Visualized study of displacement mechanisms by injecting viscosity reducer and non-condensable gas to assist steam injection

Some unavoidable problems occurred in steam injection make it urgent to find a technique that can enhance heavy oil production using the same or less amount of steam but more profitable. Viscosity reducer (VR) and non-condensable gas have become potential additives to assist thermal recovery processes. In this study, a 2D visualized physical model was used to investigate displacement mechanisms and effects of injecting VR solution and nitrogen to assist steam injection. Two injection methods of VR solution, cold VR solution injection (CVR) and hot VR solution injection (HVR), were compared to provide a reference for the selection of VR injection. The results showed that the injected VR solution was able to transfer viscous oil into O/W emulsions with lower viscosity and stronger fluidity, leading to more trapped oil mobilized and displaced. Continuous nitrogen could be cut off into small bubbles and trapped in porous media, resulting in the distribution changes of liquids in the pores and more contaction among oil, steam, condensate and VR solution. In comparison with the incremental oil recovery induced by CVR, the value caused by HVR was 5.4 percentage points larger, indicating that the co-injection of steam and VR solution was more beneficial for the further oil production.