Using a CCS Simulator to Maintain Liquid CO2 in the Completion

Depleted oil and gas fields may provide important locations for Carbon Capture and Storage (CCS). However, injection of carbon dioxide into pressure depleted oil and gas fields can be problematic due to the low reservoir pressure and the phase change behavior of carbon dioxide. The change of carbon dioxide from a liquid into a gas can trigger physical phenomena, such as significant cooling of the fluid as a result of the Joule-Thomson effect and the latent heat of vaporization, which can cause material embrittlement and loss of equipment functionality, and unstable or surging injection rates. Current mitigations restrict the quantity of carbon dioxide able to be injected by use of multiple injection tubing strings that can be costly or technically prohibitive. A more attractive alternative may be the use of downhole variable flow restricting devices which will autonomously respond to the changing well conditions, without the need for intervention or a workover in later well life. There is limited software currently available to model flow control to ensure carbon dioxide remains in liquid form in the completion. Through nodal analysis, the CCS simulator developed in this study can simulate the choking effect of downhole flow control devices placed at intervals in the completion that are sized and numbered to achieve the desired pressure distribution and CO2 injection rate. The modelling can then illustrate the required operating parameters of the downhole flow control solution with the results indicating the equivalent orifice sizes required for the flow control devices. The adjustable flow control devices can be removed or fully opened when the reservoir pressure increase and injection rate climbs and thus deemed to be no longer necessary. The use of downhole flow control devices can replace the need for a multiple string completion as the reservoir pressures and injection rates vary over the life of the well.