Renewable Energy Global Innovations features: Dynamic filtration control performance of N2/liquid CO2 foam in porous media

Significance 

In the extraction of oil and gas, fracturing fluids are used to create and widen a fracture for easier production. The fluid should be compatible with the rocks. Liquid CO₂ has been used as a fracturing fluid because it is highly soluble in most oil extracts therefore less damaging to the oil extracted as compared to water-based fluids. The high solubility in oil helps in lowering the viscosity of oil and improves the extraction of oil from the ground.

Liquid CO₂ is, however, difficult to control in porous media due to its low viscosity and lack of filter cake formation properties for controlled filtration. This may affect the shape of the desired fracture. Researchers have tried to improve on the viscosity of liquid CO₂ by adding thickening agents, however, improvement of viscosity of liquid CO₂ by enhancement does not guarantee a change in its filtration performance and liquid CO₂ dissolves poorly with thickening agents making the insoluble residues potential pollutants.

Filtration control performance of liquid CO₂ was improved without pollution by mixing it with Nitrogen (N₂). Gupta et al. stabilized the N₂ and CO₂ mixture by introducing fluorochemical stabilizers into the liquid CO₂ and then bubbling N₂ into the liquid to form the N₂/liquid CO₂ foam. The liquid CO₂ was the external phase while the N₂ was the inner face and the fluorochemical stabilizers separated the two phases.

Qichao Lv, under the guidance of Professor Zhaomin Li, at China University of Petroleum investigated the dynamic filtration control performance of N₂/liquid CO₂ foam with a fluorochemical (HFE) as a stabilizer.

The filtration behavior of N₂/liquid CO₂ foam is uncertain as the external phase of the foam is unstable. Temperature and pressure can affect its density, viscosity and phase and changing the flow properties of the foam. Moreover, the behavior of waterless foam with the unique fluorochemical interface is uncertain. The interface may also be a potential pollutant. The experiment seeks to study the factors that may affect the dynamic filtration performance of N₂/liquid CO₂ foam including viscosity, foam quality, temperature, pressure, permeability and the damaging effects of the foam on porous media after filtration.

The setup for the experiment was done as shown in their paper where the preparation for the foaming solution was done and the viscosity measurement and dynamic filtration tests were done. The viscosity measurement results showed that the use of foam enhanced the viscosity of liquid CO₂. The apparent viscosity is related to temperature, pressure and foam quality. The viscosity increased as the foam quality was increased from 31 % to 71 %. The viscosity of high quality foams were 1 order of magnitude larger than that of liquid CO₂ at the same conditions. The apparent viscosity is at a maximum at a foam quality of about 80 % before it starts decreasing as it becomes fragile and sensitive to disturbances such as interactions and pressure fluctuations.

The filtration control performance of the N₂/liquid CO₂ foam was compared to that of liquid CO₂ and a N₂/liquid CO₂ mixture. The results showed that the filtration control properties of the N₂/liquid CO₂ foam was better than the others. The leak off coefficient lowered with an increase in foam quality up to 80 % where it increased. Foams of 50 – 80 % quality had a high filtration performance with permeability change. Low initial foam quality foams had better filtration performance at high pressure difference. As the foam enters the porous media, the liquid part would evaporate hence increasing the foam quality with depth. Damage by the foam on the porous media depends upon the pressure difference between the two sides of the porous media.  Damage is small under low pressure difference as the CO₂ turns to gas under a high pressure media damaging the porous media.

In their study the research team were able to prove that by mixing N₂, liquid CO₂ and HFE, properties such as viscosity and filtration control performance of the resultant N₂/liquid CO₂ foam, increased substantially without damage to porous media.

About the author

Qichao Lv is currently a doctoral candidate at China University of Petroleum, East China and a research scholar of Foam Fluid Enhanced Oil & Gas Production Engineering Research Center in Shandong province. He is also a member of Nano-Technology for Energy and Environment Group in University of Calgary. His primary areas of interest include foam technology for EOR and fracturing. In particular, he has done an excellent work in green and clean foam fracturing for unconventional oil and gas reservoirs such as shale gas, tight sand oil and gas, and CBM formations. He has published more than 20 articles in peer-reviewed scientific journals and applied for 15 patents of China and US. Because of his contribution to the development of unconventional reservoirs, he has won a first prize of provincial science and technology award as first investigator.

Contact: qichaolv@s.upc.edu.cn

About the author

Prof. Zhaomin Li is vice president of the China University of Petroleum, East China and director of Foam Fluid Enhanced Oil & Gas Production Engineering Research Center in Shandong province. His research emphasis is on the flow laws and equipment for foam fluid, new technologies of heavy oil recovery, CCUS theories and their application. In recent years, he has participated in more than 10 national programs as main contributor, and published more than 100 articles, of which 34 articles are indexed by SCI and 36 articles are indexed by EI.

He also holds more than 30 invention patents, and has established 3 standards for oil and gas industry as manager. In addition, he has won three first prizes of provincial science and technology award as first investigator. In particular, one of his invention as participant, HDCS enhanced oil recovery technology for ultra-heavy oil reservoirs, has increased crude oil production by several millions of tons, which was also selected as one of ten chemical technology highlights by China Chemical Industry News in 2010. A serials of foam stimulation techniques he invented are serving B&R countries, which has been reported by the Journal of International Innovation.

Contact: lizhm@upc.edu.cn

Reference

Lv Q, Li Z, Li B, Zhang C, Shi D, Zheng C, Zhou T. Experimental study on the dynamic filtration control performance of N2/liquid CO2 foam in porous media. Fuel. 2017 Aug 15; 202:435-45.

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