Surface electromagnetic (EM) methods were tested prior to CO2 injection at the PTRC Aquistore site at Estevan, Saskatchewan to determine their applicability to carbon sequestration monitoring. Magnetotelluric surveys in 2013, 2014 and 2015 resulted in successful definition of the pre-injection response and electrical resistivity model for the Williston Basin at Aquistore. These datasets define spatially uniform MT responses with a high level of repeatability. Controlled-source EM (CSEM) studies using a horizontal electric dipole transmitter have also been implemented at Aquistore. Preliminary analyses demonstrate that the CSEM experiment is well-designed, with measurable signal levels at all sites and a configuration that maximizes sensitivity to the sequestration reservoir. However, theoretical sensitivity modeling indicates that extremely large volumes of injected CO2 are required to produce measurable anomalies in the CSEM response. Greater sensitivity of both magnetotellurics and CSEM to the resistivity of shallower strata suggests these methodologies have superior application in leakage monitoring. / February 2017

Near surface measurements of seismic velocity and Q are useful in a number of situations, for example for when carrying out re-datuming and migration for depth images, or when analysing ground conditions for building. This thesis concentrates on the estimation of surface wave group and phase velocity as well as Q structure through the use of cross correlations of ambient noise recordings. Linearised tomography estimates are made for the British Isles, the Permain Basin of Texas and New Mexico, the Ekofisk Life of Field Seismic (LoFS) array and the Aquistore CO2 storage site. The results correspond well with the known geological structure and/or structure observed in velocity maps by other researchers. For the Ekofisk array a non-linearised non-linear method was also applied and the results estimated by these two methods for the Ekofisk LoFS array are compared. By non-linearised non-linear it is meant that the inversion method is fully non-linear and no linearisation has taken place in the method, this term will be used throughout this thesis for all methods which fall into this category. The tomography results from the two methods had similarities in their general structure but differences in the finer details, and so suggest that the substantial increase in time required for the non-linearised non-linear method is not justified. Linearised tomographic inversion of the Aquistore array was used to determine the potential of using ambient noise tomography for monitoring of CO2 storage sites. It was found that the repeatability of the tomography at the Aquistore site was not good enough to allow ambient noise tomography to be used for monitoring; however, it may be possible to apply the method at other sites. A Q and phase velocity inversion of the Ekofisk array is also presented, with results mostly showing excellent correlation with known geological features. It is shown that the higher frequencies are more sensitive to the effects of sea floor subsidence at the site, while lower frequencies are more sensitive to the effects of faulting. A final near surface method called ambient noise gradiometry was applied, this concentrates on estimating locations of sources of seismic energy within receiver arrays. Ambient noise gradiometry is applied to synthetic and real data for this purpose. It was found that using ambient noise gradiometry allows internal sources of energy to be identified but they produce a bias in the phase velocity tomography result. Two methods of reducing this bias are presented, both of which also provide an estimate of the source term for different sections of time of the recording.