DF1-1 gas field in the west of the South China Sea is associated with high concentration of CO2. Many options have been assessed by the operator (CNOOC) in recent years in order to dispose the CO2 separated from the gas stream. In this study, geological storage of CO2 into offshore saline aquifers near the gas separation plant on the Hainan Island is considered, and a demonstration project is proposed and designed in terms of aquifer selection and assessment, CO2 transportation and injection, and project economics. Several aquifer structures around the gas field and near the Hainan Island were investigated and assessed with respect to geological structure, reservoir and trap features, fluid properties, storage capacity and site location. A saline aquifer (namely LT13-1), 60 km offshore the Hainan Island, was chosen as the storage site. CO2 will be transported by a long-distance subsea pipeline at high pressure and injected into the aquifer via a subsea well-head and through a horizontal well. Reservoir simulation and injectivity analysis have been conducted to estimate the injection rate and pressure, and also to predict the movement of CO2 after injection. A scoping economic analysis of the project was also conducted and presented in the paper.
The accurate measurement of condensed water content in gas reservoirs is critical for the effective development of gas reservoirs. In this study, a more accurate and faster method for measuring the condensed water content in gas reservoirs was developed by using a high-temperature and high-pressure PVT device combined with the law of conservation of matter. A condensed water content test was subsequently conducted in the Dong Fang X (DF13) gas reservoir as an example to investigate the variation of condensed water content in gas reservoirs with different temperature and pressure. The results indicate that the condensed water content decreases with the increase in pressure, demonstrating a good exponential relationship, and vice versa. Based on the test results, a comprehensive prediction model for the variation of condensed water content in different sand bodies of the DF13 reservoirs with temperature and pressure was established, which could predict the precipitation of condensed water, thereby laying a solid foundation for the design of waterproof and water control strategies of the DF13 gas reservoir.
Based on the actual geological reservoir characteristics of an abnormally high-pressure gas reservoir in the western South China Sea, and considering reservoir stress sensitivity, a single-well model for horizontal wells was established to study the law of non-steady-state productivity of horizontal wells. Based on the established single well model of horizontal wells, and considering stress-sensitive conditions, the rational allocation of single wells is studied. The research results show that the initial unobstructed flow rate of the horizontal well is high and it decreases rapidly; the non-resistance flow considering stress sensitivity is lower than the non-resistance flow without considering stress sensitivity. The difference between the two gradually reaches the maximum at the beginning of the well, and the difference gradually decreases at the later stage; there are interrelationships and constraints between single good production, stable production time, and final production.
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