Sequestration of CO2 in Salt Caverns

Abstract

Abstract Permanent storage of CO2 in dissolved salt caverns is one of the geological options for reducing anthropogenic greenhouse gas emissions into the atmosphere. Alberta is singularly well endowed with suitable salt deposits. Of these, the Lotsberg Salt of east central Alberta is the best of the three major saltbearing zones, and is geographically close to present and future sources of CO2 associated with fossil fuel development projects in Alberta. The characteristics of the Lotsberg Salt and overlying strata are presented in the context of the long-term future of stored CO2. There are a number of features that indicate a high level of security against leakage and migration of gas back to the biosphere. A procedure for the creation, testing, and filling of a salt cavern is presented. A critical requirement was to achieve a reasonable long-term prediction of the behaviour of the cavern during slow closure, while taking into account the pressure and volume behaviour of the gas within the cavern. This was achieved with a semi-analytical model that predicts long-term pressures and volume changes. There appear to be no technical obstacles or undue risks identified that would militate against the use of salt caverns for permanent CO2 sequestration. It is an option that can be seriously considered in Alberta, or in other geographical locations where the geological conditions are suitable. Introduction Anthropogenic and naturally-generated greenhouse gases (CO2, CH4,...) are thought to be important factors in atmospheric warming, known as the greenhouse effect(1). Although the debate continues to be heated and a full consensus remains elusive, increasing political pressure is being placed on the fossil fuel energy industry (responsible for ~45% of anthropogenic CO2) to address atmospheric emissions. This requires assessing options such as energy conservation and switching to non-fossil fuels for energy production, emissions reduction, CO2 fixing in biomass, and direct CO2 capture and sequestration. A great deal of discussion on the economic impacts of these options, sociological changes, and the responsibility of individual countries has taken place in the public and the scientific media. These vital and contentious issues are set aside here so that the technological aspects of one of the geological sequestration options(2, 3) can be explored. This article will address only the geological and technological factors in the potential use of salt solution caverns to permanently (>1,000 years) store CO2. More specifically, we will examine a particular salt deposit in Alberta, the Lotsberg Salt, which is near to present and future major stationary point sources of CO2 from heavy oil and oil sands development. Overview Sequestration Options(a) There are a number of options for permanent sequestration of greenhouse gases in geological media(4), and the realistic ones will be briefly reviewed. Large point sources of CO2 may arise during energy generation (coal-, oil-, or gas-fired power plants), from natural gas processing facilities that remove CO2 from produced gas, from cement kilns, oil refineries and steam generation facilities, and from other manufacturing processes where large amounts of energy are consumed.