An experimental study of water oil relative permeability of fractured rock at variable conditions of hydrostatic effective stress and capillary number

In the study of fractured systems petrophysics, the concept of relative permeability is of primary importance as it integrates into a characteristic curve, the net effect of complex interactions between matrix, fracture and fluids as a function of saturation. In most practical applications, this curve is assumed independent of the state of stresses and / or to the relative magnitude of viscous and capillary forces, normally represented by the capillary number concept Nc. In the existing coupled simulation schemes, some approaches incorporate eomechanical effects on the petrophysical attributes such as absolute permeability, porosity, fracture width and fracture permeability. There are others that incorporate the effect of capillary number on the relative permeability functions. In a practical sense, the assumption of invariant Kr with the stress and / or the capillary number actually simplifies computational requirements but can underestimate known physical effects that variable stress regime and variable viscous-capillary forces field induce on the multiphase flow. This has special relevance in the context of naturally fractured reservoirs subject to fluids injection and production. In this work, results of core flood experiments performed on a single fractured Berea core were used to obtain water-oil relative permeability curves by the unsteady state JBN method, at variable hydrostatic effective stress and capillary numbers. The aim of the present study is to advance towards a better prediction of complex dynamics in systems where matrix-fracture deformation occur due to stress changes, and variable flow regime exist as a function of relative variations of viscous-capillary forces across the reservoir. The methodology is based on the exploration of the variations of Corey relative permeability parameters with both hydrostatic effective stress and capillary number noting that studies found in the literature report the independent effect of these two variables but not of their combined effects. Results to date indicate that the features of relative permeability curves of fractured rocks (e.g. ranges of mobile saturation, curvature, endpoints) are modified when changes on the effective hydrostatic stress, the capillary number or both are induced. It is herein proposed, that the degree and configuration of the variation of the curves with respect to a reference curve is a function of the level of flow transfer between the matrix and fracture which in turn is determined by the relative importance of the capillary, viscous and deformation effects on both domains. For the set of tested conditions, an empirical correlation for Kr prediction has been developed but future phases of the investigation can include additional variables related to the anisotropic stress regime, other types of fractures and wettability conditions to broaden the applicability of predictive models.

• Autores: Restrepo Morales, Alejandro
• Fecha de publicación: 2017
• Institución: Universidad Nacional de Colombia
• Repositorio: Universidad Nacional de Colombia
• Idioma: spa
• OAI Identifier: oai:repositorio.unal.edu.co:unal/59739
• Acceso en línea: https://repositorio.unal.edu.co/handle/unal/59739; http://bdigital.unal.edu.co/57401/
• Palabra clave: 6 Tecnología (ciencias aplicadas) / Technology; 62 Ingeniería y operaciones afines / Engineering; Relative permeability,; Matrix-fracture,; Corey functions; Stress sensitive permeability,; Capillary number dependent permeability; Permeabilidad relativa,; Sistema matriz-fractura; Exponentes de Corey; Número capilar; Esfuerzo-deformación; Apertura de fractura.
• Rights: openAccess
• License: Atribución-NoComercial 4.0 Internacional