Periodic minimal surfaces of cubic symmetry

A survey of cubic minimal surfaces is presented, based on the concept of fundamental surface patches and their relation to the asymmetric units of the space groups. The software Surface Evolver has been used to test for stability and to produce graphic displays. Particular emphasis is given to those surfaces that can be generated by a finite piece bounded by straight lines. Some new varieties have been found and a systematic nomenclature is introduced, which provides a symbol (a ‘gene’) for each triply-periodic minimal surface that specifies the surface unambiguously

The impact of background water flow on the early migration of a CO2 plume in a tilted aquifer during the post-injection period

The study presents a numerical modelling analysis on CO2 plume migration in a dipping storage aquifer with background flux, which incorporates residual and dissolution trapping of CO2. The purpose of this analysis is to investigate the effect of the background flow velocity on the CO2 plume migration during the early post-injection period. Different velocities of groundwater flow from low to high were considered in the aquifer model. The distribution, migration distance and velocity of the injected CO2 plume as well as the remaining mobile CO2 plume extent are estimated to determine how fast and far the plume propagates with time. Comparison of the results indicate that increasing the background flux velocity causes the plume to migrate longer distances up-dip, while it reduces the height distribution of the plume with time. This reduces the volume of mobile CO2 in the storage aquifer at larger velocities of background flux, hence decreasing the leakage risk of CO2 to the surface. In addition, the CO2 plume decelerates immediately after cessation of injection as its bottom rises vertically and the buoyancy force reduces as the thickness of the plume reduces. However, the plume then accelerates during the initial period of its subsequent lateral migration, as the plume becomes extended, and the buoyancy forces increases somewhat. The degree of lateral extension increases with increasing background water flow velocity, with the leading tip of the plume migrating faster than the trailing edge, until residual and dissolution trapping sufficiently reduce the volume of free phase CO2 that its migration is arrested.Document Type: Original articleCited as: Awag, M., Mackay, E., Ghanbari, A. The impact of background water flow on the early migration of a CO2 plume in a tilted aquifer during the post-injection period. Advances in Geo-Energy Research, 2023, 9(2): 125-135. https://doi.org/10.46690/ager.2023.08.0

The Effect of Aquifer/Caprock Interface on Geological Storage of CO2

AbstractThe migration of CO2 stored in deep saline aquifers depends on the morphology of the top of the aquifer. Topographical highs, such as anticlines, may trap CO2 and limit the distance migrated, or elevated ridges may provide pathways enabling CO2 to migrate further from the injector. For example, seismic data of the Utsira formation at the Sleipner storage site indicates that a branch of the CO2 plume is moving to the north [1]. It is therefore important to study the interface between the aquifer and the caprock when assessing risk as CO2 storage sites.Undulations in the top surface of an aquifer may either be caused by sedimentary structures [2], or by folding. In addition, irregularities may be generated by faulting [2]. Large-scale features are detected using seismic data (i.e. structures with amplitudes greater than 10 m), and such structures will generally be included in reservoir or aquifer models. However, smaller- scale features could also have an effect on a CO2 plume migration, and this is the topic of our study. We have conducted simulations in models with a range of top-surface morphology, and have examined the distance migrated and the amount of dissolution.The results from this study suggest that the effects of sub-seismic variations in the topography of the aquifer/caprock interface are unlikely to have a significant impact on the migration and dissolution of CO2 in a saline aquifer, compared with tilt or permeability anisotropy. The results were most sensitive to the kv/kh ratio during the injection period

Assessing interactions between multiple geological CO2 storage sites to optimize capacity in regionally extensive storage sandstones

The potential resource for carbon dioxide (CO2) storage in strata underlying the North Sea is mostly within brine-saturated sandstone formations which are each many hundreds to thousands of square kilometres in extent. The immense potential to store CO2 in these rocks can only be fully achieved by the operation of more than one injection site within each formation. A UK North Sea case study anticipates the operation of two injection sites in the Captain Sandstone and assesses any interaction between the injection sites. Technical investigations to optimize the storage capacity in a regionally extensive North Sea sandstone by the operation of more than one injection site within a storage formation [1] are summarised: geological modelling; geomechanical modelling; simulation of CO2 injection; monitoring planning. The UK case study includes the Goldeneye Field, the storage site investigated for the planned Peterhead CCS project. An injection scenario was examined that comprised an initial project storing within a depleted hydrocarbon field structure followed by a second injection site within the surrounding saline aquifer. The research investigations were targeted to identify and reduce any perceived concerns specific to the operation of two sites by a risk assessment-led process. Requirements for a monitoring plan specific to a multi-user storage formation, based on the prediction of storage site performance, were also developed. Generic learning applicable to any suitable multi-user storage sandstone was captured, from the process followed and the technical knowledge acquired, on the characterisation of extensive sandstone formations, management of the planned injection operations and monitoring plannin