The implementation of CO₂ storage in sub-surface sedimentary formations can involve decision making using relevant numerical modelling. These models are often represented by 2D or 3D grids that show an abrupt boundary between the reservoir and the seal lithologies. However, in an actual geological formation, an abrupt contact does not always exist at the interface between distinct clastic lithologies such as sandstone and shale. This article presents a numerical investigation of the effect of sediment-size variation on CO₂ transport processes in saline aquifers. Using the Triassic Bunter Sandstone Formation (BSF) of the Southern North Sea (SNS), this study investigates the impact a gradation change at the reservoir-seal interface on CO₂ sequestration. This is of great interest due to the importance of enhanced geological detail in reservoir models used to predict CO₂ plume migration and the integrity of trapping mechanisms within the storage formation. The simplified strategy was to apply the Van Genutchen formulation to establish constitutive relationships for pore geometric properties, which include capillary pressure (P_c) and relative permeability (k_r), as a function of brine saturation in the porous media. The results show that the existence of sediment gradation at the reservoir-seal interface and within the reservoir has an important effect on CO₂ migration and pressure diffusion in the formation. The modelling exercise shows that these features can lead to an increase in residual gas trapping in the reservoir and localised pore pressures at the caprock’s injection point.

在地下沉积岩层中实施CO ₂封存可能需要使用相关的数值模型进行决策。这些模型通常由2D或3D网格表示，这些网格显示了储层和密封岩性之间的突然边界。然而，在实际的地质构造中，突然的接触并不总是存在于诸如砂岩和页岩之类的独特碎屑岩性之间的界面处。本文提出了盐量变化对盐水层中CO ₂输送过程影响的数值研究。本研究使用南北海（SNS）的三叠纪邦特砂岩形成（BSF），研究了储层-密封界面上的梯度变化对CO _2的影响隔离。由于用于预测CO ₂羽流运移的储层模型中的地质细节的重要性以及储层中捕集机制的完整性，这引起了极大的兴趣。简化策略是应用Van Genutchen公式建立孔几何特性的本构关系，其中包括毛细压力（P _c）和相对渗透率（k _r），作为多孔介质中盐水饱和度的函数。结果表明，储层-密封界面和储层内部的沉积物分级对CO ₂有重要影响。在地层中迁移和压力扩散。建模工作表明，这些特征可能导致残留在储层中的残余气体增加，并在盖层的注入点处产生局部孔隙压力。