Examination & interpretation of the seismic tomography data in respect to "up-lift" phenomena and stress-induced anisotropy

In recent years, global concerns about greenhouse gas emissions have stimulated considerable interest in carbon capture and storage (CCS) as a climate change mitigation option that can be used to reduce man-made CO2 emissions. This is achieved by separating and capturing CO2 from emission sources, then injecting and storing it in the subsurface. However, CCS requires the secure retention of CO2 in geological formations over thousands of years. To achieve this, there are two distinct purposes for undertaking monitoring at CO2 storage sites: (1) to ensure conformance by tracking the pressure buildup and CO2 inside the storage complex, thereby helping to indicate the long term security of the site (‘integrity monitoring’) and (2) to ensure containment by triggering timely control measures to mitigate any unexpected leakage, helping to demonstrate the current security situation, especially in the area surrounding the storage complex (‘assurance monitoring’) (Bourne et al. 2014). A significant issue for storage security is the geomechanical response of the reservoir. Concerns have been raised that geomechanical deformation induced by CO2 injection connected with pressure increase will create or reactivate fracture networks in the sealing caprocks, providing a pathway for CO2 leakage (Verdon et al. 2013). Several geochemical and geophysical (such as time-lapse seismic) techniques allow monitoring the regional distribution of CO2 in the storage complexes, seal integrity and the pressure evolution in response to the injection and therefore can be used to verify storage conformance and are valuable tools for integrity monitoring (IEA 2012). The most significant environmental risk associated with CCS technology is gradual leakage through undetected faults, fractures, or wells, or the potential problems caused by leakages due to injection well failure or leakages up through an abandoned well. In addition, other issues include the influence of a CO2 plume, reservoir pressure changes, and geomechanical changes in the multilayered subsurface with minor and major faults as migration paths. There are injection-induced stress, strain, deformations, and potential microseismic events resulting from changes in reservoir pressure and temperature and unwanted unelastic mechanical changes that might reduce sequestration efficiency and cause concerns in the local community

Concept description for the use of fibre-optic measurements for seismic tomography

High resolution mapping of CO2 plumes in the geological storage formations can be obtained using cross well seismic experiments designed to characterise velocity changes in the subsurface, see figure 1. High resolution studies are facilitated by using dense measurement surveys with many wireline operations that adjust seismic source and detector positions. Distributed fibre optic acoustic sensing may enhance traditional wireline cross wire surveys by providing an aliasing-free method for characterising seismic waveforms, and potentially enable a reduction in the number of individual measurements (and therefore cost) required for performing cost sensitive CO2 plume surveys. In addition, seismic tomography involving fibre optic receivers and ambient noise techniques, could enable permanent monitoring of subsea CO2 storage with seismic tomography. This document gives a basic concept description of cross-well seismic technology, both with active seismics and ambient noise, and their application with distributed fiber optics sensing. The document also describes the infrastructure for carrying out cross well/fibre optic measurements at Svelvik, and a proposal for a measurement campaign to be carried out as part of the DigiMon project.Concept description for the use of fibre-optic measurements for seismic tomographypublishedVersio

Cross hole seismic experiment with DAS/DTS data. Svelvik CO2 field lab

Primary purposes of the fieldwork at Svelvik include the provision of datasets which supports task 1.2 ‘determining the DAS transfer function’ and task 1.3 ‘develop DAS data processing techniques and workflow’. The fieldwork also serves as a test of the novel SV wave seismic source developed as part of Task 1.4. ‘Active source technology development and optimising monitoring design.Cross hole seismic experiment with DAS/DTS data. Svelvik CO2 field labpublishedVersio

Experimental evidence for Wigner's tunneling time

Tunneling of a particle through a potential barrier remains one of the most remarkable quantum phenomena. Owing to advances in laser technology, electric fields comparable to those electrons experience in atoms are readily generated and open opportunities to dynamically investigate the process of electron tunneling through the potential barrier formed by the superposition of both laser and atomic fields. Attosecond-time and angstrom-space resolution of the strong laser-field technique allow to address fundamental questions related to tunneling, which are still open and debated: Which time is spent under the barrier and what momentum is picked up by the particle in the meantime? In this combined experimental and theoretical study we demonstrate that for strong-field ionization the leading quantum mechanical Wigner treatment for the time resolved description of tunneling is valid. We achieve a high sensitivity on the tunneling barrier and unambiguously isolate its effects by performing a differential study of two systems with almost identical tunneling geometry. Moreover, working with a low frequency laser, we essentially limit the non-adiabaticity of the process as a major source of uncertainty. The agreement between experiment and theory implies two substantial corrections with respect to the widely employed quasiclassical treatment: In addition to a non-vanishing longitudinal momentum along the laser field-direction we provide clear evidence for a non-zero tunneling time delay. This addresses also the fundamental question how the transition occurs from the tunnel barrier to free space classical evolution of the ejected electron.Comment: 31 pages, 15 figures including appendi