The project "CO2Chalk" focuses on processes that may facilitate or endanger large-scale permanent storage of CO2 injected to enhance oil recovery in Norwegian oil producing chalk fields. It is already well known that dissolution of the chalk by CO2 charged water can increase reservoir compaction. New knowledge on chalk-fluid interaction and compaction shows that if the wrong CO2 injection strategy is used, the reservoirs will most likely collapse and all CO2 will leak out. Alternatively, development and proper application of this new fundamental knowledge could facilitate self healing of the chalk and ensure permanent storage of up to 400 Mton of CO2 in the Ekofisk oil field alone.
The main objective of the project was to develop new understanding of how chalk deforms during oil recovery and injection of fluids. To achieve this our objectives were to develop new micro-scale experimental and computational techniques to explore chalk deformation.
The project "CO2Chalk" has contributed with numerical simulation techniques, experimental techniques, new results using these techniques and a reservoir scale model building on this new knowledge. Our new, fundamental understanding of the deformation processes will allow us to predict with more certainty the outcome of different CO2 injection strategies.
Figure. Interplay between experimental and numerical simulation (peridynamic) studies of fracturing and creep of chalk has given novel insight that is the basis of a statistical model of chalk compaction that has been upscaled to predict reservoir behaviour.
The main achievements were:
- Experiments reveal sensitivity of calcite and chalk to fluid composition changes (no big surprises).
- New numerical simulation technique developed to compute failure under compression using real 3D X-ray tomography volumes of chalk: A tool to test "virtual chalk" in the future.
- Experiments performed to benchmark numerical simulations
- Numerical simulations support basic assumptions of upscaling, predictive model of chalk reservoir compaction
- Upscaling model predict Ekofisk compaction and sensitivity to fluid pressure and composition
- Final conclusion (in progress): CO2 + water injection will only weaken chalk reservoir slightly more than pure water does. Fluid pressure in reservoir is critical to avoid compaction and CO2 leakage.
These results have mainly been the result of the project 224907EOR and the EU FP7 MC ITN project FlowTrans (Grant number 316889). Collaboration with the IOR centre at UiS, Iris, the University of Copenhagen, MAXIV & ESS InterReg and the EU H2020 MSC ITN project NanoHeal (grant number 642976) has also been important. Since these collaborations have afforded us additional training and networking the resources granted to the existing project (224907EOR) have been focused on the PhD students and the necessary infrastructure for their research. This has led to a very efficient use of the resources available. We expect 4-5 more scientific papers to be published in 2017.
The computational and experimental tools developed and the large scale model of chalk deformation are very different from the tools and models currently used by the oil companies operating in chalk reservoirs. The tools and models from this project can contribute to new, fundamental understanding of the deformation processes and will allow us to predict with more certainty the outcome of different possible CO2 injection strategies.
Assuming that oil companies operating in chalk reservoirs in the North Sea will some day be willing to consider CO2 EOR and CO2 storage the tools and models developed here may have significant impact. The oil companies will probably not implement these models as is because they trust their own reservoir simulators. However, their reservoir models have been fitted to their existing exploitation regime and have low predictive power outside this regime.
The insights and models developed in this project will be most effective if included in interpretation of core scale analysis, for example at UiS/the IOR centre leading to tools at a higher technology readiness level that may be accepted by the industry. We have participated in many conferences and workshops and published articles in high quality journals to disseminate our new insights. A large number of popular science lectures on our project have been held as well
Fact sheet 224907- CO2 for enhanced oil recovery in North sea chalk oil field – can CO2 be permanently stored?