Study On Chemical Mechanism Of In Situ Combustion And Its Improving Methods

In situ combustion is an effective way of EOR, which belongs to thermal recovery.During in situ combustion process, part of the crude oil’s split product is burned constantly ascrude material for heating.EOR is achieved relying on the co-ordination of thermal and othercomprehensive driving forces. For in situ combusiton, one of the main factors that restrict itsapplication is the fuel deposition from the reservoir rock in front of the burning front, which isthe fuel density in the reservoir. Lack of the fuel deposition leads to discontinuous burningand fail to achieve combustion, just like in light oil reservoir. Except for fuel deposition,another key factor is air demand. Like most of the heavy oil reservoirs, the fuel deposition inthese resevoirs is so sufficient that more air is needed, which increases the economic costduring in situ combustion.Chemical mechanism of in situ combustion is studied in this paper, that is to improve theburning quality parameters during in situ combustion including two parameters mentionedabove. However, physical simulation experiment is one of the most direct and effectivemethods to learn about in situ combustion technology. Therfore, it is effective to research inthe chemical mechanism of in situ combustion and its improving methods through physicalsimulaiton exmeriment.Two kinds of crude oil and two kinds of metal additives are used in totally7groups ofcombustion tube experiments described in this paper. The viscosity of the crude oil is38670mPa·s and15.42mPa·s, separately. These two kinds of crude oil are derived from Liao He oilfield in China. The metal additives that are chosen to be tested are Fe（NO3）39H2O and Zn（NO3）26H20, separately.During the combustion tube experiment with SG heavy oil, Fe（NO3）39H2O and Zn（NO3）26H20can both enhance the fuel concentration. Compared with controlled experiment,the experiment with Fe（NO3）39H2O can enhance the fuel concentration of20%, but the Zn（NO3）26H20can only enhance the fuel concentraiton of5%. In addtion, in the experimentwith Fe（NO3）39H2O, fuel concentration is enhanced20%but air demant is reduced of9.8%.However, in the experiment with Zn（NO3）26H20, air dement is reduced only2.5%. This maybe because in the experiment with Fe（NO3）39H2O,fuel deposition in chemical quality isdifferent from controlled experiment. Changing in the apparent hydrogen to carbon（H\C）ratio of the fuel can provide evidence for explanation. The computed result of the apparenthydrogen to carbon（H\C） ratio in controlled experiment is2.64, and the one in the experiment with Fe（NO3）39H2O is0.57. at the same time, the additive of Fe（NO3）39H2Ocan also increase advance rate of the combustion front, but Zn（NO3）26H20decreases theadvance rate.The result of the SG combustion tube experiment with light oil shows that continuouscombustion is very hard to be achieved in the two controlled experiment. When theexperiment is started, with the formation of the combustion front, but it distinguished rapidllyafter moving forward to several millimeters. The reason for that is less amount of fuel, so thatcontinuous combustion is hindered. After Fe（NO3）39H2O solution is added, continuouscombustion can be achieved. The reason is that Fe（NO3）39H2O both enhances the fuelconcentration and efficiency so as to improve the degree of achieving continuous combustion.The experimental results show that Fe（NO3）39H2O can be a very appropriate additive inorder to improve characteristic parameters during in situ combustion, that is to improve thechemical mechanism of in situ combustion.