CO2 Sequestration [Reservoir Geo-mechanics]
1. Since, CO2 requires to be injected continuously for few years through the injection well, how about the occurrence of wellbore failure resulting from the accumulated stress around the circumference of the injection well (upon exceeding the aquifer rock strength)?
2. With continuous injection of CO2, how quickly a fault associated with an aquifer could slip, when the ratio of shear stress to effective normal stress resolved on the fault outstrips its frictional strength?
3. When exactly, the increase of aquifer/reservoir pore pressure, upon CO2 sequestration – leading to changes in the stress state of the aquifer – would remain to be (a) detrimental; & (b) beneficial – towards safe CO2 storage?
4. Whether the determination of the state of stress at the selected aquifer/reservoirs depths – would remain to be a tractable problem? And can it be addressed with the limited data? Whether the deduction of (a) vertical stress (corresponding to the weight of the over-burden); (b) maximum principal horizontal stress; (c) minimum principal horizontal stress; & (d) stress orientation – would remain to be straight-forward?
5. Particularly in deep saline aquifers, to what extent, the global and regional stress patterns would remain to be useful – as such aquifers have no pre-existing well control?
OR
Should we make an attempt to extrapolate knowledge of stress orientation and relative stress magnitudes based on an analogy of a nearby aquifer?
6. In a deep saline aquifer, whether, (a) The knowledge of stress at a particular aquifer depth; and (b) The in-situ stress field – can be directly determinable – during and following CO2 sequestration – using existing techniques?
In other words, whether, the estimation of stress magnitudes also consider the induced geologic processes – resulting from CO2 sequestration as well – in addition to its dependence on aquifer depth & pore-pressure? In such cases, whether, the conventional second-order stress tensor – which describes the density of forces acting on all surfaces passing through a point – would remain to be sufficient?
If so, then, whether such stresses ‘not’ pertain to non-homogenous and anisotropic aquifers?
Then, how to deduce the stress magnitudes in three directions and it’s associated three angles that define the orientation of the stress coordinate system with respect to geographic/wellbore coordinates?
And, how could we apply tensor transformation, in such cases (which would otherwise directly yield the principal stresses)?
Will we end up with a principal coordinate system with finite shear stresses (along with the three principal stresses)?
If so, then, principal stresses won’t correspond to the eigenvalues of the stress tensor; and the principal stress directions won’t correspond to their eigenvectors?
Suresh Kumar Govindarajan
https://home.iitm.ac.in/gskumar/
https://iitm.irins.org/profile/61643
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