AbstractIn recent years, assessing the safety and feasibility of long-term geological CO2 sequestration (GCS) usually relies on model-based forecasting of the sub-surface behaviour of CO2. In the application of two-phase flow in porous media, numerical simulations are usually implemented using empirical formulations by either Brooks-Corey (BC) or van Genuchten (vG) to describe the transport properties in a CO2/brine/rock system. The forward modelling of GCS is often prompted by uncertainties in fluid flow and transport processes, which are majorly governed by structural complexity resulting from the sedimentary properties of the porous media. Since flow characteristics can vary within the reservoir and sealing formation, this thesis investigates the consequences of sedimentary heterogeneities, such as gradation, cementation, interbedded argillaceous units, in the storage formation on the transport and flow processes of CO2/brine systems.
The study focuses on CO2 storage in siliciclastic aquifers and examines the effects of the dynamic representation of grain-scale heterogeneities on multiphase fluid flow during geological CO2 storage. This was implemented by relating a number of sedimentary processes and structures in the reservoir and caprock formation to the constitutive functions of relative permeability and capillary pressure using the van Genutchten’s empirical model. A set of continuum-scale numerical simulations was conducted to investigate the impact of variability in these constitutive functions using simulators that are based on Darcy-flow physics. Firstly, the pore geometry parameter, which is an empirical constant in both BC and vG model, was described for different clastic rocks using numerical validation of statistical data from soil physics. This enables the adaptability of the pore geometry parameter to the type of clastic rock, thus proposing a new methodology for the effective characterisation of the pore geometry parameter for different clastic rocks. The effect of key parameters in the vG empirical model, such as the pressure strength coefficient, the pore geometry parameter and the connate saturation (wetting and non-wetting), on GCS was also incorporated in the numerical investigations.
Trapping mechanisms such as structural, residual and dissolution are assessed in this thesis using Bunter Sandstone Formation (Chapter 4), Mercia Mudstone Group (Chapter 5) and Utsira Sandstone Formation (Chapter 6) as case studies. Results showed that relative permeability assumptions have a significant impact on the afore listed trapping mechanisms as well as the pore pressure distribution within the reservoir and caprock formation. It argues for the adequate representation of small-scale heterogeneities in large-scale forward modelling of CO2 storage, especially when describing the capillary pressure and relative permeability functions. The characterisation of the pore gemetry parameter serves as a formative tool for describing capillary pressure and relative permeability heterogeneities that could arise from sedimentary structures in clastic reservoir formations and their subsequent impact on CO2/brine transport processes in a porous medium.
|Date of Award||Nov 2019|
|Supervisor||Seyed Shariatipour (Supervisor), Adrian Wood (Supervisor) & John D.O. Williams (Supervisor)|