Development and Application of an In-Situ Combustion Reservoir Simulator

Abstract

Youngren, Gary K., SPE-AIME, ARCO Oil and Gas Co. Abstract This paper describes a three-dimensional, three-phase in-situ combustion reservoir simulator that rigorously models fluid flow, heat transfer, and vaporization/ condensation. It has five components: water, oxygen, nonvolatile oil, and two arbitrary volatile components. The volatile components partition between the oil and gas phases. The physical mechanisms modeled, the comprehensive mathematical solution method employed, and four applications of the simulator are presented. The applications demonstrate that the simulator can be used to interpret laboratory results and predict the effects of reservoir characteristics and operating strategy on field performance. Introduction Crookston et al. and Farouq Ali thoroughly reviewed previous developments in the mathematical simulation of in-situ combustion processes. Briefly, the earliest studies modeled certain aspects of the process using simple assumptions for the remaining process using simple assumptions for the remaining features in order to make the problem tractable. For example, Chu modeled one-dimensional thermal conduction, convection, and the thermal effects of vaporization and condensation, but multi phase fluid flow effects were simplified by assuming constant fluid saturations. Smith and Farouq Ali simulated conduction, convection, heat losses, and heat generation in two-dimensions, but assumed single-phase flow and constant fuel consumption. Recently, Farouq Ali and Crookston et al. described comprehensive three-phase, two-dimensional simulators that model the most essential features of in-situ combustion; however, results were presented only for hypothetical one- and two-dimensional examples with relatively few grid blocks.The objective of this work was to develop an in-situ combustion simulator that would rigorously model fluid flow, heat transfer, and vaporization/ condensation and still be efficient enough to allow simulation of realistic reservoir problems. Accordingly, the simulator employs a stable, efficient, highly implicit solution method. It is formulated to handle three dimensions, three phases, five components, gravity and capillary forces, heat transfer by convection and conduction within the reservoir and conductive heat loss to adjacent strata. Quantitative data on high-temperature combustion kinetics of crude oils in porous media is inadequate to allow rigorous treatment of reaction kinetics; thus, the combustion reaction is treated simply, yet realistically, by assuming that the combustion rate is limited only by the oxygen flux. This paper first describes the simulator, outlining the physical mechanisms modeled and the numerical solution method employed. It concludes by presenting analysis of real laboratory and field data in one, two, and three dimensions. Simulator Description Physical Properties Physical Properties The most significant features of the simulator are listed in Table l and detailed in Appendix A.The simulator has five components: water, nonvolatile (dead) oil, oxygen, and two arbitrary volatile components that partition between the oil and gas phases. The last four components are considered insoluble in water. The last two components are arbitrary and may be any one of the combinations: nitrogen (N2) and solution gas, N2 and carbon dioxide (CO2), N2 and a distillable hydrocarbon, CO2 and solution gas, or CO2 and a distillable hydrocarbon. SPEJ p. 39