Deep Underground Science and Engineering最新文献

In March 2022, construction was started at Yunlong Lake Laboratory of Deep Underground Science and Engineering, China, on an underground gas storage experimental facility with the capacity to achieve composite structure design and material development. Underground gas storage can provide a solution to address the intermittency of renewable energy supply. Currently, lined rock caverns (LRCs) are regarded as the best option for compressed air and hydrogen storage, since they have excellent sealing properties and minimum environmental impacts. However, the load transfer, damage, and failure mechanisms of LRCs are not clear. This prevents the design and selection of mechanical structures. Particularly, the gas sealing capacity in specific gas conditions (e.g., stored hydrogen-induced chemical reaction) remains poorly understood, and advanced materials to adapt the storage conditions of different gases should be developed. This experimental facility aims at providing a solution to these technical issues. This facility has several different types of LRCs, and study of the mechanical behavior of various structures and evaluation of the gas-tight performance of the sealing material can be carried out using a distributed fiberoptic sensing approach. The focus of this study is on the challenges in sealing material development and structure design. This facility facilitates large-scale and long-term energy storage for stable and continuous energy supply, and enables repurposing of underground space and acceleration of the realization of green energy ambitions in the context of Paris Agreement and China's carbon neutralization plan.

Attributed to its superior water-to-solid ratio and quick setting time, the high-water material is widely adopted in underground spaces as a cost-effective and environmentally friendly backfill material. To elucidate the bleeding mechanism of high-water material under the high confining pressure, a total of 57 tubular specimens were prepared and tested, critical parameters of which included the water-to-solid ratio, curing time, and lateral confinement pressure. Test results showed that no obvious cracks were observed from the surface of confined high-water material, which is different from that of unconfined high-water material, which featured shear cracks. Moreover, the volume of these confined high-water materials under compaction exhibited a continuous shrinkage associated with the water bleeding. The threshold values of the water bleeding are significantly affected by the water-to-solid ratio, followed by the confining pressure and curing time. When other parameters are constant, the higher confinement is requested for these specimens with a small water-to-solid ratio. Meanwhile, the mass of bleeding water increased with the lateral confinement, showing a quick increase at the initial stage. During the bleeding process, the free water stored in the pores was compacted, the evidence of which is the transformation of the hydration products (calcium aluminate hydrate) from its natural fibrous structure into the rod-shaped or dense agglomerate structures. These research outcomes provide an in-depth insight into the fundamental mechanics of the high-water material under the high lateral confinement when it is used for underground spaces.

This paper presents an investigation of well integrity during low-temperature CO₂ injection using a model of thermo-poroelasticity with interface damage mechanics. The casing–cement and cement–formation interfaces are described using cohesive interface elements and a bilinear traction–separation law. Verification testing is performed to establish the correct implementation of the coupled thermal, hydraulic, and mechanical equations. Simulation scenarios are developed to determine well interface damage initiation and development for intact wells and wells with an initial defect in the form of a 45$��\; ��°��$ debonded azimuth. Each intact and defective well was simulated for 30 days of CO₂ injection at selected temperatures. Under the conditions considered, tensile radial stress developed at both the casing–cement and cement–formation interfaces. Hoop stress in the cement sheath remained compressive after 30 days but with reduced magnitude at the lower injection temperature, indicating greater risk of tensile stress and radial cracking as the injection temperature was reduced. Damage occurred in two of four scenarios considered, namely, the intact and defective wells at an injection temperature of 10$��\; ��°�\; �C��$, and was limited to the casing–cement interface, with no damage to the cement–formation interface. Inclusion of the pre-existing defect led to earlier damage initiation, at 2.75 days compared to 4 days, and produced a microannulus with over double the peak aperture at 0.077 mm compared to 0.037 mm. These findings emphasize the importance of accounting for initial defects and damage evolution when investigating the integrity of CO₂ injection wells.

Carbon capture and storage (CCS) remains one of the most feasible techniques for the control of Greenhouse gas emission levels. However, there will always be risks attached to the subsurface injection of CO₂. These could be in the form of leakages from the injection wellbore due to completion failure; escape of the injected CO₂ to neighboring aquifers due to the heterogeneous or fractured nature of the storage site; or seepage at the surface due to inadequacy of the sealing cap rock. While all these may occur, the most cost-effective and timely way to reduce the risk of leakages is by plugging the pathways. This is done using either traditional Cementous materials or more augmented sealants like organic gels and resins. A lot of studies in the literature have described this collection of materials within the context of CO₂ conformance control. So also, there are reviews on the classification and description of these chemicals. This review provides a more systemic evaluation of these classes of chemicals. This is by providing critical analyses of how external factors like CO₂, pH, brine salinity and hardness, rock mineralogy, pressure, temperature, and injectivity could affect the performance of different sealants that can be utilized. Based on these assessments, best practices for the application of the sealants, both at the testing stage in the laboratory and the pilot stage and field deployment, are suggested.

The geothermal resources in hot dry rock (HDR) are considered the future trend in geothermal energy extraction due to their abundant reserves. However, exploitation of the resources is fraught with complexity and technical challenges arising from their unique characteristics of high temperature, high strength, and low permeability. With the continuous advancement of artificial intelligence (AI) technology, intelligent algorithms such as machine learning and evolutionary algorithms are gradually replacing or assisting traditional research methods, providing new solutions for HDR geothermal resource exploitation. This study first provides an overview of HDR geothermal resource exploitation technologies and AI methods. Then, the latest research progress is systematically reviewed in AI applications in HDR geothermal reservoir characterization, deep drilling, heat production, and operational parameter optimization. Additionally, this study discusses the potential limitations of AI methods in HDR geothermal resource exploitation and highlights the corresponding opportunities for AI's application. Notably, the study proposes the framework of an intelligent HDR exploitation system, offering a valuable reference for future research and practice.

