1. Numerical simulation of seasonal underground hydrogen storage: Role of the initial gas amount on the round-trip hydrogen recovery efficiency.
- Author
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Huang, Tianjia, Moridis, George J., and Blasingame, Thomas A.
- Subjects
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POROUS materials , *GAS reservoirs , *UNDERGROUND storage , *MULTIPHASE flow , *GAS as fuel - Abstract
Subterranean structures such as aquifers and depleted gas reservoirs (DGRs) offer a scalable, high-pressure, secure, cost-efficient, and ecologically friendly means of hydrogen (H 2) storage. Underground H 2 storage (UHS) has emerged as a potential solution to alleviate the imbalance between the fluctuating renewable energy generation and the demand for a constant energy supply. Quantifying the recovery efficiency is of paramount importance in the effort toward large-scale UHS. In this numerical simulation study, we employed a high-resolution grid for the discretization of a synthetic (but realistic) heterogeneous anticline intended as a H 2 storage facility, and we assessed the H 2 recovery efficiency, and the purity of produced gas associated with UHS in natural reservoirs involving different pre-existing gases and their quantities. All of these studies included an initial phase of cushion gas injection, followed by 4 cycles of H 2 storage operations composed of injection-idle-withdrawal periods. The simulation results indicated that the H 2 round-trip recovery efficiency R H increased (a) with an increasing number of storage cycles, routinely exceeding 90% and providing evidence of a self-enhancement or self-optimization H 2 recovery mechanism and (b) with an increasing amount of pre-existing gas in the storage zone prior to the H 2 injections — at the end of the 4-cycle test, the highest R H is associated with a DGR with a pre-existing gas consisting of residual CH 4 and additional injected N 2 , and the lowest R H corresponds to an aquifer with no cushion gas. Conversely, the H 2 mass fraction of the produced gas F HQ (a) increased with an increasing number of storage cycles, but (b) decreased rapidly with an increasing amount of pre-existing gas. The presence of a pre-existing gas inevitably leads to severe contamination of the produced H 2 , which never exceeds 40% in the produced gas, can be as low as 4% in early cycles, and cannot be used as a H 2 fuel without gas separation. Aquifer storage without a cushion gas may exhibit the lowest H 2 recovery (about 75% in the long run), but yields practically pure H 2 that does not require further processing before use. A positive conclusion is that, under the conditions of this study, total H 2 losses (including H 2 escaping into the caprock, and inaccessible H 2 dissolved in the aqueous phase of the formation or remaining in the gas storage zone) are limited and manageable, indicating the technical feasibility of geologic H 2 storage. • Discussed the advantages and disadvantages of H 2 storage (UHS) in aquifers and depleted gas reservoirs (DGRs). • Explained reasons for the benefits of cushion gas (CG) or DGRs in UHS performance using material balance theory. • Injecting CG or adding cycles enhances the UHS performance by improving the overall compressibility of reservoirs. • Pre-existing gas improves the H 2 recovery efficiency but leads to the contamination of produced H 2. • Quantified the H 2 loss evolution during a UHS consisting of four injection-idle-withdrawal cycles. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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