An In-Situ Combustion Reservoir Simulator With a New Representation of Chemical Reactions

Abstract

Summary Numerical simulation of in-situ combustion processes poses numerical problems related to the representation of chemical reactions in the burning zone. This paper presents a new approach to the description of the combustion front. The fully implicit thermal compositional model developed to simulate oil recovery by wet or dry forward combustion is formulated to handle three dimensions, three phases, gravity and capillary forces, heat transfer by convection and conduction within the reservoir, and conductive heat loss to adjacent strata. Two options are available. The first includes four components and one fuel combustion reaction. The second allows any number of components and several reactions. The first option emphasizes description of the combustion front with a new formulation that uses a heat-release curve to improve numerical stability and to give accurate temperature distribution with large gridblocks. The paper compares different representations of chemical reactions and includes results of a sensitivity study on the mesh size. Thermal-balance considerations are given for wet or dry combustion to provide calculated values of the peak temperature and steam-plateau characteristics. The thermal-balance results agree well with those predicted by the numerical model.