Improvement of Medium And Light Oil Recovery With Thermocatalytic In Situ Combustion
Authors: Ranjbar M. 
Published: March 2010

Abstract
The objective of this paper was to improve the understanding of the basic mechanisms responsible for fuel formation in in situ combustion (ISC) and to use that understanding to identify the conditions under which the ISC process can be applied to improve the recovery of heavy, medium and light oils. Using rocks of varying mineralogical composition and crude oils with different contents of asphalteoes and resins, pyrolysis and combustion tests were performed to examine the influence of thermocatalytic mocatalytic reactions on the amount and reactivity of fuel in an ISC process.
From the results, it appears that the controlling mechanism of fuel formation is the conversion of crude oil components by radical polymerization. The conversion rate is influenced by many factors such as process condition and the nature of the crude oil and reservoir rock minerals. The formation of resins from lighter hydrocarbons and their polymerization into asphalrenes can be accelerated by clay minerals and metal components existing in the fuel formation zone. Therefore the importance of low tem-perature oxidation reactions is increasing in the thermocatalytic recovery process of even light and medium oils.

Introduction
The application of thermal energy to hydrocarbon reservoirs for increasing crude oil recovery has been given much attention. There are two main types of thermal recovery process, namely hot fluid injection and in situ combustion (ISC). ISC is thermal oil recovery method with a large theoretical potential but limited success in field application. This technique is also known to be the most complicated oil recovery method. It includes some aspects of nearly every oil recovery process.
An important parameter to be considered in the design of an ISC project is the amount of fuel deposited ahead of the combustion front. Excessive fuel deposition causes a slow rate of advance of the burning front and large air compression costs and reduces the maximum oil recovery. On the other hand, if the fuel concentration is too low, the heat of combustion will not be sufficient to raise the temperature of the rock and the contained fluids to a level of self-sustained combustion. This leads to an unstable burning front and combustion failure. Thus, it is necessary to understand the reactions occurring at different temperatures as the combustion front moves in the reservoir.
The most important controlling factors of the fuel formation are the nature of the crude oil and reservoir rock minerals and During this work, experiments were conducted to describe how the clay minerals and heavy metals derivatives, such as iron, affect the thermocatalytic conversion of crude oil compounds as well as the fuel formation and combustion.

Thermocatalytic Oxidation of Crude Oil Compounds
It has been confirmed by many authors, for example, Bousaid and Ramey(3), Dabous and Fulton(4) Burger and Sahuquet(5), that basically three major reactions occur at different temperature levels in an ISC process. These reactions are known as:Low temperature oxidation (LTO)Fuel deposition reactions (FDR)High temperature oxidation (HTO)