Laboratory simulation of geochemical changes of heavy crude oils during thermal oil recovery

During thermal oil recovery the elevated reservoir temperature and pressure in combination with rock matrix could cause significant changes in oil composition and its physical properties, especially the viscosity. This paper presents the results of static laboratory experiments on the thermal alteration of two heavy crude oils of different chemical compositions (one rich in resin content, the other one rich in asphaltenes) as a function of temperature, pressure and admixture of water and/rock matrix. Especially the effects of heating time and temperature were studied. l cracking at temperatures up to 380 °C led to the formation of a gas phase consisting mainly of methane. The generation of CO2, H2S and the hydrocarbon gases depended on oil composition. The production of CO2 was enhanced in the presence of water. a 24 h test, the resin rich crude oil yielded significant amounts of insoluble organic material (pyrobitumen) at temperatures above 340 °C. For the asphaltene rich crude oil this occurred above 360 °C. Both qualitative and quantitative analyses of the products formed during the thermal degradation show their dependence on the chemical composition of the crude oils.