A New Simulator for Naturally Fractured Reservoirs

Abstract

ABSTRACT This paper describes a three-dimensional, three-phase, simulator designed for modelling fluid flow in a naturally fractured reservoir. A dual permeability system and/or a dual porosity system, is used to describe complex porous media including highly-fractured, micro-fractured and non-fractured regions. In addition to the viscous and capillary pressure forces, the matrix-fracture exchange terms can handle gravity effects with differing results depending on matrix block sizes or matrix block connections. The conservation equations are expressed in compositional form and equilibrium K-values are used. The fully implicit equations are linearized by a Newton-Raphson iteration scheme. The method of checking the changes of phase allows a complete compatibility with the conservation equations. Because of the multi-purpose nature of the model, several different choices of discretized time-solution techniques are available. Various sequential solutions and the IMPES solution are obtained as simplified versions of the fully implicit technique. This multi-purpose simulator is designed for solving full-field reservoir problems as well as laboratory experiments. Standard one porous medium black-oil problems can be solved with this simulator without any computer-time penality. Examples are presented to illustrate the stability of the model, the differences in performance depending on the time-solution schemes used and the essential differences between the new approach and those used in earlier naturally fractured reservoir models.