Core Research Projects: Storage & transport, B1 – Pressure propagation and control

Why is this research needed?

For the storage potential of the UK North Sea to be realised, CO₂ will have to be stored over a range of reservoir types, from older lithified and less permeable rocks to much younger more permeable sites^[1].

Injecting CO₂ into the subsurface will cause a temporary increase in the pressure of fluids trapped within the rocks. Understanding how this pressure wave travels through the rocks and the possible effects of increasing pressure in the subsurface are important to ensure the safe containment of the CO₂.

^[1] Noy D.J., Holloway S., Chadwick R.A., Williams J.D.O, Hannis S.A. & Lahann R. 2012. Int. J. Greenh. Gas Control, 9, 220-233

What is this research investigating?

To improve our ability to predict the volume of CO₂ which can be stored, we are modelling the propagation of pressure throughout the reservoir. By constructing reduced models to explain this surface ground deformation in current storage sites, we can increase our understanding of the distribution of pressure over time within storage reservoirs.

Research will focus on understanding transient pressure response, pressure propagation, induced strain ^[2] and post-injection pressure decay in aquifers of varying degrees of cementation, rigidity, and sedimentological and structural complexity via multi-scale numerical and analytical modelling. This will examine the impact of small-scale rock heterogeneity, the effect of compartmentalisation by faults and their damage zones, and by stratigraphical and diagenetic complexity, on the amount of CO₂ that can be stored in each reservoir type^[3].

Data will be obtained from a number of reservoirs covering the range of length scales that control the pressure response both proximally and distally. Data scale-up from these reservoirs will include core-size pore distribution, outcrop, 3D seismics and extended-period satellite surface elevation records. The work will focus on faults and fault damage zones (e.g. deformation bands) as the flow behaviour of these to different fluids is not well understood. The bulk flow properties of these features will be established, so they can be properly incorporated into storage assessments and storage security evaluations.

^[2] Hewitt D. R., Neufeld J. A., & Balmforth N. J. 2015. Journal of Fluid Mechanics, 778, 335–360.

^[3] Chadwick R.A., Noy D.J. & Holloway S. Petroleum Geoscience, 2009, 15, 59-73.

What does the research hope to achieve?

In the short term this work will increase certainty in the development of priority UK storage sites. In the longer term this will help improve site efficiency and handover in many reservoirs for a realistic rollout of UK CO₂ storage.

A key outcome of the work will be the ability to upscale the results from core/outcrop scale to reservoir scale through the use of multi-scale flow models, analytical models and numerical upscaling tools. Results will interface with the process models developed in the research work package of B2 CO₂ Migration and Storage. Modelling will be calibrated by real datasets from large-scale production and storage including: injection pressures; long-term pressure recharge; dynamic well tests; time-lapse seismics; syn and post-injection InSAR surface elevations. It will utilise findings from the DiSECCS project (EP/K035878/1) which has developed new seismic tools for identifying and characterising pressure changes in injection reservoirs. The work will result in improved understanding of pressure build-up, propagation and decay in faulted and heterogeneous reservoirs.