In situ assessment of the stone conservation state by its water absorbing behaviour : a hands-on methodology

This paper describes the use of the water absorbing behaviour (WAB) for assessment of the conservation state of stone in situ. A test methodology, consisting of a combination of techniques for in situ measurement of the WAB, was applied in a case study on Lede stone, a sandy limestone, used in a medieval facade in Ghent, Belgium. The methods used were the contact sponge method (CSM), the Karsten tube (KT) and the droplet method (DM). Additionally, the residual hardness of the stone was measured by Schmidt hammer (SH). After careful selection of representative measuring points, a qualitative analysis of the stone’s condition could be made, based on its WAB, residual hardness, reference data from laboratory experiments and thorough visual observations. From this analysis it could be concluded that CSM, KT and SH generated coherent and compatible results; that DM could indicate superficial alterations which were not necessarily representative for the subsuperficial WAB and that this methodology could give an insight on the conservation state, beyond visual observations, when combined with reference data

Dynamic micro-CT analysis of fracture formation in rock specimens subjected to multi-phase fluid flow

In this study, fracture formation in rocks is being studied at the pore-scale through the combination of high-resolution X-ray CT scanning with custom-made add-on modules. The Deben CT5000 system, an in-situ load cell, was used at the scanners at the Centre for X-ray Tomography at Ghent University (UGCT), providing information on mechanical properties of the tested rocks. Micro-CT scans made at the High Energy CT system Optimised for Research (HECTOR) allowed the visualisation of the fracturesk and their formation as well as the analysis of porosity changes in the material, related to the changes in stress

Pore-scale characterization and modelling of CO2 flow in tight sandstones using X-ray micro-CT; Knorringfjellet formation of the Longyearbyen CO2 lab, Svalbard

Rocks of the Knorringfjellet Formation in Central Spitsbergen form a potential storage reservoir for CO2 below Longyearbyen. They are characterised by a moderate porosity and low permeability. However, water injection tests have shown positive results and fractures are considered to facilitate fluid flow. Therefore, hard data on fracture parameters and pore characteristics schould be analysed to better understand flow characteristics. Consequently, sandstone and conglomerate samples from the Knorringfjellet Formation were sampled and characterised with High Resolution X-ray Computed Tomography (HRXCT) at the Centre for X-ray Tomography at Ghent University, Belgium (UGCT). The dataset includes samples taken from drillholes in the vicinity of Longyearbyen, drilled during the pilot phase at the Longyearbyen CO2 project, as well as from the Knorringfjellet Formation outcrops at Konusdalen and Criocerasdalen. This was done in order to compare micro-fracture and pore parameters in both settings. With HRXCT, the samples were analysed at pore scale and quantitative information of the pore network and fractures were extracted. Pore networks were used for the modelling of CO2 flow in specific samples and information on fracture aperture was obtained at a micrometre scale. The acquired dataset can be directly used for a better understanding of flow in the aquifer