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 salt-bearing zones and is geographically close to present and future point sources of CO2 associated with fossil fuel development projects.

The characteristics of the Lotsberg Salt and overlying strata are presented in the context of the long-term fate 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 proposed procedure for the creation, testing, and filling of a salt cavern is presented. The critical factor is to achieve a reasonable long-term prediction of the behavior of the cavern during slow closure, coupled to the pressure and volume behavior of the gas within the cavern. This was achieved with a semi-analytical model which predicts long-term pressures and volume changes.

There are no technical obstacles or undue risks yet identified that would mitigate 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 gases (CO2, CH4 ⋅ ⋅ ⋅) are thought to be important factors in atmospheric warming through the "greenhouse effect ".i Although the debate continues to be heated and a full consensus remains elusive, increasing political pressure is being slowly brought to bear on the fossil fuel energy industry (responsible for ∼45% of anthropogenic CO2) to address emissions. This requires assessing options such as emission reduction, CO2 fixing in the biomass, and direct capture and sequestration of CO2. A great deal of discussion on the economic impacts of these options, society changes, and the responsibility of individual countries has taken place in the public and the scientific media, but these vital and contentious issues are set aside here so that the technological aspects of one of the geological sequestration optionsiiiii can be explored.

This article will address only the geological and technological factors in the possible use of salt solution caverns to permanently (>1000 years) store CO2. More specifically, we will examine a particular salt deposit in Alberta, the Lotsberg Salt, which is near to major present and future point sources of CO2.

Overview
Sequestration Options1

There are a number of options for permanent sequestration of greenhouse gases in geological media,iv and the realistic ones will be briefly reviewed. Large point sources of CO2 may be from 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. Landfills for municipal waste generate approximately equal parts of CO2 and CH4 through partially aerobic biodegradation.

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