CO2 Joule-Thomson effect: Application on premium connections for CCS well

Abstract

CCS (Carbon Capture and Storage) is a major technology aiming to reduce greenhouse gases and reduce carbon footprint. In these applications, Oil Country Tubular Goods (OCTG) and associated premium connections are used to inject industrial CO2 into stable geological formations such as depleted oil and gas fields or saline aquifers, in liquid or dense phase to permanently store it. While current standards (API RP 5C5, ISO 13,679) allow qualification of premium connections for Oil & Gas application, no standard exists for CCS applications. In that frame, a new test methodology was developed to evaluate the impact of Joule-Thomson effect on premium connection, in the scenario of a CO2 blow-out and intermittent operation of the injection wells, such as shut-in of the subsurface safety valve (SSSV) or injection phase. To confirm that premium connections remain tight and safe after being exposed to a rapid depressurization of CO2, they have been physically tested in a horizontal load frame. The test consisted in the filling of the sample with CO2 up to a minimum of 100 bar and a temperature below 30 °C to ensure liquid state, or above 32 °C to ensure supercritical state inside the sample, and then depressurizing the sample through an orifice of 2 or 4 mm until complete drop of pressure. Minimum measured temperature on outer pipe wall reached around -50 °C before dry ice CO2 formation. Maximum measured gradient of temperature observed was around 70 °C. No leakage nor connection damages were observed during the pressure release sequences. Sealability was then confirmed during the internal pressure and external pressure test performed afterwards.