The installed capacity of geothermal systems for direct use of heat is increasing worldwide. As their number and density is increasing, the their interaction with subsurface faults becomes more important as they could lead to safety risks from induced seismicity. Assessment and management of such risks is essential for the further development and extension of geothermal energy for heating. At the same time, the economic output of geothermal systems can be marginal and is hence often supported by subsidy schemes. A combined assessment of fault stability and economic output could help operators to balance economic and safety aspects, but this is currently not common practice. In this study we present a methodology to assess field development plans based on fault stability and Net Present Value (NPV) using reservoir simulations of a fluvial, heterogeneous sandstone representative of the majority of direct-use Dutch geothermal systems. We find that the highest friction coefficient leading to exceedance of the Mohr–Coulomb failure criteria in this sandstone is 0.17; such values could be encountered in clay-rich fault gouges. Similar or lower fault permeability compared to the reservoir results in no changes and an increase respectively of both NPV and fault stability with larger Fault-to-Well Distance (FWD). Fault permeability higher than the reservoir permeability results in a minor increase in NPV with smaller FWD. Our results demonstrate that a combined analysis of thermal, hydraulic, mechanical and economic assessment supports a responsible and viable development of geothermal resources at a large scale. The importance of a high spatial density of supporting stress data will be essential for a better understanding and quantification of economic and fault stability effects of geothermal operations.

中文翻译：

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直接使用型热液储层地热田开发的经济性和断层稳定性分析

在全球范围内，直接利用热量的地热系统的装机容量正在增加。随着它们的数量和密度的增加，它们与地下断层的相互作用变得更加重要，因为它们可能导致感应地震活动带来安全风险。对此类风险的评估和管理对于进一步开发和扩展地热能供热至关重要。同时，地热系统的经济产出可能是微不足道的，因此经常受到补贴计划的支持。对故障稳定性和经济产出进行综合评估可以帮助操作员在经济和安全方面取得平衡，但这目前并不普遍。在这项研究中，我们提出了一种利用断层稳定性和净现值（NPV）来评估油田开发计划的方法，该方法使用了一个河流相的油藏模拟，非均质砂岩代表了大多数直接使用的荷兰地热系统。我们发现，导致该砂岩中超过Mohr-Coulomb破坏准则的最高摩擦系数为0.17；而导致最大摩擦系数的则为0.17。在富含粘土的断层泥中可能会遇到这样的值。与较大的断层间距离（FWD）相比，与储层相比相似或较低的断层渗透率不会导致净值和断层稳定性的变化，并且不会增加。断层渗透率高于储层渗透率，导致FPV较小时NPV略有增加。我们的结果表明，对热力，水力，机械和经济评估的综合分析可支持大规模负责任和可行的地热资源开发。