To constrain the increase in atmospheric carbon dioxide (CO2) concentrations, there are European and national drives to develop carbon capture and storage (CCS) schemes for the permanent geological storage of CO2 from industrial sources in deeply buried strata. Currently, offshore sites are considered preferable to geological store in strata onshore. Although the target storage reservoirs, saline aquifers or former hydrocarbon fields are often at depths of 1km or more, knowledge of the shallow area is important. This is not only for the positioning of infrastructure, wells, pipelines, etc., but also in the monitoring of any potential leakage from the reservoir over the site's lifetime, which may span 25–50 years. Baseline and repeat surveys are necessary and may need to cover a considerably wider area than the expected plume extent in the reservoir, depending on the predicted gas leakage pathways. Hence a complete geological model is required from the proposed reservoir at a depth that is up to and includes the seabed.

1. Introduction

It is a recognised concern that carbon dioxide (CO2) concentrations are increasing both in the atmosphere and the oceans, and that there are consequent adverse effects on the climate (Intergovernmental Panel on Climate Change (IPCC), 2007). The rising CO2 concentrations are raising global temperatures because of their greenhouse gas effect, as well as increasing acidity in the world's oceans. Targets for reducing national emissions of greenhouse gases to the atmosphere have been set by legislation within the UK by the Climate Change Act 2008 and the Climate Change (Scotland) Act 2009. Plans to achieve the targets include greater efficiency in the use of electricity, decreased electricity use and implementation of low-carbon technologies for power generation, such as generation of electricity from renewable resources (wind, wave, solar, nuclear powered and hydro-electrical generation schemes).

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