Steam-assisted gravity drainage (SAGD) method of heavy oil reserves development involves continuous injection of a large volume of steam into injection horizontal wells drilled at a distance of 5-7 m above and parallel to producing wells. The injected steam forms a steam chamber in the pore space between the well pair making oil flow into the lower producing well. The method is, thus, associated with heating of formation rock and fluids, as well as heat loss in the environment.
On occasion, because of operational, economic, or environmental considerations injection wells alone, or both injection and producing wells have to be shut down. The effects of shutdown of SAGD-wells were evaluated on a model of a Sheshminskian heavy oil reservoir in the Republic of Tatarstan. The model study showed that as soon as steam injection is stopped the steam chamber diminishes in its size, the heat is dissipated in the reservoir, and the fluids are redistributed in accordance with their density–oil tends to go the reservoir top, because of a less density compared with water. If several well pairs contributed to development of a large steam chamber, oil will tend to migrate into areas with higher elevations. As a result, a large amount of condensate will accumulate in the vicinity of a producing well, which is much the same as hitting a water-saturated layer while drilling. However, the case providing for resuming the SAGD process while the formation has not cooled completely might be less expensive vs. the case providing for tapping of water-filled layer.
The results of the research may be helpful to determine operational parameters relating to shutdown of SAGD-wells. Understanding of mechanisms and processes that take place in-situ during cooling of steam chamber following shutdown of wells will help to find most effective methods to return wells to production.
