Abstract Drilling costs, induced seismicity, scaling and corrosion, emissions, and assessment of the inherent uncertainty associated with the reservoir properties for long-term sustainable provision of thermal energy are the major challenges of deep geothermal systems. In particular, the cost of drilling typically comprises 50–70 % of the total capital investment of a geothermal power plant. As drilling costs are definitive for the accomplishment of deep geothermal systems, the concept to use one single drill hole for extraction and injection is arisen to reduce the overall drilling costs. The aim of this study is to overcome some simplifications made in the previous published studies to investigate such single-well systems in more detail and further resolve the governing physical processes. Focus of the study is on reservoirs with a low natural permeability (around 10−14 m2). Firstly, an analytical solution is applied for justifying the numerical approach to produce consistent results for the presented simplest single-well design. Secondly, the efficiency of different single-well concepts is investigated via sensitivity analysis of variations in reservoir and operational parameters. Lastly, the previous study results are compared with the current approach for the gas-filled porous medium application. The results for the single-well system either with multi-laterals or without laterals demonstrate that the variation of permeability in different directions and the porosity play a crucial role on the overall performance. Single-well systems with multi-laterals are efficient, if the permeability is isotropic and in a range between 1 × 10−14 and 1 × 10-12 m2. The results of gas-filled pore space applications show that the capillary entry pressure has a significant impact on the wetting phase saturation. Simultaneous injection and extraction affect the saturation and heat exchange localized around the wells which decreases the thermal output power.

中文翻译：

---

多侧钻单井地热系统的效率

摘要 钻井成本、诱发地震活动、结垢和腐蚀、排放以及与长期可持续提供热能的储层特性相关的固有不确定性的评估是深层地热系统的主要挑战。特别是，钻井成本通常占地热发电厂总投资的 50-70%。由于钻井成本对于完成深层地热系统来说是决定性的，因此出现了使用单个钻孔进行提取和注入的概念，以降低整体钻井成本。本研究的目的是克服之前发表的研究中所做的一些简化，以更详细地研究此类单井系统并进一步解决控制物理过程。研究的重点是天然渗透率低（约 10-14 平方米）的储层。首先，应用解析解来证明数值方法的合理性，以便为所提出的最简单的单井设计产生一致的结果。其次，通过对储层和操作参数变化的敏感性分析来研究不同单井概念的效率。最后，将先前的研究结果与当前用于充气多孔介质应用的方法进行了比较。多支管和无支管单井系统的结果表明，不同方向渗透率和孔隙度的变化对整体性能起着至关重要的作用。多分支的单井系统是高效的，如果渗透率是各向同性的并且在 1 × 10-14 和 1 × 10-12 m2 之间的范围内。充气孔隙空间应用的结果表明，毛细管入口压力对润湿相饱和度有显着影响。同时注入和抽取会影响井周围的饱和度和热交换，从而降低热输出功率。