The positive impact that natural fractures can have on geothermal heat production from low-permeability reservoirs has become increasingly recognised and proven by subsurface case studies. In this study, we assess the potential impact of natural fractures on heat extraction from the tight Lower Buntsandstein Subgroup targeted by the recently drilled NLW-GT-01 well (West Netherlands Basin (WNB)). We integrate: (1) reservoir property characterisation using petrophysical analysis and geostatistical inversion, (2) image-log and core interpretation, (3) large-scale seismic fault extraction and characterisation, (4) Discrete Fracture Network (DFN) modelling and permeability upscaling, and (5) fluid-flow and temperature modelling. First, the results of the petrophysical analysis and geostatistical inversion indicate that the Volpriehausen has almost no intrinsic porosity or permeability in the rock volume surrounding the NLW-GT-01 well. The Detfurth and Hardegsen sandstones show better reservoir properties. Second, the image-log interpretation shows predominately NW–SE-orientated fractures, which are hydraulically conductive and show log-normal and negative-power-law behaviour for their length and aperture, respectively. Third, the faults extracted from the seismic data have four different orientations: NW–SE, N–S, NE–SW and E–W, with faults in proximity to the NLW-GT-01 having a similar strike to the observed fractures. Fourth, inspection of the reservoir-scale 2D DFNs, upscaled permeability models and fluid-flow/temperature simulations indicates that these potentially open natural fractures significantly enhance the effective permeability and heat production of the normally tight reservoir volume. However, our modelling results also show that when the natural fractures are closed, production values are negligible. Furthermore, because active well tests were not performed prior to the abandonment of the Triassic formations targeted by the NLW-GT-01, no conclusive data exist on whether the observed natural fractures are connected and hydraulically conductive under subsurface conditions. Therefore, based on the presented findings and remaining uncertainties, we propose that measures which can test the potential of fracture-enhanced permeability under subsurface conditions should become standard procedure in projects targeting deep and potentially fractured geothermal reservoirs.

中文翻译：

---

天然裂缝对西荷兰盆地三叠系致密砂岩热提取的影响：结合井、地震和数值数据的案例研究

天然裂缝对低渗透储层地热产热的积极影响已越来越多地被地下案例研究认可和证明。在这项研究中，我们评估了天然裂缝对最近钻探的 NLW-GT-01 井（西荷兰盆地 (WNB)）所针对的致密的 Lower Buntsandstein 亚组的热量提取的潜在影响。我们整合了：（1）使用岩石物理分析和地质统计反演的储层特性表征，（2）图像测井和岩心解释，（3）大规模地震断层提取和表征，（4）离散裂缝网络（DFN）建模和渗透率放大，以及 (5) 流体流动和温度建模。第一的，岩石物理分析和地质统计反演结果表明，在 NLW-GT-01 井周围的岩体中，Volpriehausen 几乎没有固有孔隙度或渗透率。Detfurth 和 Hardegsen 砂岩显示出更好的储层特性。其次，图像测井解释显示主要是 NW-SE 方向的裂缝，这些裂缝具有水力传导性，并分别显示其长度和孔径的对数正态和负幂律行为。第三，从地震数据中提取的断层有四个不同的方向：NW-SE，N-S，NE-SW和E-W，靠近NLW-GT-01的断层与观察到的裂缝具有相似的走向。第四，检查水库规模的二维 DFN，放大的渗透率模型和流体流动/温度模拟表明，这些潜在开放的天然裂缝显着提高了通常致密储层体积的有效渗透率和产热。然而，我们的建模结果也表明，当天然裂缝闭合时，产量值可以忽略不计。此外，由于在放弃 NLW-GT-01 所针对的三叠纪地层之前没有进行主动试井，因此没有关于观察到的天然裂缝是否在地下条件下连接和水力传导的结论性数据。因此，根据提出的调查结果和剩余的不确定性，