Geological controls on upper crustal heat flow for deep geothermal energy in Cornwall

康沃尔郡深层地热能上地壳热流的地质控制

• 批准号: 2073014
• 金额: --
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2073014
• 关键词: Geological; controls; upper; crustal; heat

SW England has locally high surface heat flows associated with elevated levels of radioactive elements (U, Th and K) within the granites of the Cornubian Batholith. As such, it is one of the most prospective areas in the UK for deep geothermal energy. Previous investigations into the regional potential for high temperature geothermal energy production included the 42 million pound geothermal Hot Dry Rock research programme, undertaken by Camborne School of Mines (1975-1991). There has been renewed strategic impetus to ensure that at least one of the two sites in Cornwall with planning permission for deep geothermal is funded. The £18M United Downs Deep Geothermal Power project, near Redruth in Cornwall, will commence drilling two wells in October 2018, one 2.5 km deep and the other 4.5 km deep; this activity, which will result in the UK's deepest onshore geothermal borehole, provides the framework for the PhD. The purpose of the project is to address uncertainties regarding heat production and conduction models in the Cornish crust which include: (i) radioactive elements U, Th and K are not present in sufficiently high quantities within the previously investigated upper parts of the granite to account for observed heat flow, (ii) He-4 production from historical deep geothermal wells is higher than anticipated, (iii) geophysical modelling has progressively reduced the interpreted volume of the Cornubian granites. These inconsistences imply substantive heat source(s) may occur within, or below, the deeper parts of the batholith.The project will develop further understanding of the controls on upper crustal temperatures and deep geothermal energy exploitation in Cornwall and how this might relate to: (i) heterogeneous radiogenic heat production within the composite Cornubian Batholith (presently unsampled below 2.6 km), (ii) heat contributions from mid/lower crustal and mantle sources, and (iii) modification by fracture-controlled deep groundwater circulation. Drilling within the Carnmenellis Granite will occur over a depth range of approximately 1.5-4.5 km. The arisings will permit mineralogical and whole rock geochemical characterisation of the granites, including the U, Th, K budget and their mineralogical hosts and evidence for high-temperature alteration and leaching. Analytical techniques include optical microscopy, QEMSCAN (automated SEM), electron microprobe and XRF/ICP-MS). The use of QEMSCAN is novel as it permits rapid mineralogical analysis and host rock interpretation from fine-grained drilling arisings. These data will be complemented by those obtained during downhole logging (gamma ray, formation fluid composition / temperature). Radiogenic heat production will be modelled and compared with measured heat flow data. Discrepancies will be evaluated in terms of the potential role of upper crustal convective fluid flow and/or mid / lower crustal and mantle heat contributions using existing deep geophysical data and an understanding of admissible scenarios during the post-Variscan tectonic evolution of SW England. Confirmation of deeper heat sources would have profound implications for regional geothermal and crustal models and deep geothermal projects in granitic terrains globally. The student will receive training at Camborne School of Mines in: (i) mineralogical and geochemical analytical and interpretation skills, (ii) petrological and heat flow modelling skills, and (iii) regional crustal evolution. Training in downhole log interpretation and fracture-controlled fluid flow models will be provided by GeoScience Limited.

英格兰西南部具有局部较高的表面热流，这与 Cornubian 岩基花岗岩内放射性元素（U、Th 和 K）水平升高有关。因此，它是英国深层地热能最有前景的地区之一。此前对区域高温地热能生产潜力的调查包括坎伯恩矿业学院 (Camborne School of Mines) 开展的耗资 4200 万磅的地热干热岩研究计划（1975-1991 年）。已获得新的战略动力，以确保康沃尔郡拥有深层地热规划许可的两个地点中至少一处获得资助。耗资 1800 万英镑的联合唐斯深层地热发电项目位于康沃尔郡雷德鲁斯附近，将于 2018 年 10 月开始钻探两口井，一口深 2.5 公里，另一口深 4.5 公里；这项活动将形成英国最深的陆上地热钻孔，并为博士学位提供了框架。该项目的目的是解决康沃尔地壳产热和传导模型的不确定性，其中包括：（i）在先前研究的花岗岩上部，放射性元素 U、Th 和 K 的数量不足以解释观测到的热流，（ii）历史深层地热井的 He-4 产量高于预期，（iii）地球物理模型已逐渐减少了 Cornubian 的解释体积 花岗岩。这些不一致意味着大量的热源可能出现在岩基较深处的内部或下方。该项目将进一步了解对康沃尔郡上地壳温度和深层地热能开发的控制，以及这可能与以下因素之间的关系：(i) 复合康努比亚岩基内的异质放射热产生（目前未在 2.6 公里以下进行采样），(ii) 来自康沃尔的热贡献 中/下地壳和地幔来源，以及（iii）裂缝控制的深层地下水循环的改变。 Carnmenellis 花岗岩内的钻探深度范围约为 1.5-4.5 公里。这些产物将允许对花岗岩进行矿物学和全岩地球化学表征，包括 U、Th、K 预算及其矿物学主体以及高温蚀变和淋滤的证据。分析技术包括光学显微镜、QEMSCAN（自动 SEM）、电子显微探针和 XRF/ICP-MS。 QEMSCAN 的使用很新颖，因为它可以快速进行矿物学分析，并对细粒钻探产生的主岩进行解释。这些数据将由井下测井期间获得的数据（伽马射线、地层流体成分/温度）进行补充。将对放射热产生进行建模并与测量的热流数据进行比较。将使用现有的深层地球物理数据以及对英格兰西南部后瓦里西亚构造演化过程中可接受情景的理解，根据上地壳对流流体流和/或中/下地壳和地幔热量贡献的潜在作用来评估差异。确认更深的热源将对区域地热和地壳模型以及全球花岗岩地形的深层地热项目产生深远的影响。学生将在坎伯恩矿业学院接受以下方面的培训：（i）矿物学和地球化学分析和解释技能，（ii）岩石学和热流建模技能，以及（iii）区域地壳演化。 GeoScience Limited 将提供井下测井解释和裂缝控制流体流动模型方面的培训。