Sensitivity Study on Well Tubing Selection for CO2 Injection in the Morecambe Net Zero Project

Abstract Spirit Energy operates carbon storage licence CS010 covering the South Morecambe and North Morecambe depleted gas fields, which have a combined theoretical CO2 storage capacity of 1 GT. In order to support pre-FEED studies, Spirit Energy have used PETEX Prosper modelling to evaluate well tubing size designs for a range of CO2 injection scenarios into the South Morecambe reservoir. The study assessed sensitivities in steady-state conditions for well completion design and operating parameters for stable CO2 injection. CO2 injection well models were evaluated for 9⅝-inch and 7-inch tubing configurations against erosional velocity limits. Lower wellhead pressures in early time result in higher in-situ tubing velocities due to gas expansion, and injection rates can be increased as reservoir pressure rises. Development concepts for wells with 7-inch and 9⅝-inch tubing were modelled to understand potential well rates, multi-phase flow and erosional velocity constraints. The modelling showed that for gas phase injection at higher mass flow rates, well designs with 9⅝-inch monobore should be considered for highest injection rates. Other well designs considered for the development include 7-inch monobore or 9⅝-inch with a 7-inch SSSV. Surface modelling shows that at no point does the CO2 fluid enter the liquid phase during steady-state flow. As reservoir pressure increases, the CO2 transitions to a dense phase, resulting in very high bottom-hole pressure. This could allow for a higher injection rate, but the injectivity performance under these conditions requires further study. No 9⅝-inch Subsurface Safety Valve (SSSV) has been qualified for use in a CO2 injection well. Further testing and design modifications may be required to meet industry standards for CO2-resistant SSSVs of this size before conclusion of the selection of completion design for the MNZ project. Flow assurance modelling in both steady-state and transient flow conditions is essential for the project. Further project optimisation and design will be achieved by well modelling as part of Spirit Energy's ongoing work programme.