A Study of Dimethyl Ether-Steam Coinjection Using a Large-Scale Physical Model

Abstract

Summary Dimethyl ether (DME) as a water-soluble solvent has been studied as a potential additive to steam for improving the energy efficiency of steam-assisted gravity drainage (SAGD). The main objective of this research was to study in-situ flow characteristics and energy efficiency of DME-SAGD using a large-scale physical model. Results from DME-SAGD were compared with the control experiment of SAGD with no solvent injection using the same experimental setup. The main novelty of this research lies in the experimental data that demonstrated enhanced bitumen drainage by DME-SAGD in comparison with SAGD. The experiment was conducted in a cylindrical pressure vessel with a diameter of 0.425 m and a length of 1.22 m, which contained a sandpack with a porosity of 0.34 and a permeability of 5.0 darcies. The DME-SAGD experiment used a DME concentration of 10 mol% and a steam coinjection rate of 27.6 cm3/min [cold-water equivalent (CWE)] at 3000 kPa. Temperature distributions within the sandpack, along with injection and production histories, were recorded during the experiment. Subsequently, numerical simulations were performed to history match the experimental data, and the calibrated simulation model was used to analyze the details of compositional flow characteristics. Results showed that the 10 mol% DME-SAGD experiment yielded a recovery factor (RF) of 92.7% in 4.2 days, and the SAGD experiment yielded an RF of 68.6% in 6.0 days; for both experiments, the first 2 days were the preheating and the steam-only injection (SAGD) stages. The peak rate of bitumen production was 43.8 mL/min in the DME-SAGD experiment, which was more than twice greater than the peak rates observed in the SAGD experiment. The substantially increased rate of bitumen production resulted in a cumulative steam/oil ratio in DME-SAGD that was less than half of that in SAGD. Analysis of experimental results indicated that the solubility of DME in the aqueous and oleic phases caused different flow characteristics between DME-SAGD and SAGD. For example, the oleic and aqueous phases were more uniformly distributed in the sandpack in the former. Simulations indicated that DME-SAGD had a greater distribution of grid-scale inverse mobility ratio and increased oleic-phase mobilities in comparison with SAGD.