NI: DEEPHEAT: Digging deep Earth for heat to promote environmental sustainability

地热能为取暖和发电提供了一种重要的化石燃料替代品。EGS(增强型地热系统)能够将目标对准深部岩层，深度约为2至5公里，用于提取热量。然而，开发EGS的尝试很少达到商业阶段。最近的一项审查发现，全球约有30个EGS地点位于花岗岩或其他结晶岩中，其中很大一部分已经失败。一个主要原因是很难在不产生不必要的地震活动的情况下开发EGS。在英国，位于康沃尔西部Carnmenellis花岗岩岩体中的Rosemanowes项目未获成功，在多年的水力压裂未能建立任何重要的井间水力连接后，该项目于20世纪90年代初被关闭。这一失败扼杀了英国EGS研发部门一代人的时间。最近，从2019年开始钻探开始，第二个项目--联合唐斯工地--已经在卡恩梅内利斯花岗岩中进行。然而，尽管开发商尚未发表任何官方声明，但英国地热界的小道消息已经讨论了该项目陷入困境的原因，包括地震活动和井与井之间缺乏水力连接。这一最新的失败涉及2000万GB的投资损失，突显了在EGS方面需要更多专业知识。尽管有大量关于油藏刺激的研究，但控制油藏刺激过程中地应力演化的一般过程以及与之相关的人为地震活动仍然知之甚少。例如，化学刺激如何改变断层表面的机械状态？化学反应会产生新的次生矿物，会以有利于不稳定的方式改变断层的摩擦特性吗？当物质被溶解带走时，断层上的牵引力是如何演变的？我们如何管理流体注入速度和压力以避免人为地震？该项目旨在创造一个新的多学科环境，并确定需要解决的关键科学问题，以减轻未来EGS项目失败的风险。我们从英国格拉斯哥大学、美国威斯康星大学麦迪逊分校和劳伦斯·伯克利国家实验室以及中国的中石化石油工程研究院汇聚了一支热情高涨、在地球科学、地质力学和地球物理领域具有较高国际地位和专业知识的早期热情和更资深的研究人员团队。只有通过合作，我们才能利用我们互补的专业知识、先进的实验室设施、独特的实地资源和现场数据来涵盖单个机构无法实现的多个规模和方面。我们将采用综合实验室、模拟和现场方法，对如何控制和消除地热储层刺激引起的人为地震活动产生新的科学理解。华盛顿大学和LBNL将利用他们的实验室设施领导这项实验研究。实验室研究将为由UG牵头的耦合建模提供数据。SRIPE将领导实地研究，并从他们的共和EGS站点(中国的第一个也是最重要的EGS站点)引入独特的资源和数据。在独一无二的共和EGS现场进行的实地研究将提供广阔的未来合作机会。我们还设计了外展和伙伴关系活动，以促进研究人员之间的互动和合作，并发展长期可持续的合作。这些活动包括两次实地考察(对共和EGS现场)、一年一度的为期两天的讲习班(2022年在华盛顿大学和2023年在UG)、6次在线小组会议和一个项目网站。我们预计该项目将对英国和世界各地公众和政府对EGS的态度产生重大影响，有助于以证据为基础的地震活动控制，从而打破EGS项目失败的现有模式。

Geothermal energy provides an important alternative to fossil fuels, both for heating and for electricity generation. EGS (enhanced geothermal systems) enables the targeting of deep rock formations, at ~2 to 5 km depth for heat extraction. However, few attempts at EGS development have reached the commercial stage. A recent review identifies ~30 EGS sites in granites or other crystalline rocks worldwide, a large proportion of which have failed. One main reason is difficulty in developing EGS without generating unwanted seismicity. In the UK, the unsuccessful Rosemanowes project, in the Carnmenellis granite pluton in west Cornwall, was shut down in the early 1990s, after years of hydraulic fracturing failed to establish any significant inter-well hydraulic connection. This failure killed UK EGS R&D for a generation. Most recently, starting with drilling in 2019, a second project - at the United Downs site - has proceeded in the Carnmenellis granite. However, although the developer has not yet made any official announcement, for months the UK geothermal community 'grapevine' has discussed reasons why this project is in trouble, involving both seismicity and the lack of hydraulic connection between wells. This latest failure, involving the loss of a ~£20 million investment, highlights the need for greater expertise in EGS. Despite the body of research on reservoir stimulation, the general processes that govern the evolution of in-situ stress during reservoir stimulation, and the associated anthropogenic seismicity, still remain poorly understood. For example, how does chemical stimulation change the mechanical state of a fault surface? Will chemical reactions, creating new secondary minerals, alter the frictional properties of a fault in a manner that favours instability? How does the traction on a fault evolve as material is removed by dissolution? How do we manage fluid injection rates and pressures to avoid anthropogenic seismicity? This project aims to create a new multidisciplinary environment and identify key scientific questions that need to be addressed to mitigate risks of failure for future EGS projects. We have assembled a team of enthusiastic early-career and more senior researchers with high international standing and expertise in geoscience, geomechanics, and geophysics, from University of Glasgow (UG) in the UK, University of Wisconsin-Madison (UW) and Lawrence Berkeley National Laboratory (LBNL) in the USA, and Sinopec Research Institute of Petroleum Engineering (SRIPE) in China. Only by working together, can we use our complementary expertise, advanced laboratory facilities, unique field resources and site data to cover multiple scales and aspects that cannot be achieved by individual institutions. We will apply integrated laboratory, modelling and field approaches to develop new scientific understanding of how anthropogenic seismicity caused by geothermal reservoir stimulation can be controlled and eliminated. UW and LBNL will lead the experimental study using their laboratory facilities. The laboratory study will provide data for coupled modeling, which will be led by UG. SRIPE will lead field study and bring in unique resources and data from their Gonghe EGS site (the first and the most important EGS site in China). The field study at the unique Gonghe EGS site will provide vast future collaboration opportunities. We have also designed outreach and partnership activities to facilitate interaction and collaboration between researchers, and to develop long-term sustainable collaborations. These activities include two site visits (to Gonghe EGS site), annual 2-day workshops (in 2022 at UW and in 2023 at UG), 6 online smaller group meetings, and a project website. We expect this project will have significant impact on public and governmental attitudes to EGS in the UK and worldwide by contributing to evidence-based seismicity control and thus to breaking the existing pattern of EGS project failure.