Evaluation of fault leakage rates in the context of subsurface hydrogen and carbon storage

在地下临时储存氢气或永久储存二氧化碳需要深刻理解相关的泄漏风险，承受环境、政治和经济风险，这些风险仍有待量化。沿井或断层渗漏的风险最高。后者（图1）可能已经具有流体动力导电性，或者由于注入CO2或H2导致流体压力增加而引发导电性。流体压力的增加，从而导致有效应力的降低，取决于断层与注入井的距离。在已知断层附近钻注井是不可取的，而在小于1万年的工程时间尺度上，断层是否可以作为泄漏通道仍然是未知的。在此背景下，我们将研究多相流效应对用于储液的地质储层断层泄漏的影响，特别关注CCS和氢气。这项研究将基于最近从瑞士光源的多尺度4D x射线成像中获得的数据。该博士项目将为粗糙裂缝中的多相流体动力学提供新的和详细的见解。使用同步加速器实验的新数据将支持对地下储层潜在流体泄漏率的更准确预测。这些都是迫切需要的，以提高我们对长期地下流体储存的信心。本研究可分为以下几个目标：1。基于四维流动数据，对粗糙裂缝中的多相流动有了更深入的了解。将对数据进行位移分析，以获得给定有效应力下的相对渗透率和毛管压力曲线，但具有不同的表面粗糙度、孔径非均质性和流速（毛管数）。在裂缝和裂缝网络的物理模型中以达西尺度表示裂缝流动现象。通过整合裂缝网络数据（来自PI/co- i之前的研究）和本次研究中升级的流体驱替模型，这将提高我们对泄漏率确定的信心，从而支持盖层泄漏风险评估。

Temporary storage of hydrogen or permanent storage of carbon dioxide in the subsurface requires a profound understanding of associated risks for leakage, bearing environmental, political, and economic risks that are still to be quantified. Risks are highest for leakage along wells or faults. The latter (Fig. 1) might already be hydro-dynamically conductive, or conductivity might be triggered by an increase in fluid pressures due to CO2 or H2 injection. Fluid pressure increase, and thus effective stress decrease, depends on the vicinity of the faults to the injection well. Drilling an injection well near a known fault is rather discouraged, while it remains unknown if faults can act as leakage pathways over engineered time scales on the order of < 10,000 years.In this context, we will investigate the impact of multiphase flow effects on fault leakage from geological reservoirs used for fluid storage, focusing specifically on CCS and hydrogen. This research will ground on recent data that has been obtained from multiscale 4D X-ray imaging at the Swiss Light Source. This PhD project will provide new and detailed insights into the multiphase fluid dynamics in rough fractures. Using novel data from synchrotron experiments will support more accurate predictions of the potential fluid leak rates from subsurface reservoirs. These are urgently needed to improve our confidence in subsurface fluid storage over long periods of time. This research can be divided into the following objectives:1. Develop a robust understanding of multiphase flow in rough fractures, based on 4D flow data. The data will be analysed towards displacement to obtain relative permeability and capillary pressure curves at a given effective stress but with varying surface roughness, aperture heterogeneity, and flow rates (capillary numbers).2. Represent fracture flow phenomena at the Darcy scale in physical models for fractures and fracture networks. This will support caprock leakage risk assessments by improving our confidence in the determination of leak rates by bringing together fracture network data (from previous research by the PI/co-Is) and upscaled fluid displacement models from this research.