Managing CO2 Phase Behaviour in Depleted Reservoirs

Abstract

Dealing with the phase behaviour management of Carbon Dioxide (CO2) in Carbon, Capture and Storage (CCS) (CCS) in depleted gas reservoirs generates technical challenges related to low temperatures. These challenges are not observed in Enhanced Oil Recovery (EOR) (EOR) or aquifer injection as these are normally carried out at pressures above hydrostatic. This paper shares some of the experience in selecting/developing solutions for depleted reservoirs (for reservoir pressures higher than 45bar). It describes the technical challenges related to uncontrolled injection of CO2 in depleted reservoirs and the requirement to manage the phase behaviour, then proposes different concept solutions for steady injection and highlights the selection process considering the different project conditions. Advantages and disadvantages and issues for the different concept solutions are presented with an emphasis on projects where the CO2 arrives cold. The paper gives an overview of the installation of simple and reliable long term solutions using the friction concept. It considers the applicability of the planned solution, its limitations and how to manage them. Very low temperatures along the well can be observed under uncontrolled phase behaviour injection of CO2 in depleted reservoirs. Simulation models and analysis of the well elements indicate the requirement to manage the CO2 phase behaviour to avoid integrity problems. Conceptual solutions like friction with relatively small tubing, downhole choke,, heatingheating are required to be considered early in the maturation phase by the projects. The selection process depends on project variables and project life limitations. The use of the friction concept has been favoured in different projects because of its long term reliability. The alternative of heating is variable and mainly influenced by injection bottomhole pressure. In general this incurs high expenditure. The downhole choke concept is promising but reliability needs to be improved and delta pressure across the choke needs to be increased. There are limitations to the operating envelope per well using the friction concept. However, a combination of multiple wells allows for managing the desired ranges of injection in the project. This paper also highlights the level of integration along the chain required for developing CCS in depleted reservoirs. This level of integration must not be neglected.