Global greenhouse gas emissions, due to human activities, have increased since the beginning of the industrial revolution in the mid-19th century, with an increase of 70% the last 40 years. (IPCC 2005). Growth in emissions is linked to the increasing demands for energy services that will keep high the use of fossil fuels to the foreseeable future (IEA 2004). A promising method under increasing consideration for reducing greenhouse gas emissions and mitigating climate change, is capturing CO2 from large stationary sources, such as coal - power plants and refineries, and injecting it at supercritical conditions into deep underground geological formations. Formations considered as potential ...view middle of the document...
e. permeable against impermeable units. Second, fault rocks may reduce cross fault flow by acting as low permeability membranes between juxtaposed units of higher permeability. Third, they may provide fault-parallel pathways between vertically distinctive flow units.
Faults in conventional simulation models are usually represented as 2D planes, in which the single phase fault-rock properties, i.e.permeability and thickness, are included using transmissibility multipliers (Manzocchi et al. 1999). Fault permeability is usually determined as a function of SGR Manzocchi et al. 1999; Jolley et al. 2007), whereas fault-rock thickness is determined as a function of fault displacement (Childs et al. 1997). Fluid-phase specific fault-rock properties, that is relative permeability and capillary pressure, are usually omitted during flow simulation studies due to the absence two-phase fault-rock data, and the difficulties and complexities to implement them in full field simulation models (Manzocchi et al. 2002; Al-Hinai et al. 2008). Nevertheless, relatively recent studies (Manzocchi et al. 2002; Al-Busafi, B. 2005; Al-Busafi et al. 2005; Al-Hinai et al. 2008) have highlighted the importance of considering the multiphase flow properties of faults in flow simulation studies.
To the authors’ knowledge, only one study has explored the implications of considering two-phase fluid flow properties of fault-rocks in modelling CO2 injection in faulted saline aquifers (Tueckmantel et al. 2012). That study concluded that when these properties are considered, pressure in the injection compartment can reach values high enough to trigger hydraulic fracturing of the caprock and/or reactivation of existing faults. As a result, either lower injection rates or more injection rates than would be considered necessary on the basis of accounting only for single phase properties, may be required to accommodate the two-phase fault-rock effects.
In this study we have used idealized 2D flow simulation models to investigate the relationship between pressure compartmentalization, two-phase fault- rock properties and fault displacement. The results suggest that overpressurization of the injection compartment is not solely dependent on the inclusion of two-phase properties, but is caused by the formation of a CO2 plug that inhibits pressure equilibration across the fault; formation of this plug is a function of aquifer thickness, fault displacement as well as the fault-rock properties, and depends also on the mobility characteristics of the CO2-brine system adjacent to the fault, and at very low water saturations.
Al-Busafi, 2005. Incorporation of fault rock properties into production simulation models. PhD Thesis, University of Leeds, United Kingdom.