Positive measure and potential implication for heavy oil recovery of dip reservoir using SAGD based on numerical analysis

摘要

To investigate the effect of the formation dip angle on the heavy oil recovery, a numerical model with the formation dip angle was established based on CMG-STARS. Using the numerical model, the steam chamber evolution and the production index were analyzed for the dip reservoir recovery. The results show that: 1) the steam chamber has an obvious asymmetrical distribution on the injection well; 2) the production index of the dip reservoir is lower than the one of the level reservoir. Furthermore, the reason of low production was analyzed from three aspects, namely, the direct reason, the root reason and the intermediate reason. The direct reason is the higher residual oil for the dip reservoir, especially in the downdip zone. The root reasons are the low steam injection amount and the non-uniform distribution of the injected steam. The intermediate reason is that the dip reservoir has a higher cumulative heat loss, especilly in the updip zone. To improve the low production, the well location was optimized as an effective measure, from the perspective of decreasing the area of the downdip zone. Especially, two evaluation objectives were set to determine the reasonable well locations under the dip unknown and the dip angle known. The well location can be reasonable with 10 m away from the center of the reservoir width under the formation dip angle known (8°). Additionally, the optimal matching relation was given between the well location and the formation dip angle, when considering the formation dip angle unknown. Finally, potential implications were obtained as the formation dip angle changing, including: 1) the steam migrates much farther in the updip zone and much nearer in the downdip zone, as the formation dip angle increasing; 2) the cumulative oil production and the cumulative oil-steam ratio show the decreasing trend as the formation dip angle increasing.