CO2 - H2 Optimisation in Rocks for Underground Storage (CHORUS)

英国准备采用净零碳排放技术，以实现其巴黎协议目标，包括与氢(H2)燃料经济性和碳捕获使用和储存(CCUS)计划相关的海上天然气储存。地下储氢(UHS)意味着周期性的注入/耗尽活动，以应对与能源需求相关的季节性波动。为了使循环成功，需要一种缓冲气体来保持储气罐的压力，二氧化碳(CO2)是一种很有前途的环境友好型替代方案。在大多数储油工程中，通过将地震振幅的变化与流体含量相关联来对储集层流体进行地震监测。然而，如果将H2注入CO2缓冲的储集层，有几个因素会模糊H2的地震能见度：H2和CO2具有相似的声学特性，并且它们在注入/开采周期内的稳定时间较短，通常成片地吸入岩石，降低了有效流体的流动性。我们建议通过测试粘性对比是地震H2可探测性的关键这一假设来解决这些问题。我们建议利用我们目前在色散波传播方面的专业知识，分三个阶段检验这一假说。首先，我们将对饱和了流体的储集岩的弹性性质进行超声实验室测量，预计在UHS应用中会发现这些流体。其次，我们将应用为CCUS建立的现有岩石物理模型来计算不同饱和条件下储集岩的地震速度、衰减和频散，包括盖层盖层下饱和的H2水和CO2水的储集岩，并使用实验室测量来校准这些模型。第三，我们将通过计算与垂直地震剖面时间推移实验对应的合成地震数据来确定这些发现是如何放大的。利用这个合成数据集，我们将进行敏感性分析，以了解H2的地震可探测性极限。这一提议的结果有可能被用来通过提高H2-CO2界面的地震分辨率来增强我们量化H2的能力，从而降低注入过程的风险。它们可以用来通过确定泄漏风险的替代指标向政策制定者提供信息，并促进规划工业季节性超高有害物质的注入和监测战略。这种方法可以进一步用于评价盖层的完整性，方法是结合压裂对合成地震信号的地质力学效应，这是我们打算在进一步研究中探索的方向。我们建议以两份(六个月)报告、一份主要学术期刊上的合作科学出版物、一份合作会议出版物以及公开获取岩石物理实验和合成地震实验的数据的形式来传播我们的成果。以这个项目作为跳板的概念验证，我们打算通过NERC推动前沿基金提案寻求与英国的长期合作来巩固其发现。这样的建议将包括基础研究，以及裂隙顶封层/储集层和地震数据的详细各向异性建模。此外，我们的理论进步可以通过岩石物理知识的补充，为正在进行的与UHS相关的研究增加价值，包括NOC(NERC Moet)和UOE(EPSRC HyStorPore)。

The UK is poised to embrace net zero carbon emission technologies to meet its Paris agreement targets, including offshore gas storage associated with the hydrogen (H2) fuel economy and Carbon Capture Usage and Storage (CCUS) schemes. Underground H2 storage (UHS) implies cyclic injection/depletion activities to deal with seasonal fluctuations associated with energy demands. For the cycle to be successful, a cushion gas is needed to keep the reservoir pressurised, with carbon dioxide (CO2) being a promising environmentally friendly alternative. In most storage projects, reservoir fluids are seismically monitored by associating the variation of seismic amplitude with fluid content. However, if H2 is injected in CO2-cushioned reservoir, several factors obscure the H2 seismic visibility: both H2 and CO2 have similar acoustic properties, and they have short timescales to settle within an injection/extraction cycle, often imbibing the rock in patches and lowering effective fluid mobility. In CHORUS we propose to address these issues by testing the hypothesis that a viscosity contrast is the key to seismic H2 detectability. We propose to test this hypothesis in three stages using our current expertise with dispersive wave propagation. First, we will perform ultrasonic laboratory measurements of elastic properties of reservoir rocks saturated with fluids expected to be found in UHS applications. Second, we will apply existing rock physics models established for CCUS to calculate the seismic velocities, attenuation and dispersion of reservoir rocks under different saturation conditions involving reservoir rocks saturated with H2-water and CO2-water below a caprock seal and calibrate these models using laboratory measurements. Third, we will identify how these finds scale up by calculating synthetic seismic data corresponding to a vertical seismic profile time-lapse experiment. Using this synthetic dataset, we will conduct a sensitivity analysis in order to understand the limits of seismic detectability of H2. Outcomes of this proposal have the potential to be used to de-risk the injection process by enhancing our ability to quantify H2 through better seismic resolution of the H2-CO2 interface. They can be used to inform policy-makers by identifying proxies for leakage risk and facilitate the planning of injection and monitoring strategies for industrial seasonal UHS. The methodology can be further used to asses caprock integrity by incorporating geomechanical effects from fracturing on the synthetic seismic signatures, a direction that we intend to explore in further research. We propose to disseminate our results in the form of two (six monthly) reports, a collaborative scientific publication in a lead academic journal, a collaborative conference publication and openly accessible data from the rock physics experiment and the synthetic seismic experiment. Using this project as springboard proof-of-concept, we intend to consolidate its finds by pursuing a long-term UK collaboration through a NERC Pushing Frontiers funding proposal. Such a proposal would incorporate fundamental research, as well as detailed anisotropic modelling of fractured top-seal/reservoir and seismic data. In addition, our theoretical advancements can add value to ongoing studies associated with UHS, both in NOC (NERC MOET), and UoE (EPSRC HyStorPore) by complementing them with rock physical knowledge.