ABSTRACT. Availability study of an installation dedicated to CO2 capture, optimization of the design and of the injection strategy via Petri nets

Conference: ESREL 2023.
Session: Maritime and Offshore Technology III.
Time and place: September 4th, 17:15. Southampton, UK, 3-8 September. Room 16/1083 - Lecture Room C.

Abstract title: Availability study of an installation dedicated to CO2 capture, optimization of the design and of the injection strategy via Petri nets.
Authors: Céline Vinuesa, Maider EstÉcahandy and Nicolas Clavé.

In recent years, the fact that environmental constraints increases has prompted all sectors of industry to reduce their greenhouse gas emissions and limit the impact of their activities on the environment. TotalEnergies is one of the companies the most committed to reducing emissions, primarily through innovation in the field of CO2 capture and injection. The underlying idea is quite simple: converting disused gas production reservoirs into CO2 storage. Several projects in the North Sea have recently been launched. The main principle of the process is to transport liquid or gaseous CO2 to facilities located close to the sea, download, regas (partially) and compress the gas and then inject it under pressure into a storage reservoir via disused production wells.

The subject of the research presented in this paper is unique in many respects because both it is carried out jointly with other industrialists and the chemical composition of CO2 being very different from raw gas, many complex constraints must be considered to preserve the reservoir. Concerning the project under study, the CO2 injected comes from two different sources: in gaseous form (from compression) or in liquid form (transported by ship). Mixing these two types of CO2 results in a new composition that will be injected into disused production wells. However, since the nature of the reservoir does not allow to inject continuously, injectivity envelopes linked to CO2 composition, temperature and pressure in the wells must be taken into account.

Due to the fact that it is a new type of project, the main issues are profitability and, from technical point of view, the injection capacity of the wells. In order to address these two essential points, a production availability study was carried out based on a Petri net model. To achieve this, first, it was necessary to define the complex constraints applicable to injection in terms of reservoir pressure, molecular composition of the gas and temperature. Once this step was completed, we were able to start building the model using the software suite GRIF, a technology of TotalEnergies. The GRIF Petri module, which combines stochastic Petri nets with Assertions and Predicates, with Monte-Carlo Simulation, was used to model the behaviour of the installation. It was also used, via algorithms, to define the optimisation strategy for filling the injection wells according to their available envelopes. This modelling technique is applied for more than 30 years within TotalEnergies, but never before in a CO2 injection context. Petri nets can handle complex constraints and allow to obtain a wide range of results on the system under study and provide decision aid support.

This study validated the feasibility of such a project through a production availability model. It also helped the teams to compare different design options between them for several parts of the installation. For instance, it enabled them to optimise the sizing of the storage tanks and confirmed that it would still be possible to inject CO2 into the wells after their 15-year operating period.