Burying carbon dioxide for more energy.

Recently, the world's first pilot CO2 drive and storage project for tight gas reservoirs, the Yan'an Gas Field Tight Gas Reservoir CO2 Drive and Storage Pilot Project, has successfully injected more than 20,000 tonnes of CO2. The project was organised and implemented by Shaanxi Yanchang Petroleum (Group) Co. The model predicts that this technology can improve the gas field recovery rate by 5 to 10 percentage points, and the stable production period of the 10 billion cubic metre gas field can be extended by 5 to 8 years. According to the data, 20,000 tonnes of carbon dioxide is equivalent to the amount of carbon dioxide absorbed by 1.7 million trees in a year.

 

Inventory of inefficient assets

 

 

Wang Xiangzeng, chief scientist and chief geologist of Yanchang Petroleum Group, introduced that carbon dioxide capture, utilisation and storage (CCUS) technology, as an emerging technology that is expected to realise large-scale low-carbon utilisation of fossil energy, is an important means for China to reduce carbon dioxide emissions, guarantee energy security and achieve sustainable development in the future.The 2018 update of China's Carbon Capture, Utilisation and Storage (CCUS) Technology Development Roadmap Study" proposes to build a low-cost, low-energy, safe and reliable CCUS technology system and industrial clusters to provide technical options for the low-carbon utilisation of fossil energy, and to provide technical guarantee and support for addressing climate change and sustainable economic and social development.

 

 

The main technologies of CCUS include carbon dioxide geological storage and oil driving technology, carbon dioxide geological storage and gas driving technology, and carbon dioxide driving coalbed methane technology. Among them, CO2 geological storage and gas driving technology is to inject CO2 into the bottom of gas reservoirs and drive out the unrecoverable residual natural gas by restoring the formation pressure to improve the recovery rate. At the same time, carbon dioxide will be sealed in the depleted gas reservoir to achieve the purpose of emission reduction.

 

 

The reporter learnt that the final average recovery rate of gas reservoirs is 65%, which is about twice that of oil reservoirs. Meanwhile, natural gas is 30 times more compressible than crude oil or formation water. Therefore, with the same hydrocarbon pore volume, gas reservoirs can bury more carbon dioxide than oil reservoirs. In addition, some gas wells in tight gas reservoirs are low-producing and inefficient because of the dense reservoir. If CO2 storage is realised in such gas wells, inefficient assets can be revitalised and a new way of carbon reduction can be explored in the context of carbon trading. Internationally, Hungary, the Netherlands, Australia and Germany have carried out pilot projects on CO2 storage and gas drive in low-permeability and medium-high-permeability gas reservoirs. The results show that natural gas reservoirs can not only achieve geological storage of carbon dioxide, but also increase natural gas production to varying degrees.