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

地热能在供热和发电方面都是化石燃料的重要替代品。EGS（增强型地热系统）能够瞄准2至5公里深处的深层岩层进行热量提取。然而，很少有EGS开发的尝试达到商业阶段。最近的一篇综述在世界范围内的花岗岩或其他结晶岩中发现了约30个EGS点，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，由于多年的水力压裂未能建立任何重要的井间水力连接，位于康沃尔西部carmenellis花岗岩岩体的Rosemanowes项目于20世纪90年代初关闭。这一失败扼杀了英国EGS研发的一代人。最近，从2019年的钻探开始，第二个项目-在United Downs现场-在carmenellis花岗岩中进行。然而，尽管开发商尚未发表任何官方声明，几个月来，英国地热社区的“小道消息”已经讨论了这个项目陷入困境的原因，包括地震活动和井之间缺乏水力连接。最近的失败导致了约2000万英镑的投资损失，这凸显了对EGS专业知识的需求。尽管对储层增产进行了大量研究，但对储层增产过程中控制地应力演化的一般过程以及相关的人为地震活动仍知之甚少。例如，化学刺激是如何改变断层表面的机械状态的？化学反应会产生新的次生矿物，从而改变断层的摩擦特性，使其变得更不稳定吗？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活动？该项目旨在创建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项目的失败风险。我们汇集了来自英国格拉斯哥大学（UG）、美国威斯康星大学麦迪逊分校（UW）和劳伦斯伯克利国家实验室（LBNL）以及中国中石化石油工程研究院（SRIPE）的一批热情的、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资深研究人员。只有通过合作，我们才能利用互补的专业知识、先进的实验室设施、独特的现场资源和现场数据，覆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、建模和现场方法，对如何控制和消除地热储层刺激引起的人为地震活动形成新的科学认识。UW和LBNL将使用他们的实验室设备领导实验研究。实验室研究将为耦合建模提供数据，这将由UG领导。SRIPE将领导实地研究，并带来共和EGS站点（中国第一个也是最重要的EGS站点）的独特资源和数据。在共和独特的EGS基地进行的实地研究将为未来的合作提供巨大的机会。我们还设计了推广和伙伴关系活动，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（共和EGS现场），每年为期两天的研讨会（2022年在华盛顿大学和2023年在UG）， 6次在线小型小组会议，以及一个项目网站。我们预计该项目将对英国和全世界公众和政府对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，从而打破现有的EGS项目失败模式。

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.