TY - JOUR A1 - Ma, Jianli A1 - Li, Qi A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Hydromechanical response and impact of gas mixing behavior in subsurface CH4 storage with CO2-based cushion gas JF - Energy & fuels N2 - Power-to-gas (PtG) stores chemical energy by converting excess electrical energy from renewable sources into an energy-dense gas. Due to its higher available capacity compared to surface-based storage technologies, subsurface storage in geological systems is the most promising approach for efficient and economic realization of the PtG system’s storage component. For this purpose, methane (CH4) produced by methanation by means of hydrogen (H2) and carbon dioxide (CO2) is stored in a geological reservoir until required for further use. In this context, CO2 is used as the cushion gas to maintain reservoir pressure and limiting working gas, i.e., (CH4) losses during withdrawal periods. Consequently, mixing of both gases in the reservoir is inevitable. Therefore, it is necessary to minimize the gas mixing region to optimize the efficiency of the PtG system’s storage component. In the present study, the physical properties of CH4, CO2 and their mixtures are reviewed. Then, a multicomponent flow model is implemented and validated against published data. Next, a hydromechanically coupled model is established, considering fluid flow through porous media and effective stresses to investigate the mixing behavior of both gases and the mechanical reservoir stability. The simulation results show that, with increasing reservoir thickness and dip angle, the mixing region is reduced during gas injection if CO2 is employed as the cushion gas. In addition, the degree of mixing is lower at higher temperatures. Feasible injection rates and injection schedules can be derived from the integrated reservoir stability analysis. The methodology developed in the present study allows the determination of optimum strategies for storage reservoir selection and gas injection scheduling by minimizing the gas mixing region. Y1 - 2019 U6 - https://doi.org/10.1021/acs.energyfuels.9b00518 SN - 0887-0624 SN - 1520-5029 VL - 33 IS - 7 SP - 6527 EP - 6541 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Ma, Jianli A1 - Li, Qi A1 - Kühn, Michael A1 - Nakaten, Natalie Christine T1 - Power-to-gas based subsurface energy storage BT - a review JF - Renewable and Sustainable Energy Reviews N2 - The Renewable energy power generation capacity has been rapidly increasing in China recently. Meanwhile, the contradiction between power supply and demand is becoming increasingly more prominent due to the intermittence of renewable energies. On the other hand, on the mitigation of carbon dioxide (CO2) emissions in China needs immediate attention. Power-to-Gas (PtG), a chemical energy storage technology, can convert surplus electricity into combustible gases. Subsurface energy storage can meet the requirements of long term storage with its large capacity. This paper provides a discussion of the entire PtG energy storage technology process and the current research progress. Based on the comparative study of different geological storage schemes for synthetic methane, their respective research progress and limitations are noted. In addition, a full investigation of the distribution and implementation of global PtG and CO2 capture and storage (CCS) demonstration projects is performed. Subsequently, the opportunities and challenges of the development of this technology in China are discussed based on techno-economic and ecological effects analysis. While PtG is expected to be a revolutionary technology that will replace traditional power systems, the main issues of site selection, energy efficiency and the economy still need to be adequately addressed. Additionally, based on the comprehensive discussion of the results of the analysis, power-to-gas and subsurface energy storage implementation strategies, as well as outlook in China are presented. KW - Renewable energy KW - Power-to-Gas KW - Subsurface energy storage KW - Underground gas storage KW - Carbon dioxide KW - Methane Y1 - 2018 U6 - https://doi.org/10.1016/j.rser.2018.08.056 SN - 1364-0321 VL - 97 SP - 478 EP - 496 PB - Elsevier CY - Oxford ER -