(638b) Impacts of Realistic and Varying Rates of CO2 Injection on Safe CO2 Storage in the Bunter Sandstone of the Southern North Sea

Carbon capture and storage (CCS) has been recognized as a key technology to reduce CO₂ emissions and mitigate global climate change. Recently, CCS was included in several countriesâ?? emissions reduction target as part of the United Nations Framework Convention on Climate Change Paris agreement. In the UK, CCS will enable us to meet an 80% target reduction in CO₂ emissions from 1990 levels by 2050 as set by the Climate Change Act 2008.

In order to maximize the potential for CCS in any region, it is vital to develop a thorough understanding of a countryâ??s potential storage reservoirs and their dynamic behavior in response to CO₂ injection. This is particularly key as the pore volume of a reservoir does not equate in a simple way to storage capacity. This is because pressure constraints limit the rates of injection. This in turn has complex dependencies on reservoir geometry, and nature of connectivity and the bounding seals.

Carbon storage in the UK is recognized as an important transition technology for mitigating emissions of fossil fuel power plants while the capacity factor of renewable energy sources increase over time. For that reason, we investigate scenarios of gradual CCS deployment, with plants starting capture at different times and eventually shutting down progressively. Accordingly CO₂ capture rates and injection into storage reservoirs vary over time.

The Bunter Sandstone Saline Aquifer in the UK Southern North Sea is believed to provide one of the largest storage potentials for the UK. In this work we have simulated dynamic injection of CO₂ into the Bunter Sandstone â?? using a geological model and the commercial reservoir simulator Eclipse. The study assumes that the field has closed boundaries and contains 12 injection sites. We do not consider reservoir management techniques such as brine production. Limiting the bottomhole pressure at each injection site to 75% of the lithostatic pressure imposes a conservative constraint minimizing risk to fracturing of the sealing caprocks.

Four different geographical and market-based scenarios of the UKâ??s CCS deployment and CO₂ capture rates are fed to a pipeline network towards the Bunter Sandstone field. We have found that there may be a significant start up time delay before CO₂ injection can be achieved at the target rates provided by the plants. This is caused by limited early-time CO₂ injectivity which evolves as more CO₂ is injected into the reservoir. The effect is sensitive to reservoir permeability, depth of the injection site and the bottomhole pressure limit at the injection point. Our results show that limited CO₂ injectivity may persist for the first few years of injection and play a significant role in planning for large scale deployment of CO₂ storage.

The key outcome of this work is demonstrating the ability to use reservoir simulation to reflect prospective consequences and responses to realistic CCS deployment and reaction to CO₂ supply. Hence, the reservoir generates a feedback to the CO₂ transport network system - controlling the injection rates delivered to the storage site - the capture system - feeding into the network - and the market demand for fossil fuel products that in turn controls the CO₂ supply. Understanding this link between CO₂ supply and reservoir behavior allows us to inform decision makers on how best to develop CO₂ storage in line with capture and transport system deployment.