Field Scale Simulation Study of In-Situ Combustion in High Pressure Light Oil Reservoirs

Abstract

Abstract Air injection may be an efficient EOR process for deep high-pressure light petroleum reservoirs, for example those found in the North Sea area. Based on phase behaviour analysis by a pseudo-compositional approach and combustion tube simulations, comparative reservoir simulation studies have been conducted to evaluate the potential and displacement characteristics of processes in high-pressure, volatile light petroleum reservoirs. The primary objective of the study is to examine the feasibility of in-situ combustion processes in North Sea type high-pressure, volatile light oil reservoirs. The reservoir operational parameters have been optimized, and the results of this study are useful for screening of EOR processes, as well as the design and interpretation of in-situ combustion projects. A simulation study has examined the sensitivities of important in-situ combustion parameters on a field scale. Variations in well pattern size, air injection rates and injection fluid (air, O2, CO2, N2 ) were also examined. Techniques were devised to model the combustion process in a large field-size grid. Results from areal and cross-sectional models were combined to obtain a three-dimensional analysis of the fire flood performance for various well patterns. Simulation runs revealed combustion front extinction problems due to large grid block size expected for well spacing higher than 2.5 acres also with kinetic controlled field scale models. Extinction of the combustion front significantly reduces predicted areal sweep and oil recovery, resulting in shorter project lifetimes. Kinetic controlled field scale models for well spacing lower than 2.5 acres can predict combustion front formation and vaporization of water and light petroleum components, when simulated with commercial simulators having about 200 grid blocks. The simulations also show that the vertical sweep efficiency is predominately controlled by the vertical permeability variation in the reservoir. The detailed simulation output showed that mass transfer between phases, oil vaporization, cross flow between layers and heat loss to the adjacent formations are important processes in this thermal recovery process. Front tracking and a thin flame technique are considered to be important for enhancing simulation capability. The development of more advanced non-isothermal simulators with these capabilities will increase the reliability of air-flood simulation predictions in high pressure light petroleum reservoirs necessary to reveal higher recovery potential than predicted by current simulation predictions. The Improved Oil Recovery (IOR) potential performance of thermal IOR processes, such as air and oxygen injection in-situ combustion processes, is predicted the highest among the alternative options.