In situ combustion is the most energy efficient of the thermal recovery methods. In light oil reservoirs, too little fuel may be deposited thus making combustion impossible while in heavy oil reservoirs too much fuel may be deposited thus ruining the economics of the process. Water soluble metallic additives were tested to attempt to modify the fuel deposition reactions.
28 experiments were conducted to study the effects of metallic additives on light crude oil oxidation in limestone medium. Karakus (API = 29 °) and Beykan (API = 32 °) crude oils from Turkish oil fields were used. The metallic additives were ferric chloride, copper chloride and magnesium chloride. The mixture of aqueous solutions of three metallic salts with limestone and the crude oils was subjected to a controlled heating schedule under constant flow rate of air. The produced gas was analyzed for its oxygen and carbon oxides contents. The results of reaction kinetics showed that the molar CO2/CO ratio values of fuel combustion increased when additives were added. A decrease in the atomic H/C ratio with an increase in temperature was observed for all runs. The reaction order, m in Arrhenius equation increases as concentration of copper and magnesium chloride additive increases but decreases as ferric chloride decreased the Arrhenius constant, Ar, for both crude oils. As concentration of ferric chloride increases the activation energy of Karakus crude oil increases while activation energy of Beykan crude oil decreases. The copper chloride additive shows same trend for both crude oils. The 1.0 mol % concentration decreases the activation energies. The 2.0 mol % magnesium chloride increases the activation energy of Karakus crude oil while decreases the activation energy of Beykan crude oil more than 1.0 mol % does. For Karakus crude oil, the oxygen consumption curves of 2.0 mol % metallic additives show one peak. There is similar behavior between runs with 1.0 mol % ferric chloride and magnesium chloride and runs with no additive, but the oxidation reaction peaks with metallic additives at both concentrations occurs at lower temperatures. For Beykan crude oil, all the additives lower the peak temperature when they are compared to standard run. The trends of the curves are actually the same. Copper chloride shows one peak with the 1.0 and 2.0 mol % runs for both crude oils.
In-situ combustion is a technique suitable for recovery of oil from medium to heavy crude oil reservoirs. In this process, crude oil is ignited at the wellbore and a heat front is generated by continuous injection of air into the reservoir. The combustion front is sustained as long as cracking of crude oil to be consumed as fuel produces enough coke. The major constraint limiting the applicability of in-situ combustion is the amount of fuel formed on the reservoir matrix ahead of the combustion zone. If insufficient fuel were deposited, as can be the case for light oils, the combustion front would not be self-sustaining and will die out quickly.