In this paper, it is proposed an enhanced sequential fully implicit ESFI algorithm with a fixed stress split to approximate robustly poro-elastoplastic solutions related to reservoir geomechanics. The constitutive model considers the total strain effect on porosity/permeability variation and associative plasticity. The sequential fully implicit algorithm SFI is a popular solution to approximate solutions of a coupled system. Generally, the SFI consists of an outer loop to solve the coupled system, in which there are two inner iterative loops for each equation to implicitly solve the equations. The SFI algorithm occasionally suffers from slow convergence or even convergence failure. In order to improve the convergence (robustness) associated with SFI, a new nonlinear acceleration technique is proposed employing Shanks transformations in vector-valued variables to enhance the outer loop convergence, with a Quasi-Newton method considering the modified Thomas method for the internal loops. In this ESFI algorithm, the fluid flow formulation is defined by Darcy's law including nonlinear permeability based on Petunin model. The rock deformation includes a linear part being analyzed based on Biot's theory and a nonlinear part being established using Mohr-Coulomb associative plasticity for geomechanics. Temporal derivatives are approximated by an implicit Euler method and spatial discretizations are adopted using finite element in two different formulations. For the spatial discretization, two weak statements are obtained: the first one uses a continuous Galerkin for poro-elastoplastic and Darcy's flow; the second one uses a continuous Galerkin for poro-elastoplastic and a mixed finite element for Darcy's flow. Several numerical simulations are presented to evaluate the efficiency of ESFI algorithm in reducing the number of iterations. Distinct poromechanical problems in 1D, 2D, and 3D are approximated with linear and nonlinear settings. Where appropriate, the results were verified with analytic solutions and approximated solutions with an explicit Runge-Kutta solver for 2D axisymmetric poroelastoplastic problems.

An innovative numerical scheme to improve integration algorithm for critical state elastoplasticity is presented and detailed with special consideration to the modified Cam-Clay model. The scheme is based on a rotation of the principal stresses and represent the elastoplastic model in a rotated Haigh-Westergaard space. Such an approach allows the calculation of modified Cam-Clay to be computationally efficient and easy to implement. The validity of the proposed scheme is verified by comparing the numerical results with analytic solutions.

Permeability as an important property plays a key role in reservoir performance, numerical reservoir simulation, drilling and production planning. In such reservoirs, stress and strain alters induced by extraction and injection of fluid may substantially change permeability in an irreversible manner.With regard to this phenomenon, several reservoirs may require to consider strain-dependent permeability, in order to have an accurate performance.In this paper, the strain-dependent permeability is analyzed using coupled reservoir geomechanical modeling. This coupling is implemented using a fixed stress iterative coupled scheme. In this coupling, the fluid flow is presented by Darcy's law with considering nonlinear permeability models. The

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Mechanical stability analyses are mandatory to identify suitable candidates for openhole completions. These analyses should comprehend the effects of production drawdown and reservoir depletion state anticipated by the production plan. The understanding and modeling of the physico-chemical interactions between rock and flown fluids and their impacts on the rock mechanical properties have been presented in a companion paper. This paper introduces the three methodologies intended for the wellbore stability analyses, namely the i) elastic analytical; the ii) empirical solids production and the iii) 2D elastoplastic finite element simulator (FE) and describes the reasons two of them have failed to incorporate the dissolution-induced rock weakening effects on the wellbore stability. The resulting numerical model has been implemented as a standalone specialist 2D FE Simulator. The simulator provides the well design engineers a user-friendly interface upon which they can evaluate the effects of the wellbore and reservoir pressure changes, as well as the aforementioned rock weakening effects from an acidizing job, on the wellbore stability. The mechanical wellbore response presented by the simulator elucidates how the stress and strain patterns change after an acid well stimulation job. Wellbores under virgin rock conditions tend to fail by localized plastified zones, also referred to as breakouts, whereas wells subjected to acidizing jobs present extensive straining due to rock weakening. The boundaries of the acidized zone encloses a much less rigid rock prone to deform and compact. On one side this compliant zone provides a gradual shear distribution along the well radius inside the formation and mechanical confinement to the surrounding intact rock and therefore helps this rock in supporting the stresses as if the wellbore were much larger. However, on the other side this significant weakened rock volume poses uncertainties about its own stability or solids production risks. The installation of a perforated or slotted liner/casing acting as a bearing element tends to hold this compliant material back and accounts for the material uncertainties and lack of model representativeness in terms of eventual preferential dissolution patterns. The unprecedented results presented by the developed simulator are assisting the company on the standalone completion decisions and increasing the robustness of well completion designs, therefore assuring the perennity of the CAPEX.