Steam Assisted Gravity Drainage (SAGD) is widely used as an in-situ technology to recover heavy oil and bitumen. But due to serious heat losses, large energy requirements and enormous CO2 emissions, pure SAGD may not be sufficiently efficient to allow economical production.
The main objective of addition of viscosity reducer is to couple viscosity reduction capability of heat and surfactant. It strengthens the formation of emulsions of O/W type that have much lower viscosity than the oil from which they are formed, and enhances oil production under the same amount of steam to make the thermal process more profitable. With regard to the non-condensable gas, its distribution and movement is essential for the expansion of the steam chamber.
In this paper, the performances of a set of selected viscosity reducers under high temperatures are firstly evaluated. Then based on a high temperature and high pressure two-dimension physical model, different injection processes are conducted to study the separate and combined effect of nitrogen and viscosity reducer on the vertical and horizontal expansion rates of steam chamber. The results show that the injection of nitrogen helps the steam chamber expand more quickly in the horizontal direction. And the combination of viscosity reducer and nitrogen makes the steam chamber expand more quickly than the pure SAGD and Nitrogen-SAGD processes. The following sand pack physical models are conducted to further investigate the mechanisms of viscosity reducer and nitrogen in porous media, such as the steam profile correction relying on the blocking capacity of emulsions, heat loss reduction and the combination effect of gas expansion and viscosity reducer on the displacement of residual oil. In addition, numerical simulations are conducted to demonstrate the feasibility of SAGD assisted by viscosity reducer and nitrogen in Du 84 ultra-heavy oil reservoir. Besides optimizing operation parameters, such as nitrogen steam ratio, effective nitrogen injection volume, interval time between viscosity reducer injection and nitrogen injection, the study results show the effect of this technology on the improvement of thermal oil recovery.
In summary, this study is beneficial for the application of viscosity reducer and nitrogen in the process of SAGD.