Abstract
The injection of CO2 into a depleted reservoir will alter the pore pressure, which if sufficiently perturbed could result in fault reactivation. This paper presents an experimental study of fault reactivation potential in fully saturated kaolinite and Ball Clay fault gouges. Clear differences were observed in fault reactivation pressure when water was injected, with the addition of mica/illite in Ball Clay seen to reduce the pressure necessary for reactivation. Slip occurred once pore-pressure within the gouge was sufficient to overcome the normal stress acting on the fault. During gas injection localised dilatant pathways are formed with approximately only 15% of the fault observing an elevated gas pressure. This localisation is insufficient to overcome normal stress and so reactivation is not initiated. Therefore faults are more likely to conduct gas than to reactivate. The Mohr approach of assessing fault reactivity potential gave mixed results. Hydro-mechanical coupling, saturation state, mineralogical composition and time-dependent features of the clay require inclusion in this approach otherwise experiments that are predicted to be stable result in fault reactivation.
Highlights
The capture of CO2 from large point source emitters and storage in the form of a supercritical fluid within geological formations has been identified as a key technology in tackling anthropogenic climate change (Haszeldine, 2009; Bickle, 2009)
This paper presents results from an experimental study aimed at evaluating fault reactivation potential within the laboratory in two fault gouges
Tests on kaolinite gouge ranged in vertical stress from 1.1 to 6.4 MPa, while for Ball Clay the range was 2.6 to 6.3 MPa
Summary
The capture of CO2 from large point source emitters and storage in the form of a supercritical fluid within geological formations has been identified as a key technology in tackling anthropogenic climate change (Haszeldine, 2009; Bickle, 2009). To achieve a reduction in emissions, significant quantities of CO2 need to be injected into suitable geological formations capable of containing the fluid for thousands of years. Several demonstration projects have been conducted injecting megatonne scale CO2 into depleted hydrocarbons reservoirs, such as at Sleipner (Norwegian North Sea; Arts et al., 2008), Weyburn (Saskatchewan Province, Canada; Wilson et al, 2004) and In Salah (Algeria; Mathieson et al, 2010). Storage of CO2 in depleted reservoirs offers the security of storage with an effective top-seal that previously acted as a seal to hydrocarbons.
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