Permeability in Rotliegend gas sandstones to gas and brine as predicted from NMR, mercury injection and image analysis

Permeability characterisation of low permeability, clay-rich gas sandstones is part of production forecasting and reservoir management. The physically based Kozeny (1927) equation linking permeability with porosity and pore size is derived for a porous medium with a homogeneous pore size, whereas the pore sizes in tight sandstones can range from nm to μm. Nuclear magnetic resonance (NMR) transverse relaxation was used to estimate a pore size distribution for 63 samples of Rotliegend sandstone. The surface relaxation parameter required to relate NMR to pore size is estimated by combination of NMR and mercury injection data. To estimate which pores control permeability to gas, gas permeability was calculated for each pore size increment by using the Kozeny equation. Permeability to brine is modelled by assuming a bound water layer on the mineral pore interface. The measured brine permeabilities are lower than predicted based on bound water alone for these illite rich samples. Based on the fibrous textures of illite as visible in electron microscopy we speculate that these may contribute to a lower brine permeability

On the mechanism of backward erosion piping in a CSB

Backward erosion tests on vertically layered sand samples, as for example are present in a coarse sand barrier, result in failure patterns that are different from the ones found in tests using one homogeneous sand layer. In this paper, it is explored what are the underlying erosion mechanisms for vertically layered sands. It appears that there are at least 2 erosion mechanisms caused by the hydraulic gradients in the soil: instability of a sandy slope due to an outward directed gradient and high horizontal gradients due to flow line contraction. Both these mechanisms are present in different erosion conditions. This paper describes the mechanisms and quantifies them to some extent

Scénarios de ruptures complexes sur les digues

Levee breaches are often the result of a combination of mechanisms, which may happen simultaneously, and/or successively. These interactions are complex and difficult to anticipate in design and assessment as well as during a forensic analysis of an actual breach. The ISSMGE TC201 has published a report on the failure paths (that can also be called failure scenarios). It is available on the ISSMGE Onlline Library: https://www.issmge.org/online-library/reportsThe basis for this report is a compilation of case histories, and of failure paths used for assessment and design. Part A of the report provides an overview of the key concepts in this report and presents the proposed failure tree and overview of important aspects per event in the tree. The section finishes with a discussion and recommendations. Part B contains the collection of the contributed failure paths for case studies, these failure paths are illustrated in the framework. Part C contains the collection of contributed failure paths that are used for assessment and design. A glossary of key terms used is added at the end of the report