A Numerical Model to Study the Formation Damage by Rock Deformation from Well Test Analysis Jose Gildardo Osorio; Jose Gildardo Osorio Universidad Nacional de Colombia Search for other works by this author on: This Site Google Scholar Alejandro Wills; Alejandro Wills New Mexico Institute of Mining and Technology Search for other works by this author on: This Site Google Scholar Osmar Rene Alcalde Osmar Rene Alcalde New Mexico Institute of Mining and Technology Search for other works by this author on: This Site Google Scholar Paper presented at the International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, February 2002. Paper Number: SPE-73742-MS https://doi.org/10.2118/73742-MS Published: February 20 2002 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Osorio, Jose Gildardo, Wills, Alejandro, and Osmar Rene Alcalde. "A Numerical Model to Study the Formation Damage by Rock Deformation from Well Test Analysis." Paper presented at the International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, February 2002. doi: https://doi.org/10.2118/73742-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Conference and Exhibition on Formation Damage Control Search Advanced Search AbstractIn oil/gas reservoirs, the state of stress changes as fluid production/injection from/into the reservoir takes place. Also, petrophysical and geomechanical properties may change due to the variation of the effective stress. However, this consideration is seldom taken into account in well test analysis.This paper presents a numerical, fully coupled, fluid-flow/geomechanical model to perform well test analysis in stress-sensitive reservoirs. The governing equations are developed in cylindrical coordinates honoring the geometry of the flow lines characterizing the drainage area in most well tests. The model is a 3D, point distributed, finite-difference simulator which applies a fully implicit discretization scheme to ensure maximum stability.The model assumes isothermal, single-phase fluid-flow (slightly compressible fluid). Infinite and finite acting behavior is allowed during the well test. Reservoir properties are allowed to change from one layer to another. Both cases isotropic and anisotropic rock property behaviors are considered in the model. The rock behaves as elastic system whose deformation is described by nonlinear theory (the mechanical properties are function of the mean effective stress).The results show that in stress-sensitive reservoirs the permeability decreases with production time reaching its minimum value near the wellbore and moving more and more into the reservoir as production time increases. After a certain production time, the permeability distribution reaches a constant value. An important finding from this study is that the damage caused by rock deformation is irreversible; therefore, its early detection and treatment is essential for optimum reservoir management.IntroductionConventionally, well test analysis models are based on the following implicit assumptions:constant fluid-flow and geomechanical rock properties, andconstant stress state. However, published laboratory studies show that in stress sensitive reservoirs rock properties may change significantly with variation of the pore pressure and the stress state.1–7 Also, the variation in the well pressure produces a variation in the stress state. In fact, the largest deviations from the initial stress state are found at the borehole wall and its neighborhood where the pore pressure variation is always maximum.To study the impact that the above mentioned assumptions have on well testing, it is necessary to solve the governing equations describing the deformation of the solid part of the rock coupled with the governing equations describing the changes in the pore pressure. Due to their strong nonlinear behavior, the solution of this set of differential equations must be performed numerically.This paper presents a 3D, point-distributed, finite-difference model discribing the formation damage caused by rock deformation in stress-sensitive reservoirs. The physical system is represented in cilyndrical coordinates and discretized by means of a point-distributed grid (Fig. 1). The governing equations are based mainly on the following assumptions:isothermal, single-phase fluid flow,the deformation of the solid part of the rock behaves as a nonlinear elastic medium with small strains, andthe mechanical and fluid-flow properties are assumed to be functions of the mean effective stress. The primary variables in the resulting system of governing equations are the incremental displacements and the pore pressure. Keywords: compressibility, incremental displacement, drillstem testing, effective stress, stress-sensitive reservoir, upstream oil & gas, stencil element, numerical model, permeability reduction, reservoir characterization Subjects: Reservoir Characterization, Formation Evaluation & Management, Reservoir geomechanics, Drillstem/well testing This content is only available via PDF. 2002. 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