Closed-loop geothermal systems represent an emerging approach to geothermal energy utilization that operates without the need for sustained external fluid injection. However, their thermal performance is frequently constrained by the limited interfacial area available for heat transfer between the wellbore and the adjacent geological formation. Incorporating a thermally conductive fracture is a potential approach to improving closed-loop systems heat extraction. However, the heat extraction improvement effect of a multi-wing fracture has not been clarified yet. This work introduces an upgraded closed-loop geothermal system (UCGS) featuring a multi-wing fracture filled with thermally conductive proppants and connected to the well bottom, thereby improving heat transfer efficiency in the near-well region. A fully coupled three-dimensional hydrothermal numerical model is developed for the UCGS, on the basis of which a numerical study is conducted to evaluate heat extraction behavior under varying fracture dimensions and geometries. The results demonstrate that incorporating conductive fractures outperforms a conventional closed-loop system in terms of thermal production. Increase in fracture wing length and that in fracture height both lead to heat production improvement. For an identical fracture cross-sectional area, increasing fracture height is more effective in enhancing heat extraction than enlarging fracture thickness. As the number of fracture wings increases, both production temperature and cumulative net heat output increase at diminishing rates. Introducing a multi-wing fracture increases the 10-year cumulative thermal output by up to 19.23%. Results obtained from this study can inform improved design of closed-loop systems in future projects.

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