This paper summarizes horizontal well cyclic steam stimulation with solvent (HW-CSS-S) process strategies that were examined for a Cold Lake type reservoir. The strategies included coinjection of n-hexane (C6H14) and steam, injection of C6H14 prior to steam-only injection, and injection of steam and C6H14 in alternate series of cycles. 2-D and 3-D single well and twowell simulations were preformed using the CMG STARS thermal simulator. The simulations used the Beattie-Boberg model to represent dilation and recompaction. The effects of solvent concentration, soak period, maximum allowed liquid production rate, and pay thickness on the HW-CSS-S process were considered. The performance of horizontal and slant wells were compared.
The simulation results indicated:
The most promising injection strategy was a combination of steam-only, steam-C6H14, and C6H14- only injection cycles. However, the less complex coinjection of 5 mole% C6H14 in steam also performed well.
For steam-C6H14 co-injection, oil production increased significantly with C6H14 concentration but the increase was marginal above 5 mole% C6H14 in the steam.
Increasing the maximum allowed liquid production rate from 1 to 5 m3/d/m of well length had a major impact on HW-CSS-S behaviour. The oil rate had a maximum value when the allowed liquid production rate was 4 m3/d/m of well length and the cumulative steam oil ratio (CSOR) increased with the allowed liquid production rate.
An increase in pay thickness resulted in increased oil production and a lower steam-oil ratio, but the net solvent to oil ratio was greater due to a reduction in solvent recovery.
Water injection at an infill well increased the reservoir pressure and reduced both the amount of steam injected and oil production.
An infill horizontal producer midway between two cyclic horizontal wells (spaced 402 m apart) increased the oil rate by 31%, reduced the CSOR by 9%, and decreased the net C6H14 to oil ratio by a factor of 3. The closer the infill producer was to the bottom of the pay, the better was its performance.
For a uniform formation, horizontal wells performed better than slant wells.
It is recommended that, when injecting steam and solvent separately in a particular cycle, that the solvent before the steam rather than after it. Injection of steam before the solvent increases the reservoir temperature and reduces solvent solubility. Although injecting solvent before steam in the same cycle may temporarily result in increased solvent retention in the reservoir, solvent may be recovered by steam-only or steam CH4 injection in subsequent cycles.
This paper summarizes simulations that were performed to develop steam-solvent injection strategies focused on horizontal well applications and to estimate the effect on the process of a number of reservoir and fluid parameters. Solvents and steam when used together in a cyclic mode provide synergistic effects such as reduced viscosity, solution gas drive due to methane and hexane dissolution, improved gravity drainage, and much faster diffusion of solvent as the reservoir becomes heated by steam. Horizontal wells improve oil recovery as compared to CSS with vertical wells since they improve contact with the reservoir and more effectively utilize gravity drainage.
