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

英国准备采用净零碳排放技术，通过将更多地使用可再生能源与高效的地下氢气储存(UHS)和长期规划的碳捕获使用和储存(CCUS)计划相结合，来实现其巴黎协议的目标。这一建议将通过开发一种新的地震监测工具来捕获储存的氢(H2)的关键地球物理性质，从而促进将UHS与CCUS相结合所需的知识(即双赢战略)。具体地说，UHS意味着循环注入/耗尽活动，以应对与能源需求相关的季节性波动。但要想让循环成功，需要一种缓冲气体来保持储油层的压力。二氧化碳(CO2)是一种丰富的温室气体，是一种很有前途的环境友好的替代品。在大多数储气项目中，注入到地质地层中的流体是通过将地震速度和振幅的变化与流体含量联系起来进行地震监测的。然而，如果将H2注入二氧化碳缓冲的储集层，两种气体的相似声学特性以及在注入/提取周期内稳定下来的短时间尺度掩盖了H2的地震能见度。CHALUS将测试这一假设，即粘性对比是在H2-CO2储存情况下地震H2可探测性的关键。我们建议分三个阶段验证这一假设，利用我们目前的专业知识，通过多流实验室测试、建模和频散波传播。首先，我们将在实验室测量被UHS应用中存在的流体饱和的储集岩的弹性和运输特性。我们将控制这些实验，以模拟H2-CO2在油藏条件下的粘度对比。其次，我们将应用为CCUS建立的现有岩石物理模型来计算这些岩石在不同饱和条件下的地震速度、衰减和频散。这将涉及盖层盖层下面饱和了H2水和CO2水的储集岩。我们将使用新的数据集来校准这些模型。第三，我们将通过计算与垂直地震剖面(不同流体状态之间具有衰减对比的时间推移实验)相对应的合成地震数据来扩大我们的发现，该剖面由粘性对比控制并由实验数据提供信息。使用这一合成数据集，我们将进行敏感性分析，以评估H2的地震可探测性极限。这项建议的结果有可能通过提高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UHS监测的风险。更好地了解氢饱和岩石的弥散特性，将使政策制定者能够识别与压裂相关的地震属性，并量化泄漏风险。总而言之，这将有助于为工业季节性UHS制定有效的监测战略。我们建议以两份(半年一次)报告的形式传播我们的成果，一份主要学术期刊和一份会议出版物上的合作科学出版物，以及来自岩石物理和合成地震实验的公开可获取的数据集。以该项目作为跳板概念验证，我们打算通过NERC推动前沿基金提案与英国进行长期合作，以巩固其发现，其中包括通过将压裂的地质力学效应纳入地震特征来评估盖层完整性。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补充正在进行的UHS研究，包括NOC(NERC Moet)和UOE(EPSRC HyStorPore)，以及新的岩石物理知识。

The UK is poised to embrace net zero carbon emission technologies to meet its Paris accord targets, by combining an increasing use of the renewables with efficient underground hydrogen storage (UHS) and long-planned Carbon Capture Usage and Storage (CCUS) schemes. This proposal will advance knowledge needed to combine UHS with CCUS (i.e., a win-win strategy), by developing a novel seismic monitoring tool to capture key geophysical properties of the stored hydrogen (H2). Specifically, UHS implies cyclic injection/depletion activities to deal with seasonal fluctuations associated with energy demands. But for the cycle to be successful, a cushion gas is needed to keep the reservoir pressurised. Carbon dioxide (CO2) being an abundant greenhouse gas, is a promising, environmentally friendly alternative. Its use as cushion gas, if successful, could significantly reduce the cost of seasonal H2 retrieval and open up novel research directions.In most storage projects, fluids injected in geological formations are seismically monitored by associating the variation of seismic velocity and amplitude with fluid content. However, if H2 is injected in a CO2-cushioned reservoir, the similar acoustic properties of both gases together with the short timescales to settle within an injection/extraction cycle obscure the H2 seismic visibility. CHORUS will test the hypothesis that a viscosity contrast is the key to seismic H2 detectability in a H2-CO2 storage scenario. We propose to test this hypothesis in three stages, using our current expertise with multi-flow laboratory tests, modelling and dispersive wave propagation. First, we will perform laboratory measurements of the elastic and transport properties of reservoir rocks saturated with the fluids present in UHS applications. We will control these experiments to emulate viscosity contrasts of H2-CO2 at reservoir conditions. Second, we will apply existing rock physics models established for CCUS to calculate the seismic velocities, attenuation and dispersion of these rocks under different saturation conditions. This will involve reservoir rocks saturated with H2-water and CO2-water below a caprock seal. We will calibrate these models using the novel dataset. Third, we will scale up our finds by calculating synthetic seismic data corresponding to a vertical seismic profile (time-lapse experiment with attenuation contrast between different fluid regimes) controlled by the viscosity contrast and informed by the experimental data. Using this synthetic dataset, we will conduct a sensitivity analysis to assess the limits of seismic detectability of H2.Outcomes of this proposal have the potential to de-risk UHS monitoring by enhancing our ability to quantify H2 through better seismic resolution of the H2-CO2 interface. A better understanding of the dispersive properties of H2-saturated rocks will enable policy-makers to identify seismic attributes associated with fracturing and quantifying leakage risk. Altogether will facilitate both the planning of efficient monitoring strategies for industrial seasonal UHS. We propose to disseminate our results in the form of two (6-monthly) reports, a collaborative scientific publication in a lead academic journal and a conference publication, and openly accessible datasets from the rock physics and the synthetic seismic experiments. 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, to include the assessment of caprock integrity by incorporating geomechanical effects from fracturing on seismic signatures. 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 complement ongoing UHS studies, both in NOC (NERC MOET), and UoE (EPSRC HyStorPore) with novel rock physical knowledge.