CO2 Sequestration

[Reservoir Geo-mechanics; Pore pressure; Over pressure; Elastic-Plastic/Visco-Elastic Rock]

1. Feasible to estimate the vertical stress from the integration of density logs - by assuming that the over-burden amounts to principal stress, following CO2 sequestration?

2. Whether wellbore observations would remain to suffice - towards determining the orientation of the principal stress – in the context of ‘monitoring CO2 leakage pathways’?

OR

Should we need earthquake focal mechanisms?

3. Can we comfortably go ahead with Leak-off tests – in saline aquifers towards deducing the minimum horizontal principal stress?

4. Following CO2 sequestration, can we simply use geo-physical logs or seismic data – in order to estimate the resulting pore pressure?

OR

A direct measurement of pore pressure remains preferable?

5. To what extent, will we be able to precisely estimate the maximum horizontal stress, in the absence of having details on the frictional strength of the crust (which provide bounds, as a function of pore-p & depth); and wellbore failures (drilling-induced tensile fractures & breakouts)?

6. In CO2 sequestration applications in saline aquifers, whether, ‘recording the trace of a hydraulic fracture on a wellbore’ (open-hole hyd fracturing) towards determining stress orientation (the least principal stress magnitude) – remains completely ruled out (even, if the wells are cased) – considering CO2-leakage aspect?

7. In CO2 sequestration applications, should we also consider the lateral variations of pore pressure, on top of, considering the variations of pore pressure with depth?

8. Following CO2 sequestration, would it remain feasible to delineate disequilibrium compaction (under-compaction) – that leads to over-pressure? Whether tectonic compression and compaction disequilibrium would still remain to be distinct?

9. During/Following CO2 sequestration, whether the presence of brine in the pores of the aquifer would result in time-dependent deformation of the poro-elastic aquifer – leading to viscous compaction of uncemented sands in the saline aquifer?

10.                  Feasible to monitor the trade-off between CO2 injection rate, permeability of the aquifer and the viscosity of the pore fluid – following CO2 sequestration?

In the long run, is there a possibility of the saline aquifer behaving elastically to the stress level at which it yields and then getting deformed plastically without limit?

OR Greater probability of the saline aquifer behaving such that the deformation in response to an applied stress/strain remains rate dependent?

11.                  Even after the completion of CO2 injection, whether, the stresses acting on individual grains of the aquifer would result exactly from the difference between the externally applied normal stresses and the internal fluid pressure?

Suresh Kumar Govindarajan

Professor (HAG)

IIT-Madras

https://home.iitm.ac.in/gskumar/

https://iitm.irins.org/profile/61643