In the heart of China, researchers are delving deep into the earth to unlock new possibilities for energy storage, and their findings could reshape how we think about repurposing abandoned mines. Zhanguo Ma, a professor at the School of Mechanics and Civil Engineering at China University of Mining and Technology in Xuzhou, has been leading a team that’s exploring the behavior of sandstone rock under the cyclic loading of gas charging and discharging. Their work, published in the journal ‘Deep Underground Science and Engineering’ (which translates to ‘Deep Underground Science and Engineering’), could have significant implications for the energy sector.
The idea of storing natural gas in abandoned mines is not new, but understanding how the surrounding rock behaves under the stress of repeated gas injections and withdrawals is crucial for ensuring the safety and longevity of these storage facilities. Ma and his team have been using the discrete element method (DEM) to create a true triaxial numerical model of rock mass, allowing them to simulate the crack evolution in the surrounding rock during these cyclic loading and unloading processes.
“The surrounding rock of gas storage reservoirs undergoes damage and deformation under the cyclic loading of gas charging and discharging,” Ma explains. “This can pose a risk to the safety of the reservoirs, so it’s vital that we understand these processes.”
The team’s research has revealed some fascinating insights. They found that cyclic loading and unloading can result in fatigue damage in the rock, leading to strength deterioration. During the loading process, the force chains within the rock mass redistribute, evolving from a uniform distribution to mostly transverse force chains. This redistribution can contribute to the appearance of blank areas in the force chains, which can eventually lead to through cracks.
One of the most striking findings is the ratio of tensile cracks to shear cracks. Initially, this ratio is high, but it gradually decreases and stabilizes at 7:1. This has important implications for predicting and preventing rock failure in gas storage facilities.
The team also developed a damage evolution model that considers residual deformation, which can be mutually verified with numerical simulation results. This model could be a game-changer for the energy sector, providing a more accurate way to predict the long-term mechanical behavior of surrounding rock in gas storage facilities.
But the insights don’t stop there. The researchers found that there’s a certain threshold of confining pressure. When this pressure exceeds 30 MPa, the deformation to ductility of sandstone samples begins to accelerate, with a greater residual strength. This could have significant implications for the design and operation of gas storage facilities.
So, what does all this mean for the future of energy storage? Well, it could shape how we repurpose abandoned mines, making them safer and more efficient for natural gas storage. It could also influence the design and operation of these facilities, ensuring they’re built to withstand the stresses of cyclic loading and unloading.
As Ma puts it, “This study provides a theoretical basis for analyzing the long-term mechanical behavior of surrounding rock of gas storage in abandoned mines.” And that, in turn, could pave the way for more innovative and sustainable energy solutions. The energy sector is always looking for new ways to store and distribute natural gas, and this research could be a significant step forward. It’s a testament to the power of scientific inquiry and the potential it holds for shaping our future.