Well Integrity Assessment and Assurance: The Operational Approach for Three CO2 Storage Fields in Italy

Abstract

In 2004 Eni E&P launched the "GHG (GreenHouse Gases) Project?? to develop technologies and select fields suitable for geological sequestration of CO₂.

For the well area, such project has implied:

• Well Integrity Assessment - Verify and (if necessary) reinstate the structural integrity of the existing wells.
• Well Integrity Assurance - Establish the technical requirements to ensure the integrity of new CO₂ injection wells.

Well Integrity Assessment has been carried out by developing and implementing an operational methodology for three Italian fields: Cortemaggiore, PACS (Palino-Ascoli-Candela-Satriano) and Giaurone-Armatella-Gela. Such methodology includes the comparison between the Sustained Casing Pressures (SCP's) measured in the annuli and the relevant Maximum Allowable Pressures (MAP's) to estimate how much each well is close to lose its safety conditions. Then, the methodology foresees specific investigations for the critical wells to identify the magnitude and possible causes of the SCP's occurrence. Finally, it includes the preparation of suitable remedial and/or monitoring plans.

Stress Analysis studies supported the above activities by calculating the mechanical resistance, under the planned operational conditions, of production casings and tubings of the CO₂ injection wells.

As far as Well Integrity Assurance, technical requirements for new CO₂ injection wells have been established based on the project for the well Cortemaggiore 157 Dir, constructed to carry out the pilot test for the injection of CO₂ in a depleted level of the Cortemaggiore field.

Specific studies have been carried out for the PACS and Giaurone-Armatella-Gela fields. The former is a gas field with high CO₂ content: CO₂ will be separated and re-injected; the latter is an oil field: CO₂ injection will be used as an effective means for enhancing oil recovery.

This paper describes the operational approach followed for the above mentioned activities and the main requirements for the new CO₂ injection well.

Introduction

What we usually refer to as the "problem of the greenhouse effect?? is actually a natural process which has been always present on Earth and is essential for life. Small natural concentrations of greenhouse gases in the atmosphere contribute to regulate the temperature of Earth, which would otherwise be an average of 30°C lower than it currently is.

After water vapour, the main greenhouse gases are carbon dioxide, methane and ozone, which:

• Filter radiations coming from the Sun, thus avoiding the most dangerous ones to reach the Earth's surface.
• Absorb and re-emit back to Earth radiations within the thermal infrared range, thereby trapping heat before it is lost to space, and consequently acting as a giant greenhouse.

The greenhouse effect has started becoming a problem since concentrations of such gases (mainly carbon dioxide, CO₂) became excessive due to human activities, which have been distorting and accelerating the natural process: the higher the concentration of greenhouse gases in the atmosphere, the more heat is being reflected back to Earth.