GAS EVOLUTION AND CHANGE OF OIL COMPOSITION DURING STEAM FLOODING OF OIL RESERVOIRS

The injection of steam into oil reservoirs is a technique commonly used for improving the production of heavy crude oils. Very often, a change in the composition of the oil and gas produced may be observed during steam flooding. In general, corrosive gases, such as H₂S and CO₂, are produced in increased quantities.
In laboratory experiments on sulphur-bearing reservoir minerals and crude oils the origin of the change in oil and gas composition was investigated. Temperatures up to 370°C were applied to study temperature- and rate-dependent phenomena. By means of X-ray fluorescence, gas chromatography and chemical precipitation methods, the change in the sulphur material balance was studied.
It was shown that gas evolution depends strongly on the temperature of the steam injected. Furthermore, it was possible to prove that the gases evolved during steam flooding (such as CO₂, H₂S etc.) originate from the decomposition of crude oil components. Besides these investigations, a drastic viscosity increase of the residual crude oil was observed after steam injection was applied.
It is concluded that the production of H₂S and CO₂ may be controlled by temperature adjustment of the steam being injected.