Laboratory simulation of CO₂ immiscible gas flooding and characterization of seepage resistance

Abstract

CO₂ flooding can significantly improve the recovery rate, effectively recover crude oil, and has the advantages of energy saving and emission reduction. At present, most domestic researches on CO₂ flooding seepage experiments are field tests in actual reservoirs or simulations with reservoir numerical simulators. Although targeted, the promotion is poor. For the characterization of seepage resistance, there are few studies on the variation law of seepage resistance caused by the combined action in the reservoir. To solve this problem, based on the mechanism of CO₂, a physical simulation experiment device for CO₂ non-miscible flooding production manner is designed. The device adopts two displacement schemes, gas-displacing water and gas-displacing oil, it mainly studies the immiscible gas flooding mechanism and oil displacement characteristics based on factors such as formation dip angle, gas injection position, and gas injection rate. It can provide a more accurate development simulation for the actual field application. By studying the variation law of crude oil viscosity and start-up pressure gradient, the characterization method of seepage resistance gradient affected by these two factors in the seepage process is proposed. The field test is carried out for the natural core of the S oilfield, and the seepage resistance is described more accurately. The results show that the advancing front of the gas drive is an arc, and the advancing speed of the gas drive oil front is slower than that of gas drive water; the greater the dip angle, the higher the displacement efficiency; the higher the gas injection rate is, the higher the early recovery rate is, and the lower the later recovery rate is; oil displacement efficiency is lower than water displacement efficiency; taking the actual core of S oilfield as an example, the mathematical representation method of core start-up pressure gradient in low permeability reservoir is established.

Graphical abstract

Keywords

laboratory simulation / viscosity / starting pressure gradient / CO₂ immiscible flooding / characterization of seepage resistance

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Acknowledgments

Parts of this work were supported by the Dongying Science Development Fund Project (Nos. DJ2022009 and DJ2020003), the Shandong Provincial Higher Education Research and Development Program (Science and Technology A Class) (No. J18KA201), the High-level Talent Research Start-up Fund of Shengli College of China University of Petroleum (No. KQ2019-008), the Chunhui Project of Shengli College of China University of Petroleum (No. KY2017004) and the Research Cultivation Project of College of Big Data and Basic Science of Shandong Institute of Petroleum and Chemical Technology (No. XYPY2201) which supports are appreciated. We also thank all editors and anonymous reviewers for their comments and suggestions.

Competing interests

The authors declare that they have no competing interests.

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