Abstract
Chemical additives for co-injection with steam at low dosages were evaluated for enhancement of SAGD operations. The additives were selected based on their commercial scalability, water solubility and transportability inside the SAGD chamber (volatility). A custom-designed oil-recovery experiment, mimicking actual mechanisms of a SAGD chamber edge, was utilized for additive evaluation in the laboratory. The apparatus is a steam-soaking system composed of a synthetically prepared oil sand core suspended above an additive solution. The core was internally cooled to drive steam condensation and create co-current oil/water drainage inside the core. The additive effect on the recovery rate was quantified by comparison with a steam-only baseline. Amongst 20 additives tested, Additives A and B showed the most promising performance. Additive A improved the rate of oil recovery by 18% at a dosage of 5000 ppm. When the dosage was doubled (1 wt %), improvement in the rate of recovery increased favorably by 5 times (93% over baseline). Additive B showed significantly higher oil recovery of 240% over the baseline at 5000 ppm.
The transport behaviors of Additives A and B inside the steam chamber were also evaluated with reservoir modeling for potential field implementation. A homogeneous reservoir model was used to predict the transport behavior of the additives in a growing chamber and evaluate multiple injection scenarios. Compared with Additive A, Additive B was less volatile and required longer travel time from the injector to the chamber edge. Hence, Additive B can be injected in a younger (smaller) steam chamber, where the chamber edge is more accessible by the additive. Additive A, on the other hand, can target regions away from the injector in a more developed steam chamber. Additives A and B could also be co-injected or alternatively injected regardless of chamber size to simultaneously enhance oil production from different regions of the chamber.
