Gravity drainage of bitumen under controlled thermodynamic conditions in DME-steam co-injection

Abstract

Dimethyl ether (DME), a water-soluble solvent, has been studied as a potential additive to steam for improving the efficiency of steam-assisted gravity drainage (SAGD) for bitumen recovery. This paper presents an experimental study of bitumen gravity drainage in DME-SAGD in comparison to SAGD and butane-SAGD (C4-SAGD).Small-scale experiments were conducted using a sand pack with a diameter of 1.5 inches and a length of 15 inches, which was housed inside a 25-L cylindrical steel vessel. A DME-SAGD experiment with 10 mol% DME was conducted at 3500 kPa with a total in-situ injection rate of 3897 cm3/min. Temperature distributions inside and outside the sand pack, as well as injection and production histories, were recorded during the experiment. Results were compared with previous studies of SAGD and C4-SAGD (20 mol% C4) that used the same experimental program. Then, numerical simulations were performed to history-match the experimental data and investigate the bitumen recovery mechanisms.The peak bitumen rate was 16.8 cm3/min for 10 mol% DME-SAGD, 9.8 cm3/min for SAGD, and 14.6 cm3/min for 20 mol% C4-SAGD. That is, DME was more effective than C4 as a steam additive even at the concentration reduced by half. The observed enhancement in bitumen drainage was attributed partly to the combined thermal and dilution effects on bitumen viscosity reduction, in which DME-SAGD exhibited a higher chamber-edge temperature than C4-SAGD. Furthermore, the oleic (L) and aqueous (W) phases were more evenly distributed with less gravity segregation in the sand pack in DME-SAGD than in SAGD and C4-SAGD, which facilitated the overall bitumen flow in the sand pack. Results collectively show that the slight polarity of DME as a solvent additive to steam enhanced the bitumen flow not only by L-phase viscosity reduction, but also by more uniformly enhanced bitumen flow in the sand pack.