CO2 Sequestration
[Reservoir Geo-mechanics: Normal fault; Strike-Slip Fault; Reverse Fault]
1. How easy would it remain to delineate the magnitudes of horizontal principal stress - with reference to the vertical stress - in deep saline aquifers (in the absence of any data) – with reference to that of depleted oil/gas reservoirs (with some finite data set) – during and following CO2 sequestration?
2. How could we deduce the values of (a) the vertical stress (the maximum principal stress in normal faulting regime, equivalent to the integration of aquifer rock densities, from the surface up to aquifer-depth; and which depends on mean over-burden density); (b) the intermediate principal stress (in strike-slip regime); and (c) the least principal stress (in reverse faulting regime) – (i) in deep saline aquifers; and (ii) in depleted oil/gas reservoirs with ease – during and following CO2 sequestration?
Will we also require the details on the dip and strike of the normal, strike-slip and reverse fault regimes (with reference to the principal stress)?
Following CO2 sequestration, whether, the stress magnitudes for normal, strike-slip and reverse faulting environments (a) when pore pressure remains hydrostatic; and (b) when pore pressure approaches lithostatic values – at respective aquifer depths – would indicate the possible CO2-leakage pathways?
3. What are the possible modes of CO2 leakage, when the horizontal principal stresses (a) remain to be lesser than the vertical stress; and (b) remain to be greater than the vertical stress?
4. Upon accumulation of pore pressure – following CO2 sequestration; whether, (a) the least principal stress would always exceed the pore pressure? (b) the difference between the minimum and maximum principal stress will never exceed the strength of the crust?
5. In the absence of over-pressured formations at aquifer depths, whether, the differences between the 3 principal stresses could still be significant and can we expect them to grow rapidly, upon pore pressure reaching hydrostatic? Whether such scenario would remain to be feasible, following CO2 sequestration?
6. If the depth of deep saline aquifer (say, 800 m) is assumed to be relatively shallow, then, can we go ahead with stress measurement techniques including over-coring; and strain recovery techniques including strain relief measurements? In such cases, how easy to get azimuthally oriented core samples from wells associated with the aquifer? If yes, then, how to go about data analysis that would require environmental corrections (assuming that we have a sound knowledge on the sample’s elastic properties)?
Suresh Kumar Govindarajan
https://home.iitm.ac.in/gskumar/
https://iitm.irins.org/profile/61643
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