Dimethyl Ether as a Novel Solvent for Bitumen Recovery: Mechanisms of Improved Mass Transfer and Energy Efficiency

Abstract

Summary A solvent-based thermal recovery process has the advantages of low capital expenditure, less energy consumption, and less greenhouse gas emission. Dimethyl ether (DME), as a renewable solvent, has been considered as a novel additive in the thermal bitumen recovery process. Being soluble in both water and oil phases, DME has the potential to enhance mass transfer and improve oil production. In this work, a phase behavior model of the DME-bitumen-water system is first developed considering DME partitioning between oil and water. A field-scale numerical simulation model with fine gridblocks is developed to investigate the heat and mass transfer mechanisms between DME and bitumen in the interface of a DME vapor chamber. The numerical model is validated with physical experiment results. The close agreement between measured and simulated production profiles indicates that the mechanisms are adequately captured. Meanwhile, various simulation scenarios are performed to evaluate the production performance and the energy efficiency, which is defined as the energy/oil ratio. It is found that the oil production rate in DME injection is 15% higher than that in butane injection at the early stage of production. The solvent penetration depth in DME injection is larger than that in butane injection. This is attributed to the enhanced mass transfer between DME and bitumen caused by the high diffusion of DME in the water phase and preferential partitioning of DME into the oil phase. Furthermore, energy consumption in the warm DME injection process is 48% less than that in warm butane injection and 75% less than that in steam-assisted gravity drainage (SAGD). This is because DME injection can be operated at a lower-temperature condition, leading to less energy transferred to heat reservoir rock/fluids and less heat loss to over/underburden. Therefore, DME is proved to be a technically promising and environmentally friendly solvent to enhance bitumen recovery. The DME-based thermal recovery technique exhibits superior advantages in unlocking poor-quality reservoirs, especially in high water saturation reservoirs and thin reservoirs.

Numerical Modeling of the Steam Chamber Ramp-Up Phase in Steam-Assisted Gravity Drainage

“…As a consequence, the impact of numerical diffusion/dispersion on the numerically simulated steam chamber ramp-up phase could be neglected by applying the grid size of 5.0 cm × 5.0 cm. The findings were consistent with the results of previous studies in that millimeter-sized grids led to an accurate numerical diffusion/dispersion for the representation of the physical process [47]. Thus, to obtain an efficient simulation model, the grid size of 5.0 cm × 5.0 cm (scenario 2) was chosen as the base grid size.…”

“…In the numerical reservoir simulation of the SAGD process, it was essential to apply sufficiently fine grids for the accurate estimation of the steam chamber [46]. Recent work on the effects of grid dimensions on thermal oil recovery simulation has further indicated that a fine grid system eliminates the impact of numerical diffusion on the numerical estimation, which is caused by the discretization in space and time [47]. In this work, a field-scale numerical simulation model with fine grids was built to investigate the multiphase fluid flow mechanisms and dynamic steam chamber expansion during the ramp-up phase of an SAGD process.…”

“…Due to the significant effects of numerical diffusion/dispersion on the numerical simulation results, which was caused by the discretization in space and time [47], a sensitivity analysis on the impact of grid size on the SAGD ramp-up phase performance was conducted by comparing the cumulative oil production of varying grid sizes from 2.5 cm to 20 cm, as summarized in Table 2. The cumulative oil production by time, which was used as the grid size quality testing parameter [59], were plotted in curves, which are presented in Figure 7.…”

“…Thus, to obtain an efficient simulation model, the grid size of 5.0 cm × 5.0 cm (scenario 2) was chosen as the base grid size. Furthermore, the grids (5.0 cm × 5.0 cm) that were used in this work were finer than the relatively coarse grids (20 cm × 20 cm) that are used in simple SAGD models [56] and in situ combustion models [47], in which isothermal relative permeability curves are used when neglecting the impact of the countercurrent flows. Thus, the temperature-dependent oil-water-gas multiphase flows and buoyancy-induced countercurrent flows required fine grids for an effective numerical simulation.…”

In-Situ Combustion for Heavy Oil and Oil Sands Recovery: Recent Progress, Field Applications, and Future Perspectives

“…Usually numerical simulation is used as a powerful tool to predict oil recovery performance and design operational parameters for many different process and geological scenarios. 89,90 However, simulation of an ISC process is very complicated mainly associated with the complex chemical reactions involved and three-phase fluid flow in the presence of noncondensable gases.…”