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Abstract

The paper is aimed to the assessment of the CO₂ underground storage potential of Lombardia Region (Italy), one of the most populated and industrialized area of the Country. The study is intended to locate adequate sites for the potential application of carbon capture and geologic storage in deep underground formations.

The first part of the study concerns the evaluation and analysis of the mass of CO₂ generated in Lombardia Region (the largest CO₂ producer in Italy, with over 70 million metric tonnes per year of CO₂ released in the atmosphere) by investigating both the localized sources (industry, power generation, etc.) and the diffused ones (transport, domestic heating, etc.). The second part of the study concerns the technical evaluation of the possibility to put into practice the geologic storage of CO₂ in deep underground formations of Lombardia Region. Finally, the study reports some preliminary evaluation for the possible implementation of a CO₂ storage pilot plant in the area. In particular, a potential candidate located in a deep saline aquifer has been identified, and its geological and hydrodynamic modelling has been extensively studied and analyzed. The investigated reservoir has a storage capacity of more than 370 million metric tonnes of CO₂, corresponding to about 30 years of CO₂ emissions produced by the main thermoelectric power plants located in the same area.

Introduction

CO₂ Capture and Storage (CCS) is a 3-step process including a) CO₂ capture from power plants, industrial sources, and natural gas wells with high CO₂ content; b) transportation (usually via pipelines) to the storage site; c) geological storage in deep saline aquifers, depleted oil or gas fields, unmineable coal seams, and enhanced oil or gas recovery (EOR or EGR) sites. It must be remembered that CO₂ can be utilized as well to produce fertilizers and other chemicals, for enhanced plant growth and as algae growth promoter, an interesting technique to capture CO₂ and transforming it into liquid fuel (as biodiesel) via biological and chemical processes. In combustion processes, CO₂ can be captured either in pre-combustion mode (by fossil fuel treatment) or in post-combustion mode (from flue gas or by oxyfuel).

Today, CO₂ concentration in the atmosphere has drastically increased from 280 ppm during the pre-industrial age to its current level of 380 ppm. It is proven that this is mainly due to the dramatic increase in the fossil fuel combustion. This has caused climate changes concerns among environmentalists and it is gaining more publicity as international agencies and governmental sectors in different countries are seriously considering CO₂ reduction policies. It should be mentioned that there is no direct proven evidence showing the relation between climate change and the CO₂ emissions. However, due to the greenhouse effect of CO₂ it is mainly suspected that a higher CO₂ concentration in the atmosphere has caused these climate changes. Fossil fuel power plants are responsible for one third of the total CO₂ emissions. Reducing CO₂ atmospheric concentrations by capturing emissions at the source and then storing them in subsurface reservoirs is thought by many scientists to be a reliable solution until emission-free energy sources are developed and viable.

As recalled above, the main options for geological CO₂ storage are saline formations, depleted or partially depleted oil and gas reservoirs, and deep unmineable coal seams. Here, CO₂ can be stored using a variety of different mechanisms (CO₂ as single phase in pore space, dissolved in water, absorbed on surfaces, trapped by relative permeability and fixed in minerals), with several options for underground storage. As reported in the “Stategic Deployment Document” of the European Technology Platform for Zero Emission Fossil Fuel Power Plants (ZEP, http://www.zero-emissionplatform.eu/website /docs/ETP%20ZEP/ZEP%20SDD%20-%20draft%2012.pdf, the relative order of magnitude potential of the various storage methods may be basically described as follows: 1000, deep saline aquifer storage (porous rocks); 100, oil and gas field use and storage; 10 deep unmineable coal bed use and storage; 1, mineral sequestration.