Geothermal wells have evolved in the past decade, moving from a concept copying oil and gas well construction and completion to modern and unconventional solutions applied to local conditions. In general, geothermal wells are optimized based on their flow rate output. The optimization results are visible as the modern geothermal wells have large casing sizes, no production tubing down to the reservoir, and so on. When doublets are required, drilling them from the same location can reduce costs. However, this approach must first answer the following questions: which well should be the injector, the producer, and shall these wells have the same design? In previously published papers, it was presented that well cementing and the drilling process affects the heat transfer along the wellbore. Using appropriate cement composition and by controlling the filter cake thickness and mud filtrate invasion, the heat transfer can be reduced or enhanced. These finding are used in this paper to improve well design with the focus on maximizing the heat output. The paper herein is proposing a theoretical discussion about wellbore overall heat transfer coefficient with a focus on geothermal well optimization based on the downhole heat exchange, leading to an improved geothermal well design. Furthermore a new well construction will be shown based on the proposed optomization method.

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