Geological Carbon Storage

Subsurface Seals and Caprock Integrity

Stéphanie Vialle, Jonathan Ajo-Franklin, J. William Carey, Stéphanie Vialle, Jonathan Ajo-Franklin, J. William Carey

• Publisher: American Geophysical Union
• Year: 2018
• ISBN:
  9781119118671
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Geological Carbon Storage Subsurface Seals and Caprock Integrity

Seals and caprocks are an essential component of subsurface hydrogeological systems, guiding the movement and entrapment of hydrocarbon and other fluids. Geological Carbon Storage: Subsurface Seals and Caprock Integrity offers a survey of the wealth of recent scientific work on caprock integrity with a focus on the geological controls of permanent and safe carbon dioxide storage, and the commercial deployment of geological carbon storage.

Volume highlights include:

• Low-permeability rock characterization from the pore scale to the core scale
• Flow and transport properties of low-permeability rocks
• Fundamentals of fracture generation, self-healing, and permeability
• Coupled geochemical, transport and geomechanical processes in caprock
• Analysis of caprock behavior from natural analogues
• Geochemical and geophysical monitoring techniques of caprock failure and integrity
• Potential environmental impacts of carbon dioxide migration on groundwater resources
• Carbon dioxide leakage mitigation and remediation techniques

Geological Carbon Storage: Subsurface Seals and Caprock Integrity is an invaluable resource for geoscientists from academic and research institutions with interests in energy and environment-related problems, as well as professionals in the field.

Part I
Caprock Characterization

1
Microstructural, Geomechanical, and Petrophysical Characterization of Shale Caprocks

David N. Dewhurst, Claudio Delle Piane, Lionel Esteban, Joel Sarout, Matthew Josh, Marina Pervukhina, and M. Ben Clennell

CSIRO Energy, Perth, Australia

ABSTRACT

Geological storage of carbon dioxide requires extensive characterization of potential selected sites in terms of injectivity, storage capacity, and containment integrity. The latter item on that list requires a multi‐scale evaluation of all aspects of the subsurface geology that can trap CO₂ underground and keep it there long term. One part of a containment integrity strategy includes characterization of the caprock at a given site. Many selected sites have clay‐rich shales as caprocks, and this contribution will concentrate on workflows and methods for characterizing such rocks in the laboratory. Shale preservation is the most critical step in the process as dehydration from the native in situ water content significantly affects shale properties. Various mineralogical, microscopical, petrophysical, and geomechanical properties and associated testing methods are discussed, and where possible, examples are shown of the impact of lack of preservation. Results are discussed in the context of interaction of CO₂ with caprocks and trapping mechanisms. Finally, the discussion looks at a number of the uncertainties associated with laboratory testing of shales in terms of both results obtained to date and our limited understanding as yet of the behavior and interaction of supercritical CO₂ with clay‐rich caprocks.

1.1. INTRODUCTION

Geological storage of carbon dioxide (CO₂) has been mooted as a greenhouse gas mitigation strategy for over 20 years. The practical mechanics of such a strategy have been tested out at small scale at sites such as the Otway Basin in Australia [Sharma et al., 2009] and Frio in Texas [Doughty et al., 2008] and during industrial‐scale projects, for example, at Sleipner [Arts et al., 2008] and In Salah [Ringrose et al., 2013]. Many years of effort have been put into defining the critical parameters for potential CO₂ storage sites [e.g., IPCC, 2005], and these include depth, storage capacity of the site, injectivity of the reservoir, and the containment integrity of the structure into which the CO₂ is injected. Containment integrity is usually thought of in similar terms as traps and seals in petroleum systems, and similar technologies can be used to evaluate the properties of the fault and/or top seals that provide the trapping mechanisms for keeping injected CO₂ in the deep subsurface. Fault seals usually result from the incorporation of material into the fault zone during fault movement, and this can comprise smearing out of ductile clay‐rich units, abrasion of harder shales, cataclasis of rigid grains, and syn‐/post‐kinematic cementation of the fault rock products [e.g., Lindsay et al., 1993; Yielding et al., 1997; Fisher and Knipe, 1998; Dewhurst et al., 2005]. Top seals are usually characterized in terms of their thickness (especially in relation to fault throw), areal extent, seal capacity (pore‐scale capillary properties), and seal integrity (mechanical properties). There are multiple techniques for assessing the potential sealing capacity of faults [e.g., Watts, 1987; Lindsay et al., 1993; Yielding et al., 1997], and these will not be discussed further here. This paper will concentrate on methods that can be used to characterize caprocks in the laboratory and the relationship between these measurement techniques and the properties noted above. In this contribution, we will concentrate on shale‐rich caprocks but acknowledge that other rocks such as anhydrites [e.g., Hangx et al., 2010] are being evaluated as caprocks for CO₂ storage sites. However, it should be emphasized that any seal evaluation for a storage site or petroleum prospect should be fully integrated across both fault and top seals and for a wide range of scales.

Shale caprock properties are dependent on a number of factors, including depositional environment and resultant lithology, electrochemical conditions at deposition, mineralogy, the presence of organic matter, compaction, and diagenetic alteration. All of these processes have a significant impact on porosity and permeability, as well as the mechanical, capillary, and petrophysical properties of shales [e.g., Bennett et al., 1991a,b; Vernik and Liu, 1997; Dewhurst et al., 1998, 1999a, 1999b; Clennell et al., 2006]. A number of these properties are also controlled by human intervention during and after the coring process, such as stress relief microfracture development and drying out and desiccation of recovered core, and care must be taken for certain properties that adequate sample preservation is undertaken [e.g., Schmitt et al., 1994; Dewhurst et al., 2012; Ewy, 2015]. This study will therefore review possible preservation methods and discuss multiple mechanical and petrophysical characterization techniques that can be used to either directly measure or estimate relevant properties required for shale caprocks.

1.2. SHALE PRESERVATION

The most critical stage for deriving high‐quality laboratory results from shales is their immediate preservation on recovery. Loss of pore water from the in situ state can result in changing mechanical, physical, and petrophysical properties [Schmitt et al., 1994] no matter whether the shale i...

Table of contents

• Cover
• Table of Contents
• PREFACE
• Part I: Caprock Characterization
• Part II: Fracture Generation, Permeability, and Geochemical Reactions in Damaged Shale
• Part III: Monitoring Caprock Failure
• Part IV: Environmental Impacts and Remediation Techniques
• INDEX
• End User License Agreement