Abstract

The Sustainable Development Goals adopted by all United Nations Member States aim at promoting prosperity while protecting the planet. In this context, CO2 emissions reduction is becoming a strategic goal for many Companies and Carbon Capture and Storage (CCS) activity is quickly developing.

As underground CO2 storage can be achieved through the exploitation of aquifers or depleted hydrocarbon reservoirs, all possible synergies with existing wells and facilities are scouted. One of the main criticalities recognized during drilling and completion activities is related to the Joule-Thomson effect during the injection phase. A rapid depressurization of the string or the injection in highly depleted reservoirs can cause gas expansion and the consequent cooling of the entire system in both operational and critical conditions. In the latter case, temperatures can be as low as -70 degrees Celsius according to CO2 phase diagram. In this scenario, a thermal contraction due to the very low temperatures might lead to well integrity events.

Purpose of this experimental work is to set up a testing program consisting of numerical analysis and full-scale tests on gas-tight premium connections with a dedicated focus on performances in a sub-zero environment.

In the experiment, the sealing mechanism and structural integrity of a premium connection are investigated under mechanical and pressure loads before, during and after exposure to extreme low temperature. Effects of connection make-up torques combined with axial loads are also considered. The low-temperature testing protocol developed in this activity is an industry first, opening to a new perspective for the well design of CO2 injector wells in terms of load conditions and OCTG selection.

Introduction

Being Eni involved in an increasing number of CCS projects in the upcoming years, it was deemed necessary to study more in depth the CO2 effects on wellbore environment, with particular focus on the effects of the CO2 phase change in the well.

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