A Three-Phase, Two-Dimensional Compositional Thermal Simulator For Steam Injection Processes

Abstract

Abstract A numerical model for simulating steam injection into a porous medium is described. The model simulates three-phase, three-dimensional, multi-component flow, with interphase mass and heat transfer, and thus accounts for changes in oil composition during steam injection. The example problems consider a system made up of water (or steam) and three hydrocarbon components. The partial differential equations describing the mass balance for each component were solved, together with a heat balance and auxiliary relations. Examples are presented illustrating the use of the model for cyclic steam stimulation and steamflooding. The sensitivity of the predictions to the input parameters is examined. It was found that steam distillation and gravity segregation are important mechanisms in the steam injection processes. Simultaneous solution of heat and mass balances and compositional constraint equations appear to represent the best procedure for efficient simulation. Other solution schemes tested are also discussed. Introduction EARLY EFFORTS in the mathematical modeling of steam injection processes utilized modifications of the Buckley-Leverett equation to allow for temperature variations(1,2), flow-pattern representation by means of stream tubes and subsequent temperature4 dependent Buckley-Leverett type displacement (3,4), and still simpler treatments where oil recovery was based only on the oil saturation reduction in the steam zone. Three-phase, one- and two-dimensional models for steam injection were first presented by Shutler (5,6). He solved the three-phase (oil, water and gas) mass balances simultaneously using Newtonian iteration. The energy balance equation was solved separately by the non-iterative ADIP. Interphase mass transfer between water and gas phases was allowed, but the oil phase was assumed to be nonvolatile, and the hydrocarbon gas was insoluble in the liquid phases. The implicit-pressure, explicit-saturation (IMPES) method was used by Abdalla and Coats'" to simulate steam drive. They developed a two-dimensional, three-phase (oil, water and steam) model. A new stabilized IMPES method was described by Vinsome(8). He simulated steam drive and steam soak by means of a three-phase (oil, water and steam) model. This model did not account for steam distillation. Coats, George, Chu and Marcum(10) presented a three-phase (oil, water and steam), three-dimensional numerical model for the steam injection process. The mass and energy balance equations were solved simultaneously. Water and steam equations were combined to avoid iteration on the mass transfer condensation term. No distillation of the oil was assumed. Weinstein, Wheeler and Woods(11) developed a model that describes three-phase (oil, water and gas) flow in one dimension and accounts for inter-phase mass transfer. The model does not include gravity and capillary pressure effects. "Sequential solution" (Spillette, Hillestad and Stone 12) was basically used as the method of solution. Recently, Coats(13) described a three-dimensional, three-phase (oil, water and gas) model that accounted for steam distillation. Sequential solution(15) was basically used as the method of solution. The present work describes a compositional simulator designed to simulate the steam injection processes in two-dimensional geometry.