DF1-1 gas field is located in the west of the South China Sea, which is associated with high concentration of CO2. Currently CO2 separated from the natural gas stream is emitted into the atmosphere. In this study, a demonstration project of CO2 capture and storage (CCS) is considered, proposing to inject CO2 separated on the platform back into the original gas reservoir. The CO2 storage site considered is a nearly abandoned gas block in the DF1-1 gas field. Membrane separation technique will be installed on the platform for the separation. CO2 is compressed at supercritical state and injected through a single well (used to be a producer). A new platform auxiliary to the main platform will be built to accommodate the compressor and separation equipment. CO2 will be injected at the rate of 0.14 million Sm3/d for 10 years over the field development period. At the end of the project, the pressure of the CO2 storage reservoir will be increased to its original pressure. Scoping economic analysis shows that the CO2 storage cost of the project is around US$20 per ton CO2, in which the auxiliary platform is the main cost factor.
Many natural gas fields in the South China Sea are associated with high concentration of CO2 as shown in Table 1[1]. There is and will be a considerable amount of CO2 separated from natural gas during the development of these gas fields. How to utilize and dispose the huge amount of the associated CO2 from gas production is not only a challenge for the local oil and gas producers, but also will be a key research topic in China and in the Southeast Asia, in order to develop the natural gas resources in the region.
DF1-1 gas field is one of the CO2 associated gas fields under development by the China National Offshore Oil Corporation (CNOOC), which is located in the Yinggehai Basin of the South China Sea, 113km away in the southwest of Dongfang City, Hainan Island (see location map of Figure 1). The area around DF1-1 is in low-latitude tropics, in which both climate and sea condition are under the impact of typhoons and monsoon. The average temperature in the region is 26 °C and the water depth is between 64–70 m.
DF1-1 gas field was discovered in 1991. The main compositions of the natural gas are CH4 and CO2. The proven reserve is 99.68 billion Sm3, while the hydrocarbon gas is 61.2 billion Sm3 and CO2 is 22.50 billion Sm3. The gas field started production in 2003. Currently, all the produced gas is transported to the Dongfang gas terminal on the Hainan Island via a subsea pipeline. The amount of CO2 separated from the natural gas is around 0.18 billion Sm3 (0.36 million tons) each year, most of which is emitted into the atmosphere [1]. Pressure has been mounted on the operator to dispose this greenhouse gas from the Hainan Island in a proper way to combine with national and international regulations and moral obligations.
