery; Unconventional reservoirs

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