Work Package 4

Sealing integrity of faulted and fractured caprock systems

Leader: TNO

Participants: BRGM, BGR, BGS, IFPEN, PHIMECA, TNO, UU

Objectives

The objective of this work package is to investigate the long-term integrity of sealed faults or fractured caprocks after CO₂ injection in saline aquifers or depleted gas reservoirs. Integrity studies performed in the context of CO2 storage projects usually focus on the sealing capacity of caprocks and faults at the time of CO₂ injection. However, the long-term effects of fluid-rock interaction and evolving basin conditions (such as ongoing basin uplift/burial or changes in column height), on the mechanical and sealing integrity of faults and fractures in the caprock, are often ignored. Changes in the mechanical and fluid flow properties of faults and  caprocks due to gas production and CO₂ injection need to be taken into account when assessing long-term seal integrity for depleted gas reservoirs. In order to assess the long-term integrity of such potentially vulnerable discontinuities, a number of factors that may affect their sealing characteristics must be considered. These include:

• fault and fracture network properties based on field data for such systems
• the effects of chemical degradation on the mechanical and transport properties of fractures and faults
• changes in sealing efficiency of fractures and faults in response to (i) long-term changes in thermo-mechanical basin conditions (stress, fluid pressure and  temperature conditions) and (ii) pressure history in case of storage in depleted gas reservoirs
• the consequences of long-term coupling between chemical, mechanical and transport processes

This work package incorporates a combined approach of observation, experimental testing and modelling to deal with each of these aspects.

Tasks

Task 4.1 Evidence for the impact of faults and fractures on CO₂ migration from natural analogue studies

Task 4.2: Laboratory investigation of long-term hydro-mechanical properties of fractured caprock

Task 4.3 Modelling of chemical processes effects on long-term hydro-mechanical behaviour of fractured caprock and/or faulted system