Study on Prevention of Gas Channelling of Acid-resistant Gel Foam in CO2 Flooding of Low Permeability Reservoir

Zhaoxia Liu,Wanlu Liu,Ming Gao,Shanyan Zhang,R Weerasinghe,J Wu,C.-H Weng

doi:10.1051/e3sconf/202019401041

Zhaoxia Liu, Wanlu Liu + Show 5 more

Open Access

https://doi.org/10.1051/e3sconf/202019401041

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Abstract

With the shortage of recoverable reserves in conventional oil reservoirs, the development of low-permeability oil reservoirs has received more and more attention. The oil recovery of low-permeability reservoirs can be significantly improved by CO2 flooding, as it can effectively supply formation energy. CO2 flooding is an effective technology for increasing oil production in low-permeability reservoirs. However, because of the heterogeneity of the reservoir and the effect of natural fractures, CO2 gas channelling easily occurs during CO2 flooding, seriously reducing CO2 flooding effect. In this study, the gas channelling technology of acid-resistant gel foam was investigated. Preferred acid-resistant gel foam system formula was found as 0.1% by mass of AOS foaming agent with 0.3% to 0.4% by mass of instant HPAM polymer and 1% to 2% by mass of water-soluble phenolic resin crosslinking agent. This system still has a good foaming ability and blocking performance under at pH=2 and a salinity of 10×104 mg/L. After 60 days of aging under oil reservoir conditions, there is no obvious water separation, and the plugging strength retention rate reached more than 60%. The gel foam channelling system can be applied to highly heterogeneous and low permeability reservoirs with a permeability gradient higher than 14 and can increase the recovery rate by more than 20% based on the CO2 flooding. Acid-resistant gel foam channelling technology can effectively inhibit CO2 gas channelling and improve CO2 flooding effect in low permeability reservoirs.

Highlights

Low-permeability reservoirs have been developed at an increasing rate [1]; problems such as difficulty in replenishing formation energy and rapid decline in production have been observed in the development of water injection
2.3.2 Gel system optimization The pH of the formation water was adjusted to 2, and different concentrations of polymer and cross-linking agent solutions were prepared for gel evaluation experiments
After the gel is frozen, it was aged at 80 °C, and the water separation and gel strength of the gel system at 30 d, 45d, and 60d aging were measured to evaluate the stability of the gel, and the acid-resistant gel system was preferred

Summary

Introduction

Low-permeability reservoirs have been developed at an increasing rate [1]; problems such as difficulty in replenishing formation energy and rapid decline in production have been observed in the development of water injection. Because gas has stronger mobility than water and can enter the micro pore throat structure[2], gas injection has remarkably improved the development of low permeability reservoirs. Because of the heterogeneity of low-permeability reservoirs and the existence of natural fractures, gas channelling is prone to occur during CO2 flooding[7,8], which is severely reducing the stimulation effect of CO2 flooding. The injection process parameters were optimized[10] to provide technical support for suppressing CO2 gas channelling and improving the CO2 flooding in low permeability reservoirs [11]

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Results

Conclusion