Sammendrag
Worries are growing with the upsurge of GHG emissions and accumulation into our atmosphere where the chief producer of GHG is the combustion of fossil fuel for producing useful energy. Energy scientists, researchers and technologists have been working relentlessly to provide solutions to limit this frightening issue and have suggested numerous measures, including wind, solar and hydroelectric power to name a few, as alternative energy solutions. But this is not enough to decrease the impact of the already present GHGs that are becoming foremost influence to the global warming issue. A comparatively fresh and an innovative solution is the use of CCUS for mitigating these GHGs. Out of the three branches of this proposed solution, the one concerning petroleum engineers the most, is storage. The first storage project in an aquifer commenced in Norway in the Sleipner field in 1996 and since then this project has successfully managed to store amounts in Mega tonnes of CO2 into the geological formations. Many countries like USA, UK, Netherlands, China, and South Korea have shown a great curiosity in this field and have realized its significance in attaining the global net zero target of 2070.
Out of the three prominent options available for storage, depleted oil and gas reservoirs are one of them. In this thesis, which is a preparation of the work for alliance with ACT RETUN project, CO2 injection in a depleted gas reservoir is studied and sensitivity analysis of the impact of storage on reservoir, based on different reservoir heterogeneities, initial fluid properties, end point saturations of the relative permeability data, reservoir properties and characteristics, injection rates and aquifer support is performed. Key concepts related to the storage process and special considerations regarding it are presented initially which gives a greater insight of important reservoir engineering concepts revolving around, capacity injectivity, containment and monitoring of CO2 storage. The reservoir modelling and simulation was done using Eclipse 300 (a compositional simulator) and the Norne field model was used from open source (grid properties). The results of simulation revealed that reservoir heterogeneity impacted the storage efficiency slightly. The injection rates must be controlled to avoid fractures and leakages, having high initial reservoir temperature is not advisable for injection, having a lower initial water saturations is favorable for increased capacity, high critical gas saturation is needed for enhanced residual gas trapping and aquifer can be very useful for storage activities provided it is a strong one (having large aquifer volume).
Overall, this thesis opens up windows to explore on working with larger data sets and actual depleted gas models where even more comprehensive studies (like thermal runs, fault scenarios, monitoring wells etc.) can be performed using the knowledge gained and skills developed within this thesis.