Thermal Cracking Models For Athabasca Oil Sands Oil
Authors: Hayashitani Masao , Bennion Douglas W. , Donnelly John K. , Moore Robert Gordon 
Published: December 2007

The prime purpose of this work was to provide thermal cracking reaction models which can be incorporated into numerical simulators of thermal recovery processes for the Athabasca Oil Sands. processes for the Athabasca Oil Sands. Athabasca bitumen, free of water and minerals, was thermally cracked at constant temperatures in a closed system under an inert atmosphere. The products of cracking were separated into six pseudo products of cracking were separated into six pseudo components: coke, asphaltenes, heavy oils, middle oils, light oils, and gases. Experimental runs were made over the temperature range from 303 deg. C to 452 deg. C. Three series of runs were made at 360 deg. C, 397 deg. C, and 422 deg. C in which the reactions were terminated at various degrees of cracking. For these runs, reaction time versus product concentration curves were obtained for the above six pseudo components.

Several pseudo reaction mechanisms are proposed to simulate the experimental results. The reaction rate constants were represented by an Arrehnius type expression, the activation energies and corresponding frequency factors were determined for each reaction mechanism proposed.

Introduction

Recently, the use of numerical simulators to predict the performance of steamfloods has become predict the performance of steamfloods has become a common practice.

As far as the numerical simulation of in situ combustion is concerned, a number of simulators have been developed and many of them have been successful in predicting the fluid flow and the temperature profiles along with the production history. The model presented by Crookston et al. incorporates most of the physical and chemical phemonema including the fluid flow, the phase phemonema including the fluid flow, the phase behavior and oxidation and thermal cracking reactions. Although it is claimed that the model can be applied to any thermal recovery process, it has not yet been thoroughly tested.

In the case of the in situ combustion process, the fuel which is a coke-like material is deposited on the reservoir rock by a combination of gas stripping, vaporization and thermal cracking. The major operational cost of the in situ combustion process is for compressing air. The quantity of process is for compressing air. The quantity of air required depends on the amount of fuel available underground, thus the quantitative prediction of the extent of thermal cracking is directly related to the economic evaluation of an in situ combustion project.

Thermal cracking reactions also play an important role in fluid flow in the reservoir because the flowing oils do not have the same fluid properties as the original oil in place. Thermal cracking reactions are also important for the design of bitumen upgrading facilities.

Although rather extensive studies have been made of thermal cracking reactions involving Athabasca bitumen, most studies reported so far are concerned with the chemical and physical properties of the cracked products. In this study emphasis was placed on the collection of experimental data and the development of a prediction model of the thermal cracking reactions.

EXPERIMENTAL PROGRAM

A. Equipment

The experimental apparatus used in this study is schematically shown in Figure 1. The reaction vessel was placed in an electrically heated furnace which was equipped with a stirrer in order to obtain an even temperature distribution within the furnace. The temperature of the bitumen sample was measured with a 1.59 mm O.D. stainless steel sheathed C/A K type thermocouple. The pressure of the system was monitored by a pressure transducer. Vacuum and helium gas lines were provided as shown in Figure 1 to achieve an inert gas atmosphere in the reaction vessel at the beginning of each experimental run.