Experimental and numerical studies on initial stages of SAGD process for heavy oil recovery

Experiments and numerical simulations on initial stages of the steam-assisted gravity drainage (SAGD) process were carried out using two-dimensional scaled reservoir models in order to investigate oil production mechanism and performance. The rising or growing process of the initial steam chamber was visualized using video and thermal-video pictures. For the case of conventional SAGD, oil production rate increased with increasing vertical well spacing; however, the lead-time for the gravity drainage to initiate oil production became longer. The results suggest that the well spacing can be used as a governing factor to evaluate oil production rate and lead-time in the initial stage of the SAGD process.
Furthermore, micro-phenomena at the inclined interface of the steam chamber with high-resolution optical-fiber scope were visualized. The fine water droplets approximately 0.02 mm in diameter were observed at the interface between steam and oil phases. The behavior was seemed that the droplets diffuse into heated oil and then create water-in-oil emulsion. The water droplets with same range of size were also observed in the produced emulsion.
The numerical simulation using the STARSTM was also performed to carry out history-matching with the experimental results for the conventional SAGD process. The simulation uses a two-component (water and heavy oil) black oil, three-phase (water, heavy oil and steam) and three-dimensional numerical model. The results from the history-matched numerical simulation are found to be in reasonable agreement with those of the experiment for oil production rate, cumulative oil production, steam chamber shape and temperature contours in the initial stages to create the steam chamber.
Based on these results, it was found that the instability over the steam chamber is not enough to recover the upper regime of the oil seam after the initial stage. The modified SAGD process by adding intermittent steam stimulation from the lower well (named SAGD-ISSLW) has been proposed to enhance the oil production from the upper regime.