In MODFLOW, what kind of Boundary Condition that is suitable for Horizontal Dewatering Well?

Whether the permeability enhancement resulting from swelling of shale expansion has NO use at all?

Background:

Shale expansion from swelling increases the resultant over-burden stress in the vertical direction, and thereby leads to significante micro-fracturing in the horizontal direction; and in turn, enhances the resultant permeability of the shale reservoir.

However, this enhancement in permeability results at the expense of reducing the enhanced pore-fluid pressure; and hence, it may probably lead to sloughing and/or other drilling related problem.

Thus, I am NOT sure about the real benefit of experiencing this enhanced permeability associated with the swelling of shale expansion. However, this volume expansion of shale can be effectively mitigated by striking a balance among the following factor: (a) enhancing the drilling rate; (b) using the oil-based mud (that maintains the reservoir pore-pressure without losing it and thereby reduces the induced instability) as against using the water-based mud; (c) following under-balanced drilling; (d) cooling the mud (that induces the reservoir shrinkage; and in turn; mitigates any enhancement in over-burden stress); and (e) the selection of proper chemical composition of the drilling fluid.

Among the geological risks related to the drilling is the normal pressure of the subsoil, so I look for the limit value of it and it is due to what?

The earth pressure at the tunneling face is not equal to the earth pressure at the bulkhead of shield machine. We generally adjust the bulkhead pressure by changing the speed of the screw conveyor during drilling. What is the control standard of bulkhead pressure?

In my recent studies, I found references, where the equations presented were incorrect. Especially in a case like Eaton's pore pressure estimation equation, these mistakes were widespread.

Haimson and Fairhurst (1967) derived equations for the near-wellbore stresses (axial σ_yy, tangential σ_θθ, radial σ_rr...) around a pressurized hole in a porous, permeable "poroelastic" medium considering fluid infiltration from the borehole into the surrounding rock. Their expressions include Biot's constant, A which depends on the Biot poroelastic coefficient, α_B.

Should at α_B = 1.0 those expressions give the same answer as when using the standard near-wellbore stress equations for linearly elastic media (the Kirsch solutions modified later by Hubbert and Willis to incorporate p_p, on pages 170 and 174 in Zoback, 2010)? I was of the impression that the answer will be "yes" but the math seems to prove me wrong.

Geo-mechanics based Pore-geometry

Since the magnitude of ‘threshold capillary pressure’ (the minimum entry pressure required to initiate the displacement of a defending phase by an invading phase from the pore/throat) essentially governs - the order by which - the displacement sequences occur - in a petroleum reservoir - at the pore-scale, to what extent the concept of pore-geometry with its associated geo-mechanical parameters are given importance – while investigating the invasion of either drilling or fracturing fluid into a petroleum reservoir – which may possibly – significantly mitigate the recovery of oil and/or gas production?

What is the minimum and maximum thickness of intra-reservoir shale, below which the shale shall have pore pressure in equilibrium with associated reservoir, above which the shale shall have their own compaction derived pore pressure..?

Gas Formation Volume Factor (GFVF) as a function of Reservoir Pressure:

Isothermal Compressibility below Bubble-Point (BP) Pressure:

Since the conventional isothermal compressibility on crude oil ‘below BP pressure’ would lead to negative compressibility (as the volume of crude oil mitigates with pressure decline), the shrinkage effect of saturated-oil (variation of oil formation volume factor as a function of reservoir pressure) and the expansion effect of the gas coming out of solution (variation of solution GOR & GVFV as a function of reservoir pressure) needs to be considered explicitly.

If so, can we comfortably estimate the isothermal compressibility of a saturated crude-oil with ‘changing liquid oil composition’, below BP pressure?

I am working on wellbore stability issue in oil and gas wells. I saw some works about borehole collapse pressure in deviated and horizontal wellbores like Al-jammi and Zimmerman articles. But I could not find any article or formula for upper limit of wellbore stable condition (break down or fracture pressure).