Improving enhanced geothermal systems performance using adaptive fracture conductivity

• Published in: Applied thermal engineering 2023-10, Vol.233 (C), p.121206, Article 121206
• Main Authors: Al Balushi, Faras, Zhang, Qitao, Dahi Taleghani, Arash
• Format: Article
• Language: English
• Subjects: Enhanced geothermal systems; Heat sweeping; Hydraulic fracturing; Modeling; Temperature-sensitive proppant; Tunable fracture conductivity
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2023.121206

•Efficient heat sweeping through fracture networks greatly enhances EGS production.•A novel concept of temperature-sensitive proppant is proposed to manage the fluid flow.•An innovative integrated simulation workflow is built from the proppant scale to the field scale.•A new correlation relating fracture conductivity and proppant deformation is derived.•The proposed proppants increase heat extraction efficiency in EGS by 47.8%. Maximizing heat extraction from enhanced geothermal systems (EGS) depends heavily on an efficient heat sweeping or basically an effective circulation of water through fracture networks. Fracture hydraulic conductivity can play a critical role in controlling potential thermal breakthroughs; however, the exact geometry and properties of these fractures cannot be determined in practice. Thermal breakthrough remains a main challenge for maintaining efficient heat extraction throughout the lifespan of an EGS project. In this work, we explore the concept of fracture conductivity tuning using temperature-sensitive proppants to extract more heat and delay thermal breakthrough from the particle scale to the reservoir scale. We derive an empirical equation to describe fracture conductivity as a function of proppant properties and in-situ conditions including closure stress and temperature. Sensitivity analysis are performed to determine which parameters are the most crucial in determining the temperature-sensitive proppant permeability. Temperature and thermal expansion coefficient are the main contributing factors to the change in proppant permeability. Poisson’s ratio is found to have negligible impact on the proppant permeability. The derived equation is used to quantify the improvement in heat extraction from EGS at the field scale. The outcome shows that using temperature-sensitive proppant can increase the heat extracted by 47.8% compared to using typical proppant. This work assesses the feasibility of using temperature-sensitive proppants to effectively delay thermal breakthrough and sweep larger amounts of heat from EGS. In addition, this paper provides a quick and robust method to determine the required properties of such temperature-sensitive proppants to achieve uniform thermal gradient along different flow paths in the subsurface autonomously.