Paper: Sable Unit Automatic CO2 Injection System

The automation system was designed to provide accurate measurement and control of the CO2 injection process and to provide communications between the wells and a central terminal unit. The central terminal unit was to make automatic scans of the field and generate alarm/alert reports in the event of a malfunction at a well. In addition, the central terminal unit would provide historical
reports of injection volumes, rates and pressures from all wells. The planned injection pressure was between 1600 and 1700 psig and the expected temperature was between 40 and 70 degrees F. Under these conditions, the CO2 is in the critical phase. In this phase, the density and therefore the flow rate are sensitive to changes in temperature and pressure. It was determined that, in order to obtain accurate measurement, it would be necessary to compensate the flow equation for specific gravity based on process temperature and pressure and on composition of the CO2 injection stream.