Compositional and Black Oil Reservoir Simulation

Abstract

SPE Members Abstract This paper describes a three-dimensional, three-phase reservoir simulation model for black oil and compositional applications. Both IMPES and fully implicit formulations are included. The model's use of a relaxed volume balance Concept effectively conserves both mass and volume and reduces Newton iterations. A new implicit well rate calculation method improves IMPES stability. It approximates wellbore crossflow effects with high efficiency and relative simplicity in both IMPES and fully implicit formulations. Multiphase flow in the tubing and nearwell turbulent gas flow effects are treated implicitly. Initial saturations are calculated as a function of water-oil and gas-oil capillary pressures which are optionally dependent upon the Leverett J function or initial saturations may be entered as data arrays. A normalization of the relative permeability and capillary pressure curves is used to calculate these terms as a function of rock type and grid block residual saturations. Example problems are presented, including several of the SPE Comparative Solution problems and field simulations. Introduction This paper describes a numerical model for simulating three- dimensional, three-phase flow in heterogeneous, single-porosity reservoirs. The model, which is referred to as Sensor, incorporates black oil and fully compositional capabilities formulated in both IMPES and fully implicit modes. The formulations include a relaxed volume Concept and a new method for implicit treatment of well rates with wellbore crossflow. Following model description, several example problems are presented. They include five SPE Comparative Solution Project problems, a turbulent gas flow problem, a crossflow problem, and three field studies. General Description of the Model The model simulates three-dimensional, three-phase flow in heterogeneous, single-porosity porous media. The usual viscous, gravity and capillary forces are represented by Darcy's law modified for relative permeability. The flow is isothermal although, as an option, a spatially variable, time invariant temperature distribution may be specified in the compositional case. The conventional seven-point orthogonal Cartesian xyz grid and the cylindrical grid are used. Mapping or linear indexing is used to require storage and arithmetic only for active grid blocks. The model includes both black oil and fully compositional capabilities. The black oil option includes the, stb/scf term as well as the normal solution gas term. It therefore applies to gas condensate and black oil problems. Interfacial tension, modifying gas-oil capillary pressure, is also entered versus pressure in the black oil PVT table. P. 149