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.

英格兰西南部的地表热流较高，这与 Cornubian 岩基花岗岩中放射性元素（U、Th 和 K）含量升高有关，因此它是英国最有前景的深层地热能地区之一。对区域高温地热能生产潜力的调查包括由坎伯恩矿业学院承担的 4200 万磅地热干热岩研究计划（1975-1991 年）。确保康沃尔郡拥有深层地热规划许可的两个地点中的至少一个获得资助 位于康沃尔郡雷德鲁斯附近、耗资 1800 万英镑的 United Downs 深层地热发电项目将于 2018 年 10 月开始钻探两口井，一口深 2.5 公里，一口深 2.5 公里。另一个 4.5 公里深的活动将形成英国最深的陆上地热钻孔，为博士项目提供了框架，该项目的目的是解决热量生产的不确定性。康沃尔地壳中的传导模型，其中包括：(i) 放射性元素 U、Th 和 K 在先前研究的花岗岩上部中的含量不足以解释观测到的热流，(ii) He-4 的产生来自历史深层地热井的热量高于预期，(iii) 地球物理模型逐渐减少了 Cornubian 花岗岩的解释体积，这些不一致意味着大量的热源可能出现在更深的部分之内或之下。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，以及这可能与以下方面有何关系：（i）复合康努布基岩内的异质放射热产生（目前在 2.6 公里以下未采样）， (ii) 中/下地壳和地幔来源的热量贡献，以及 (iii) 裂缝控制的深层地下水循环的改变将发生在一定深度。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 预算及其矿物学宿主以及高温蚀变和浸出的分析技术的证据。 QEMSCAN（自动 SEM）、电子显微探针和 XRF/ICP-MS） QEMSCAN 的使用很新颖，因为它可以进行快速矿物学分析和主机。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，并将对放射热产生进行建模，并与测量的热流数据进行比较。使用现有的深层地球物理数据和对瓦里西亚后构造演化期间可接受情景的理解，研究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英格兰西南部更深部热源的确认将对全球花岗岩地形的区域地热和地壳模型以及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) 井下测井解释和裂缝控制流体流动模型方面的培训。