The Effects of Reservoir Minerals on the Composition Changes of Heavy Oil During Steam Stimulation
Authors: Fan H. 
Published: July 2010

Abstract
The catalytic effect of minerals on the hydrocarbon groups, viscosity, and element distribution of heavy oil during the thermal recovery process studied are in this paper. The results show that minerals have a catalytic effect in the aquathermolysis of heavy oil. When 10 wt% mineral was added to the reaction system, the saturate and aromatic content increased, while the resins and asphaltenes components decreased. The results also show that the average molecular weight of heavy oil and asphaltene was reduced after treatment, and the content of sulphur decreased. The viscosity of the heavy oil used in our study decreased by 23.4 - 25.6% in the reaction system after treatment with steam.

Introduction
Thermal recovery processes have been the most effective EOR technologies to recover heavy oil in the world. In addition to the fact that steam can reduce the viscosity of heavy oil, there are chemical reactions between steam and heavy oil. It has been observed that this chemical reaction can play an important role in the process and induce the formation of gaseous components such as carbon dioxide, hydrogen sulfide, and hydrogen during steam injection. Hyne et al. used the term "aquathermolysis" to describe the chemical interaction of high-temperature, high-pressure water with the reactive components of heavy oil and tar sands bitumen, and to distinguish this process from the term "hydrothermolysis" which has come to be associated with the interaction with hydrogen at elevated temperature and pressure(1). Their results, obtained from model compounds, show that some mineral components, in particular trace metals such as vanadium and nickel, can accelerate the breakdown of organosulphur components present in heavy oil, producing carbon monoxide and other gases noted previously. The aquathermolysis of heavy oil can result in an increase in the content of saturates and aromatics and a decrease in resins and asphaltenes, lowering the average molecular weight and viscosity, and improving the properties of the oil.
Many researchers have studied how to apply reservoir minerals to accelerate the aquathermolysis of heavy oil to realize down-hole catalytic upgrading of heavy oil. Belgrave et al. investigated the kinetic models for the aquathermolysis of heavy oil and pointed out that the mineralogy plays an important role in the generation of CO2 and H2S(2). Clark et al. studied the steam-oil chemical reaction and pointed out that some of metal ions, minerals, and reservoir sands can result in the change of composition of heavy oil(3, 4). Monin et al. have studied the thermal cracking of heavy-oil/mineral matrix systems at temperature and pressures encountered during thermal recovery. They pointed out that chemical reactions involving oil, possibly water, and mineral matrix may lead to significant changes in composition of the heavy oil. Their work focused on four thermal crude oils with different geochemical compositions. They observed that a large number of light hydrocarbons, CO2, and H2S was produced if minerals existed in the reaction system(5) Hamid Pahlavan et al. also studied the geochemical changes of heavy crude oil during thermal recovery(6).