Integrated Well Network Design Mode for CO2 EOR and Storage and its Application in L Reservoir
Authors: Wu Zangyuan , Tang Yongliang , Lian Liming , Zhou Daiyu , Zhao Haitao , Shao Guangqiang , Feng Qihong , Zhou Wei , Li Hong , Bian Wanjiang , Zhang Liang , Du Hongbao , Luo Min , Huang Xingning 
Published: February 2025

This paper addresses the challenge of difficulty in adjusting late-stage production in water-flooded reservoirs and proposes an integrated well network design mode for CO2 enhanced oil recovery (EOR) and storage. The well network is designed according to the full life cycle of carbon capture, utilization, and storage (CCUS), meeting the requirements of both CO2 EOR and storage phases. It extends the implementation time of CO2 EOR schemes to enhance oil recovery while ensuring effective CO2 storage, aligning with the overall strategy of global green and low-carbon development.

The overall approach involves the use of a three-dimensional CO2 flooding injection and recovery well network, with progressive development in the vertical stratigraphic layers to maximize the utilization of existing old wells. The stratigraphic reconstruction involves the CO2 flooding injection and recovery well network, ensuring that new gas injection wells meet the requirements for CO2 injection processes and production rates, while also serving as replacements for gas injection in other stratigraphic layers. Production wells make use of the original old wells, and well completion methods are adjusted to achieve the development of replacement layers. The "top injection, middle production, bottom support" three-stage development method is designed to fully utilize the high points of reservoir microstructures and bottom water energy. Finally, well network optimization is achieved through streamline tracking simulation methods.

The proposed technology has been applied in the CO2 enhanced oil recovery plan for the L reservoir. Initially focusing on CO2 flooding for oil recovery and shifting to CO2 storage later, it is projected to achieve a cumulative CO2 injection of tens of millions of tons over 46 years (including 40% recycled injection), with a displacement factor reaching 1.57PV. After deducting the recycled carbon amount, the cumulative carbon storage exceeds 6 million tons, affecting a volume of 0.96PV. The accumulated gas production over phases is 2.141 billion cubic meters, and the cumulative incremental oil production exceeds 3 million tons. The CO2-to-oil exchange rate is 0.32 tons of crude oil per ton of CO2, representing a 25.10 percentage point increase compared to the water flooding scheme in terms of oil recovery efficiency.

The "Integrated Well Network Design for CO2 EOR and Storage" proposed in this paper provides an effective means of implementing CCUS technology in oilfield production, offering technical support for the achievement of integrated CO2 EOR and storage objectives. This allows for a smooth transition from CO2 EOR to storage in oil reservoirs, requiring minimal or no adjustment of the well network, thereby reducing the complexity of adjustment plans and processes. Simulation of the scheme and on-site experimental results also demonstrate the effectiveness of this technology.