Petroleum Geo-mechanics
1. Whether Karl Terzaghi’s ‘effective stress principle’ on ‘consolidation’ – with reference to ‘fluid-rock interaction’ – associated with a ‘transient hydraulic behavior of a saturated, deformable, permeable porous medium’ - can be extended to a ‘saturated petroleum reservoir’; and could we still justify that the ‘changes in pore-water pressure (or neutral stress)’ – ‘@ same effective stress’ conditions – have practically ‘no influence’ on the resulting ‘stress-strain behavior of a saturated petroleum reservoir’?
2. Albeit, the concept of ‘effective stress’ in ‘saturated petroleum reservoir’ gets along closely with the equivalents of
(a) ‘effective stress’ representing the ‘average stress’ acting over the solid-phase alone (Fillunger); or,
(b) the ‘intergranular stress’ (Skempton); whether, will we be able to justify the equivalent of ‘effective stress’ being dependent on the applied (total) stress and the pore-pressure, while the same effective stress remains capable of producing the same effect (strain) on the same petroleum reservoir ‘in dry conditions’?
In other words, whether, the ‘stress’ applied over a ‘dry porous body’ @ p = 0, would provide the ‘same strain behavior’ (both geometrically and mechanically) as observed @ reservoir pressures of either @ 5000 psi, or, @ 15,000 psi?
For example, as against ‘normally-varied porosity’, if we are focused on ‘log-normally varied permeability’, then, would it remain feasible for us to define ‘effective stress’ as an ‘external stress’ that, if applied on a dry sample, would produce the ‘same effect’ on ‘permeability’ as a combination of ‘tension’ and ‘pore-pressure’?
Whether the associated evolution of ‘internal stresses’ and ‘deformations’ are quite straight-forward and simple in a petroleum reservoir, where, we will be ‘both’
(a) interested in comparing ‘overall volume changes’ associated with ‘different pore-pressures’ (subsidence); and,
(b) interested in ‘volume variations’ associated with ‘variations in pore-geometry’ (that essentially controls the mechanical and hydraulic properties of a petroleum reservoir)?
3. Under what circumstances, the ‘stress-strain behavior’ of ‘saturated petroleum reservoir’ would have a complete linear dependence of ‘effective stress’ on both ‘total stress’ and ‘pore-pressure’, where the coefficient of pore-pressure remains unity (as per Terzaghi)?
And, when exactly, the role of the ‘pore-pressure coefficient’ starts behaving critically in a petroleum reservoir, whereby we may have to look for the expressions
by Fillunger (as a function of porosity), or,
by Skempton (as a function of contact area ratio), or,
by Suklje, or,
by Skempton, Biot, Nur & Byerlee
(as a function of solid fraction, bulk moduli of non-porous rock and of the rock)?
4. How exactly the concept of ‘concentrated stress’ (local stress tensor) could effectively be used in the application of a petroleum reservoir, in which at least one component remains greater than all the components of the stress tensor acting on the surface of representative volume by any order of magnitude?
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