Novel insights on initial water mobility: Its effects on steam-assisted gravity drainage performance

Steam-assisted gravity drainage (SAGD) is a primary commercial in-situ thermal recovery method for oil sands/bitumen in Alberta, Canada. Evidence of initial water mobility during the SAGD processes has been observed by previous studies, yet little research has been done on its effects on SAGD performance. In this study, initial water movement ahead of the steam chamber is investigated and its effects on the steam chamber development, as well as well production performance are quantified. Initial water mobility is firstly classified into two categories (low and high) based on the shapes of their steam chambers. Results show that initial water mobility can change the shape of steam chamber, pressure distribution in the reservoir and the steam condensate flow pattern along steam chamber edge. Cumulative oil production in nine years for the low initial water mobility scenario is 18.1% higher than that of the immobile initial water scenario due to the convective heat transfer induced by initial water flow ahead of the steam chamber. On the other hand, cumulative oil production in nine years of the high initial water scenario is 34.6% lower than that of immobile scenario. For the adjacent well pairs located in the same pad, compared to immobile initial water case, low initial water mobility case with the same injection pressure has the highest NPV, while high initial water mobility has a negative impact on SAGD performance. An injection pressure difference of only 200 kPa for the high initial water mobility case can reduce NPV by 40%.