The two-phase flow in porous media is affected by multiple factors. In the present study, a two-dimensional numerical model of porous media was developed using the actual pore structure of the core sample. The phase field method was utilized to simulate the impact of displacement velocity, the water–gas viscosity ratio, and the density ratio on the flow behavior of two-phase fluids in porous media. The effectiveness of displacement was evaluated by analyzing CO₂ saturation levels. The results indicate that the saturation of CO₂ in porous media increased as the displacement velocity increased. When the displacement velocity exceeded 0.01 m/s, there was a corresponding increase in CO₂ saturation. Conversely, when the displacement velocity was below this threshold, the impact on CO₂ saturation was minimal. An “inflection point,” M3, was present in the viscosity ratio. When the viscosity of CO₂ is less than 8.937 × 10⁻⁵Pa·s (viscosity ratio below M3), variations in the viscosity of CO₂ had little impact on its saturation. Conversely, when the viscosity of CO₂ exceeded 8.937 × 10⁻⁵Pa·s (viscosity ratio greater than M3), saturation increased with an increase in the viscosity ratio. In terms of the density ratio, the saturation of CO₂ increased monotonically with an increase in the density ratio. Similarly, increasing density ratios resulted in a monotonic increase in CO₂ saturation, though this trend was less pronounced in numerical simulations. Analysis results of displacement within dead-end pores using pressure and velocity diagrams reveal eddy currents as contributing factors. Finally, the impact of pore throat structure on the formation of dominant channels was examined.

The development of deep reservoirs is an emerging topic in the energy industry. This paper analyzes the challenges in simulations of flow and transport in deep reservoirs and introduces models and algorithms aimed at resolving these challenges. A fast, accurate, and robust phase equilibrium model is developed with the aid of deep learning algorithms to accelerate the thermodynamic analysis of deep reservoir fluids. A pixel-free search algorithm is developed to generate a pore-network model that describes pore connectivity and porous media fluidity. A fully conservative Implicit Pressure Explicit Saturation algorithm is developed to simulate the Darcy-scale two-phase flow while achieving a reliable result for production evaluation. Numerical examples are presented to validate the performance of the developed models and algorithms. This paper also presents suggestions for future studies on deep reservoirs to achieve both scientific and engineering progress.

Salt cavern hydrogen storage (SCHS) is an important component of large-scale underground hydrogen storage, with advantages such as large hydrogen storage capacity and economic feasibility. However, the uniqueness of the salt cavern structure and the inherent high risk of hydrogen storage pose a potential leakage risk. This study aims to assess the leakage risk of salt cavern hydrogen storage through a comprehensive assessment. First, the three major influencing factors of leakage risk are summarized, taking into account the unique engineering, geological conditions, and operating conditions of salt cavern storage. Subsequently, the salt cavern hydrogen storage leakage risk evaluation index system was established, and the weights of the evaluation indexes were assigned using the combination assignment method. On the basis of the two-dimensional cloud model, a new leakage risk assessment method was proposed. In addition, the risk level assessment of the salt cavern hydrogen storage facility proposed to be constructed in Pingdingshan City, Henan Province, was carried out. Finally, corresponding risk control and preventive measures are proposed. The results of the study are useful and instructive for the safe construction of deep salt cavern hydrogen storage.

The potential for CO₂ sequestration in the goaf of abandoned coal mines is significant due to the extensive fracture spaces and substantial residual coal present. Firstly, the adsorption characteristics of residual coal in goaf on CO₂ were studied by the isothermal adsorption test of CO₂. Then, to accurately calculate the amount of adsorbed CO₂ within the residual coal in the goaf, the bidisperse diffusion numerical model considering only Fick diffusion was modified in combination with the diffusion mechanisms. The simulation results showed that the modified model can well describe the diffusion behavior of CO₂ in the residual coal matrix. Finally, the numerical simulation of CO₂ sequestration in the goaf of abandoned coal mines was carried out, and the influence of different injection well deployment positions and various thicknesses of residual coal on the migration law and storage effect of CO₂ in goaf was analyzed. The results showed that CO₂ preferentially flowed into the caving zone with higher permeability. The distribution of CO₂ streamlines in the goaf was the most dense in the caving zone and the streamlines in the fracture zone were gradually sparse from bottom to top. When the injection well was deployed at the interface of the two zones, the CO₂ had the best seepage path. The total storage capacity within 90 days was 7.702754 × 10⁶ kg, of which the free state storage capacity in the fracture of the goaf and the adsorbed state storage capacity in the residual coal were 6.611451 × 10⁶ and 1.091303 × 10⁶ kg, respectively. When the injection well was deployed in the middle of the residual coal seam in the goaf and the middle of the fracture zone, the total storage capacity at the same time was 7.613508 × 10⁶ and 6.021495 × 10⁶ kg, respectively. The coal with different thicknesses remaining at the bottom of the goaf significantly affected the adsorbed state storage, but had little effect on the free state storage. When the thickness of the residual coal seam was 0.20, 0.35, and 0.50 m, the adsorbed state storage capacity within 130 days was 4.37623 × 10⁵, 7.65791 × 10⁵, and 1.093406 × 10⁶ kg, respectively.