A Compositional Simulator for Performing Large Field Studies in a Vector Computing Environment

Abstract

ABSTRACT This paper describes COSMOS, a new equation-of-state, compositional simulator. COSMOS is designed for full-field studies of hydrocarbon gas and carbon dioxide injection for miscible flooding, gas condensate reservoirs and volatile oil reservoirs. The numerical procedures in this simulator are based on Newton's method and couple together the phase equilibrium constraints and species continuity equations. The transport flux terms in the flow equations may depend on pressure alone, or may be treated as implicit functions of both pressure and saturation. With this latter option, COSMOS contains the coupling terms which give fully-implicit, black-oil simulators their stability. The well management package is flexible and provides for platform and field limits as well as individual well controls. The coupling of the well flow equations with the continuity equations parallels the implicit treatment of the transport terms. This implicit option also affects our linear algebra routines which are capable of solving matrices with one or three unknowns per grid block. COSMOS was constructed as an efficient vector code which can be easily modified as simulation needs or capabilities arise. Structured design methodologies were employed to achieve as high a degree of modularity as is consistent with extensive vectorization. COSMOS contains a resource manager to efficiently run large and small problems within a limited central memory. Additional resource management software determines a critical path to optimally schedule computations and data traffic. We have also developed a flexible, hierarchical data base package for the storage and retrieval of data which provides printing and restarting capabilities. Although the COSMOS code and these software packages were targeted for the CRAY-1, the simulator is designed to run on other machines with a minimal number of changes.