Preliminary study on the CO2 injectivity and storage capacity of low-permeability saline aquifers at Chenjiacun site in the Ordos Basin

Abstract

Deep saline aquifers are a promising choice for geological carbon dioxide (CO2) sequestration due to their greater storage capacity compared to other geological storage options. Injectivity and storage capacity are key concerns especially considering injection of CO2 into low-permeability reservoirs. Estimation of the CO2 injectivity and storage capacity was conducted with an analytical method and dynamic numerical modeling for an active demonstration site (Chenjiacun) of CO2 sequestration in the Ordos Basin. The analytical estimate of the mass injectivity of the Liujiagou reservoir is 4.06×10−6kgPa−1s−1, which is about 64% of the injectivity of the entire reservoir system, followed by the Shiqianfeng unit, which accounts for some 15.8%. The maximum injection rate for the Liujiagou reservoir was estimated to be roughly 15.1kg/s, leading to 476,000t of CO2 injected per year. The maximum injection rates for the other four reservoirs are substantially smaller than that for the Liujiagou reservoir. The injectivity of the Liujiagou reservoir estimated by numerical simulation ranges from 0.7 to 3.0×10−6kgPa−1s−1. The injectivity of the Shiqianfeng reservoir was estimated to be from 0.2 to 1.1×10−6kgPa−1s−1. The injectivities of the remaining reservoirs (i.e., Shihezi downward) are smaller than 0.6×10−6kgPa−1s−1. The maximum injection rate estimated from the numerical simulation is approximately 17kg/s, leading to 536,000t storage of CO2, with the injection pressure limited to 1.5 times hydrostatic pressure. The annual CO2 storage capacity of the Chenjiacun site is estimated to be 0.53–0.69Mt, for a single vertical injection well. About 5 injection wells may be required to deal with the current CO2 emission rate from CSCLC coal liquefaction processes, which is about 3Mt per year.The injectivity and storage capacity at Chenjiacun are not much smaller than that at In Salah and Ketzin, owing to the relatively great thickness and long perforated interval at Chenjiacun. In order to improve the reservoir injectivity and storage capacity further at Chenjiacun for large-scale CO2 storage in the future, possible injection strategies and reservoir management options include introduction of stimulation measures and water-production wells at approximately 1000m or even further away from the injection well, as well as using fully penetrating vertical wells with long perforated intervals.