Sleipner (North Sea) is the world’s first commercial-scale carbon capture and storage (CCS) project, active since 1996, with ∼17 million tonnes of CO₂ stored. The main reservoir, Utsira Sand, constitutes an ideal host formation of exceptionally high porosity-permeability and large lateral extent. However, the extensive seismic time-lapse, gravity and electromagnetic monitoring surveys deployed at Sleipner have not been well-supported by laboratory measurements. Here, we investigate the geophysical and geomechanical response of an Utsira core sample for the first time, using controlled inflation/depletion cycles at variable CO₂-to-brine fractional flow rates. Ultrasonic P-wave velocities and attenuations are measured together with electrical resistivity (converted into CO₂-saturation), along with continuous axial and radial strain monitoring. Ultrasonic velocity and attenuation data were simultaneously inverted and results extrapolated to field-scale seismic-frequencies using a new rock physics theory, which combines patchy fluid distribution and squirt flow effects. It provides a velocity-saturation relationship of practical importance to CO₂ plume monitoring. Furthermore, by combining ultrasonic and deformation data, we report empirical relations between pore pressure changes and geomechanical effects in the reservoir, for different saturation ranges. Our dataset complements and constrains existing geophysical monitoring surveys at Sleipner and, more generally, improves the understanding of shallow weakly-cemented sand reservoirs.

Sleipner（北海）是世界上第一个商业规模的碳捕集与封存（CCS）项目，自1996年以来一直活跃，储存了约1700万吨的CO ₂。主储层Utsira Sand是孔隙度高，渗透率大和横向范围大的理想基质。但是，在Sleipner进行的广泛的地震时差，重力和电磁监测勘测并没有得到实验室测量的良好支持。在这里，我们使用可变的CO _2-盐水分流速率下的受控充气/耗竭循环，首次研究了Utsira岩心样品的地球物理和地球力学响应。测量超声波P波的速度和衰减以及电阻率（转换为CO ₂-饱和），以及连续的轴向和径向应变监测。超声速度和衰减数据同时被反转，结果使用一种新的岩石物理学理论将结果外推到现场规模的地震频率，该理论结合了斑驳的流体分布和喷流效应。它提供了对CO ₂羽流监测具有实际重要性的速度-饱和关系。此外，通过结合超声和变形数据，我们报告了在不同饱和度范围内，孔隙压力变化与储层中地质力学效应之间的经验关系。我们的数据集补充并限制了Sleipner现有的地球物理监测调查，并且更广泛地提高了对浅层弱水泥砂岩储层的了解。