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Stress variations around wellbores and in the reservoirs are of much interest in subsequent drilling operations, future production, and petroleum reservoir development. Stress variations induced by in situ stresses, pore pressure, and temperature changes during drilling operations may lead to various modes of instabilities in forms of induced fractures and borehole breakouts. Previous studies of thermally induced stresses were primarily based on either assumptions of heat conduction through rock matrix or heat convection, in this case, without considering the effect of solid grain thermal conductivity. To analyze wellbore stability, in the present work, a thermo-poro-mechanical model that is... 

The coupling of rock and thermal stresses along with fluid pressure are particularly important in fractured rock masses, since stress-induced changes in permeability can be large and irreversible under perturbations resulting from various natural and induced activities. A new method is presented to model fracture permeability changes during drilling in fractured rocks. The approach includes finite element method (FEM) for fully coupled thermo-poroelastic analysis of stress distribution around borehole and displacement discontinuity method (DDM) to model fracture deformation. Three cases of overbalanced, underbalanced, and balanced drilling fluid pressure conditions are employed. The... 

The wellbore represents one of the most crucial components in the hydrocarbon and geothermal reservoir system, as it is the sole conduit to the reservoir for fluid production or injection. Therefore, predicting and controlling of the permeability variations close to the wellbore has been one of the most challenging issues in geothermal and petroleum reservoir systems. A new method is presented to model fracture permeability changes during drilling in fractured rocks. The approach includes finite element method (FEM) for fully coupled thermo-poroelastic analysis of stress distribution around borehole and displacement discontinuity method (DDM) to model fracture deformation. Four models of... 

Permeability variations in reservoirs and around boreholes are of great interest in petroleum engineering due to the fact that they can significantly affect reserve estimates, reservoir development, well production or injection rate, and the likely success of remedial actions of near-wellbore damage. A fully coupled transient thermo-poroelastic concept with and without rock mechanical damage models is employed to evaluate stress distribution and permeability variation around the boreholes and breakouts. The anisotropy concept is applied to permeability, rock modulus, and uniaxial compressive strength using Weibull distribution. The Mogi–Coulomb failure criterion is employed to model breakout... 

In this paper we explore the existence of periodic solutions of a nonautonomous semi-ratio-dependent predator-prey dynamical system with functional responses on time scales. To illustrate the utility of this work, we should mention that, in our results this system with a large class of monotone functional responses, always has at least one periodic solution. For instance, this system with some celebrated functional responses such as Holling type-II (or Michaelis-Menten), Holling type-III, Ivlev, mx (Holling type I), sigmoidal [e.g., Real and mx2/((A + x)(B +x))] and some other monotone functions, has always at least one ω-periodic solution. Besides, for some well-known functional responses...