EGMS insights into ground deformation patterns in Underground Gas Storage (UGS) activities

Abstract

The importance of natural gas in meeting human energy needs persists, even amid the ongoing global energy transition. Fossil fuels, including coal, oil, biomass, and natural gas, remain central for providing essential energy services such as cooking, heating, and electricity generation for homes and businesses. Despite the increasing emphasis on renewable energy sources, total reliance on electricity is not yet feasible, necessitating a transitional phase wherein natural gas will play a key role. Natural gas, particularly in the form of methane (CH4), remains an indispensable resource due to its efficiency and versatility. This is particularly evident during periods of increased energy demand, such as the winter season, when natural gas serves as a reliable source for heating and power generation. The importance of a steady and uninterrupted supply of natural gas is highlighted by the challenges posed by seasonal fluctuations in demand. In response to the dynamic energy landscape, Underground Gas Storage (UGS) facilities have gained prominence as a strategic solution. With 160 active projects in Europe at the end of 2021, UGS activities provide the flexibility to store and deliver natural gas continuously, adapting to daily and seasonal fluctuations. This adaptability is critical to maintain a stable energy supply, especially during peak demand periods. On the other hand, UGS cycles have the potential to induce three-dimensional deformations within the affected reservoir that are subsequently transmitted to the surface. These deformations should be monitored since they can compromise the integrity of wells and nearby infrastructure. In this context, Interferometric Synthetic Aperture Radar (InSAR) is emerging as a valuable tool for continuous monitoring ground displacement resulting from UGS activities. InSAR analysis can provide millimetre-precision measurement points, overcoming the spatial coverage of in-situ instruments. The Yela site exploits a fractured aquifer reservoir located in the Madrid Basin (Spain) currently employed for UGS activities by Enagás, the Spanish main Transmission System Operator. A correlation between long-term records of gas volume (2019-2022) with vertical and horizontal (E-W) ground displacement data (2015-2020) from the European Ground Motion Service (EGMS) and the UGS activity rates can be established. The temporal evolution of vertical ground displacement shows a clear sinusoidal signal aligned with the amplitude and periodicity of the load/discharge curve of natural gas in the reservoir. This result highlights the versatility of the InSAR approach for UGS monitoring, complementing in-situ data, enhancing safety and improving facility management. In addition, InSAR technology can allow continuous monitoring analysis for detecting changes in the UGS environment, for risk management purposes and calibration of geomechanical models useful for estimating maximum pressure values. This work introduces a replicable approach to investigate freely available ground movement data, presenting a comprehensive comparison of InSAR results for the Yela UGS site. Leveraging open-source and easily accessible data, the study offers insights into the volumetric variation model and it identifies a significant correlation between natural gas injection/withdrawal rates and InSAR ground displacement over time.