Abstract

The reduction of Greenhouse Gases emission is a growing concern of many industries. Following the mitigation solutions recommended by the Kyoto Protocol, underground sequestration of CO2 is a way to meet this goal, as oil and gas fields offer huge CO2 storage capacities, while preserving the environment.

The oil and gas industry has a long commercial practice of gas injection: EOR, natural gas storage. Using a depleted oil or gas reservoir for CO2 storage has several interesting advantages among which the relatively large pressure range available for injection, allowing the storage of significant gas quantities for a low compression power, without altering the cap-rock integrity. Besides, the availability of reservoir dynamical and geological characterization and existing production/injection wells contributes to the optimization of the project, both technically and economically.

This CO2 storage can be permanent in the case of mineral trapping or very long term (several thousand years) in the case of hydrodynamic trapping. The long-term risk analysis of the CO2 behavior and its impact on the environment is a key objective of the project. That is why the selection of an appropriate reservoir is crucial to the success of the sequestration.

Two major steps have been identified while sequestering CO2. The injected CO2 dissolves and diffuses in oil and water and follows the pressure gradient (hydrodynamic trapping). Then, the dissolved CO2 reacts with the minerals within the formation and induces dissolution/precipitation reactions (mineral trapping), that may impair the well injectivity and/or the cap-rock sealing properties.

For the first time, this study investigates both sides using reservoir simulator with improved CO2 thermodynamics (ATHOS) and reactive transport simulator (DIAPHORE) to evaluate the extend of mineral trapping (kinetically controlled reaction) and long term behavior of CO2 within the reservoir and its neighboring geological formations (cap rock, aquifer).

This work is funded by Institut Français du Pétrole (IFP), Geostock, TotalFinaElf and sponsored by the French Ministry of Industry (FSH).

Introduction

The Kyoto Protocol1 of the United Nations Framework Convention on Climate change calls for Annex I Parties (developed countries) to reduce emissions of greenhouse gases (GHG) by an average of 5.2% below the 1990 levels by 2008 to 2012. Non-Annex I Parties (developing countries) have no new obligations to reduce greenhouse gases. In addition to these reduction objectives, the Kyoto Protocol outlines a set of mechanisms to support sustainable development, technology transfer and capacity building objectives of the United Nations Framework Convention on Climate Change. These mechanisms are collectively known as the Kyoto Mechanisms.

Under the Kyoto Protocol, a key issue is the capture and storage of CO2. Underground CO2 storage in depleted oil or gas reservoirs offers interesting and eventually permanent long-term environmentally safe possibilities. The long-term risk analysis of the CO2 behavior and its impact on the environment is a key objective of the project initiated by Institut Français du Pétrole (IFP) with TotalFinaElf and Geostock with the financial support of the French Ministry of Industry (FSH). In this research project, underground CO2 sequestration focuses on oil and gas reservoirs either depleted or in production in order to optimize the economy of the oil recovery and CO2 sequestration trapping at the end of field life.

Capture and deposition of CO2.

Technologies for capture and storage of CO2 exist already today. However, they are neither developed nor optimized for these purposes and they are expensive. A huge development effort has been initiated in many countries to capture and store CO2.. It has been described and summarized extensively within the IEA Greenhouse Gas Programme3.

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