Publication

Hydro-mechanical characterization of gas shales and Opalinus Clay shale in partially saturated conditions

Alberto Minardi
2018
EPFL thesis
Abstract

An experimental study on the behaviour of shales in partially water saturated conditions is presented in this thesis. The Opalinus Clay shale and gas shales from different unconventional reservoirs have been studied. Opalinus Clay is currently considered as a host rock for the disposal of radioactive waste in Switzerland; the importance of partial saturation is fundamental in predicting the short-term behaviour of the host rock during the excavation-resaturation phases, and the long-term behaviour during the propagation of gas generated by the waste. Shale gas reservoirs are partially saturated in their in-situ state due to the simultaneous presence of gas and liquids; these hydraulic conditions influence the mechanical behaviour during the drilling, fracturing, and extraction stages. The analysis of the geomaterials' behaviour considering partial saturation is a well-established practice in Soil Mechanics. However, in the case of shales several challenges arise. These challenges are mainly related to their features, which make most of the experimental and theoretical frameworks adopted for soils not suitable for providing a comprehensive understanding of the behaviour of shales. The aim of this thesis is to improve upon the existing understanding of the behaviour of partially saturated gas shales and the Opalinus Clay shale and to provide a quantitative assessment of the impact of such conditions on their mechanical behaviour. A key part of this work is dedicated to the establishment of experimental methodologies and testing protocols to highlight the most important features of the response of the tested materials under partially saturated conditions. The high water retention capacity of shales necessitates the use of the vapour equilibrium technique; this experimental technique allows for the imposition of wetting/drying processes on the tested materials and introduces suction as a key parameter when performing the hydro-mechanical characterization in partially saturated conditions. Three different testing set-ups have been developed to investigate the hydro-mechanical response of the tested shales. The obtained experimental results demonstrate that the considering of partial saturation is fundamental for a reliable and comprehensive hydro-mechanical characterization of the tested shales; despite the different origins of these materials, the main outcomes show a very similar impact of wetting and drying processes on the volumetric response and the mechanical properties. The volumetric response observed in the tests performed in free stress conditions is characterized by significant anisotropy and irreversibility. However, when a mechanical stress is applied to simulate in-situ conditions, a less pronounced volumetric response is systematically observed. The elastic response is also highly dependent on the hydraulic state of the tested materials; in particular, significant reductions (up to 50%) of Young's modulus and compressive strength are observed during wetting processes. Gas injection is also studied in the Opalinus Clay to better understand the dominant flow mechanisms and to assess the possible impact of partial saturation on the movement of gas in the host rock. Experimental results obtained with a testing device specifically developed for this purpose indicate the impact of gas injection on the deformation state of the material; this aspect clearly highlights the involved hydro-mechanical coupling.

About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related concepts (41)
Shale gas
Shale gas is an unconventional natural gas that is found trapped within shale formations. Since the 1990s a combination of horizontal drilling and hydraulic fracturing has made large volumes of shale gas more economical to produce, and some analysts expect that shale gas will greatly expand worldwide energy supply. Shale gas has become an increasingly important source of natural gas in the United States since the start of this century, and interest has spread to potential gas shales in the rest of the world.
Strength of materials
The field of strength of materials (also called mechanics of materials) typically refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the response of a structure under loading and its susceptibility to various failure modes takes into account the properties of the materials such as its yield strength, ultimate strength, Young's modulus, and Poisson's ratio.
Oil shale
Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitutes inorganic substance and bitumens. Based on their deposition environment, oil shales are classified as marine, lacustrine and terrestrial oil shales. Oil shales differ from oil-bearing shales, shale deposits that contain petroleum (tight oil) that is sometimes produced from drilled wells.
Show more
Related publications (113)

Insights from an extensive triaxial testing campaign on a shale for comparative site characterization of a deep geological repository

Lyesse Laloui, Alessio Ferrari, Eleonora Crisci

Several boreholes were drilled for site comparison of a deep geological repository (DGR) in Northern Switzerland. The main target of the exploration program was the >100m thick Opalinus Clay, the designated host rock encountered at approximately 450 to 100 ...
Amsterdam2024

Computational Homogenization for Inverse Design of Surface-based Inflatables

Mark Pauly, Florin Isvoranu, Francis Julian Panetta, Uday Kusupati, Seiichi Eduardo Suzuki Erazo, Yingying Ren

Surface-based inflatables are composed of two thin layers of nearly inextensible sheet material joined together along carefully selected fusing curves. During inflation, pressure forces separate the two sheets to maximize the enclosed volume. The fusing c ...
2024

Mesh d-refinement​ An efficient data-driven computational framework

Jean-François Molinari, Antonio Joaquin Garcia Suarez, Sacha Zenon Wattel

Model-free data-driven computational mechanics (DDCM) is a new paradigm for simulations in solid mechanics. As in traditional approaches, the boundary-value problem is formulated with physics-based PDEs, such as the balance of momentum and compatibility eq ...
2023
Show more
Related MOOCs (15)
Sorption and transport in cementitious materials
Learn how to study and improve the durability of cementitious materials.
Cement Chemistry and Sustainable Cementitious Materials
Learn the basics of cement chemistry and laboratory best practices for assessment of its key properties.
The Art of Structures I - Cables and arcs
Ce cours présente les principes du fonctionnement, du dimensionnement et de la conception des structures. L'approche est basée sur une utilisation de la statique graphique et traite en particulier des
Show more

Graph Chatbot

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.