Pseudokinetic Model for Field-Scale Simulation of In-Situ Combustion

Abstract

Summary Chemical reactions of the in-situ-combustion (ISC) process take place in a thin zone of less than a meter thick. Numerical simulations at the field scale typically use gridblocks that are at least two orders of magnitude greater than that. Such divergence leads to improper representations of key aspects of the process, such as the temperature distribution and the reaction kinetics. In accordance with that, the reaction occurrence is not controlled by the activation energy in the simulation models. The major shortcoming is on fuel deposition, a key issue in ISC. In the simulator, the cracking reaction may proceed slowly at initial reservoir temperature, generating coke from the beginning of the simulation job. The main focus of the paper is on a new pseudokinetic model to improve the representation of the combustion-zone effects and the fuel consumption in the field-scale ISC simulation. Along with the development of the pseudokinetic model, remedies are proposed for some shortcomings of the current reservoir simulation of ISC. The model allows maintaining the dependence of reaction rate with temperature through the use of appropriate activation-energy values. Furthermore, the model reduces the temperature-distribution effect by controlling the reaction rate on the basis of average-temperature values observed in the field-simulation model.