Coupled modelling, based on laboratory data, indicated that the storage seal above the Captain reservoir of the Peterhead CCS project could be affected by stresses caused by clay swelling due to CO₂ interaction. In particular, calculations indicate that, over a period of 100 – 10,000 years, local shear failure in rock exposed to CO₂ may occur under unfavourable stress conditions. The likelihood and consequences of local shear failure are however difficult to assess. We therefore defined passive safeguards against this potential risk to seal integrity. The basis for these safeguards is data and information given in the Peterhead CCS Storage Permit Application (storage seal thicknesses, lithologies, reservoir conditions etc.), chemical, thermodynamic and mechanical data from laboratory measurements, as well as the coupled model built and described earlier by Wentinck and Busch (2017).

The passive safeguards provided in this study address the mineralogy of the caprock and more specifically its swellable clay content. Furthermore, the geometry of the reservoir is addressed, particularly with respect to the presence of pre-existing faults. Our model shows that for shear failure to be a risk a fault offset on the order of the thickness of the sealing layer needs to be present and in contact with the CO₂ plume. It should be noted that swelling stress build-up may relax by creep of the surrounding shale matrix, thereby buffering this effect. Finally, the risk of CO₂ to escape the storage container only exists when slip on pre-existing faults leads to permeability enhancement as well as reduction of capillary entry pressures along the fault.

Our analyses show that the smectite contents of the unit at the base of the caprock is significant with an average of 57 %, substantiating the threat of clay swelling. Taking the locations of interpreted faults and the total storage seal thickness of 117−165 m, we find no potential offsets similar to this thickness, as identified offsets are up to 33 m. Unquantified uncertainties remain in the creep behaviour of the caprock as well as the fault permeability. Given however that a maximum fault offset is lower than the seal thickness, we classify loss of containment due to fault reactivation caused by swelling clays, and concomitant fluid leakage, to be a low geological risk for the Peterhead CCS project.

基于实验室数据的耦合建模表明，Peterhead CCS项目船长储层上方的储层封盖可能会受到由于CO ₂相互作用引起的粘土膨胀所引起的应力的影响。特别是，计算表明，在100至10,000年的时间里，暴露于CO _2的岩石的局部剪切破坏可能会在不利的压力条件下发生。然而，局部剪切破坏的可能性和后果很难评估。因此，我们定义了被动防护措施来防止这种潜在的密封完整性风险。这些保障措施的基础是Peterhead CCS储存许可证申请书中提供的数据和信息（储存密封件的厚度，岩性，储层条件等），来自实验室测量的化学，热力学和机械数据，以及先前建立和描述的耦合模型。 Wentinck和Busch（2017）。

这项研究中提供的被动防护措施针对的是盖层的矿物学，尤其是其可溶胀的粘土含量。此外，特别是针对已经存在的断层的存在，解决了储层的几何形状。我们的模型表明，要使剪切破坏成为一种风险，就必须存在与密封层厚度成比例的断层偏移，并且要与CO ₂羽流接触。应当注意的是，膨胀应力的积累可能会因周围页岩基质的蠕变而松弛，从而缓冲了这种影响。最后，仅当先前存在的断层发生滑动导致渗透率提高以及沿着断层的毛细管进入压力降低时，CO ₂才可能逃脱储罐。

我们的分析表明，盖层底部单元的蒙脱石含量显着，平均为57％，证实了粘土膨胀的威胁。取解释的断层的位置和总的储层密封厚度为117-165 m，我们发现没有潜在的与该厚度相似的偏移量，因为确定的偏移量最大为33 m。未量化的不确定性仍然存在于盖层的蠕变行为以及断层渗透率中。但是，考虑到最大断层偏移量小于密封层厚度，我们将由于膨胀粘土引起的断层再活化和随之而来的流体泄漏所造成的密闭性损失归类为Peterhead CCS项目的低地质风险。