Development of a Comprehensive and General Approach to In Situ Combustion Modelling
Creators: name: Gutiérrez, Dubert
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: Air Injection
subject: In Situ Combustion
subject: Fireflooding
subject: Kinetic Modelling
subject: Reservoir Simulation
subject: Thermal Cracking
subject: Engineering--Petroleum
subject: Engineering
subject: Applied Sciences

description: Modelling of the in situ combustion (ISC) process is a challenging task, mostly due to the complexity of the chemical reactions taking place. Also, the applicability of currently available kinetic models is typically limited to the reservoir systems they were originally developed for. The objective of this study was to derive a general chemical reaction framework that could be used to develop a kinetic model for a wide variety of crude oils. The work is based on the modelling of high-pressure ramped temperature oxidation (HPRTO) experiments, and combustion tube (CT) tests, performed on three different oil systems: a volatile oil which is near critical at reservoir conditions (38.8°API), a low-shrinkage light oil (33.1°API), and a bitumen sample (6.5°API). A kinetic model was derived for each of the cases based on the history match of a HPRTO experiment. The resulting models were validated by history matching a CT test for each of the crude oils, while using the same set of developed reactions. The modelling approach chosen is an extension of the methodology originally proposed by Belgrave et al. in 1993, which is arguably the most comprehensive kinetic model available in the air injection literature. However, their model was developed from experiments performed on Athabasca bitumen, and it fails to represent the ISC process as it occurs in light oil reservoirs encountered at high pressure. For example, Belgrave’s model is based on the deposition and combustion of semi-solid residue commonly known as “coke”, which is rarely present during the ISC of light oils at high pressure. As in Belgrave’s model, this study also describes the original oil in terms of maltenes and asphaltenes. The main difference lies on the presence and importance of oxygen-induced cracking reactions, as well as the combustion of a flammable mixture, which takes place in the gas phase. Also, a unique feature of these simulations is that, apart from history matching traditional variables such as thermocouple temperatures, produced gas composition and fluid recovery, they also capture changes in the physical properties of the produced oil, such as viscosity and density, as well as the amount of the residual phases in the post-test cores. This thesis changes a paradigm deeply rooted in the original ISC theory, by deriving a general chemical reaction framework that is used to develop a kinetic model for a wide variety of crude oils, with API gravities ranging between 6.5 and 38.8. This allows the consolidation of a new and comprehensive general theory for the description of the in situ combustion process as applied to oil reservoirs. One of the features of the modelling approach is that the pseudo-components representing the fuel used by the ISC process are not present in the original oil. Such fuel species are products of oxidation and cracking reactions, which may undergo combustion reactions when in contact with oxygen. Therefore, the method is not limited to a fluid characterization based in terms of maltenes and asphaltenes, and could potentially be applied along with any other type of characterization of the original oil. This facilitates its implementation and coupling with existing field-scale models (i.e., black oil, thermal, or fully compositional), which seek to assess the feasibility of the in situ combustion process on a particular reservoir of interest.