Comprehensive Kinetic Models For the Aquathermolysis of Heavy Oils
Authors: Belgrave J.D.M. , Moore R.G. , Ursenbach M.G. 
Published: March 2010

Aquathermolysis experiments over the temperature range 360 to 422 ºC were performed on core samples taken from three large bitumen and heavy oil deposits found in Alberta: Athabasca, North Bodo, and Frisco Countess. The purpose of this work was to facilitate the development of comprehensive thermal cracking models for predicting gas and liquid phase product distributions under conditions anticipated during thermal recovery. Previous studies. have shown by material balance on oxygen that water is implicated in many of the chemical reactions leading to the formation of H2S and CO2, yet most of the reported thermal cracking studies have not included water. Additionally, experimental investigations in this area have, for the most part, not involved realistic time frames, and as such certain phenomena observed in this work have not been previously reported.

The experiments conducted using Athabasca bitumen included runs with an initially previously oxidized oil sample (designed to simulate conditions preceding the arrival of the firefront during in situ combustion) and runs with a change in core mineralogy. Pre-oxidizing the oil was found to substantially increase the amount of H2 generated. Core mineralogy played an important role in the generation of CO2; and the amount of H2S produced was. dependent on oil composition, mineralogy, and time. Gas production was observed to be largely associated with the conversion of the heavy. oil and asphaltenes oil fractions.

The cracking models developed in this work offer useful directional insight as to the effect of core mineralogy and oil composition on the kinetic parameters, and a much needed means of estimating the calorific value and acidic gas content of the produced gases during thermal recovery operations.

Introduction

The purpose of this work was to develop thermal cracking models capable of describing the liquid and gas phase compositional changes that occur during thermal recovery operations. Although rather extensive laboratory studies have been performed concerning the thermal cracking of heavy oils and bitumen, few in comparison have included water as part of the reactants. Laboratory studies(1, 2, 3) and field applications of thermal recovery processes(4) have demonstrated that appreciable amounts of gaseous environmental contaminants such as H2S and CO2 arecreated by the aquathermolysis (steam/oil reactions) of heavy oils. hese problems are all the more severe as the sulphur and oxygen content of the oil increases(5).

It has also been demonstrated(2) that H2 and light saturated hydrocarbons are also produced by steam/oil reactions over the temperature range 200 to 300 ºC. Accordingly, casing gas produced from cyclic steam stimulation projects has sometimes been collected and condensed yielding between 0.015 and 1.5 m3 of condensate per well per day(6), with the noncondensible gas (which contains mostly methane) being used as a supplementary fuel for the steam generators. Thus, aside from the pollution aspect there is the potential to recover chemical energy from the effluent gases.

In this paper we present thermal cracking models based on aquathermolysis experiments performed on core samples from three large bitumen and heavy oil deposits in Alberta: Athabasca, North Bodo, and Frisco Countess. The oils from these deposits have contrastingly different elemental compositions and API gravities. For the experiments involving Athabasca oil sands we report on three sets of tests: two involving significantly different core minera