Impact of chemical reactions in the gas phase on the in-situ combustion process: An experimental study

Impact of chemical reactions in the gas phase on the in-situ combustion process: An experimental study

Hoekstra, B.E.

Rudolph, E.S.J. (mentor)

Civil Engineering and Geosciences

Geotechnology

Section Petroleum Engineering

2011-09-30

In-Situ Combustion (ISC) is a thermal enhanced oil recovery method. Therefore, air or oxygen-enriched air is injected in the reservoir. The oxygen reacts with part of the hydrocarbon forming heat and combustion products. The released heat increases the temperature locally in the reservoir and lowers the viscosity of the oil. Formed gaseous products additionally enhance the oil production due to miscible and immiscible gas drive. Although worldwide the application of ISC is limited, research on the underlying processes is extensive. In particular, discussions focus on the question whether it is better to describe oil recovery by ISC as thermal recovery method with minimal description of the occurring chemical reaction or if it is crucial to include more detailed descriptions of the occurring chemical reactions. Most ISC research focuses on the description of reaction kinetics and lacks the description of other phenomena involved, e.g. gas phase reactions, the influence of porous media and the effect of flow. The focus of this experimental study is to determine the relevance of chemical reactions in the gas phase for the success of ISC and to get a better understanding of the temperature influence on ISC. For the experiment a vertically-positioned stainless steel tube filled with a mixture of sand and oil was heated to a desired temperature. From below air was injected, oil and exhaust gases are produced from the top of the tube. The outlet gas was analysed with the help of a gas chromatograph. Liquid produced from the tube was collected and characterized with the help of refractive index analysis. The sand was retrieved after the experiment and categorized based on visual observations. Additionally, the organic content in the sand after the experiment was determined by weight loss by heating the sand gradually to 500°C. Thermal Gravity Analysis under nitrogen and air atmosphere of oil, sand and oil+sand samples was performed. The determined weight loss as function of the temperature together with the analysis of the outlet gas helped to identify the occurring chemical reactions. The experiments showed that gas phase reactions should be incorporated in the description of ISC processes. The actual gas phase combustion could not be proven unambiguous, typical ISC temperature profiles were not seen and the reactions were not self-sustaining. It was shown that reactions occur in the gas phase. For a pure component oil cracking and recombination in combination with combustion was behaving similar as the crude oil in ISC, although the temperature range for these reactions are wider for the crude oil. Initial low oil saturations have no impact on the general chemical combustion behaviour; the position of oxidation products depends on the initial saturation. At low temperature the formation of solid components was due to oxygenation and not to anaerobic cracking. Still a number of underlying processes occurring during ISC are not completely understood. In particular, the effect of pressure on the chemical reactions, on the occurrence of a gas phase and the resulting outlet gas need further investigation.

in-situ combustion
gas phase reactions
temperature
cracking
oxidation
saturation

http://resolver.tudelft.nl/uuid:13ffab18-84c8-4454-941f-aa9d4bb528f9

Student theses

master thesis

(c) 2011 Hoekstra, B.E.