Disp-lace-ment front

Ther-mal front

Combustion front

T

C⁰

Fig. 11.3. The scheme of wet-situ combustion

Reference representations: а - air; б -water; в – steam and air mixture; г - oil; д – steam and combustion gases mixture; е – combustion gases .

The zones of: 1 – the injected water and air filtration; 2,4 – superheated steam; 5 – saturated steam; 6 – oil displacement by hot water; 7 – oil displacement by water under the reservoir temperature conditions; 8 – oil filtration at the original conditions; 3 – combustion front.

Heat transfer to the region ahead of the combustion front is carried out during wet combustion mainly by convection by the flows of evaporated injected water and combustion products, and thermal conductivity. In the front of the combustion front there is formed several temperature zones. The zone of superheated steam, where the temperature decreases from the combustion front temperature to the steam condensation temperature, joints directly to the combustion front The size of this area is relatively small, because the heat loss in the surrounding reservoir rocks leads to rapid cooling of filtering gaseous water steam and combustion products, characterized by low heat capacity.

The main share of the transferred heat to the zone in front of the combustion front is concentrated in the zone of saturated steam – the zone of steam plateau, where the heat loss in the surrounding rocks accompanied by steam condensation of steam in the transition temperature zone - the zone of hot water, generated in the result of the condensation of saturated steam. The temperature in the zone of saturated steam mainly depends on the level of the reservoir pressure with a glance of steam share in the gas flow. Usually within the limits of this zone, it changes slightly and is approximately 80-90 % from the temperature of the saturated steam. The temperature in the transition zone changes from the temperature of steam condensation to the initial reservoir temperature.

Finally, ahead of the transition zone there is situated an area not covered by thermal stimulation, corresponding to the original reservoir temperature. The amount of the formation heating zone in front of the combustion front is largely determined by the rate of heat generation at the combustion front and, (consequently, the rate of air injection) and water-air factor. With the increasing of water-air factor the size of the formation heating zone increases. If the wet combustion process is carried out with the maximum possible value of water-air factor or close to it, almost all the accumulated heat in the reservoir will be located in the area ahead of the combustion front, and the size of this area will be the maximum.

The distribution of temperature field in wet-situ combustion is determined mainly by steam generating at the combustion front and heating by the steam of the area of the reservoir ahead the combustion front. So, temperature conditions, ahead the combustion front during wet-situ combustion, are very similar to the temperature distribution during steam injection to the reservoir (fig. 11.4.).